Multi-rod burst behavior under a loss-of-coolant accident condition, (1)

International Nuclear Information System (INIS)

Hashimoto, Masao; Otomo, Takashi; Furuta, Teruo; Kawasaki, Satoru; Uetsuka, Hiroshi

1980-12-01

Multi-rod burst tests have been planned since 1977 to estimate quantitative channel restriction during a LOCA transient in LWRs. For this purpose, many bundle tests have been making to burst in a steam in varying a few parameters which influence the degree of channel restriction. The purpose of this report is to provide a background document for final reports to be published in the future. This report includes the results of No. 7805 bundle test, namely temperature, internal pressure, burst behavior of rods and channel restriction of the bundle. (author)

Channel coupling in heavy quarkonia: Energy levels, mixing, widths, and new states

International Nuclear Information System (INIS)

Danilkin, I. V.; Simonov, Yu. A.

2010-01-01

The mechanism of channel coupling via decay products is used to study energy shifts, level mixing as well as the possibility of new near-threshold resonances in cc, bb systems. The Weinberg eigenvalue method is formulated in the multichannel problems, which allows one to describe coupled-channel resonances and wave functions in a unitary way, and to predict new states due to channel coupling. Realistic wave functions for all single-channel states and decay matrix elements computed earlier are exploited, and no new fitting parameters are involved. Examples of level shifts, widths, and mixings are presented; the dynamical origin of X(3872) and the destiny of the single-channel 2 3 P 1 (cc) state are clarified. As a result a sharp and narrow peak in the state with quantum numbers J PC =1 ++ is found at 3.872 GeV, while the single-channel resonance originally around 3.940 GeV becomes increasingly broad and disappears with growing coupling to open channels.

Experiments and CFD Modelling of Turbulent Mass Transfer in a Mixing Channel

DEFF Research Database (Denmark)

Hjertager Osenbroch, Lene Kristin; Hjertager, Bjørn H.; Solberg, Tron

2006-01-01

. Three different flow cases are studied. The 2D numerical predictions of the mixing channel show that none of the k-ε turbulence models tested is suitable for the flow cases studied here. The turbulent Schmidt number is reduced to obtain a better agreement between measured and predicted mean......Experiments are carried out for passive mixing in order to obtain local mean and turbulent velocities and concentrations. The mixing takes place in a square channel with two inlets separated by a block. A combined PIV/PLIF technique is used to obtain instantaneous velocity and concentration fields...... and fluctuating concentrations. The multi-peak presumed PDF mixing model is tested....

Chaotic mixing in a planar, curved channel using periodic slip

International Nuclear Information System (INIS)

Garg, P.; Picardo, J. R.; Pushpavanam, S.

2015-01-01

We propose a novel strategy for designing chaotic micromixers using curved channels confined between two flat planes. The location of the separatrix between the Dean vortices, induced by centrifugal forces, is dependent on the location of the maxima of axial velocity. An asymmetry in the axial velocity profile can change the location of the separatrix. This is achieved physically by introducing slip alternatingly at the top and bottom walls. This leads to streamline crossing and Lagrangian chaos. An approximate analytical solution of the velocity field is obtained using perturbation theory. This is used to find the Lagrangian trajectories of fluid particles. Poincare sections taken at periodic locations in the axial direction are used to study the extent of chaos. We study two microchannel designs, called circlet and serpentine, in which the Dean vortices in adjacent half cells are co-rotating and counter-rotating, respectively. The extent of mixing, at low Re and low slip length, is shown to be greater in the serpentine case. Wide channels are observed to have much better mixing than tall channels; an important observation not made for separatrix flows till now. Eulerian indicators are used to gauge the extent of mixing, with varying slip length, and it is shown that an optimum slip length exists which maximizes the mixing in a particular geometry. Once the parameter space of relatively high mixing is identified, detailed variance computations are carried out to identify the detailed features

Chaotic mixing in a planar, curved channel using periodic slip

Science.gov (United States)

Garg, P.; Picardo, J. R.; Pushpavanam, S.

2015-03-01

We propose a novel strategy for designing chaotic micromixers using curved channels confined between two flat planes. The location of the separatrix between the Dean vortices, induced by centrifugal forces, is dependent on the location of the maxima of axial velocity. An asymmetry in the axial velocity profile can change the location of the separatrix. This is achieved physically by introducing slip alternatingly at the top and bottom walls. This leads to streamline crossing and Lagrangian chaos. An approximate analytical solution of the velocity field is obtained using perturbation theory. This is used to find the Lagrangian trajectories of fluid particles. Poincare sections taken at periodic locations in the axial direction are used to study the extent of chaos. We study two microchannel designs, called circlet and serpentine, in which the Dean vortices in adjacent half cells are co-rotating and counter-rotating, respectively. The extent of mixing, at low Re and low slip length, is shown to be greater in the serpentine case. Wide channels are observed to have much better mixing than tall channels; an important observation not made for separatrix flows till now. Eulerian indicators are used to gauge the extent of mixing, with varying slip length, and it is shown that an optimum slip length exists which maximizes the mixing in a particular geometry. Once the parameter space of relatively high mixing is identified, detailed variance computations are carried out to identify the detailed features.

Multirods burst tests under loss-of-coolant conditions

International Nuclear Information System (INIS)

Kawasaki, S.; Uetsuka, H.; Furuta, T.

1983-01-01

In order to know the upper limit of coolant flow area restriction in a fuel assembly under loss-of-coolant accidents in LWRs, burst tests of fuel bundles were performed. Each bundle consisted of 49 rods(7x7 rods), and bursts were conducted in flowing steam. In some cases, 4 rods were replaced by control rods with guide tubes in a bundle. After the burst, the ballooning behavior of each rod and the degree of coolant flow area restriction in the bundle were measured. Ballooning behavior of rods and degree of coolant flow channel restriction in bundles with control rods were not different from those without control rods. The upper limit of coolant flow channel restriction under loss-of-coolant conditions was estimated to be about 80%. (author)

Investigation of Size Effects to the Mixing Performance on the X-shaped Micro-Channels

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S Tu

2016-09-01

Full Text Available Due to the developing of micro-electro-mechanical-system, MEMS, the fabrication of the microminiaturization devices becomes obviously important. The advances in the basic understanding of fluid physics have opened an era of application of fluid dynamics systems using microchannels. The purpose of this study is to research the flow transport phenomenon by employing different kinds of micro-channel sizing in X-shaped micro-channels. As the working fluid, water is injected to microchannel at different mass flow rate. Over a wide range of flow condition, 1.06 < Re < 514, in X-shaped micro-channels, the mixture performances of numerical simulation, flow visualization, and temperature distribution remain the same. At the same mass flow rate as the Reynolds number below 112.53, the biggest channel size had the slowest flow velocity and got the best mixing performance; as the Reynolds number above 112.53, the smaller the channel sizing, the lower the pressure drops and the faster velocity becomes. The transition form early from laminar flow, the unsteady flow is an advantage for mixing in the limited mixing area, therefore 0.7 mm got the best mixing performance. It is clear that the size of the channel plays an important role in the X-shaped micro-channels.

Turbulent mixed convection in asymmetrically heated vertical channel

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Mokni Ameni

2012-01-01

Full Text Available In this paper an investigation of mixed convection from vertical heated channel is undertaken. The aim is to explore the heat transfer obtained by adding a forced flow, issued from a flat nozzle located in the entry section of a channel, to the up-going fluid along its walls. Forced and free convection are combined studied in order to increase the cooling requirements. The study deals with both symmetrically and asymmetrically heated channel. The Reynolds number based on the nozzle width and the jet velocity is assumed to be 3 103 and 2.104; whereas, the Rayleigh number based on the channel length and the wall temperature difference varies from 2.57 1010 to 5.15 1012. The heating asymmetry effect on the flow development including the mean velocity and temperature the local Nusselt number, the mass flow rate and heat transfer are examined.

INTEGRAL monitoring of unusually long X-ray bursts

DEFF Research Database (Denmark)

Chenevez, Jérôme; Falanga, M.; Kuulkers, E.

2008-01-01

of exceptional burst events lasting more than ~10 minutes. Half of the dozen so-called intermediate long bursts registered so far have been observed by INTEGRAL. The goal is to derive a comprehensive picture of the relationship between the nuclear ignition processes and the accretion states of the system leading...... up to such long bursts. Depending on the composition of the accreted material, these bursts may be explained by either the unstable burning of a large pile of mixed hydrogen and helium, or the ignition of a thick pure helium layer. Intermediate long bursts are particularly expected to occur at very...

An effective implementation scheme of just-in-time protocol for optical burst switching networks

Science.gov (United States)

Wu, Guiling; Li, Xinwan; Chen, Jian-Ping; Wang, Hui

2005-02-01

Optical burst switching (OBS) has been emerging as a promising technology that can effectively support the next generation IP-oriented transportation networks. JIT signaling protocol for OBS is relatively simple and easy to be implemented by hardware. This paper presented an effective scheme to implement the JIT protocol, which not only can effectively implement reservation and release of optical channels based on JIT, but also can process the failure of channel reservation and release due to loss of burst control packets. The scheme includes: (1) a BHP (burst head packet) path table is designed and built at each OBS node. It is used to guarantee the corresponding burst control packet, i.e. BHP, BEP (burst end packet) and BEP_ACK (BEP acknowledgement), to be transmitted in the same path. (2) The timed retransmission of BEP and the reversed deletion of the item in BHP path tables triggered by the corresponding BEP_ACK are combined to solve the problems caused by the loss of the signaling messages in channel reservation and release process. (3) Burst head packets and BEP_ACK are transmitted using "best-effort" method. Related signaling messages and their formats for the proposed scheme are also given.

Understanding the Generation of Network Bursts by Adaptive Oscillatory Neurons

Directory of Open Access Journals (Sweden)

Tanguy Fardet

2018-02-01

Full Text Available Experimental and numerical studies have revealed that isolated populations of oscillatory neurons can spontaneously synchronize and generate periodic bursts involving the whole network. Such a behavior has notably been observed for cultured neurons in rodent's cortex or hippocampus. We show here that a sufficient condition for this network bursting is the presence of an excitatory population of oscillatory neurons which displays spike-driven adaptation. We provide an analytic model to analyze network bursts generated by coupled adaptive exponential integrate-and-fire neurons. We show that, for strong synaptic coupling, intrinsically tonic spiking neurons evolve to reach a synchronized intermittent bursting state. The presence of inhibitory neurons or plastic synapses can then modulate this dynamics in many ways but is not necessary for its appearance. Thanks to a simple self-consistent equation, our model gives an intuitive and semi-quantitative tool to understand the bursting behavior. Furthermore, it suggests that after-hyperpolarization currents are sufficient to explain bursting termination. Through a thorough mapping between the theoretical parameters and ion-channel properties, we discuss the biological mechanisms that could be involved and the relevance of the explored parameter-space. Such an insight enables us to propose experimentally-testable predictions regarding how blocking fast, medium or slow after-hyperpolarization channels would affect the firing rate and burst duration, as well as the interburst interval.

The supernova-gamma-ray burst-jet connection.

Science.gov (United States)

Hjorth, Jens

2013-06-13

The observed association between supernovae and gamma-ray bursts represents a cornerstone in our understanding of the nature of gamma-ray bursts. The collapsar model provides a theoretical framework for this connection. A key element is the launch of a bipolar jet (seen as a gamma-ray burst). The resulting hot cocoon disrupts the star, whereas the (56)Ni produced gives rise to radioactive heating of the ejecta, seen as a supernova. In this discussion paper, I summarize the observational status of the supernova-gamma-ray burst connection in the context of the 'engine' picture of jet-driven supernovae and highlight SN 2012bz/GRB 120422A--with its luminous supernova but intermediate high-energy luminosity--as a possible transition object between low-luminosity and jet gamma-ray bursts. The jet channel for supernova explosions may provide new insights into supernova explosions in general.

INTEGRAL monitoring of unusually long X-ray bursts

DEFF Research Database (Denmark)

of the accreted material, these bursts may be explained by either the unstable burning of a large pile of mixed hydrogen and helium, or the ignition of a thick pure helium layer. Long duration bursts are particularly expected at very low accretion rates and make possible to study the transition from a hydrogen......Thermonuclear bursts on the surface of accreting neutron stars in low mass X-ray binaries have been studied for many years and have in a few cases confirmed theoretical models of nuclear ignition and burning mechanisms. The large majority of X-ray bursts last less than 100s. A good number......-rich bursting regime to a pure helium regime. Moreover, a handful of long bursts have shown, before the extended decay phase, an initial spike similar to a normal short X-ray burst. Such twofold bursts might be a sort of link between short and super-bursts, where the premature ignition of a carbon layer could...

A review on the analysis and experiment of fluid flow and mixing in micro-channels

International Nuclear Information System (INIS)

Kang, Sang Mo; Suh, Yong Kweon; Jayaraj, Simon

2007-01-01

The studies with respect to micro-channels and micro-mixers are expanding in many dimensions. Most significant area of micro-mixer study is the flow analysis in various micro-channel configurations. The flow phenomena in microchannel devices are quite different from that of the macro-scale devices. An attempt is made here to review the important recent literature available in the area of micro-channel flow analysis and mixing. The topics covered include the physics of flow in micro-channels and integrated simulation of the micro-channel flow. Also, the flow control models and electro-kinetically driven micro-channel flows are dealt in detail. A survey of important numerical methods, which are currently popular for micro-channel flow analysis, is carried out. Different options for mixing in microchannels are provided, in sufficient detail

Self-mixing differential vibrometer based on electronic channel subtraction

International Nuclear Information System (INIS)

Donati, Silvano; Norgia, Michele; Giuliani, Guido

2006-01-01

An instrument for noncontact measurement of differential vibrations is developed, based on the self-mixing interferometer. As no reference arm is available in the self-mixing configuration, the differential mode is obtained by electronic subtraction of signals from two (nominally equal) vibrometer channels, taking advantage that channels are servo stabilized and thus insensitive to speckle and other sources of amplitude fluctuation. We show that electronic subtraction is nearly as effective as field superposition. Common-mode suppression is 25-30 dB, the dynamic range (amplitude) is in excess of 100 μm, and the minimum measurable (differential) amplitude is 20 nm on aB=10 kHz bandwidth. The instrument has been used to measure vibrations of two metal samples kept in contact, revealing the hysteresis cycle in the microslip and gross-slip regimes, which are of interest in the study of friction induced vibration damping of gas turbine blades for aircraft applications

Teleportation with an Arbitrary Mixed Resource as a Trace-Preserving Quantum Channel

Institute of Scientific and Technical Information of China (English)

Sergio Albeverio; FEI Shao-Ming; YANG Wen-Li

2002-01-01

General conditions are given in order to perform a perfect teleportation process in the case where theHilbert spaces involved have different dimensions. An explicit expression is obtained for the quantum channel associatedwith the standard teleportation protocol To with an arbitrary mixed state resource. The transmission fidelity of thecorresponding quantum channel is given.

Seasonal variability of the diapycnal mixing in the Canary Islands channels

Science.gov (United States)

Rodríguez-Santana, Angel; Marrero-Díaz, Angeles; Machín, Francisco Jose; García-Weil, Luis; Sangrà, Pablo; Vélez-Belchí, Pedro; Fraile-Nuez, Eugenio; Estrada-Allis, Sheila

2014-05-01

Trimonthly surveys of XBT and XCTD (Expandable Bathytermograph and Conductivity-Temperature-Depth) crossing the whole Canary Islands channels were carried out (projects TRAMIC and PROMECA) from November 2012 until September 2013 using opportunity ships (Naviera Armas Ferries). With this data set and using salinity analytical relationships (Machín et al, 2010), vertical sections of temperature and potential density were obtained for each channel and season. In order to estimate the intensity of the diapycnal mixing in the first 500 m of the pycnocline, vertical sections of Thorpe length scale, Turner angle and gradient Richardson number (from the geostrophic vertical shear) were calculated for all the cases. The first results show how the diapycnal mixing due to the vertical shear instabilities is more intense close to the islands and in summer when the seasonal pycnocline is present. Mixing due to double diffusion processes (salt fingers) was found without sizable changes in the permanent pycnocline. Net turbulence diffusivities and diapycnal diffusive fluxes with their variability spatial and temporal will be estimate for each channel taking into account that processes of double diffusion and turbulence induced by vertical shear are present at the same time. Additionally the results obtained from hydrographic data from the cruise RAPROCAN-2013 (IEO) (October 2013) around Canary Islands will be used to compare them with the channels results. This work was co-funded by Canary Government (TRAMIC project: PROID20100092), European Union (FEDER) and Spanish Government (PROMECA: CTM2008-04057/MAR and CTM2009-06993-E/MAR)

Thermonuclear Bursts with Short Recurrence Times from Neutron Stars Explained by Opacity-driven Convection

Energy Technology Data Exchange (ETDEWEB)

Keek, L. [X-ray Astrophysics Laboratory, Astrophysics Science Division, NASA/GSFC, Greenbelt, MD 20771 (United States); Heger, A., E-mail: laurens.keek@nasa.gov [Monash Center for Astrophysics, School of Physics and Astronomy, Monash University, Victoria, 3800 (Australia)

2017-06-20

Thermonuclear flashes of hydrogen and helium accreted onto neutron stars produce the frequently observed Type I X-ray bursts. It is the current paradigm that almost all material burns in a burst, after which it takes hours to accumulate fresh fuel for the next burst. In rare cases, however, bursts are observed with recurrence times as short as minutes. We present the first one-dimensional multi-zone simulations that reproduce this phenomenon. Bursts that ignite in a relatively hot neutron star envelope leave a substantial fraction of the fuel unburned at shallow depths. In the wake of the burst, convective mixing events driven by opacity bring this fuel down to the ignition depth on the observed timescale of minutes. There, unburned hydrogen mixes with the metal-rich ashes, igniting to produce a subsequent burst. We find burst pairs and triplets, similar to the observed instances. Our simulations reproduce the observed fraction of bursts with short waiting times of ∼30%, and demonstrate that short recurrence time bursts are typically less bright and of shorter duration.

Investigating the Lateral Mixing Coefficient in a Compound Channel with Emergent Vegetation over the Floodplain

Directory of Open Access Journals (Sweden)

Hossein hamidifar

2017-02-01

Full Text Available Introduction: Water quality control is very important for people, animals and plants. Predicting the spread of contaminants is important for managing and protecting rivers and streams to the balance of the ecosystem. Pollutants are introduced into waterways, though a variety of sources such as point and non-point sources. Under steady state conditions, where longitudinal mixing is not significant, studying the lateral mixing is essential in evaluating the influence of pollutants on water quality. Lateral or transverse mixing is the hydraulic process by which a plume of contaminant spreads laterally and dilutes. In water quality management, the transverse mixing is more significant than either vertical or longitudinal dispersion, especially, when dealing with the release of wastes from point sources. Hence, a wide range of field, laboratory and numerical modelling approaches, including laboratory and field measurements, and analytical and numerical investigations have been developed, to quantify the lateral mixing coefficient. However, most of the researchers have ignored the effects of vegetation on the lateral mixing process in their studies. Many studies have shown that the flow characteristics through vegetation are different from those in non-vegetated waterways. For example, laboratory studies have revealed that flow velocity and large-scale turbulence tend to be greatly decreased within a plant canopy, because the resistance to flow by the vegetation. Also, vegetation affects the transport of dissolved and particulate material, such as sediment, nutrients and pollutants. In this study, the effect of the floodplain vegetation on lateral mixing coefficient in compound channels is investigated experimentally. Also, a comparison is made between the results of the present study with those obtained by previous researchers. Materials and Methods: Experiments were carried out in a laboratory flume 18m long, 0.9m wide and 0.6m high with an

One-dimensional Turbulence Models of Type I X-ray Bursts

Energy Technology Data Exchange (ETDEWEB)

Hou, Chen [Univ. of Minnesota, Minneapolis, MN (United States)

2016-01-06

Type I X-ray bursts are caused by thermonuclear explosions occurring on the surface of an accreting neutron star in a binary star system. Observations and simulations of these phenomena are of great importance for understanding the fundamental properties of neutron stars and dense matter because the equation of state for cold dense matter can be constrained by the mass-radius relationship of neutron stars. During the bursts, turbulence plays a key role in mixing the fuels and driving the unstable nuclear burning process. This dissertation presents one-dimensional models of photospheric radius expansion bursts with a new approach to simulate turbulent advection. Compared with the traditional mixing length theory, the one-dimensional turbulence (ODT) model represents turbulent motions by a sequence of maps that are generated according to a stochastic process. The light curves I obtained with the ODT models are in good agreement with those of the KEPLER model in which the mixing length theory and various diffusive processes are applied. The abundance comparison, however, indicates that the differences in turbulent regions and turbulent diffusivities result in more ¹²C survival during the bursts in the ODT models, which can make a difference in the superbursts phenomena triggered by unstable carbon burning.

One-dimensional Turbulence Models of Type I X-ray Bursts

International Nuclear Information System (INIS)

Hou, Chen

2016-01-01

Type I X-ray bursts are caused by thermonuclear explosions occurring on the surface of an accreting neutron star in a binary star system. Observations and simulations of these phenomena are of great importance for understanding the fundamental properties of neutron stars and dense matter because the equation of state for cold dense matter can be constrained by the mass-radius relationship of neutron stars. During the bursts, turbulence plays a key role in mixing the fuels and driving the unstable nuclear burning process. This dissertation presents one-dimensional models of photospheric radius expansion bursts with a new approach to simulate turbulent advection. Compared with the traditional mixing length theory, the one-dimensional turbulence (ODT) model represents turbulent motions by a sequence of maps that are generated according to a stochastic process. The light curves I obtained with the ODT models are in good agreement with those of the KEPLER model in which the mixing length theory and various diffusive processes are applied. The abundance comparison, however, indicates that the differences in turbulent regions and turbulent diffusivities result in more 12 C survival during the bursts in the ODT models, which can make a difference in the superbursts phenomena triggered by unstable carbon burning.

Effects of elevated line sources on turbulent mixing in channel flow

Science.gov (United States)

Nguyen, Quoc; Papavassiliou, Dimitrios

2016-11-01

Fluids mixing in turbulent flows has been studied extensively, due to the importance of this phenomena in nature and engineering. Convection effects along with motion of three-dimensional coherent structures in turbulent flow disperse a substance more efficiently than molecular diffusion does on its own. We present here, however, a study that explores the conditions under which turbulent mixing does not happen, when different substances are released into the flow field from different vertical locations. The study uses a method which combines Direct Numerical Simulation (DNS) with Lagrangian Scalar Tracking (LST) to simulate a turbulent channel flow and track the motion of passive scalars with different Schmidt numbers (Sc). The particles are released from several instantaneous line sources, ranging from the wall to the center region of the channel. The combined effects of mean velocity difference, molecular diffusion and near-wall coherent structures lead to the observation of different concentrations of particles downstream from the source. We then explore in details the conditions under which particles mixing would not happen. Results from numerical simulation at friction Reynolds number of 300 and 600 will be discussed and for Sc ranging from 0.1 to 2,400.

Bursting and critical layer frequencies in minimal turbulent dynamics and connections to exact coherent states

Science.gov (United States)

Park, Jae Sung; Shekar, Ashwin; Graham, Michael D.

2018-01-01

The dynamics of the turbulent near-wall region is known to be dominated by coherent structures. These near-wall coherent structures are observed to burst in a very intermittent fashion, exporting turbulent kinetic energy to the rest of the flow. In addition, they are closely related to invariant solutions known as exact coherent states (ECS), some of which display nonlinear critical layer dynamics (motions that are highly localized around the surface on which the streamwise velocity matches the wave speed of ECS). The present work aims to investigate temporal coherence in minimal channel flow relevant to turbulent bursting and critical layer dynamics and its connection to the instability of ECS. It is seen that the minimal channel turbulence displays frequencies very close to those displayed by an ECS family recently identified in the channel flow geometry. The frequencies of these ECS are determined by critical layer structures and thus might be described as "critical layer frequencies." While the bursting frequency is predominant near the wall, the ECS frequencies (critical layer frequencies) become predominant over the bursting frequency at larger distances from the wall, and increasingly so as Reynolds number increases. Turbulent bursts are classified into strong and relatively weak classes with respect to an intermittent approach to a lower branch ECS. This temporally intermittent approach is closely related to an intermittent low drag event, called hibernating turbulence, found in minimal and large domains. The relationship between the strong burst and the instability of the lower branch ECS is further discussed in state space. The state-space dynamics of strong bursts is very similar to that of the unstable manifolds of the lower branch ECS. In particular, strong bursting processes are always preceded by hibernation events. This precursor dynamics to strong turbulence may aid in development of more effective control schemes by a way of anticipating dynamics

Plasma streams mixing in two-channel t-shaped magnetic filter

International Nuclear Information System (INIS)

Aksyonov, D.S.; Aksenov, I.I.; Luchaninov, A.A.; Reshetnyak, E.N.; Strel'nitskij, V.E.

2011-01-01

Ti-Al-N films were deposited by vacuum arc method. T-shaped magnetic filter with two channels was used for films preparation. Deposition was performed after aluminum and titanium separate plasma streams from two plasma sources were mixed into single one inside plasma duct having weakened magnetic field near its output. Obtained films have uniform distribution of composition and thickness on 180 mm diameter substrate surface. It was found that mixing and homogenization degree depends on nitrogen pressure, output magnetic field intensity and output- to-substrate distance. Film self-sputtering and aluminum preferential sputtering were observed for elevated negative substrate bias potentials.

Effect of flow and peristaltic mixing on bacterial growth in a gut-like channel

Science.gov (United States)

Cremer, Jonas; Segota, Igor; Yang, Chih-yu; Arnoldini, Markus; Sauls, John T.; Zhang, Zhongge; Gutierrez, Edgar; Groisman, Alex; Hwa, Terence

2016-01-01

The ecology of microbes in the gut has been shown to play important roles in the health of the host. To better understand microbial growth and population dynamics in the proximal colon, the primary region of bacterial growth in the gut, we built and applied a fluidic channel that we call the “minigut.” This is a channel with an array of membrane valves along its length, which allows mimicking active contractions of the colonic wall. Repeated contraction is shown to be crucial in maintaining a steady-state bacterial population in the device despite strong flow along the channel that would otherwise cause bacterial washout. Depending on the flow rate and the frequency of contractions, the bacterial density profile exhibits varying spatial dependencies. For a synthetic cross-feeding community, the species abundance ratio is also strongly affected by mixing and flow along the length of the device. Complex mixing dynamics due to contractions is described well by an effective diffusion term. Bacterial dynamics is captured by a simple reaction–diffusion model without adjustable parameters. Our results suggest that flow and mixing play a major role in shaping the microbiota of the colon. PMID:27681630

Mixed convective magnetohydrodynamic flow in a vertical channel filled with nanofluids

Directory of Open Access Journals (Sweden)

S. Das

2015-06-01

Full Text Available The fully developed mixed convection flow in a vertical channel filled with nanofluids in the presence of a uniform transverse magnetic field has been studied. Closed form solutions for the fluid temperature, velocity and induced magnetic field are obtained for both the buoyancy-aided and -opposed flows. Three different water-based nanofluids containing copper, aluminium oxide and titanium dioxide are taken into consideration. Effects of the pertinent parameters on the nanofluid temperature, velocity, and induced magnetic field as well as the shear stress and the rate of heat transfer at the channel wall are shown in figures and tables followed by a quantitative discussion. It is found that the magnetic field tends to enhance the nanofluid velocity in the channel. The induced magnetic field vanishes in the cental region of the channel. The critical Rayleigh number at onset of instability of flow is strongly dependent on the volume fraction of nanoparticles and the magnetic field.

Mixed convection flow and heat transfer in a vertical wavy channel ...

African Journals Online (AJOL)

Mixed convection flow and heat transfer in a vertical wavy channel filled with porous and fluid layers is studied analytically. The flow in the porous medium is modeled using Darcy-Brinkman equation. The coupled non-linear partial differential equations describing the conservation of mass, momentum and energy are solved ...

Thermal and hydrodynamic characteristics of forced and mixed convection flow through vertical rectangular channels

Directory of Open Access Journals (Sweden)

Hanafi Abdalla S.

2008-01-01

Full Text Available This paper presents experimental and numerical studies for the case of turbulent forced and mixed convection flow of water through narrow vertical rectangular channel. The channel is composed of two parallel plates which are heated at a uniform heat flux, whereas, the other two sides of the channel are thermally insulated. The plates are of 64 mm in width, 800 mm in height, and separated from each other at a narrow gap of 2.7 mm. The Nusselt number distribution along the flow direction normalized by the Nusselt number for the case of turbulent forced convection flow is obtained experimentally with a comparison with the numerical results obtained from a commercial computer code. The quantitative determination of the nor- malized Nusselt number with respect to the dimension-less number Z = (Gr/Re21/8Pr0.5 is presented with a comparison with previous experimental results. Qualitative results are presented for the normalized temperature and velocity profiles in the transverse direction with a comparison between the forced and mixed convection flow for both the cases of upward and downward flow directions. The effect of the axial locations and the parameter Gr/Re on the variation of the normalized temperature profiles in the transverse direction for both the regions of forced and mixed convection and for both of the upward and downward flow directions are obtained. The normalized velocity profiles in the transverse directions are also determined at different inlet velocity and heat fluxes for the previous cases. It is found that the normalized Nusselt number is greater than one in the mixed convection region for both the cases of upward and downward flow and correlated well with the dimension-less parameter Z for both of the forced and mixed convection regions. The temperature profiles increase with increasing the axial location along the flow direction or the parameter Gr/Re for both of the forced and mixed convection regions, but this increase is

Spatiotemporal chaos from bursting dynamics

International Nuclear Information System (INIS)

Berenstein, Igal; De Decker, Yannick

2015-01-01

In this paper, we study the emergence of spatiotemporal chaos from mixed-mode oscillations, by using an extended Oregonator model. We show that bursting dynamics consisting of fast/slow mixed mode oscillations along a single attractor can lead to spatiotemporal chaotic dynamics, although the spatially homogeneous solution is itself non-chaotic. This behavior is observed far from the Hopf bifurcation and takes the form of a spatiotemporal intermittency where the system locally alternates between the fast and the slow phases of the mixed mode oscillations. We expect this form of spatiotemporal chaos to be generic for models in which one or several slow variables are coupled to activator-inhibitor type of oscillators

Revisiting the Correlations of Peak Luminosity with Spectral Lag and Peak Energy of the Observed Gamma-ray Bursts

Directory of Open Access Journals (Sweden)

Yun-A Jo

2016-12-01

Full Text Available An analysis of light curves and spectra of observed gamma-ray bursts in gamma-ray ranges is frequently demanded because the prompt emission contains immediate details regarding the central engine of gamma-ray bursts (GRBs. We have revisited the relationship between the collimation-corrected peak luminosity and the spectral lag, investigating the lag-luminosity relationships in great detail by focusing on spectral lags resulting from all possible combinations of channels. Firstly, we compiled the opening angle data and demonstrated that the distribution of opening angles of 205 long GRBs is represented by a double Gaussian function having maxima at ~ 0.1 and ~ 0.3 radians. We confirmed that the peak luminosity and the spectral lag are anti-correlated, both in the observer frame and in the source frame. We found that, in agreement with our previous conclusion, the correlation coefficient improves significantly in the source frame. It should be noted that spectral lags involving channel 2 (25-50 keV yield high correlation coefficients, where Swift/Burst Alert Telescope (BAT has four energy channels (channel 1: 15-25 keV, channel 2: 25-50 keV, channel 3: 50-100 keV, channel 4: 100-200 keV. We also found that peak luminosity is positively correlated with peak energy.

Swift-BAT: The First Year of Gamma-Ray Burst Detections

Science.gov (United States)

Krimm, Hans A.

2006-01-01

The Burst Alert Telescope (BAT) on the Swift has been detecting gamma-ray bursts (GRBs) since Dec. 17,2004 and automated burst alerts have been distributed since Feb. 14,2005. Since commissioning the BAT has triggered on more than 100 GRBs, nearly all of which have been followed up by the narrow-field instruments on Swift through automatic repointing, and by ground and other satellite telescopes after rapid notification. Within seconds of a trigger the BAT produces and relays to the ground a position good to three arc minutes and a four channel light curve. A full ten minutes of event data follows on subsequent ground station passes. The burst archive has allowed us to determine ensemble burst parameters such as fluence, peak flux and duration. An overview of the properties of BAT bursts and BAT'S performance as a burst monitor will be presented in this talk. BAT is a coded aperture imaging system with a wide (approx.2 sr) field of view consisting of a large coded mask located 1 m above a 5200 cm2 array of 32.768 CdZnTe detectors. All electronics and other hardware systems on the BAT have been operating well since commissioning and there is no sign of any degradation on orbit. The flight and ground software have proven similarly robust and allow the real time localization of all bursts and the rapid derivation of burst light curves, spectra and spectral fits on the ground.

CFD analysis of supercritical water flow and heat transfer in single channel with mixing vane

International Nuclear Information System (INIS)

Zuo Guoping; Xie Hongyan; Yu Tao

2012-01-01

Three-dimensional rectangular channel with the mixing wane in supercritical water reactor is investigated with CFX. The mixing vane elevation influenced on temperature distribution and flow field are simulated in the model. The results showed the mixing vane cause fluid circumferential flow, making flow hot and cold fluids mixed and fluid temperature uniform distribution, effectively improve the fuel rod surface temperature distribution and reduced hot temperature. Among the mixing wing elevation of 15, 30, 45, 50, 60 and 70 angle, the 30 angle is the best case in improving temperature distribution. (authors)

Properties of gamma-ray burst time profiles using pulse decomposition analysis

Energy Technology Data Exchange (ETDEWEB)

Lee, A.

2000-02-08

The time profiles of many gamma-ray bursts consist of distinct pulses, which offers the possibility of characterizing the temporal structure of these bursts using a relatively small set of pulse shape parameters. This pulse decomposition analysis has previously been performed on a small sample of bright long bursts using binned data from BATSE, which comes in several data types, and on a sample of short bursts using the BATSE Time-Tagged Event (TTE) data type. The authors have developed an interactive pulse-fitting program using the phenomenological pulse model of Norris, et. al. and a maximum-likelihood fitting routine. They have used this program to analyze the Time-to-Spill (TTS) data for all bursts observed by BATSE up through trigger number 2000, in all energy channels for which TTS data is available. They present statistical information on the attributes of pulses comprising these bursts, including relations between pulse characteristics through the course of a burst. They carry out simulations to determine the biases that their procedures may introduce. They find that pulses tend to have shorter rise times than decay times, and tend to be narrower and peak earlier at higher energies. They also find that pulse brightness, pulse width, and pulse hardness ratios do not evolve monotonically within bursts, but that the ratios of pulse rise times to decay times tends to decrease with time within bursts.

VizieR Online Data Catalog: The Fermi-GBM three-year X-ray burst catalog (Jenke+, 2016)

Science.gov (United States)

Jenke, P. A.; Linares, M.; Connaughton, V.; Beklen, E.; Camero-Arranz, A.; Finger, M. H.; Wilson-Hodge, C. A.

2018-03-01

Gamma-ray Burst Monitor (GBM) is an all-sky monitor whose primary objective is to extend the energy range over which gamma-ray bursts are observed in the Large Area Telescope on Fermi (Meegan et al. 2009ApJ...702..791M). GBM consists of 12 NaI detectors with a diameter of 12.7 cm and a thickness of 1.27 cm and two bismuth germanate (BGO) detectors with a diameter and thickness of 12.7 cm. GBM has three continuous data types: CTIME data with nominal 0.256 s time resolution and 8-channel spectral resolution used for event detection and localization, CSPEC data with nominal 4.096 s time resolution and 128-channel spectral resolution, which are used for spectral modeling, and CTTE (continuous-time tagged event) data with time stamps (2 μs precision) on individual events at full 128-channel spectral resolution, which were made available in 2012 November. The Fermi-GBM X-ray Burst Monitor relies on daily inspection of CTIME channel 1 (12-25 keV) data and began operations on 2010 March 12. (3 data files).

Dependence of X-Ray Burst Models on Nuclear Masses

Energy Technology Data Exchange (ETDEWEB)

Schatz, H.; Ong, W.-J. [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824 (United States)

2017-08-01

X-ray burst model predictions of light curves and the final composition of the nuclear ashes are affected by uncertain nuclear masses. However, not all of these masses are determined experimentally with sufficient accuracy. Here we identify the remaining nuclear mass uncertainties in X-ray burst models using a one-zone model that takes into account the changes in temperature and density evolution caused by changes in the nuclear physics. Two types of bursts are investigated—a typical mixed H/He burst with a limited rapid proton capture process (rp-process) and an extreme mixed H/He burst with an extended rp-process. When allowing for a 3 σ variation, only three remaining nuclear mass uncertainties affect the light-curve predictions of a typical H/He burst ({sup 27}P, {sup 61}Ga, and {sup 65}As), and only three additional masses affect the composition strongly ({sup 80}Zr, {sup 81}Zr, and {sup 82}Nb). A larger number of mass uncertainties remain to be addressed for the extreme H/He burst, with the most important being {sup 58}Zn, {sup 61}Ga, {sup 62}Ge, {sup 65}As, {sup 66}Se, {sup 78}Y, {sup 79}Y, {sup 79}Zr, {sup 80}Zr, {sup 81}Zr, {sup 82}Zr, {sup 82}Nb, {sup 83}Nb, {sup 86}Tc, {sup 91}Rh, {sup 95}Ag, {sup 98}Cd, {sup 99}In, {sup 100}In, and {sup 101}In. The smallest mass uncertainty that still impacts composition significantly when varied by 3 σ is {sup 85}Mo with 16 keV uncertainty. For one of the identified masses, {sup 27}P, we use the isobaric mass multiplet equation to improve the mass uncertainty, obtaining an atomic mass excess of −716(7) keV. The results provide a roadmap for future experiments at advanced rare isotope beam facilities, where all the identified nuclides are expected to be within reach for precision mass measurements.

Experimental and Computational Studies of Turbulent Mass Transfer in a Mixing Channel

DEFF Research Database (Denmark)

Hjertager, Lene Kristin; Hjertager, Bjørn H.; Solberg, Tron

2008-01-01

. Three different flow cases are studied. The 2D numerical predictions of the mixing channel show that none of the k- ε turbulence models tested is suitable for the flow cases studied here. The turbulent Schmidt number is reduced to obtain a better agreement between measured and predicted mean...

Burst activity and ultrafast activation kinetics of CaV1.3 Ca²⁺ channels support presynaptic activity in adult gerbil hair cell ribbon synapses.

Science.gov (United States)

Zampini, Valeria; Johnson, Stuart L; Franz, Christoph; Knipper, Marlies; Holley, Matthew C; Magistretti, Jacopo; Masetto, Sergio; Marcotti, Walter

2013-08-15

Auditory information transfer to afferent neurons relies on precise triggering of neurotransmitter release at the inner hair cell (IHC) ribbon synapses by Ca²⁺ entry through CaV1.3 Ca²⁺ channels. Despite the crucial role of CaV1.3 Ca²⁺ channels in governing synaptic vesicle fusion, their elementary properties in adult mammals remain unknown. Using near-physiological recording conditions we investigated Ca²⁺ channel activity in adult gerbil IHCs. We found that Ca²⁺ channels are partially active at the IHC resting membrane potential (-60 mV). At -20 mV, the large majority (>70%) of Ca²⁺ channel first openings occurred with an estimated delay of about 50 μs in physiological conditions, with a mean open time of 0.5 ms. Similar to other ribbon synapses, Ca²⁺ channels in IHCs showed a low mean open probability (0.21 at -20 mV), but this increased significantly (up to 0.91) when Ca²⁺ channel activity switched to a bursting modality. We propose that IHC Ca²⁺ channels are sufficiently rapid to transmit fast signals of sound onset and support phase-locking. Short-latency Ca²⁺ channel opening coupled to multivesicular release would ensure precise and reliable signal transmission at the IHC ribbon synapse.

Protograph LDPC Codes Over Burst Erasure Channels

Science.gov (United States)

Divsalar, Dariush; Dolinar, Sam; Jones, Christopher

2006-01-01

In this paper we design high rate protograph based LDPC codes suitable for binary erasure channels. To simplify the encoder and decoder implementation for high data rate transmission, the structure of codes are based on protographs and circulants. These LDPC codes can improve data link and network layer protocols in support of communication networks. Two classes of codes were designed. One class is designed for large block sizes with an iterative decoding threshold that approaches capacity of binary erasure channels. The other class is designed for short block sizes based on maximizing minimum stopping set size. For high code rates and short blocks the second class outperforms the first class.

Experimental and numerical studies on the mixing at the intersection of millimetric channels

Energy Technology Data Exchange (ETDEWEB)

Etcheverry, F; Cachile, M [LIA-Grupo de Medios Porosos, Facultad de Ingenieria, UBA, Buenos Aires (Argentina); Gomba, J M [Instituto de Fisica Arroyo Seco, UNCPBA, Tandil (Argentina); Wolluschek, C, E-mail: mcachil@fi.uba.ar [Mecanica de Fluidos e Ingenieria Termica, Centro tecnologico Cemitec, Noain, Navarra (Spain)

2011-05-01

In this work, experimental and numerical results on the effect of diffusion and geometrical dispersion on the mixing of confluent flows are presented. Two channels with an internal diameter D{sub h} = 4 mm intersect with an angle {alpha} = 30,60,90,120,150,180{sup 0}. The experimental setup allows to accurately control the flow rate and assures a constant flow at both inlets. The mixing properties are studied by injecting pure water in one inlet and colored water at the other. The effects of the inlet flow and the intersection angle on the diffusion of ink is analyzed. We observed that the mixing by convection is only important for {alpha} = 180{sup 0}. For other angles, diffusion is the main mechanism for mixing.

Experimental and numerical studies on the mixing at the intersection of millimetric channels

International Nuclear Information System (INIS)

Etcheverry, F; Cachile, M; Gomba, J M; Wolluschek, C

2011-01-01

In this work, experimental and numerical results on the effect of diffusion and geometrical dispersion on the mixing of confluent flows are presented. Two channels with an internal diameter D h = 4 mm intersect with an angle α = 30,60,90,120,150,180 0 . The experimental setup allows to accurately control the flow rate and assures a constant flow at both inlets. The mixing properties are studied by injecting pure water in one inlet and colored water at the other. The effects of the inlet flow and the intersection angle on the diffusion of ink is analyzed. We observed that the mixing by convection is only important for α = 180 0 . For other angles, diffusion is the main mechanism for mixing.

Intrinsic and cosmological signatures in gamma-ray burst time profiles: Time dilation

Energy Technology Data Exchange (ETDEWEB)

Lee, A.

2000-02-08

The time profiles of many gamma-ray bursts consist of distinct pulses, which offers the possibility of characterizing the temporal structure of these bursts using a relatively small set of pulse shape parameters. The authors have used a pulse decomposition procedure to analyze the Time-to-Spill (TTS) data for all bursts observed by BATSE up through trigger number 2000, in all energy channels for which TTS data is available. The authors obtain amplitude, rise and decay timescales, a pulse shape parameter, and the fluencies of individual pulses in all of the bursts. The authors investigate the correlations between brightness measures (amplitude and fluence) and timescale measures (pulse width and separation) which may result from cosmological time dilation of bursts, or from intrinsic properties of burst sources or from selection effects. The effects of selection biases are evaluated through simulations. The correlations between these parameters among pulses within individual bursts give a measure of the intrinsic effects while the correlations among bursts could result both from intrinsic and cosmological effects. The authors find that timescales tend to be shorter in bursts with higher peak fluxes, as expected from cosmological time dilation effects, but also find that there are non-cosmological effects contributing to this inverse correlation. The authors find that timescales tend to be longer in bursts with higher total fluences, contrary to what is expected from cosmological effects. The authors also find that peak fluxes and total fluences of bursts are uncorrelated, indicating that they cannot both be good distance indicators for bursts.

Ketamine blocks bursting in the lateral habenula to rapidly relieve depression.

Science.gov (United States)

Yang, Yan; Cui, Yihui; Sang, Kangning; Dong, Yiyan; Ni, Zheyi; Ma, Shuangshuang; Hu, Hailan

2018-02-14

The N-methyl-d-aspartate receptor (NMDAR) antagonist ketamine has attracted enormous interest in mental health research owing to its rapid antidepressant actions, but its mechanism of action has remained elusive. Here we show that blockade of NMDAR-dependent bursting activity in the 'anti-reward center', the lateral habenula (LHb), mediates the rapid antidepressant actions of ketamine in rat and mouse models of depression. LHb neurons show a significant increase in burst activity and theta-band synchronization in depressive-like animals, which is reversed by ketamine. Burst-evoking photostimulation of LHb drives behavioural despair and anhedonia. Pharmacology and modelling experiments reveal that LHb bursting requires both NMDARs and low-voltage-sensitive T-type calcium channels (T-VSCCs). Furthermore, local blockade of NMDAR or T-VSCCs in the LHb is sufficient to induce rapid antidepressant effects. Our results suggest a simple model whereby ketamine quickly elevates mood by blocking NMDAR-dependent bursting activity of LHb neurons to disinhibit downstream monoaminergic reward centres, and provide a framework for developing new rapid-acting antidepressants.

The calcium-binding protein parvalbumin modulates the firing 1 properties of the reticular thalamic nucleus bursting neurons.

Science.gov (United States)

Albéri, Lavinia; Lintas, Alessandra; Kretz, Robert; Schwaller, Beat; Villa, Alessandro E P

2013-06-01

The reticular thalamic nucleus (RTN) of the mouse is characterized by an overwhelming majority of GABAergic neurons receiving afferences from both the thalamus and the cerebral cortex and sending projections mainly on thalamocortical neurons. The RTN neurons express high levels of the "slow Ca(2+) buffer" parvalbumin (PV) and are characterized by low-threshold Ca(2+) currents, I(T). We performed extracellular recordings in ketamine/xylazine anesthetized mice in the rostromedial portion of the RTN. In the RTN of wild-type and PV knockout (PVKO) mice we distinguished four types of neurons characterized on the basis of their firing pattern: irregular firing (type I), medium bursting (type II), long bursting (type III), and tonically firing (type IV). Compared with wild-type mice, we observed in the PVKOs the medium bursting (type II) more frequently than the long bursting type and longer interspike intervals within the burst without affecting the number of spikes. This suggests that PV may affect the firing properties of RTN neurons via a mechanism associated with the kinetics of burst discharges. Ca(v)3.2 channels, which mediate the I(T) currents, were more localized to the somatic plasma membrane of RTN neurons in PVKO mice, whereas Ca(v)3.3 expression was similar in both genotypes. The immunoelectron microscopy analysis showed that Ca(v)3.2 channels were localized at active axosomatic synapses, thus suggesting that the differential localization of Ca(v)3.2 in the PVKOs may affect bursting dynamics. Cross-correlation analysis of simultaneously recorded neurons from the same electrode tip showed that about one-third of the cell pairs tended to fire synchronously in both genotypes, independent of PV expression. In summary, PV deficiency does not affect the functional connectivity between RTN neurons but affects the distribution of Ca(v)3.2 channels and the dynamics of burst discharges of RTN cells, which in turn regulate the activity in the thalamocortical circuit.

Differential Regulation of Action Potential Shape and Burst-Frequency Firing by BK and Kv2 Channels in Substantia Nigra Dopaminergic Neurons.

Science.gov (United States)

Kimm, Tilia; Khaliq, Zayd M; Bean, Bruce P

2015-12-16

channel types participate in action potential repolarization about equally, they have contrasting and partially opposite effects in regulating neuronal firing at frequencies typical of bursting. Our analysis shows that this results from their different kinetic properties, with fast-activating BK channels serving to short-circuit activation of Kv2 channels, which tend to slow firing by producing a deep afterhyperpolarization. The cross-regulation of BK and Kv2 activation illustrates that the functional role of a channel cannot be defined in isolation but depends critically on the context of the other conductances in the cell. Copyright © 2015 the authors 0270-6474/15/3516404-14$15.00/0.

Effective preemptive scheduling scheme for optical burst-switched networks with cascaded wavelength conversion consideration

Science.gov (United States)

Gao, Xingbo

2010-03-01

We introduce a new preemptive scheduling technique for next-generation optical burst switching (OBS) networks considering the impact of cascaded wavelength conversions. It has been shown that when optical bursts are transmitted all optically from source to destination, each wavelength conversion performed along the lightpath may cause certain signal-to-noise deterioration. If the distortion of the signal quality becomes significant enough, the receiver would not be able to recover the original data. Accordingly, subject to this practical impediment, we improve a recently proposed fair channel scheduling algorithm to deal with the fairness problem and aim at burst loss reduction simultaneously in OBS environments. In our scheme, the dynamic priority associated with each burst is based on a constraint threshold and the number of already conducted wavelength conversions among other factors for this burst. When contention occurs, a new arriving superior burst may preempt another scheduled one according to their priorities. Extensive simulation results have shown that the proposed scheme further improves fairness and achieves burst loss reduction as well.

Neutron stars as X-ray burst sources. II. Burst energy histograms and why they burst

International Nuclear Information System (INIS)

Baan, W.A.

1979-01-01

In this work we explore some of the implications of a model for X-ray burst sources where bursts are caused by Kruskal-Schwarzschild instabilities at the magnetopause of an accreting and rotating neutron star. A number of simplifying assumptions are made in order to test the model using observed burst-energy histograms for the rapid burster MXB 1730--335. The predicted histograms have a correct general shape, but it appears that other effects are important as well, and that mode competition, for instance, may suppress the histograms at high burst energies. An explanation is ventured for the enhancement in the histogram at the highest burst energies, which produces the bimodal shape in high accretion rate histograms. Quantitative criteria are given for deciding when accreting neutron stars are steady sources or burst sources, and these criteria are tested using the X-ray pulsars

Thermonuclear model for γ-ray bursts

International Nuclear Information System (INIS)

Woosley, S.E.

1981-01-01

The evolution of magnetized neutron stars with field strengths of approx. 10 12 gauss that are accreting mass onto kilometer-sized polar regions at a rate of approx. 13 M 0 yr -1 is examined. Based on the results of one-dimensional calculations, one finds that stable hydrogen burning, mediated by the hot CNO-cycle, will lead to a critical helium mass in the range 10 20 to 10 22 g km -2 . Owing to the extreme degeneracy of the electron gas providing pressure support, helium burning occurs as a violent thermonuclear runaway which may propagate either as a convective deflagration (Type I burst) or as a detonation wave (Type II burst). Complete combustion of helium into 56 Ni releases from 10 38 to 10 40 erg km -2 and pushes hot plasma with β > 1 above the surface of the neutron star. Rapid expansion of the plasma channels a substantial fraction of the explosion energy into magnetic field stress. Spectral properties are expected to be complex with emission from both thermal and non-thermal processes. The hard γ-outburst of several seconds softens as the event proceeds and is followed by a period, typically of several minutes duration, of softer x-ray emission as the subsurface ashes of the thermonuclear explosion cool. In this model, most γ-ray bursts currently being observed are located at a distance of several hundred parsecs and should recur on a timescale of months to centuries with convective deflagrations (Type I bursts) being the more common variety. An explanation for Jacobson-like transients is also offered

Inward-rectifying potassium (Kir) channels regulate pacemaker activity in spinal nociceptive circuits during early life

Science.gov (United States)

Li, Jie; Blankenship, Meredith L.; Baccei, Mark L.

2013-01-01

Pacemaker neurons in neonatal spinal nociceptive circuits generate intrinsic burst-firing and are distinguished by a lower “leak” membrane conductance compared to adjacent, non-bursting neurons. However, little is known about which subtypes of leak channels regulate the level of pacemaker activity within the developing rat superficial dorsal horn (SDH). Here we demonstrate that a hallmark feature of lamina I pacemaker neurons is a reduced conductance through inward-rectifying potassium (Kir) channels at physiological membrane potentials. Differences in the strength of inward rectification between pacemakers and non-pacemakers indicate the presence of functionally distinct Kir currents in these two populations at room temperature. However, Kir currents in both groups showed high sensitivity to block by extracellular Ba2+ (IC50 ~ 10 µM), which suggests the presence of ‘classical’ Kir (Kir2.x) channels in the neonatal SDH. The reduced Kir conductance within pacemakers is unlikely to be explained by an absence of particular Kir2.x isoforms, as immunohistochemical analysis revealed the expression of Kir2.1, Kir2.2 and Kir2.3 within spontaneously bursting neurons. Importantly, Ba2+ application unmasked rhythmic burst-firing in ~42% of non-bursting lamina I neurons, suggesting that pacemaker activity is a latent property of a sizeable population of SDH cells during early life. In addition, the prevalence of spontaneous burst-firing within lamina I was enhanced in the presence of high internal concentrations of free Mg2+, consistent with its documented ability to block Kir channels from the intracellular side. Collectively, the results indicate that Kir channels are key modulators of pacemaker activity in newborn central pain networks. PMID:23426663

Bud burst and flowering phenology in a mixed oak forest from Eastern Romania

Directory of Open Access Journals (Sweden)

Ecaterina Nicoleta Chesnoiu

2009-12-01

Full Text Available Bud burst and flowering phenology have been observed in year 2008 in a natural white oak species complex situated in eastern Romania. A total of 300 mature individuals was mapped and identified based on leaf morphology. The community consists of four oak species: Quercus pedunculiflora, Q. robur, Q. pubescens and Q. petraea. A set of 28 individuals could not be unambiguously classified to one or another species. Data on bud burst showed a normal distribution and the differences among species were small. The "very late" flushing was recorded on 15th of April, three weeks later when compared to early flushing individuals. The time period between the bud burst and the complete development of leaves was nearly the same in all oak species, varying on average, between 18.4 and 20.6 days. The spatial distribution of phenological groups within the complex appears to be non-randomly, because in many parts of the study plot exist groups in which most of the trees belong to the same phenological category. Our results indicate an overlap in flowering time for all oak species which occur in the area. The data support the hypothesis that interspecific gene flow is possible between closely related oak species.

Bud burst and flowering phenology in a mixed oak forest from Eastern Romania

Directory of Open Access Journals (Sweden)

Ecaterina Nicoleta Chesnoiu

2009-11-01

Full Text Available Bud burst and flowering phenology have been observed in year 2008 ina natural white oak species complex situated in eastern Romania. A total of 300 mature individuals was mapped and identified based on leaf morphology. The community consists of four oak species: Quercus pedunculiflora, Q. robur, Q. pubescens and Q. petraea. A set of 28 individuals could not be unambiguously classified to one or another species. Data on bud burst showed a normal distribution and the differences among species were small. The "very late" flushing was recorded on 15th of April, three weeks later when compared to early flushing individuals. The time period between the bud burst and the complete development of leaves was nearly the same in all oak species, varying on average, between 18.4 and 20.6 days. The spatialdistribution of phenological groups within the complex appears to be non-randomly, because in many parts of the study plot exist groups in which most of the trees belong to the same phenological category. Our results indicate an overlap in flowering time for all oak species which occur in the area. The data support the hypothesis that interspecific gene flow is possible between closely related oak species.

Multi-rod burst test under a loss-of coolant accident condition, (4)

International Nuclear Information System (INIS)

Otomo, Takashi; Hashimoto, Masao; Kawasaki, Satoru; Furuta, Teruo; Uetsuka, Hiroshi

1983-06-01

Multi-rod burst test of No.7808 bundle was performed in steam to estimate quantitative coolant flow channel restriction caused by the ballooning of zircaloy claddings in a fuel assembly during a LOCA transient in LWRs. The test was conducted under the condition that the initial internal pressure in each rod was 35kg/cm 2 (RT) and the heating rate was 9 0 C/s in steam with flow rate of 0.4g/cm 2 .min. The following results were obtained; (1) Maximum and burst pressures in rods were in the range 45 to 48kg/cm 2 and 41 to 45kg/cm 2 , respectively. The burst temperature of cladding were estimated to be 850 to 880 0 C. (2) Axial portions of tubes with greater than 34% strain were observed in the range 0 to 40mm in most rod. The mean length was 19mm in the bundle. (3) The degree of maximum increase in cross-sectional area is 54.2% in the bundle(7 x 7) and 66.9% in the internal rods(5 x 5). (4) Maximum channel area restriction was 40.5% in the bundle(7 x 7) and 51.4% in the internal rods(5 x 5). (author)

Dynamic radio bursts associated with important flare activity in Hale region 16923 and the problem of the relative locations of type II 'slow drift' bursts and coronal transients

Energy Technology Data Exchange (ETDEWEB)

Mckenna-Lawlor, S.M.P.

1983-03-01

Seven type-II radio bursts associated with solar flares in the Hale region 16923 on June 27-29, 1980, are characterized on the basis of data from dynamic radio spectra, white-light observations, radioheliograms, SMM-C/P observations, and Helios I magnetic-field and solar-wind measurements. The data are summarized in tables and graphs and discussed in terms of transient events occurring in the same region. The magnetic shock waves recorded during the period by Helios are described, and channeling effects which may have prevented the detection of type-II burst shocks are examined.

Robust Multiparty Quantum Secret Key Sharing Over Two Collective-Noise Channels via Three-Photon Mixed States

International Nuclear Information System (INIS)

Wang Zhangyin; Yuan Hao; Gao Gan; Shi Shouhua

2006-01-01

We present a robust (n,n)-threshold scheme for multiparty quantum secret sharing of key over two collective-noise channels (i.e., the collective dephasing channel and the collective rotating channel) via three-photon mixed states. In our scheme, only if all the sharers collaborate together can they establish a joint key with the message sender and extract the secret message from the sender's encrypted message. This scheme can be implemented using only a Bell singlet, a one-qubit state and polarization identification of single photon, so it is completely feasible according to the present-day technique.

Estimation of Flow Channel Parameters for Flowing Gas Mixed with Air in Atmospheric-pressure Plasma Jets

Science.gov (United States)

Yambe, Kiyoyuki; Saito, Hidetoshi

2017-12-01

When the working gas of an atmospheric-pressure non-equilibrium (cold) plasma flows into free space, the diameter of the resulting flow channel changes continuously. The shape of the channel is observed through the light emitted by the working gas of the atmospheric-pressure plasma. When the plasma jet forms a conical shape, the diameter of the cylindrical shape, which approximates the conical shape, defines the diameter of the flow channel. When the working gas flows into the atmosphere from the inside of a quartz tube, the gas mixes with air. The molar ratio of the working gas and air is estimated from the corresponding volume ratio through the relationship between the diameter of the cylindrical plasma channel and the inner diameter of the quartz tube. The Reynolds number is calculated from the kinematic viscosity of the mixed gas and the molar ratio. The gas flow rates for the upper limit of laminar flow and the lower limit of turbulent flow are determined by the corresponding Reynolds numbers estimated from the molar ratio. It is confirmed that the plasma jet length and the internal plasma length associated with strong light emission increase with the increasing gas flow rate until the rate for the upper limit of laminar flow and the lower limit of turbulent flow, respectively. Thus, we are able to explain the increasing trend in the plasma lengths with the diameter of the flow channel and the molar ratio by using the cylindrical approximation.

Cosmic gamma-ray burst

International Nuclear Information System (INIS)

Yamagami, Takamasa

1985-01-01

Ballon experiments for searching gamma-ray burst were carried out by employing rotating-cross modulation collimators. From a very long observation of total 315 hours during 1975 to 1979, three gamma-ray intensity anomalies were observed which were speculated as a gamma-ray burst. As for the first gamma-ray intensity anomaly observed in 1975, the burst source could be located precisely but the source, heavenly body, could not be specified. Gamma-ray burst source estimation was made by analyzing distribution of burst source in the celestial sphere, burst size distribution, and burst peak. Using the above-mentioned data together with previously published ones, apparent inconsistency was found between the observed results and the adopted theory that the source was in the Galaxy, and this inconsistency was found due to the different time profiles of the burst observed with instruments of different efficiency. It was concluded by these analysis results that employment of logN - logP (relation between burst frequency and burst count) was better than that of logN - logS (burst size) in the examination of gamma-ray burst because the former was less uncertain than the latter. Analyzing the author's observed gamma-ray burst data and the related published data, it was clarified that the burst distribution was almost P -312 for the burst peak value larger than 10 -6 erg/cm 2 .sec. The author could indicate that the calculated celestial distribution of burst source was consistent with the observed results by the derivation using the logN - logP relationship and that the burst larger than 10 -6 erg/cm 2 .sec happens about one thousand times a year, about ten times of the previous value. (Takagi, S.)

Impairments due to Burst-Mode Transmission in a Raman-based Long Reach PON Link

DEFF Research Database (Denmark)

Kjær, Rasmus; Tafur Monroy, Idelfonso; Oxenløwe, Leif Katsuo

2007-01-01

A recently proposed passive-optical-network (PON) link based on distributed Raman amplification is tested with disturbing burst-mode traffic. The resulting impairments are quantified through penalty measurements on a single surviving data channel as a function of the disturbing channel power. When...... the disturbing channels co- or counter propagate with the data channel, penalties of less than 1 dB are found for disturbing input powers up to 7 and 11 dBm, respectively. The penalty is further reduced when a moderate amount of continuous-wave light is used to clamp the gain. The results indicate...

Swift pointing and gravitational-wave bursts from gamma-ray burst events

International Nuclear Information System (INIS)

Sutton, Patrick J; Finn, Lee Samuel; Krishnan, Badri

2003-01-01

The currently accepted model for gamma-ray burst phenomena involves the violent formation of a rapidly rotating solar-mass black hole. Gravitational waves should be associated with the black-hole formation, and their detection would permit this model to be tested. Even upper limits on the gravitational-wave strength associated with gamma-ray bursts could constrain the gamma-ray burst model. This requires joint observations of gamma-ray burst events with gravitational and gamma-ray detectors. Here we examine how the quality of an upper limit on the gravitational-wave strength associated with gamma-ray bursts depends on the relative orientation of the gamma-ray-burst and gravitational-wave detectors, and apply our results to the particular case of the Swift Burst-Alert Telescope (BAT) and the LIGO gravitational-wave detectors. A result of this investigation is a science-based 'figure of merit' that can be used, together with other mission constraints, to optimize the pointing of the Swift telescope for the detection of gravitational waves associated with gamma-ray bursts

Mixed-Modality Stimulation to Evoke Two Modalities Simultaneously in One Channel for Electrocutaneous Sensory Feedback.

Science.gov (United States)

Choi, Kyunghwan; Kim, Pyungkang; Kim, Kyung-Soo; Kim, Soohyun

2017-12-01

One of the long-standing challenges in upper limb prosthetics is restoring the sensory feedback that is missing due to amputation. Two approaches have previously been presented to provide various types of sensory information to users, namely, multi-modality sensory feedback and using an array of single-modality stimulators. However, the feedback systems used in these approaches were too bulky to be embedded in prosthesis sockets. In this paper, we propose an electrocutaneous sensory feedback method that is capable of conveying two modalities simultaneously with only one electrode. The stimulation method, which we call mixed-modality stimulation, utilizes the phenomenon in which the superposition of two electric pulse trains of different frequencies is able to evoke two different modalities (i.e., pressure and tapping) at the same time. We conducted psychophysical experiments in which healthy subjects were required to recognize the intensity of pressure or the frequency of tapping from mixed-modality or two-channel stimulations. The results demonstrated that the subjects were able to discriminate the features of the two modalities in one electrode during mixed-modality stimulation and that the accuracies of successful recognitions (mean ± standard deviation) for the two feedback variables were 84.3 ± 7% for mixed-modality stimulation and 89.5 ± 6% for two-channel dual-modality stimulation, showing no statistically significant difference. Therefore, mixed-modality stimulation is an attractive method for modulating two modalities independently with only one electrode, and it could be used for implementing a compact sensory feedback system that is able to provide two different types of sensory information from prosthetics.

Numerical study of mixed convection heat transfer enhancement in a channel with active flow modulation

Science.gov (United States)

Billah, Md. Mamun; Khan, Md Imran; Rahman, Mohammed Mizanur; Alam, Muntasir; Saha, Sumon; Hasan, Mohammad Nasim

2017-06-01

A numerical study of steady two dimensional mixed convention heat transfer phenomena in a rectangular channel with active flow modulation is carried out in this investigation. The flow in the channel is modulated via a rotating cylinder placed at the center of the channel. In this study the top wall of the channel is subjected to an isothermal low temperature while a discrete isoflux heater is positioned on the lower wall. The fluid flow under investigation is assumed to have a Prandtl number of 0.71 while the Reynolds No. and the Grashof No. are varied in wide range for four different situations such as: i) plain channel with no cylinder, ii) channel with stationary cylinder, iii) channel with clockwise rotating cylinder and iv) channel with counter clockwise rotating cylinder. The results obtained in this study are presented in terms of the distribution of streamlines, isotherms in the channel while the heat transfer process from the heat source is evaluated in terms of the local Nusselt number, average Nusselt number. The outcomes of this study also indicate that the results are strongly dependent on the type of configuration and direction of rotation of the cylinder and that the average Nusselt number value rises with an increase in Reynolds and Grashof numbers but the correlation between these parameters at higher values of Reynolds and Grashof numbers becomes weak.

The initial study on supercritical water flow and heat transfer in square rod bundle channel with mixing vane

International Nuclear Information System (INIS)

Zuo Guoping; Cao Can; Yu Tao

2010-01-01

Three-dimensional rectangular channel with the mixing wine in supercritical water reactor was studied in the paper using the FLUENT software. The mixing wing elevation influence on temperature distribution and flow field were studied in the model. The results showed the mixing wing caused fluid circumferential flow, making flow hot and cold fluids mixed and fluid temperature uniform distribution, effectively improved the fuel rod surface temperature distribution and reduced hot temperature. Among the four cases of mixing wing elevation of 15, 30, 45 and 50 angle, 30 angle is the best case in improving temperature distribution. (authors)

Quantum key based burst confidentiality in optical burst switched networks.

Science.gov (United States)

Balamurugan, A M; Sivasubramanian, A

2014-01-01

The optical burst switching (OBS) is an emergent result to the technology concern that could achieve a feasible network in future. They are endowed with the ability to meet the bandwidth requirement of those applications that require intensive bandwidth. There are more domains opening up in the OBS that evidently shows their advantages and their capability to face the future network traffic. However, the concept of OBS is still far from perfection facing issues in case of security threat. The transfer of optical switching paradigm to optical burst switching faces serious downfall in the fields of burst aggregation, routing, authentication, dispute resolution, and quality of service (QoS). This paper deals with employing RC4 (stream cipher) to encrypt and decrypt bursts thereby ensuring the confidentiality of the burst. Although the use of AES algorithm has already been proposed for the same issue, by contrasting the two algorithms under the parameters of burst encryption and decryption time, end-to-end delay, it was found that RC4 provided better results. This paper looks to provide a better solution for the confidentiality of the burst in OBS networks.

Quantum Key Based Burst Confidentiality in Optical Burst Switched Networks

Directory of Open Access Journals (Sweden)

A. M. Balamurugan

2014-01-01

Full Text Available The optical burst switching (OBS is an emergent result to the technology concern that could achieve a feasible network in future. They are endowed with the ability to meet the bandwidth requirement of those applications that require intensive bandwidth. There are more domains opening up in the OBS that evidently shows their advantages and their capability to face the future network traffic. However, the concept of OBS is still far from perfection facing issues in case of security threat. The transfer of optical switching paradigm to optical burst switching faces serious downfall in the fields of burst aggregation, routing, authentication, dispute resolution, and quality of service (QoS. This paper deals with employing RC4 (stream cipher to encrypt and decrypt bursts thereby ensuring the confidentiality of the burst. Although the use of AES algorithm has already been proposed for the same issue, by contrasting the two algorithms under the parameters of burst encryption and decryption time, end-to-end delay, it was found that RC4 provided better results. This paper looks to provide a better solution for the confidentiality of the burst in OBS networks.

Burst suppression probability algorithms: state-space methods for tracking EEG burst suppression

Science.gov (United States)

Chemali, Jessica; Ching, ShiNung; Purdon, Patrick L.; Solt, Ken; Brown, Emery N.

2013-10-01

Objective. Burst suppression is an electroencephalogram pattern in which bursts of electrical activity alternate with an isoelectric state. This pattern is commonly seen in states of severely reduced brain activity such as profound general anesthesia, anoxic brain injuries, hypothermia and certain developmental disorders. Devising accurate, reliable ways to quantify burst suppression is an important clinical and research problem. Although thresholding and segmentation algorithms readily identify burst suppression periods, analysis algorithms require long intervals of data to characterize burst suppression at a given time and provide no framework for statistical inference. Approach. We introduce the concept of the burst suppression probability (BSP) to define the brain's instantaneous propensity of being in the suppressed state. To conduct dynamic analyses of burst suppression we propose a state-space model in which the observation process is a binomial model and the state equation is a Gaussian random walk. We estimate the model using an approximate expectation maximization algorithm and illustrate its application in the analysis of rodent burst suppression recordings under general anesthesia and a patient during induction of controlled hypothermia. Main result. The BSP algorithms track burst suppression on a second-to-second time scale, and make possible formal statistical comparisons of burst suppression at different times. Significance. The state-space approach suggests a principled and informative way to analyze burst suppression that can be used to monitor, and eventually to control, the brain states of patients in the operating room and in the intensive care unit.

The golden-mean surface pattern to enhance flow mixing in micro-channel.

Science.gov (United States)

Wang, J F; Liu, Y; Xu, Y S

2009-04-01

Mixing of analytes and reagents in microfluidic devices is often crucial to the effective functioning of lab-on-a-chip. It is possible to affect the mixing in microfluidics by intelligently controlling the thermodynamic and chemical properties of the substrate surface. Numerous studies have shown that the phase behavior of mixtures is significantly affected by surface properties of microfluidics. For example, the phase separation between the fluids can be affected by heterogeneous patterns on the substrate. The patterned substrate can offer an effective means to control fluid behavior and in turn to enhance mixing. The golden mean is a ratio that is present in the growth patterns of many biological systems--the spiral formed by a shell or the curve of a fern, for example. The golden mean or golden section was derived by the ancient Greeks. Like "pi" the golden mean ratio is an irrational number 1.618, or (square root{5} + 1) / 2. It was found that the golden mean was an optimum ratio in natural convection heat transfer problem (Liu and Phan-Thien, Numer Heat Transf 37:613-630, 2000). In this study, we numerically studied the effect of optimum surface pattern on mixing in a micro channel and found that the flow oscillation and chaotic mixing were enhanced apparently when the ratio of hydrophobic and hydrophilic boundary follows the golden mean.

Solar radio bursts and their relation of coronal magnetic structures

International Nuclear Information System (INIS)

Kattenberg, A.

1981-01-01

Following a general introduction, chapters II and III describe a model for coronal flux tubes. The model tube is a cylindrically symmetric localized force free current, that is embedded in a potential field. In both chapters the growth rates and sizes of the kink mode instability are calculated by solving the linearized equation of motion. In chapters IV and V, observations of solar Type-I radio bursts are presented and analysed. The observations were gathered with the 60-channel radio spectrograph in Dwingeloo. Chapters VI, VII, VIII, IX and X are concerned with observations of solar microwave bursts. The observations, with high time resolution (0.1 s) and high one-dimensional angular resolution (max. 4'') were made with the Westerbork Synthesis Radio Telescope. (Auth.)

THE FERMI-GBM X-RAY BURST MONITOR: THERMONUCLEAR BURSTS FROM 4U 0614+09

International Nuclear Information System (INIS)

Linares, M.; Chakrabarty, D.; Connaughton, V.; Bhat, P. N.; Briggs, M. S.; Preece, R.; Jenke, P.; Kouveliotou, C.; Wilson-Hodge, C. A.; Van der Horst, A. J.; Camero-Arranz, A.; Finger, M.; Paciesas, W. S.; Beklen, E.; Von Kienlin, A.

2012-01-01

Thermonuclear bursts from slowly accreting neutron stars (NSs) have proven difficult to detect, yet they are potential probes of the thermal properties of the NS interior. During the first year of a systematic all-sky search for X-ray bursts using the Gamma-ray Burst Monitor aboard the Fermi Gamma-ray Space Telescope we have detected 15 thermonuclear bursts from the NS low-mass X-ray binary 4U 0614+09 when it was accreting at nearly 1% of the Eddington limit. We measured an average burst recurrence time of 12 ± 3 days (68% confidence interval) between 2010 March and 2011 March, classified all bursts as normal duration bursts and placed a lower limit on the recurrence time of long/intermediate bursts of 62 days (95% confidence level). We discuss how observations of thermonuclear bursts in the hard X-ray band compare to pointed soft X-ray observations and quantify such bandpass effects on measurements of burst radiated energy and duration. We put our results for 4U 0614+09 in the context of other bursters and briefly discuss the constraints on ignition models. Interestingly, we find that the burst energies in 4U 0614+09 are on average between those of normal duration bursts and those measured in long/intermediate bursts. Such a continuous distribution in burst energy provides a new observational link between normal and long/intermediate bursts. We suggest that the apparent bimodal distribution that defined normal and long/intermediate duration bursts during the last decade could be due to an observational bias toward detecting only the longest and most energetic bursts from slowly accreting NSs.

Fuzzy-Based Adaptive Hybrid Burst Assembly Technique for Optical Burst Switched Networks

Directory of Open Access Journals (Sweden)

Abubakar Muhammad Umaru

2014-01-01

Full Text Available The optical burst switching (OBS paradigm is perceived as an intermediate switching technology for future all-optical networks. Burst assembly that is the first process in OBS is the focus of this paper. In this paper, an intelligent hybrid burst assembly algorithm that is based on fuzzy logic is proposed. The new algorithm is evaluated against the traditional hybrid burst assembly algorithm and the fuzzy adaptive threshold (FAT burst assembly algorithm via simulation. Simulation results show that the proposed algorithm outperforms the hybrid and the FAT algorithms in terms of burst end-to-end delay, packet end-to-end delay, and packet loss ratio.

Spiking and bursting patterns of fractional-order Izhikevich model

Science.gov (United States)

Teka, Wondimu W.; Upadhyay, Ranjit Kumar; Mondal, Argha

2018-03-01

Bursting and spiking oscillations play major roles in processing and transmitting information in the brain through cortical neurons that respond differently to the same signal. These oscillations display complex dynamics that might be produced by using neuronal models and varying many model parameters. Recent studies have shown that models with fractional order can produce several types of history-dependent neuronal activities without the adjustment of several parameters. We studied the fractional-order Izhikevich model and analyzed different kinds of oscillations that emerge from the fractional dynamics. The model produces a wide range of neuronal spike responses, including regular spiking, fast spiking, intrinsic bursting, mixed mode oscillations, regular bursting and chattering, by adjusting only the fractional order. Both the active and silent phase of the burst increase when the fractional-order model further deviates from the classical model. For smaller fractional order, the model produces memory dependent spiking activity after the pulse signal turned off. This special spiking activity and other properties of the fractional-order model are caused by the memory trace that emerges from the fractional-order dynamics and integrates all the past activities of the neuron. On the network level, the response of the neuronal network shifts from random to scale-free spiking. Our results suggest that the complex dynamics of spiking and bursting can be the result of the long-term dependence and interaction of intracellular and extracellular ionic currents.

Windowless microfluidic platform based on capillary burst valves for high intensity x-ray measurements

International Nuclear Information System (INIS)

Vig, Asger Laurberg; Enevoldsen, Nikolaj; Thilsted, Anil Haraksingh; Eriksen, Johan; Kristensen, Anders; Haldrup, Kristoffer; Feidenhans'l, Robert; Nielsen, Martin Meedom

2009-01-01

We propose and describe a microfluidic system for high intensity x-ray measurements. The required open access to a microfluidic channel is provided by an out-of-plane capillary burst valve (CBV). The functionality of the out-of-plane CBV is characterized with respect to the diameter of the windowless access hole, ranging from 10 to 130 μm. Maximum driving pressures from 22 to 280 mbar corresponding to refresh rates of the exposed sample from 300 Hz to 54 kHz is demonstrated. The microfluidic system is tested at beamline ID09b at the ESRF synchrotron radiation facility in Grenoble, and x-ray scattering measurements are shown to be feasible and to require only very limited amounts of sample, <1 ml/h of measurements without recapturing of sample. With small adjustments of the present chip design, scattering angles up to 30 deg. can be achieved without shadowing effects and integration on-chip mixing and spectroscopy appears straightforward.

A FAST RADIO BURST IN THE DIRECTION OF THE CARINA DWARF SPHEROIDAL GALAXY

International Nuclear Information System (INIS)

Ravi, V.; Shannon, R. M.; Jameson, A.

2015-01-01

We report the real-time discovery of a fast radio burst (FRB 131104) with the Parkes radio telescope in a targeted observation of the Carina dwarf spheroidal galaxy. The dispersion measure of the burst is 779 cm –3  pc, exceeding predictions for the maximum line-of-sight Galactic contribution by a factor of 11. The temporal structure of the burst is characterized by an exponential scattering tail with a timescale of 2.0 −0.5 +0.8  ms at 1582 MHz that scales as frequency to the power –4.4 −1.8 +1.6 (all uncertainties represent 95% confidence intervals). We bound the intrinsic pulse width to be <0.64 ms due to dispersion smearing across a single spectrometer channel. Searches in 78 hr of follow-up observations with the Parkes telescope reveal no additional sporadic emission and no evidence for associated periodic radio emission. We hypothesize that the burst is associated with the Carina dwarf galaxy. Follow-up observations at other wavelengths are necessary to test this hypothesis

Cognitive digital receiver for burst mode phase modulated radio over fiber links

DEFF Research Database (Denmark)

Guerrero Gonzalez, Neil; Zibar, Darko; Tafur Monroy, Idelfonso

2010-01-01

A novel cognitive receiver for modulation format recognition with reconfigurable carrier recovery scheme is proposed and experimentally demonstrated for phase modulated radio-over-fibre links. Demodulation of burst-mode mixed modulation formats (PSK and QAM) is demonstrated after 40km...

Fast Burst Synchronization for Power Line Communication Systems

Directory of Open Access Journals (Sweden)

Lampe Lutz

2007-01-01

Full Text Available Fast burst synchronization is an important requirement in asynchronous communication networks, where devices transmit short data packets in an unscheduled fashion. Such a synchronization is typically achieved by means of a preamble sent in front of the data packet. In this paper, we study fast burst synchronization for power line communication (PLC systems operating below 500 kHz and transmitting data rates of up to about 500 kbps as it is typical in various PLC network applications. In particular, we are concerned with the receiver processing of the preamble signal and the actual design of preambles suitable for fast burst synchronization in such PLC systems. Our approach is comprehensive in that it takes into account the most distinctive characteristics of the power line channel, which are multipath propagation, highly varying path loss, and disturbance by impulse noise, as well as important practical constraints, especially the need for spectral shaping of the preamble signal and fast adjustment of the automatic gain control (AGC. In fact, we regard the explicit incorporation of these various requirements into the preamble design as the main contribution of this work. We devise an optimization criterion and a stochastic algorithm to search for suitable preamble sequences. A comprehensive performance comparison of a designed and two conventional preambles shows that the designed sequence is superior in terms of (a fast burst synchronization in various transmission environments, (b fast AGC adjustment, and (c compliance of its spectrum with the spectral mask applied to the data transmit signal.

Contribution to the determination of the mixing length in a channel; Contribution a la determination de la longueur de bon melange dans un canal

Energy Technology Data Exchange (ETDEWEB)

Spitalnik, J [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

1967-04-15

A formula giving the mixing length in a rectangular channel is established. The value of that mixing length depends on the geometrical dimensions of the channel, the longitudinal, lateral and vertical diffusion coefficients, and the water average velocity in the channel. (author) [French] On etablit une formule permettant de calculer la longueur de bon melange dans un canal rectangulaire. La valeur de cette longueur depend des donnees geometriques du canal, des coefficients de diffusion longitudinal, transversal et vertical, et de la vitesse moyenne de l'eau dans le canal. (auteur)

Transient mixed convection in a channel with an open cavity filled with porous media

International Nuclear Information System (INIS)

Buonomo, B; Cresci, G; Manca, O; Mesolella, P; Nardini, S

2012-01-01

In this work transient mixed convection in a porous medium in a horizontal channel with a open cavity below is studied numerically. The cavity presents a heated wall at uniform heat flux and the other walls of the cavity and the channel are assumed adiabatic. Air flows through the horizontal channel. The heated wall of the cavity experiences a uniform heat flux in such a way that the forced flow is perpendicular to the motion due to natural convection. The study is carried out employing Brinkman-Forchheimer-extended Darcy model and two energy equations due to the local thermal non-equilibrium assumption. The flow in the channel is assumed to be two-dimensional, laminar, incompressible. Boussinesq approximation is considered. The thermophysical properties of the fluid are evaluated at the ambient temperature. The results for stream function and temperature distribution given at different times are obtained. Wall temperature value are given and also, the velocity and temperature profiles in several sections of the cavity are presented. In addition, the Nusselt number, both local and average, is presented along with the temporal variations of the average Nusselt number.

Automatic burst detection for the EEG of the preterm infant.

Science.gov (United States)

Jennekens, Ward; Ruijs, Loes S; Lommen, Charlotte M L; Niemarkt, Hendrik J; Pasman, Jaco W; van Kranen-Mastenbroek, Vivianne H J M; Wijn, Pieter F F; van Pul, Carola; Andriessen, Peter

2011-10-01

To aid with prognosis and stratification of clinical treatment for preterm infants, a method for automated detection of bursts, interburst-intervals (IBIs) and continuous patterns in the electroencephalogram (EEG) is developed. Results are evaluated for preterm infants with normal neurological follow-up at 2 years. The detection algorithm (MATLAB®) for burst, IBI and continuous pattern is based on selection by amplitude, time span, number of channels and numbers of active electrodes. Annotations of two neurophysiologists were used to determine threshold values. The training set consisted of EEG recordings of four preterm infants with postmenstrual age (PMA, gestational age + postnatal age) of 29-34 weeks. Optimal threshold values were based on overall highest sensitivity. For evaluation, both observers verified detections in an independent dataset of four EEG recordings with comparable PMA. Algorithm performance was assessed by calculation of sensitivity and positive predictive value. The results of algorithm evaluation are as follows: sensitivity values of 90% ± 6%, 80% ± 9% and 97% ± 5% for burst, IBI and continuous patterns, respectively. Corresponding positive predictive values were 88% ± 8%, 96% ± 3% and 85% ± 15%, respectively. In conclusion, the algorithm showed high sensitivity and positive predictive values for bursts, IBIs and continuous patterns in preterm EEG. Computer-assisted analysis of EEG may allow objective and reproducible analysis for clinical treatment.

QKD-Based Secured Burst Integrity Design for Optical Burst Switched Networks

Science.gov (United States)

Balamurugan, A. M.; Sivasubramanian, A.; Parvathavarthini, B.

2016-03-01

The field of optical transmission has undergone numerous advancements and is still being researched mainly due to the fact that optical data transmission can be done at enormous speeds. It is quite evident that people prefer optical communication when it comes to large amount of data involving its transmission. The concept of switching in networks has matured enormously with several researches, architecture to implement and methods starting with Optical circuit switching to Optical Burst Switching. Optical burst switching is regarded as viable solution for switching bursts over networks but has several security vulnerabilities. However, this work exploited the security issues associated with Optical Burst Switching with respect to integrity of burst. This proposed Quantum Key based Secure Hash Algorithm (QKBSHA-512) with enhanced compression function design provides better avalanche effect over the conventional integrity algorithms.

The genesis of period-adding bursting without bursting-chaos in the Chay model

International Nuclear Information System (INIS)

Yang Zhuoqin; Lu Qishao; Li Li

2006-01-01

According to the period-adding firing patterns without chaos observed in neuronal experiments, the genesis of the period-adding 'fold/homoclinic' bursting sequence without bursting-chaos is explored by numerical simulation, fast/slow dynamics and bifurcation analysis of limit cycle in the neuronal Chay model. It is found that each periodic bursting, from period-1 to 7, is separately generated by the corresponding periodic spiking pattern through two period-doubling bifurcations, except for the period-1 bursting occurring via a Hopf bifurcation. Consequently, it can be revealed that this period-adding bursting bifurcation without chaos has a compound bifurcation structure with transitions from spiking to bursting, which is closely related to period-doubling bifurcations of periodic spiking in essence

The action of blocking agents applied to the inner face of Ca(2+)-activated K+ channels from human erythrocytes.

Science.gov (United States)

Dunn, P M

1998-09-15

The actions of clotrimazole and cetiedil, two drugs known to inhibit the Gardos channel, have been studied on single intermediate conductance calcium-activated potassium (IKCa) channels in inside out patches from human red blood cells, and compared with those of TEA and Ba2+ applied to the cytoplasmic face of the membrane. TEA produced a fast block which was observed as a reduction in the amplitude of the single channel current. This effect was weakly voltage dependent with the fraction of the membrane potential sensed by TEA at its binding site (delta) of 0.18 and a Kd at 0 mV of 20.5 mM. Ba2+ was a very potent blocker of the channel, breaking the single channel activity up into bursts, inter-spersed with silent periods lasting several seconds. The effect of Ba2+ was very voltage sensitive, delta = 0.44, and a Kd at 0 mV of 0.15 microM. Clotrimazole applied to the inner face of the membrane at a concentration block resulting in bursts of channel activity separated by quiescent periods lasting many seconds. The effect of clotrimazole was mimicked by a quaternary derivative UCL 1559, in keeping with an action at the cytoplasmic face of the channel. A high concentration of cetiedil (100 microM) produced only a weak block of the channel. The kinetics of this action were very slow, with burst and inter-burst intervals lasting several minutes. While inhibition of the Gardos channel by cetiedil is unlikely to involve an intracellular site of action, if clotrimazole is able to penetrate the membrane, part of its effect may result from binding to an intracellular site on the channel.

A repeating fast radio burst.

Science.gov (United States)

Spitler, L G; Scholz, P; Hessels, J W T; Bogdanov, S; Brazier, A; Camilo, F; Chatterjee, S; Cordes, J M; Crawford, F; Deneva, J; Ferdman, R D; Freire, P C C; Kaspi, V M; Lazarus, P; Lynch, R; Madsen, E C; McLaughlin, M A; Patel, C; Ransom, S M; Seymour, A; Stairs, I H; Stappers, B W; van Leeuwen, J; Zhu, W W

2016-03-10

Fast radio bursts are millisecond-duration astronomical radio pulses of unknown physical origin that appear to come from extragalactic distances. Previous follow-up observations have failed to find additional bursts at the same dispersion measure (that is, the integrated column density of free electrons between source and telescope) and sky position as the original detections. The apparent non-repeating nature of these bursts has led to the suggestion that they originate in cataclysmic events. Here we report observations of ten additional bursts from the direction of the fast radio burst FRB 121102. These bursts have dispersion measures and sky positions consistent with the original burst. This unambiguously identifies FRB 121102 as repeating and demonstrates that its source survives the energetic events that cause the bursts. Additionally, the bursts from FRB 121102 show a wide range of spectral shapes that appear to be predominantly intrinsic to the source and which vary on timescales of minutes or less. Although there may be multiple physical origins for the population of fast radio bursts, these repeat bursts with high dispersion measure and variable spectra specifically seen from the direction of FRB 121102 support an origin in a young, highly magnetized, extragalactic neutron star.

Spike and burst coding in thalamocortical relay cells.

Directory of Open Access Journals (Sweden)

Fleur Zeldenrust

2018-02-01

Full Text Available Mammalian thalamocortical relay (TCR neurons switch their firing activity between a tonic spiking and a bursting regime. In a combined experimental and computational study, we investigated the features in the input signal that single spikes and bursts in the output spike train represent and how this code is influenced by the membrane voltage state of the neuron. Identical frozen Gaussian noise current traces were injected into TCR neurons in rat brain slices as well as in a validated three-compartment TCR model cell. The resulting membrane voltage traces and spike trains were analyzed by calculating the coherence and impedance. Reverse correlation techniques gave the Event-Triggered Average (ETA and the Event-Triggered Covariance (ETC. This demonstrated that the feature selectivity started relatively long before the events (up to 300 ms and showed a clear distinction between spikes (selective for fluctuations and bursts (selective for integration. The model cell was fine-tuned to mimic the frozen noise initiated spike and burst responses to within experimental accuracy, especially for the mixed mode regimes. The information content carried by the various types of events in the signal as well as by the whole signal was calculated. Bursts phase-lock to and transfer information at lower frequencies than single spikes. On depolarization the neuron transits smoothly from the predominantly bursting regime to a spiking regime, in which it is more sensitive to high-frequency fluctuations. The model was then used to elucidate properties that could not be assessed experimentally, in particular the role of two important subthreshold voltage-dependent currents: the low threshold activated calcium current (IT and the cyclic nucleotide modulated h current (Ih. The ETAs of those currents and their underlying activation/inactivation states not only explained the state dependence of the firing regime but also the long-lasting concerted dynamic action of the two

The genesis of period-adding bursting without bursting-chaos in the Chay model

International Nuclear Information System (INIS)

Yang Zhuoqin; Lu Qishao; Li Li

2006-01-01

According to the period-adding firing patterns without chaos observed in neuronal experiments, the genesis of the period-adding 'fold/homoclinic' bursting sequence without bursting-chaos is explored by numerical simulation, fast/slow dynamics and bifurcation analysis of limit cycle in the neuronal Chay model. It is found that each periodic bursting, from period-1 to period-7, is separately generated by the corresponding periodic spiking pattern through two period-doubling bifurcations, except for the period-1 bursting occurring via a Hopf bifurcation. Consequently, it can be revealed that this period-adding bursting bifurcation without chaos has a compound bifurcation structure with transitions from spiking to bursting, which is closely related to period-doubling bifurcations of periodic spiking in essence

INVESTIGATION OF PRIMORDIAL BLACK HOLE BURSTS USING INTERPLANETARY NETWORK GAMMA-RAY BURSTS

Energy Technology Data Exchange (ETDEWEB)

Ukwatta, T. N. [Director' s Postdoctoral Fellow, Space and Remote Sensing (ISR-2), Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Hurley, K. [University of California, Berkeley, Space Sciences Laboratory, 7 Gauss Way, Berkeley, CA 94720-7450 (United States); MacGibbon, J. H. [Department of Physics, University of North Florida, Jacksonville, FL 32224 (United States); Svinkin, D. S.; Aptekar, R. L.; Golenetskii, S. V.; Frederiks, D. D.; Pal' shin, V. D. [Ioffe Physical Technical Institute, St. Petersburg, 194021 (Russian Federation); Goldsten, J. [Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723 (United States); Boynton, W. [Department of Planetary Sciences, University of Arizona, Tucson, AZ 85721 (United States); Kozyrev, A. S. [Space Research Institute, 84/32, Profsoyuznaya, Moscow 117997 (Russian Federation); Rau, A.; Kienlin, A. von; Zhang, X. [Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, Postfach 1312, Garching, D-85748 (Germany); Connaughton, V. [University of Alabama in Huntsville, NSSTC, 320 Sparkman Drive, Huntsville, AL 35805 (United States); Yamaoka, K. [Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1 Fuchinobe, Sagamihara, Kanagawa 229-8558 (Japan); Ohno, M. [Department of Physics, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Ohmori, N. [Department of Applied Physics, University of Miyazaki, 1-1 Gakuen kibanadai-nishi, Miyazaki-shi, Miyazaki 889-2192 (Japan); Feroci, M. [INAF/IAPS-Roma, via Fosso del Cavaliere 100, I-00133, Roma (Italy); Frontera, F., E-mail: tilan@lanl.gov [Department of Physics and Earth Science, University of Ferrara, via Saragat 1, I-44122 Ferrara (Italy); and others

2016-07-20

The detection of a gamma-ray burst (GRB) in the solar neighborhood would have very important implications for GRB phenomenology. The leading theories for cosmological GRBs would not be able to explain such events. The final bursts of evaporating primordial black holes (PBHs), however, would be a natural explanation for local GRBs. We present a novel technique that can constrain the distance to GRBs using detections from widely separated, non-imaging spacecraft. This method can determine the actual distance to the burst if it is local. We applied this method to constrain distances to a sample of 36 short-duration GRBs detected by the Interplanetary Network (IPN) that show observational properties that are expected from PBH evaporations. These bursts have minimum possible distances in the 10{sup 13}–10{sup 18} cm (7–10{sup 5} au) range, which are consistent with the expected PBH energetics and with a possible origin in the solar neighborhood, although none of the bursts can be unambiguously demonstrated to be local. Assuming that these bursts are real PBH events, we estimate lower limits on the PBH burst evaporation rate in the solar neighborhood.

Mixed convection heat transfer from confined tandem square cylinders in a horizontal channel

KAUST Repository

Huang, Zhu

2013-11-01

This paper presents a numerical study on the two-dimensional laminar mixed convective flow and heat transfer around two identical isothermal square cylinders arranged in tandem and confined in a channel. The spacing between the cylinders is fixed with four widths of the cylinder and the blockage ratio and the Prandtl number are fixed at 0.1 and 0.7 respectively. The mixed convective flow and heat transfer is simulated by high accuracy multidomain pseudospectral method. The Reynolds number (Re) is studied in the range 80 ≤ Re ≤ 150, the Richardson number (Ri) demonstrating the influence of thermal buoyancy ranges from 0 to 1. Numerical results reveal that, with the thermal buoyancy effect, the mixed convective flow sheds vortex behind the cylinders and keeps periodic oscillating. The variations of characteristic quantities related to flow and heat transfer processes, such as the overall drag and lift coefficients and the Nusselt numbers, are presented and discussed. Furthermore, the influence of thermal buoyancy on the fluid flow and heat transfer are discussed and analysed. © 2013 Elsevier Ltd. All rights reserved.

Gamma Ray Bursts - Observations

Science.gov (United States)

Gehrels, N.; Cannizzo, J. K.

2010-01-01

We are in an exciting period of discovery for gamma-ray bursts. The Swift observatory is detecting 100 bursts per year, providing arcsecond localizations and sensitive observations of the prompt and afterglow emission. The Fermi observatory is observing 250 bursts per year with its medium-energy GRB instrument and about 10 bursts per year with its high-energy LAT instrument. In addition, rapid-response telescopes on the ground are providing new capabilities to study optical emission during the prompt phase and spectral signatures of the host galaxies. The combined data set is enabling great advances in our understanding of GRBs including afterglow physics, short burst origin, and high energy emission.

Proton channel HVCN1 is required for effector functions of mouse eosinophils

Science.gov (United States)

2013-01-01

Background Proton currents are required for optimal respiratory burst in phagocytes. Recently, HVCN1 was identified as the molecule required for the voltage-gated proton channel activity associated with the respiratory burst in neutrophils. Although there are similarities between eosinophils and neutrophils regarding their mechanism for respiratory burst, the role of proton channels in eosinophil functions has not been fully understood. Results In the present study, we first identified the expression of the proton channel HVCN1 in mouse eosinophils. Furthermore, using HVCN1-deficient eosinophils, we demonstrated important cell-specific effector functions for HVCN1. Similar to HVCN1-deficient neutrophils, HVCN1-deficient eosinophils produced significantly less reactive oxygen species (ROS) upon phorbol myristate acetate (PMA) stimulation compared with WT eosinophils. In contrast to HVCN1-deficient neutrophils, HVCN1-deficient eosinophils did not show impaired calcium mobilization or migration ability compared with wild-type (WT) cells. Uniquely, HVCN1-deficient eosinophils underwent significantly increased cell death induced by PMA stimulation compared with WT eosinophils. The increased cell death was dependent on NADPH oxidase activation, and correlated with the failure of HVCN1-deficient cells to maintain membrane polarization and intracellular pH in the physiological range upon activation. Conclusions Eosinophils require proton channel HVCN1 for optimal ROS generation and prevention of activation-induced cell death. PMID:23705768

A FAST RADIO BURST IN THE DIRECTION OF THE CARINA DWARF SPHEROIDAL GALAXY

Energy Technology Data Exchange (ETDEWEB)

Ravi, V. [School of Physics, University of Melbourne, Parkville, VIC 3010 (Australia); Shannon, R. M. [CSIRO Astronomy and Space Science, Australia Telescope National Facility, P.O. Box 76, Epping, NSW 1710 (Australia); Jameson, A., E-mail: v.vikram.ravi@gmail.com [Swinburne University of Technology, Centre for Astrophysics and Supercomputing, Mail H39, P.O. Box 218, VIC 3122 (Australia)

2015-01-20

We report the real-time discovery of a fast radio burst (FRB 131104) with the Parkes radio telescope in a targeted observation of the Carina dwarf spheroidal galaxy. The dispersion measure of the burst is 779 cm{sup –3} pc, exceeding predictions for the maximum line-of-sight Galactic contribution by a factor of 11. The temporal structure of the burst is characterized by an exponential scattering tail with a timescale of 2.0{sub −0.5}{sup +0.8} ms at 1582 MHz that scales as frequency to the power –4.4{sub −1.8}{sup +1.6} (all uncertainties represent 95% confidence intervals). We bound the intrinsic pulse width to be <0.64 ms due to dispersion smearing across a single spectrometer channel. Searches in 78 hr of follow-up observations with the Parkes telescope reveal no additional sporadic emission and no evidence for associated periodic radio emission. We hypothesize that the burst is associated with the Carina dwarf galaxy. Follow-up observations at other wavelengths are necessary to test this hypothesis.

Heterogeneity in Short Gamma-Ray Bursts

Science.gov (United States)

Norris, Jay P.; Gehrels Neil; Scargle, Jeffrey D.

2011-01-01

We analyze the Swift/BAT sample of short gamma-ray bursts, using an objective Bayesian Block procedure to extract temporal descriptors of the bursts' initial pulse complexes (IPCs). The sample comprises 12 and 41 bursts with and without extended emission (EE) components, respectively. IPCs of non-EE bursts are dominated by single pulse structures, while EE bursts tend to have two or more pulse structures. The medians of characteristic timescales - durations, pulse structure widths, and peak intervals - for EE bursts are factors of approx 2-3 longer than for non-EE bursts. A trend previously reported by Hakkila and colleagues unifying long and short bursts - the anti-correlation of pulse intensity and width - continues in the two short burst groups, with non-EE bursts extending to more intense, narrower pulses. In addition we find that preceding and succeeding pulse intensities are anti-correlated with pulse interval. We also examine the short burst X-ray afterglows as observed by the Swift/XRT. The median flux of the initial XRT detections for EE bursts (approx 6 X 10(exp -10) erg / sq cm/ s) is approx > 20 x brighter than for non-EE bursts, and the median X-ray afterglow duration for EE bursts (approx 60,000 s) is approx 30 x longer than for non-EE bursts. The tendency for EE bursts toward longer prompt-emission timescales and higher initial X-ray afterglow fluxes implies larger energy injections powering the afterglows. The longer-lasting X-ray afterglows of EE bursts may suggest that a significant fraction explode into more dense environments than non-EE bursts, or that the sometimes-dominant EE component efficiently p()wers the afterglow. Combined, these results favor different progenitors for EE and non-EE short bursts.

HETEROGENEITY IN SHORT GAMMA-RAY BURSTS

International Nuclear Information System (INIS)

Norris, Jay P.; Gehrels, Neil; Scargle, Jeffrey D.

2011-01-01

We analyze the Swift/BAT sample of short gamma-ray bursts, using an objective Bayesian Block procedure to extract temporal descriptors of the bursts' initial pulse complexes (IPCs). The sample is comprised of 12 and 41 bursts with and without extended emission (EE) components, respectively. IPCs of non-EE bursts are dominated by single pulse structures, while EE bursts tend to have two or more pulse structures. The medians of characteristic timescales-durations, pulse structure widths, and peak intervals-for EE bursts are factors of ∼2-3 longer than for non-EE bursts. A trend previously reported by Hakkila and colleagues unifying long and short bursts-the anti-correlation of pulse intensity and width-continues in the two short burst groups, with non-EE bursts extending to more intense, narrower pulses. In addition, we find that preceding and succeeding pulse intensities are anti-correlated with pulse interval. We also examine the short burst X-ray afterglows as observed by the Swift/X-Ray Telescope (XRT). The median flux of the initial XRT detections for EE bursts (∼6x10 -10 erg cm -2 s -1 ) is ∼>20x brighter than for non-EE bursts, and the median X-ray afterglow duration for EE bursts (∼60,000 s) is ∼30x longer than for non-EE bursts. The tendency for EE bursts toward longer prompt-emission timescales and higher initial X-ray afterglow fluxes implies larger energy injections powering the afterglows. The longer-lasting X-ray afterglows of EE bursts may suggest that a significant fraction explode into denser environments than non-EE bursts, or that the sometimes-dominant EE component efficiently powers the afterglow. Combined, these results favor different progenitors for EE and non-EE short bursts.

Time evolution of the coarse-graining-smoothed Wigner operator in an amplitude dissipative channel: from a pure state to a mixed state

International Nuclear Information System (INIS)

He, Rui; Fan, Hong-yi

2014-01-01

Based on the solution to the master equation of the density operator describing the amplitude dissipative channel, we derive the time evolution law of the coarse-graining-smoothed Wigner operator in this channel, which demonstrates how an initial pure state evolves into a mixed state, exhibiting decoherence

BurstMem: A High-Performance Burst Buffer System for Scientific Applications

Energy Technology Data Exchange (ETDEWEB)

Wang, Teng [Auburn University, Auburn, Alabama; Oral, H Sarp [ORNL; Wang, Yandong [Auburn University, Auburn, Alabama; Settlemyer, Bradley W [ORNL; Atchley, Scott [ORNL; Yu, Weikuan [Auburn University, Auburn, Alabama

2014-01-01

The growth of computing power on large-scale sys- tems requires commensurate high-bandwidth I/O system. Many parallel file systems are designed to provide fast sustainable I/O in response to applications soaring requirements. To meet this need, a novel system is imperative to temporarily buffer the bursty I/O and gradually flush datasets to long-term parallel file systems. In this paper, we introduce the design of BurstMem, a high- performance burst buffer system. BurstMem provides a storage framework with efficient storage and communication manage- ment strategies. Our experiments demonstrate that BurstMem is able to speed up the I/O performance of scientific applications by up to 8.5 on leadership computer systems.

Lithologic and hydrologic controls of mixed alluvial-bedrock channels in flood-prone fluvial systems: bankfull and macrochannels in the Llano River watershed, central Texas, USA

Science.gov (United States)

Heitmuller, Frank T.; Hudson, Paul F.; Asquith, William H.

2015-01-01

The rural and unregulated Llano River watershed located in central Texas, USA, has a highly variable flow regime and a wide range of instantaneous peak flows. Abrupt transitions in surface lithology exist along the main-stem channel course. Both of these characteristics afford an opportunity to examine hydrologic, lithologic, and sedimentary controls on downstream changes in channel morphology. Field surveys of channel topography and boundary composition are coupled with sediment analyses, hydraulic computations, flood-frequency analyses, and geographic information system mapping to discern controls on channel geometry (profile, pattern, and shape) and dimensions along the mixed alluvial-bedrock Llano River and key tributaries. Four categories of channel classification in a downstream direction include: (i) uppermost ephemeral reaches, (ii) straight or sinuous gravel-bed channels in Cretaceous carbonate sedimentary zones, (iii) straight or sinuous gravel-bed or bedrock channels in Paleozoic sedimentary zones, and (iv) straight, braided, or multithread mixed alluvial–bedrock channels with sandy beds in Precambrian igneous and metamorphic zones. Principal findings include: (i) a nearly linear channel profile attributed to resistant bedrock incision checkpoints; (ii) statistically significant correlations of both alluvial sinuosity and valley confinement to relatively high f (mean depth) hydraulic geometry values; (iii) relatively high b (width) hydraulic geometry values in partly confined settings with sinuous channels upstream from a prominent incision checkpoint; (iv) different functional flow categories including frequently occurring events (high f values (most ≤ 0.45) that develop at sites with unit stream power values in excess of 200 watts per square meter (W/m2); and (vi) downstream convergence of hydraulic geometry exponents for bankfull and macrochannels, explained by co-increases of flood magnitude and noncohesive sandy sediments that collectively

The experimental optical burst switching system

Science.gov (United States)

Li, Xinwan; Chen, Jian-Ping; Wu, Guiling; Wang, Hui; Lu, Jialin; Ye, Ailun

2005-02-01

The first optical burst switching (OBS) system has been demonstrated in China, which includes three edge routers and one core-node. A kind of fast wavelength selective optical switching was used in the system. The core OBS node consists of a kind of wavelength selective optical switch we developed. It consists of two SOA switches and one wavelength selective thin film filter with centre wavelength at one wavelength. There are one input optical fiber and two output fibers, each fiber carries two wavelengths. The Dell PE2650 servers act as the edge OBS routers. The wavelength of each data channel is located in C-band and the bit rate is at 1.25Gbps. The control channel uses bit rate of 100Mbps at wavelength of 1310 nm. A novel effective scheme for Just-In-Time (JIT) protocol was proposed and implemented. OBS services, such as Video on Demand (VOD) and file transfer protocol (FTP), have been demonstrated. Assembling and scheduling methods that are capable to guarantee the QoS (quality of service) of the transported service are studied.

A search for optical bursts from the repeating fast radio burst FRB 121102

Science.gov (United States)

Hardy, L. K.; Dhillon, V. S.; Spitler, L. G.; Littlefair, S. P.; Ashley, R. P.; De Cia, A.; Green, M. J.; Jaroenjittichai, P.; Keane, E. F.; Kerry, P.; Kramer, M.; Malesani, D.; Marsh, T. R.; Parsons, S. G.; Possenti, A.; Rattanasoon, S.; Sahman, D. I.

2017-12-01

We present a search for optical bursts from the repeating fast radio burst FRB 121102 using simultaneous observations with the high-speed optical camera ULTRASPEC on the 2.4-m Thai National Telescope and radio observations with the 100-m Effelsberg Radio Telescope. A total of 13 radio bursts were detected, but we found no evidence for corresponding optical bursts in our 70.7-ms frames. The 5σ upper limit to the optical flux density during our observations is 0.33 mJy at 767 nm. This gives an upper limit for the optical burst fluence of 0.046 Jy ms, which constrains the broad-band spectral index of the burst emission to α ≤ -0.2. Two of the radio pulses are separated by just 34 ms, which may represent an upper limit on a possible underlying periodicity (a rotation period typical of pulsars), or these pulses may have come from a single emission window that is a small fraction of a possible period.

Cosmic gamma bursts

International Nuclear Information System (INIS)

Ehstulin, I.V.

1980-01-01

A brief consideration is being given to the history of cosmic gamma burst discovery and modern knowledge of their properties. The time dependence of gamma bursts is described and their possible sources are discussed

MILLIHERTZ QUASI-PERIODIC OSCILLATIONS AND THERMONUCLEAR BURSTS FROM TERZAN 5: A SHOWCASE OF BURNING REGIMES

Energy Technology Data Exchange (ETDEWEB)

Linares, M.; Chakrabarty, D. [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139 (United States); Altamirano, D. [Astronomical Institute ' Anton Pannekoek' , University of Amsterdam and Center for High-Energy Astrophysics, P.O. BOX 94249, 1090 GE Amsterdam (Netherlands); Cumming, A. [Department of Physics, McGill University, 3600 Rue University, Montreal, QC H3A 2T8 (Canada); Keek, L. [School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States)

2012-04-01

We present a comprehensive study of the thermonuclear bursts and millihertz quasi-periodic oscillations (mHz QPOs) from the neutron star (NS) transient and 11 Hz X-ray pulsar IGR J17480-2446, located in the globular cluster Terzan 5. The increase in burst rate that we found during its 2010 outburst, when persistent luminosity rose from 0.1 to 0.5 times the Eddington limit, is in qualitative agreement with thermonuclear burning theory yet contrary to all previous observations of thermonuclear bursts. Thermonuclear bursts gradually evolved into a mHz QPO when the accretion rate increased, and vice versa. The mHz QPOs from IGR J17480-2446 resemble those previously observed in other accreting NSs, yet they feature lower frequencies (by a factor {approx}3) and occur when the persistent luminosity is higher (by a factor 4-25). We find four distinct bursting regimes and a steep (close to inverse cubic) decrease of the burst recurrence time with increasing persistent luminosity. We compare these findings to nuclear burning models and find evidence for a transition between the pure helium and mixed hydrogen/helium ignition regimes when the persistent luminosity was about 0.3 times the Eddington limit. We also point out important discrepancies between the observed bursts and theory, which predicts brighter and less frequent bursts, and suggest that an additional source of heat in the NS envelope is required to reconcile the observed and expected burst properties. We discuss the impact of NS magnetic field and spin on the expected nuclear burning regimes, in the context of this particular pulsar.

Detection circuit for gamma-ray burst

International Nuclear Information System (INIS)

Murakami, Hiroyuki; Yamagami, Takamasa; Mori, Kunishiro; Uchiyama, Sadayuki.

1982-01-01

A new gamma-ray burst detection system is described. The system was developed as an environmental monitor of an accelerator, and can be used as the burst detection system. The system detects the arrival time of burst. The difference between the arrival times detected at different places will give information on the burst source. The frequency of detecting false burst was estimated, and the detection limit under the estimated frequency of false burst was also calculated. Decision whether the signal is false or true burst was made by the statistical treatment. (Kato, T.)

Targeted deletion of Kcne2 impairs HCN channel function in mouse thalamocortical circuits.

Directory of Open Access Journals (Sweden)

Shui-Wang Ying

Full Text Available Hyperpolarization-activated, cyclic nucleotide-gated (HCN channels generate the pacemaking current, I(h, which regulates neuronal excitability, burst firing activity, rhythmogenesis, and synaptic integration. The physiological consequence of HCN activation depends on regulation of channel gating by endogenous modulators and stabilization of the channel complex formed by principal and ancillary subunits. KCNE2 is a voltage-gated potassium channel ancillary subunit that also regulates heterologously expressed HCN channels; whether KCNE2 regulates neuronal HCN channel function is unknown.We investigated the effects of Kcne2 gene deletion on I(h properties and excitability in ventrobasal (VB and cortical layer 6 pyramidal neurons using brain slices prepared from Kcne2(+/+ and Kcne2(-/- mice. Kcne2 deletion shifted the voltage-dependence of I(h activation to more hyperpolarized potentials, slowed gating kinetics, and decreased I(h density. Kcne2 deletion was associated with a reduction in whole-brain expression of both HCN1 and HCN2 (but not HCN4, although co-immunoprecipitation from whole-brain lysates failed to detect interaction of KCNE2 with HCN1 or 2. Kcne2 deletion also increased input resistance and temporal summation of subthreshold voltage responses; this increased intrinsic excitability enhanced burst firing in response to 4-aminopyridine. Burst duration increased in corticothalamic, but not thalamocortical, neurons, suggesting enhanced cortical excitatory input to the thalamus; such augmented excitability did not result from changes in glutamate release machinery since miniature EPSC frequency was unaltered in Kcne2(-/- neurons.Loss of KCNE2 leads to downregulation of HCN channel function associated with increased excitability in neurons in the cortico-thalamo-cortical loop. Such findings further our understanding of the normal physiology of brain circuitry critically involved in cognition and have implications for our understanding of

Gamma-ray burst models.

Science.gov (United States)

King, Andrew

2007-05-15

I consider various possibilities for making gamma-ray bursts, particularly from close binaries. In addition to the much-studied neutron star+neutron star and black hole+neutron star cases usually considered good candidates for short-duration bursts, there are also other possibilities. In particular, neutron star+massive white dwarf has several desirable features. These systems are likely to produce long-duration gamma-ray bursts (GRBs), in some cases definitely without an accompanying supernova, as observed recently. This class of burst would have a strong correlation with star formation and occur close to the host galaxy. However, rare members of the class need not be near star-forming regions and could have any type of host galaxy. Thus, a long-duration burst far from any star-forming region would also be a signature of this class. Estimates based on the existence of a known progenitor suggest that this type of GRB may be quite common, in agreement with the fact that the absence of a supernova can only be established in nearby bursts.

Lithologic and hydrologic controls of mixed alluvial-bedrock channels in flood-prone fluvial systems: bankfull and macrochannels in the Llano River watershed, central Texas, USA

Science.gov (United States)

Heitmuller, Frank T.; Hudson, Paul F.; Asquith, William H.

2015-01-01

The rural and unregulated Llano River watershed located in central Texas, USA, has a highly variable flow regime and a wide range of instantaneous peak flows. Abrupt transitions in surface lithology exist along the main-stem channel course. Both of these characteristics afford an opportunity to examine hydrologic, lithologic, and sedimentary controls on downstream changes in channel morphology. Field surveys of channel topography and boundary composition are coupled with sediment analyses, hydraulic computations, flood-frequency analyses, and geographic information system mapping to discern controls on channel geometry (profile, pattern, and shape) and dimensions along the mixed alluvial-bedrock Llano River and key tributaries. Four categories of channel classification in a downstream direction include: (i) uppermost ephemeral reaches, (ii) straight or sinuous gravel-bed channels in Cretaceous carbonate sedimentary zones, (iii) straight or sinuous gravel-bed or bedrock channels in Paleozoic sedimentary zones, and (iv) straight, braided, or multithread mixed alluvial–bedrock channels with sandy beds in Precambrian igneous and metamorphic zones. Principal findings include: (i) a nearly linear channel profile attributed to resistant bedrock incision checkpoints; (ii) statistically significant correlations of both alluvial sinuosity and valley confinement to relatively high f (mean depth) hydraulic geometry values; (iii) relatively high b (width) hydraulic geometry values in partly confined settings with sinuous channels upstream from a prominent incision checkpoint; (iv) different functional flow categories including frequently occurring events (< 1.5-year return periods) that mobilize channel-bed material and less frequent events that determine bankfull channel (1.5- to 3-year return periods) and macrochannel (10- to 40-year return periods) dimensions; (v) macrochannels with high f values (most ≤ 0.45) that develop at sites with unit stream power values in excess

Solar microwave bursts - A review

Science.gov (United States)

Kundu, M. R.; Vlahos, L.

1982-01-01

Observational and theoretical results on the physics of microwave bursts that occur in the solar atmosphere are reviewed. Special attention is given to the advances made in burst physics over the last few years with the great improvement in spatial and time resolution, especially with instruments like the NRAO three-element interferometer, the Westerbork Synthesis Radio Telescope, and more recently the Very Large Array. Observations made on the preflare build-up of an active region at centimeter wavelengths are reviewed. Three distinct phases in the evolution of cm bursts, namely the impulsive phase, the post-burst phase, and the gradual rise and fall, are discussed. Attention is also given to the flux density spectra of centimeter bursts. Descriptions are given of observations of fine structures with temporal resolution of 10-100 ms in the intensity profiles of cm-wavelength bursts. High spatial resolution observations are analyzed, with special reference to the one- and two-dimensional maps of cm burst sources.

Optical observations of Gamma-Ray Bursts

International Nuclear Information System (INIS)

Hjorth, J.; Pian, E.; Fynbo, J.P.U.

2004-01-01

We briefly review the status and recent progress in the field of optical observations of gamma-ray burst afterglows. We will focus on the fundamental observational evidence for the relationship between gamma-ray bursts and the final evolutionary phases of massive stars. In particular, we will address (i) gamma-ray burst host galaxies, (ii) optically dark gamma-ray burst afterglows, (iii) the gamma-ray burst-supernova connection, and (iv) the relation between X-ray flashes, gamma-ray bursts, and supernovae

Solar Radio Bursts and Space Weather

Science.gov (United States)

Gopalswamy, Natchimuthuk,

2012-01-01

Radio bursts from the Sun are produced by electron accelerated to relativistic energies by physical processes on the Sun such as solar flares and coronal mass ejections (CMEs). The radio bursts are thus good indicators of solar eruptions. Three types of nonthermal radio bursts are generally associated with CMEs. Type III bursts due to accelerated electrons propagating along open magnetic field lines. The electrons are thought to be accelerated at the reconnection region beneath the erupting CME, although there is another view that the electrons may be accelerated at the CME-driven shock. Type II bursts are due to electrons accelerated at the shock front. Type II bursts are also excellent indicators of solar energetic particle (SEP) events because the same shock is supposed accelerate electrons and ions. There is a hierarchical relationship between the wavelength range of type /I bursts and the CME kinetic energy. Finally, Type IV bursts are due to electrons trapped in moving or stationary structures. The low frequency stationary type IV bursts are observed occasionally in association with very fast CMEs. These bursts originate from flare loops behind the erupting CME and hence indicate tall loops. This paper presents a summary of radio bursts and their relation to CMEs and how they can be useful for space weather predictions.

Complex transitions between spike, burst or chaos synchronization states in coupled neurons with coexisting bursting patterns

International Nuclear Information System (INIS)

Gu Hua-Guang; Chen Sheng-Gen; Li Yu-Ye

2015-01-01

We investigated the synchronization dynamics of a coupled neuronal system composed of two identical Chay model neurons. The Chay model showed coexisting period-1 and period-2 bursting patterns as a parameter and initial values are varied. We simulated multiple periodic and chaotic bursting patterns with non-(NS), burst phase (BS), spike phase (SS), complete (CS), and lag synchronization states. When the coexisting behavior is near period-2 bursting, the transitions of synchronization states of the coupled system follows very complex transitions that begins with transitions between BS and SS, moves to transitions between CS and SS, and to CS. Most initial values lead to the CS state of period-2 bursting while only a few lead to the CS state of period-1 bursting. When the coexisting behavior is near period-1 bursting, the transitions begin with NS, move to transitions between SS and BS, to transitions between SS and CS, and then to CS. Most initial values lead to the CS state of period-1 bursting but a few lead to the CS state of period-2 bursting. The BS was identified as chaos synchronization. The patterns for NS and transitions between BS and SS are insensitive to initial values. The patterns for transitions between CS and SS and the CS state are sensitive to them. The number of spikes per burst of non-CS bursting increases with increasing coupling strength. These results not only reveal the initial value- and parameter-dependent synchronization transitions of coupled systems with coexisting behaviors, but also facilitate interpretation of various bursting patterns and synchronization transitions generated in the nervous system with weak coupling strength. (paper)

Gamma-ray burst spectra

International Nuclear Information System (INIS)

Teegarden, B.J.

1982-01-01

A review of recent results in gamma-ray burst spectroscopy is given. Particular attention is paid to the recent discovery of emission and absorption features in the burst spectra. These lines represent the strongest evidence to date that gamma-ray bursts originate on or near neutron stars. Line parameters give information on the temperature, magnetic field and possibly the gravitational potential of the neutron star. The behavior of the continuum spectrum is also discussed. A remarkably good fit to nearly all bursts is obtained with a thermal-bremsstrahlung-like continuum. Significant evolution is observed of both the continuum and line features within most events

Experimental study on the effects of channel gap size on mixed convection heat transfer characteristics in vertical rectangular channels heated from both sides

International Nuclear Information System (INIS)

Sudo, Y.; Kaminaga, M.

1990-01-01

The effects of channel gap size on mixed forced and free convective heat transfer characteristics were experimentally investigated for water flowing near atmospheric pressure in a 750 mm long and 50 mm wide channel heated from both sides. The channel gap sizes investigated were 2.5, 6, 18 and 50 mm. Experiments were carried out for both aiding and opposing forced convective flows with a Reynolds number Re x of 4x10 to 6x10 6 and a Grashof number Gr x of 2x10 4 to 6x10 11 , where the distance x from the inlet of the channel is adopted as the characteristic length in Re x and Gr x . As for the results, the following were revealed for the parameters ranges investigated in this study. (1) When the dimensionless parameter, Gr x /Re x 21/8 Pr 1/2 is less than 10 -4 , the flow shows the nature of forced convective heat transfer for a channel with any channel gap size in both aiding and opposing flows. (2) When Gr x /Re x 21/8 Pr 1/2 is larger than 10 -2 , the flow shows the nature of free convective heat transfer for a channel with any channel gap size in both aiding and opposing flows. (3) When Gr x /Re x 21/8 Pr 1/2 is between 10 -4 and 10 -2 for the channel with a channel gap size equal to or larger than 6 mm, the heat transfer coefficients in both aiding and opposing flows become, on the average, higher than those predicted by the previous correlations for either the pure turbulent forced convection or the pure free convection, and can be expressed in simple forms with a combination of Gr x /Re x 21/8 Pr 1/2 and the previous correlation for either the pure turbulent forced convection or the free convection along a flat plate. (4) When Gr x /Re x 21/8 Pr 1/2 is between 10 -4 and 10 -2 for the channel with a channel gap size of 2.5 mm, the heat transfer coefficients in both aiding and opposing flows also become, on the average, higher than those predicted by the previous correlations for either the pure turbulent forced convection or the pure free convection. (orig./GL)

Analysis of historic bursts and burst detection in water supply areas of different size

NARCIS (Netherlands)

Bakker, M.; Trietsch, E.A.; Vreeburg, J.H.G.; Rietveld, L.C.

2014-01-01

Pipe bursts in water distribution networks lead to water losses and a risk of damaging the urban environment. We studied hydraulic data and customer contact records of 44 real bursts for a better understanding of the phenomena. We found that most bursts were reported to the water company shortly

Single-channel kinetics of BK (Slo1 channels

Directory of Open Access Journals (Sweden)

Yanyan eGeng

2015-01-01

Full Text Available Single-channel kinetics has proven a powerful tool to reveal information about the gating mechanisms that control the opening and closing of ion channels. This introductory review focuses on the gating of large conductance Ca2+- and voltage-activated K+ (BK or Slo1 channels at the single-channel level. It starts with single-channel current records and progresses to presentation and analysis of single-channel data and the development of gating mechanisms in terms of discrete state Markov (DSM models. The DSM models are formulated in terms of the tetrameric modular structure of BK channels, consisting of a central transmembrane pore-gate domain (PGD attached to four surrounding transmembrane voltage sensing domains (VSD and a large intracellular cytosolic domain (CTD, also referred to as the gating ring. The modular structure and data analysis shows that the Ca2+ and voltage dependent gating considered separately can each be approximated by 10-state two-tiered models with 5 closed states on the upper tier and 5 open states on the lower tier. The modular structure and joint Ca2+ and voltage dependent gating are consistent with a 50 state two-tiered model with 25 closed states on the upper tier and 25 open states on the lower tier. Adding an additional tier of brief closed (flicker states to the 10-state or 50-state models improved the description of the gating. For fixed experimental conditions a channel would gate in only a subset of the potential number of states. The detected number of states and the correlations between adjacent interval durations are consistent with the tiered models. The examined models can account for the single-channel kinetics and the bursting behavior of gating. Ca2+ and voltage activate BK channels by predominantly increasing the effective opening rate of the channel with a smaller decrease in the effective closing rate. Ca2+ and depolarization thus activate by mainly destabilizing the closed states.

Fermi/GAMMA-RAY BURST MONITOR OBSERVATIONS OF SGR J0501+4516 BURSTS

International Nuclear Information System (INIS)

Lin Lin; Zhang Shuangnan; Kouveliotou, Chryssa; Baring, Matthew G.; Van der Horst, Alexander J.; Finger, Mark H.; Guiriec, Sylvain; Preece, Robert; Chaplin, Vandiver; Bhat, Narayan; Woods, Peter M.; Goegues, Ersin; Kaneko, Yuki; Scargle, Jeffrey; Granot, Jonathan; Von Kienlin, Andreas; Watts, Anna L.; Wijers, Ralph A. M. J.; Gehrels, Neil; Harding, Alice

2011-01-01

We present our temporal and spectral analyses of 29 bursts from SGR J0501+4516, detected with the gamma-ray burst monitor on board the Fermi Gamma-ray Space Telescope during 13 days of the source's activation in 2008 (August 22- September 3). We find that the T 90 durations of the bursts can be fit with a log-normal distribution with a mean value of ∼123 ms. We also estimate for the first time event durations of soft gamma repeater (SGR) bursts in photon space (i.e., using their deconvolved spectra) and find that these are very similar to the T 90 values estimated in count space (following a log-normal distribution with a mean value of ∼124 ms). We fit the time-integrated spectra for each burst and the time-resolved spectra of the five brightest bursts with several models. We find that a single power law with an exponential cutoff model fits all 29 bursts well, while 18 of the events can also be fit with two blackbody functions. We expand on the physical interpretation of these two models and we compare their parameters and discuss their evolution. We show that the time-integrated and time-resolved spectra reveal that E peak decreases with energy flux (and fluence) to a minimum of ∼30 keV at F = 8.7 x 10 -6 erg cm -2 s -1 , increasing steadily afterward. Two more sources exhibit a similar trend: SGRs J1550-5418 and 1806-20. The isotropic luminosity, L iso , corresponding to these flux values is roughly similar for all sources (0.4-1.5 x 10 40 erg s -1 ).

PWR clad ballooning: The effect of circumferential clad temperature variations on the burst strain/burst temperature relationship

International Nuclear Information System (INIS)

Barlow, P.

1983-01-01

By experiment, it has been shown by other workers that there is a reduction in the creep ductility of Zircaloy 4 in the α+β phase transition region. Results from single rod burst tests also show a reduction in burst strain in the α+β phase region. In this report it is shown theoretically that for single rod burst tests in the presence of circumferential temperature gradients, the temperature dependence of the mean burst strain is not determined by temperature variations in creep ductility, but is governed by the temperature sensitivity of the creep strain rate, which is shown to be a maximum in the α+β phase transition region. To demonstrate this effect, the mean clad strain at burst was calculated for creep straining at different temperature levels in the α, α+β and β phase regions. Cross-pin temperature gradients were applied which produced strain variations around the clad which were greatest in the α+β phase region. The mean strain at burst was determined using a maximum local burst strain (i.e. a creep ductility) which is independent of temperature. By assuming cross-pin temperature gradients which are typical of those observed during burst tests, then the calculated mean burst strain/burst temperature relationship gave good agreement with experiment. The calculations also show that when circumferential temperature differences are present, the calculated mean strain at burst is not sensitive to variations in the magnitude of the assumed creep ductility. This reduces the importance of the assumed burst criterion in the calculations. Hence a temperature independent creep ductility (e.g. 100% local strain) is adequate as a burst criterion for calculations under PWR LOCA conditions. (author)

Observations of short gamma-ray bursts.

Science.gov (United States)

Fox, Derek B; Roming, Peter W A

2007-05-15

We review recent observations of short-hard gamma-ray bursts and their afterglows. The launch and successful ongoing operations of the Swift satellite, along with several localizations from the High-Energy Transient Explorer mission, have provoked a revolution in short-burst studies: first, by quickly providing high-quality positions to observers; and second, via rapid and sustained observations from the Swift satellite itself. We make a complete accounting of Swift-era short-burst localizations and proposed host galaxies, and discuss the implications of these observations for the distances, energetics and environments of short bursts, and the nature of their progenitors. We then review the physical modelling of short-burst afterglows: while the simplest afterglow models are inadequate to explain the observations, there have been several notable successes. Finally, we address the case of an unusual burst that threatens to upset the simple picture in which long bursts are due to the deaths of massive stars, and short bursts to compact-object merger events.

X-ray bursts: Observation versus theory

Science.gov (United States)

Lewin, W. H. G.

1981-01-01

Results of various observations of common type I X-ray bursts are discussed with respect to the theory of thermonuclear flashes in the surface layers of accreting neutron stars. Topics covered include burst profiles; irregular burst intervals; rise and decay times and the role of hydrogen; the accuracy of source distances; accuracy in radii determination; radius increase early in the burst; the super Eddington limit; temperatures at burst maximum; and the role of the magnetic field.

Secured Hash Based Burst Header Authentication Design for Optical Burst Switched Networks

Science.gov (United States)

Balamurugan, A. M.; Sivasubramanian, A.; Parvathavarthini, B.

2017-12-01

The optical burst switching (OBS) is a promising technology that could meet the fast growing network demand. They are featured with the ability to meet the bandwidth requirement of applications that demand intensive bandwidth. OBS proves to be a satisfactory technology to tackle the huge bandwidth constraints, but suffers from security vulnerabilities. The objective of this proposed work is to design a faster and efficient burst header authentication algorithm for core nodes. There are two important key features in this work, viz., header encryption and authentication. Since the burst header is an important in optical burst switched network, it has to be encrypted; otherwise it is be prone to attack. The proposed MD5&RC4-4S based burst header authentication algorithm runs 20.75 ns faster than the conventional algorithms. The modification suggested in the proposed RC4-4S algorithm gives a better security and solves the correlation problems between the publicly known outputs during key generation phase. The modified MD5 recommended in this work provides 7.81 % better avalanche effect than the conventional algorithm. The device utilization result also shows the suitability of the proposed algorithm for header authentication in real time applications.

Microfluidic mixing through oscillatory transverse perturbations

Science.gov (United States)

Wu, J. W.; Xia, H. M.; Zhang, Y. Y.; Zhu, P.

2018-05-01

Fluid mixing in miniaturized fluidic devices is a challenging task. In this work, the mixing enhancement through oscillatory transverse perturbations coupling with divergent circular chambers is studied. To simplify the design, an autonomous microfluidic oscillator is used to produce the oscillatory flow. It is then applied to four side-channels that intersect with a central channel of constant flow. The mixing performance is tested at high fluid viscosities of up to 16 cP. Results show that the oscillatory flow can cause strong transverse perturbations which effectively enhance the mixing. The influence of a fluidic capacitor in the central channel is also examined, which at low viscosities can intensify the perturbations and further improve the mixing.

Solar Drift-Pair Bursts

Science.gov (United States)

Stanislavsky, A.; Volvach, Ya.; Konovalenko, A.; Koval, A.

2017-08-01

In this paper a new sight on the study of solar bursts historically called drift pairs (DPs) is presented. Having a simple morphology on dynamic spectra of radio records (two short components separated in time, and often they are very similar) and discovered at the dawn of radio astronomy, their features remain unexplained totally up to now. Generally, the DPs are observed during the solar storms of type III bursts, but not every storm of type III bursts is linked with DPs. Detected by ground-based instruments at decameter and meter wavelengths, the DP bursts are limited in frequency bandwidth. They can drift from high frequencies to low ones and vice versa. Their frequency drift rate may be both lower and higher than typical rates of type III bursts at the same frequency range. The development of low-frequency radio telescopes and data processing provide additional possibilities in the research. In this context the fresh analysis of DPs, made from recent observations in the summer campaign of 2015, are just considered. Their study was implemented by updated tools of the UTR-2 radio telescope at 9-33 MHz. During 10-12 July of 2015, DPs forming the longest patterns on dynamic spectra are about 7% of the total number of recorded DPs. Their marvelous resemblance in frequency drift rates with the solar S-bursts is discussed.

30 CFR 57.3461 - Rock bursts.

Science.gov (United States)

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Rock bursts. 57.3461 Section 57.3461 Mineral...-Underground Only § 57.3461 Rock bursts. (a) Operators of mines which have experienced a rock burst shall— (1) Within twenty four hours report to the nearest MSHA office each rock burst which: (i) Causes persons to...

Mixed convective thermally radiative micro nanofluid flow in a stretchable channel with porous medium and magnetic field

Energy Technology Data Exchange (ETDEWEB)

Rauf, A., E-mail: raufamar@ciitsahiwal.edu.pk; Shahzad, S. A.; Meraj, M. A. [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan); Siddiq, M. K. [Department of CASPAM, Bahauddin Zakariya University, Multan 63000 (Pakistan); Raza, J. [School of Quantitative Sciences, Universiti Utara Malaysia, 06010, Sintok, Kedah (Malaysia)

2016-03-15

A numerical study is carried out for two dimensional steady incompressible mixed convective flow of electrically conductive micro nanofluid in a stretchable channel. The flow is generated due to the stretching walls of the channel immersed in a porous medium. The magnetic field is applied perpendicular to the walls. The impact of radiation, viscous dissipation, thermophoretic and Brownian motion of nanoparticles appear in the energy equation. A numerical technique based on Runge-Kutta-Fehlberg fourth-fifth order (RFK45) method is used to express the solutions of velocity, microrotation, temperature and concentration fields. The dimensionless physical parameters are discussed both in tabular and graphical forms. The results are also found in a good agreement with previously published literature work.

Neutrino emission from gamma-ray burst fireballs, revised.

Science.gov (United States)

Hümmer, Svenja; Baerwald, Philipp; Winter, Walter

2012-06-08

We review the neutrino flux from gamma-ray bursts, which is estimated from gamma-ray observations and used for the interpretation of recent IceCube data, from a particle physics perspective. We numerically calculate the neutrino flux for the same astrophysical assumptions as the analytical fireball neutrino model, including the dominant pion and kaon production modes, flavor mixing, and magnetic field effects on the secondary muons, pions, and kaons. We demonstrate that taking into account the full energy dependencies of all spectra, the normalization of the expected neutrino flux reduces by about one order of magnitude and the spectrum shifts to higher energies, where we can pin down the exact origin of the discrepancies by the recomputation of the analytical models. We also reproduce the IceCube-40 analysis for exactly the same bursts and same assumptions and illustrate the impact of uncertainties. We conclude that the baryonic loading of the fireballs, which is an important control parameter for the emission of cosmic rays, can be constrained significantly with the full-scale experiment after about ten years.

The Drift Burst Hypothesis

OpenAIRE

Christensen, Kim; Oomen, Roel; Renò, Roberto

2016-01-01

The Drift Burst Hypothesis postulates the existence of short-lived locally explosive trends in the price paths of financial assets. The recent US equity and Treasury flash crashes can be viewed as two high profile manifestations of such dynamics, but we argue that drift bursts of varying magnitude are an expected and regular occurrence in financial markets that can arise through established mechanisms such as feedback trading. At a theoretical level, we show how to build drift bursts into the...

X-ray bursts observed with JEM-X

DEFF Research Database (Denmark)

Brandt, Søren Kristian; Chenevez, Jérôme; Lund, Niels

2006-01-01

We report on the search for X-ray bursts in the JEM-X X-ray monitor on INTEGRAL during the first two years of operations. More than 350 bursts from 25 different type-I X-ray burst sources were found.......We report on the search for X-ray bursts in the JEM-X X-ray monitor on INTEGRAL during the first two years of operations. More than 350 bursts from 25 different type-I X-ray burst sources were found....

UWB dual burst transmit driver

Science.gov (United States)

Dallum, Gregory E [Livermore, CA; Pratt, Garth C [Discovery Bay, CA; Haugen, Peter C [Livermore, CA; Zumstein, James M [Livermore, CA; Vigars, Mark L [Livermore, CA; Romero, Carlos E [Livermore, CA

2012-04-17

A dual burst transmitter for ultra-wideband (UWB) communication systems generates a pair of precisely spaced RF bursts from a single trigger event. An input trigger pulse produces two oscillator trigger pulses, an initial pulse and a delayed pulse, in a dual trigger generator. The two oscillator trigger pulses drive a gated RF burst (power output) oscillator. A bias driver circuit gates the RF output oscillator on and off and sets the RF burst packet width. The bias driver also level shifts the drive signal to the level that is required for the RF output device.

Suppression of the four-wave-mixing background noise in a quantum memory retrieval process by channel blocking

Science.gov (United States)

Zhang, Kai; Guo, Jinxian; Chen, L. Q.; Yuan, Chunhua; Ou, Z. Y.; Zhang, Weiping

2014-09-01

In a quantum memory scheme with the Raman process, the read process encounters noise from four-wave mixing (FWM), which can destroy the nonclassical properties of the generated quantum fields. Here we demonstrate experimentally that the noise from FWM can be greatly suppressed by simply reducing the FWM transition channels with a circularly polarized read beam while at the same time retaining relatively high retrieval efficiency.

Solar X-ray bursts

International Nuclear Information System (INIS)

Urnov, A.M.

1980-01-01

In the popular form the consideration is given to the modern state tasks and results of X-ray spectrometry of solar bursts. The operation of X-ray spectroheliograph is described. Results of spectral and polarization measurings of X-ray radiation of one powerful solar burst are presented. The conclusion has been drawn that in the process of burst development three characteristic stages may be distingwished: 1) the initial phase; just in this period processes which lead to observed consequences-electromagnetic and corpuscular radiation are born; 2) the impulse phase, or the phase of maximum, is characterised by sharp increase of radiation flux. During this phase the main energy content emanates and some volumes of plasma warm up to high temperatures; 3) the phase of burst damping, during which plasma cools and reverts to the initial condition

Monitoring burst (M-burst) — A novel framework of failure localization in all-optical mesh networks

KAUST Repository

Ali, Mohammed L.; Ho, Pin-Han; Wu, Bin; Tapolcai, Janos; Shihada, Basem

2011-01-01

Achieving instantaneous and precise failure localization in all-optical wavelength division multiplexing (WDM) networks has been an attractive feature of network fault management systems, and is particularly important when failure-dependent protection is employed. The paper introduces a novel framework of real-time failure localization in all-optical WDM mesh networks, called monitoring-burst (m-burst), which aims to initiate a graceful compromise between consumed monitoring resources and monitoring delay. Different from any previously reported solution, the proposed m-burst framework has a single monitoring node (MN) which launches optical bursts along a set of pre-defined close-loop routes, called monitoring cycles (m-cycles), to probe the links along the m-cycles. Bursts along different m-cycles are kept non-overlapping through any link of the network. By identifying the lost bursts due to single link failure events only, the MN can unambiguously localize the failed link in at least 3-connected networks. We will justify the feasibility and applicability of the proposed m-burst framework in the scenario of interest. To avoid possible collision among optical bursts launched by the MN, we define the problem of collision-free scheduling and formulate it into an integer linear program (ILP) in order to minimize the monitoring delay. Numerical results demonstrate the effectiveness of the proposed framework and the proposed solution.

Monitoring burst (M-burst) — A novel framework of failure localization in all-optical mesh networks

KAUST Repository

Ali, Mohammed L.

2011-10-10

Achieving instantaneous and precise failure localization in all-optical wavelength division multiplexing (WDM) networks has been an attractive feature of network fault management systems, and is particularly important when failure-dependent protection is employed. The paper introduces a novel framework of real-time failure localization in all-optical WDM mesh networks, called monitoring-burst (m-burst), which aims to initiate a graceful compromise between consumed monitoring resources and monitoring delay. Different from any previously reported solution, the proposed m-burst framework has a single monitoring node (MN) which launches optical bursts along a set of pre-defined close-loop routes, called monitoring cycles (m-cycles), to probe the links along the m-cycles. Bursts along different m-cycles are kept non-overlapping through any link of the network. By identifying the lost bursts due to single link failure events only, the MN can unambiguously localize the failed link in at least 3-connected networks. We will justify the feasibility and applicability of the proposed m-burst framework in the scenario of interest. To avoid possible collision among optical bursts launched by the MN, we define the problem of collision-free scheduling and formulate it into an integer linear program (ILP) in order to minimize the monitoring delay. Numerical results demonstrate the effectiveness of the proposed framework and the proposed solution.

Localization of Gamma-Ray Bursts Using the Fermi Gamma-Ray Burst Monitor

NARCIS (Netherlands)

Connaughton, V.; Briggs, M.S.; Goldstein, A.; Meegan, C.A.; Paciesas, W.S.; Preece, R.D.; Wilson-Hodge, C.A.; Gibby, M.H.; Greiner, J.; Gruber, D.; Jenke, P.; Kippen, R.M.; Pelassa, V.; Xiong, S.; Yu, H-F.; Bhat, P.N.; Burgess, J.M.; Byrne, D.; Fitzpatrick, G.; Foley, S.; Giles, M.M.; Guiriec, S.; van der Horst, A.J.; von Kienlin, A.; McBreen, S.; McGlynn, S.; Tierney, D.; Zhang, B..B.

2015-01-01

The Fermi Gamma-ray Burst Monitor (GBM) has detected over 1400 gamma-ray bursts (GRBs) since it began science operations in 2008 July. We use a subset of over 300 GRBs localized by instruments such as Swift, the Fermi Large Area Telescope, INTEGRAL, and MAXI, or through triangulations from the

User's Guide for Mixed-Size Sediment Transport Model for Networks of One-Dimensional Open Channels

Science.gov (United States)

Bennett, James P.

2001-01-01

This user's guide describes a mathematical model for predicting the transport of mixed sizes of sediment by flow in networks of one-dimensional open channels. The simulation package is useful for general sediment routing problems, prediction of erosion and deposition following dam removal, and scour in channels at road embankment crossings or other artificial structures. The model treats input hydrographs as stepwise steady-state, and the flow computation algorithm automatically switches between sub- and supercritical flow as dictated by channel geometry and discharge. A variety of boundary conditions including weirs and rating curves may be applied both external and internal to the flow network. The model may be used to compute flow around islands and through multiple openings in embankments, but the network must be 'simple' in the sense that the flow directions in all channels can be specified before simulation commences. The location and shape of channel banks are user specified, and all bedelevation changes take place between these banks and above a user-specified bedrock elevation. Computation of sediment-transport emphasizes the sand-size range (0.0625-2.0 millimeter) but the user may select any desired range of particle diameters including silt and finer (user may set the original bed-sediment composition of any number of layers of known thickness. The model computes the time evolution of total transport and the size composition of bed- and suspended-load sand through any cross section of interest. It also tracks bed -surface elevation and size composition. The model is written in the FORTRAN programming language for implementation on personal computers using the WINDOWS operating system and, along with certain graphical output display capability, is accessed from a graphical user interface (GUI). The GUI provides a framework for selecting input files and parameters of a number of components of the sediment-transport process. There are no restrictions in the

Biophysical Neural Spiking, Bursting, and Excitability Dynamics in Reconfigurable Analog VLSI.

Science.gov (United States)

Yu, T; Sejnowski, T J; Cauwenberghs, G

2011-10-01

We study a range of neural dynamics under variations in biophysical parameters underlying extended Morris-Lecar and Hodgkin-Huxley models in three gating variables. The extended models are implemented in NeuroDyn, a four neuron, twelve synapse continuous-time analog VLSI programmable neural emulation platform with generalized channel kinetics and biophysical membrane dynamics. The dynamics exhibit a wide range of time scales extending beyond 100 ms neglected in typical silicon models of tonic spiking neurons. Circuit simulations and measurements show transition from tonic spiking to tonic bursting dynamics through variation of a single conductance parameter governing calcium recovery. We similarly demonstrate transition from graded to all-or-none neural excitability in the onset of spiking dynamics through the variation of channel kinetic parameters governing the speed of potassium activation. Other combinations of variations in conductance and channel kinetic parameters give rise to phasic spiking and spike frequency adaptation dynamics. The NeuroDyn chip consumes 1.29 mW and occupies 3 mm × 3 mm in 0.5 μm CMOS, supporting emerging developments in neuromorphic silicon-neuron interfaces.

X-Ray Bursts from NGC 6652

Science.gov (United States)

Morgan, Edward

The possibly transient X-ray Source in the globular cluster NGC 6652 has been seen by BeppoSax and the ASM on RXTE to undergo X-ray bursts, possibly Type I. Very little is known about this X-ray source, and confirmation of its bursts type-I nature would identify it as a neutron star binary. Type I bursts in 6 other sources have been shown to exhibit intervals of millisecond ocsillation that most likely indicate the neutron star spin period. Radius-expansion bursts can reveal information about the mass and size of the neutron star. We propose to use the ASM to trigger an observation of this source to maximize the probability of catching a burst in the PCA.

Transitions to Synchrony in Coupled Bursting Neurons

Science.gov (United States)

Dhamala, Mukeshwar; Jirsa, Viktor K.; Ding, Mingzhou

2004-01-01

Certain cells in the brain, for example, thalamic neurons during sleep, show spike-burst activity. We study such spike-burst neural activity and the transitions to a synchronized state using a model of coupled bursting neurons. In an electrically coupled network, we show that the increase of coupling strength increases incoherence first and then induces two different transitions to synchronized states, one associated with bursts and the other with spikes. These sequential transitions to synchronized states are determined by the zero crossings of the maximum transverse Lyapunov exponents. These results suggest that synchronization of spike-burst activity is a multi-time-scale phenomenon and burst synchrony is a precursor to spike synchrony.

Transitions to synchrony in coupled bursting neurons

International Nuclear Information System (INIS)

Dhamala, Mukeshwar; Jirsa, Viktor K.; Ding Mingzhou

2004-01-01

Certain cells in the brain, for example, thalamic neurons during sleep, show spike-burst activity. We study such spike-burst neural activity and the transitions to a synchronized state using a model of coupled bursting neurons. In an electrically coupled network, we show that the increase of coupling strength increases incoherence first and then induces two different transitions to synchronized states, one associated with bursts and the other with spikes. These sequential transitions to synchronized states are determined by the zero crossings of the maximum transverse Lyapunov exponents. These results suggest that synchronization of spike-burst activity is a multi-time-scale phenomenon and burst synchrony is a precursor to spike synchrony

The potential roles of T-type Ca2+ channels in motor coordination

Directory of Open Access Journals (Sweden)

Young-Gyun ePark

2013-10-01

Full Text Available Specific behavioral patterns are expressed by complex combinations of muscle coordination. Tremors are simple behavioral patterns and are the focus of studies investigating motor coordination mechanisms in the brain. T-type Ca2+ channels mediate intrinsic neuronal oscillations and rhythmic burst spiking, and facilitate the generation of tremor rhythms in motor circuits. Despite substantial evidence that T-type Ca2+ channels mediate pathological tremors, their roles in physiological motor coordination and behavior remain unknown. Here, we review recent progress in understanding the roles that T-type Ca2+ channels play under pathological conditions, and discuss the potential relevance of these channels in mediating physiological motor coordination.

The Second SWIFT Burst Alert Telescope (BAT) Gamma-Ray Burst Catalog

Science.gov (United States)

Sakamoto, T.; Barthelmy, S. D.; Baumgartner, W. H.; Cummings, J. R.; Fenimore, E. E.; Gehrels, N.; Krimm, H. A.; Markwardt, C. B.; Palmer, D. M.; Parsons, A. M.;

Stimulus induced bursts in severe postanoxic encephalopathy.

Science.gov (United States)

Tjepkema-Cloostermans, Marleen C; Wijers, Elisabeth T; van Putten, Michel J A M

2016-11-01

To report on a distinct effect of auditory and sensory stimuli on the EEG in comatose patients with severe postanoxic encephalopathy. In two comatose patients admitted to the Intensive Care Unit (ICU) with severe postanoxic encephalopathy and burst-suppression EEG, we studied the effect of external stimuli (sound and touch) on the occurrence of bursts. In patient A bursts could be induced by either auditory or sensory stimuli. In patient B bursts could only be induced by touching different facial regions (forehead, nose and chin). When stimuli were presented with relatively long intervals, bursts persistently followed the stimuli, while stimuli with short intervals (encephalopathy can be induced by external stimuli, resulting in stimulus-dependent burst-suppression. Stimulus induced bursts should not be interpreted as prognostic favourable EEG reactivity. Copyright © 2016 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

Stellar Sources of Gamma-ray Bursts

OpenAIRE

Luchkov, B. I.

2011-01-01

Correlation analysis of Swift gamma-ray burst coordinates and nearby star locations (catalog Gliese) reveals 4 coincidences with good angular accuracy. The random probability is 4\\times 10^{-5}, so evidencing that coincident stars are indeed gamma-ray burst sources. Some additional search of stellar gamma-ray bursts is discussed.

Voltage-gated proton channel is expressed on phagosomes

International Nuclear Information System (INIS)

Okochi, Yoshifumi; Sasaki, Mari; Iwasaki, Hirohide; Okamura, Yasushi

2009-01-01

Voltage-gated proton channel has been suggested to help NADPH oxidase activity during respiratory burst of phagocytes through its activities of compensating charge imbalance and regulation of pH. In phagocytes, robust production of reactive oxygen species occurs in closed membrane compartments, which are called phagosomes. However, direct evidence for the presence of voltage-gated proton channels in phagosome has been lacking. In this study, the expression of voltage-gated proton channels was studied by Western blot with the antibody specific to the voltage-sensor domain protein, VSOP/Hv1, that has recently been identified as the molecular correlate for the voltage-gated proton channel. Phagosomal membranes of neutrophils contain VSOP/Hv1 in accordance with subunits of NADPH oxidases, gp91, p22, p47 and p67. Superoxide anion production upon PMA activation was significantly reduced in neutrophils from VSOP/Hv1 knockout mice. These are consistent with the idea that voltage-gated proton channels help NADPH oxidase in phagocytes to produce reactive oxygen species.

Neutrino burst identification in underground detectors

International Nuclear Information System (INIS)

Fulgione, W.; Mengotti-Silva, N.; Panaro, L.

1996-01-01

We discuss the problem of neutrino burst identification in underground ν-telescopes. First the usual statistical analysis based on the time structure of the events is reviewed, with special attention to the statistical significance of burst candidates. Next, we propose a second level analysis that can provide independent confirmation of burst detection. This exploits the spatial distribution of the single events of a burst candidate, and uses the formalism of the entropy of information. Examples of both techniques are shown, based on the LVD experiment at Gran Sasso. (orig.)

Swift: A gamma ray burst MIDEX

International Nuclear Information System (INIS)

Barthelmy, Scott

2001-01-01

Swift is a first of its kind multiwavelength transient observatory for gamma-ray burst astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of gamma-ray bursts and their afterglows as well as using bursts to probe the early Universe. Swift will also perform the first sensitive hard X-ray survey of the sky. The mission is being developed by an international collaboration and consists of three instruments, the Burst Alert Telescope (BAT), the X-ray Telescope (XRT), and the Ultraviolet and Optical Telescope (UVOT). The BAT, a wide-field gamma-ray detector, will detect ∼1 gamma-ray burst per day with a sensitivity 5 times that of BATSE. The sensitive narrow-field XRT and UVOT will be autonomously slewed to the burst location in 20 to 70 seconds to determine 0.3-5.0 arcsec positions and perform optical, UV, and X-ray spectrophotometry. On-board measurements of redshift will also be done for hundreds of bursts. Swift will incorporate superb, low-cost instruments using existing flight-spare hardware and designs. Strong education/public outreach and follow-up programs will help to engage the public and astronomical community. Swift has been selected by NASA for development and launch in late 2003

SGR J1550-5418 Bursts Detected with the Fermi Gamma-Ray Burst Monitor during Its Most Prolific Activity

Science.gov (United States)

vanderHorst, A. J.; Kouveliotou, C.; Gorgone, N. M.; Kaneko, Y.; Baring, M. G.; Guiriec, S.; Gogus, E,; Granot, J.; Watts, A. L.; Lin, L.;

Bursting synchronization in scale-free networks

International Nuclear Information System (INIS)

Batista, C.A.S.; Batista, A.M.; Pontes, J.C.A. de; Lopes, S.R.; Viana, R.L.

2009-01-01

Neuronal networks in some areas of the brain cortex present the scale-free property, i.e., the neuron connectivity is distributed according to a power-law, such that neurons are more likely to couple with other already well-connected ones. Neuron activity presents two timescales, a fast one related to action-potential spiking, and a slow timescale in which bursting takes place. Some pathological conditions are related with the synchronization of the bursting activity in a weak sense, meaning the adjustment of the bursting phase due to coupling. Hence it has been proposed that an externally applied time-periodic signal be applied in order to control undesirable synchronized bursting rhythms. We investigated this kind of intervention using a two-dimensional map to describe neurons with spiking-bursting activity in a scale-free network.

BATSE/OSSE Rapid Burst Response

National Research Council Canada - National Science Library

Matz, S. M; Grove, J. E; Johnson, W. N; Kurfess, J. D; Share, G. H; Fishman, G. J; Meegan, Charles A

1995-01-01

...) slew the OSSE detectors to burst locations determined on-board by BATSE. This enables OSSE to make sensitive searches for prompt and delayed post-burst line and continuum emission above 50 keV...

Some polarization features of solar microwave bursts

Energy Technology Data Exchange (ETDEWEB)

Uralov, A M; Nefed' ev, V P [AN SSSR, Irkutsk. Sibirskij Inst. Zemnogo Magnetizma Ionosfery i Rasprostraneniya Radiovoln

1977-01-01

Consequences of the thermal microwave burst model proposed earlier have been considered. According to the model the centimeter burst is generated at the heat propagation to the upper atmosphere. The polarization features of the burst are explained: a change of the polarization sign in a frequency range, a rapid change of the polarization sign in the development of a burst at a fixed frequency, a lack of time coincidence of the moments of the burst maximum of the polarization and of the total flux. From the model the consequences are obtained, which are still not confirmed by experiment. An ordinary-type wave prevails in the burst radiation, in the course of which the polarization degree falls on the ascending branch of bursts development. At the change of the polarization sign at the fixed frequency prior to the sign change an ordinary-type wave should be present in excess and later an extreordinary type wave.

Exploring Visualisation of Channel Activity, Levels and EQ for User Interfaces Implementing the Stage Metaphor for Music Mixing

DEFF Research Database (Denmark)

Gelineck, Steven; Uhrenholt, Anders Kirk

2016-01-01

This short précis outlines a collection of different strategies for visualising simple audio features for a GUI- based audio mixing interface that uses the stage metaphor control scheme. Audio features such as activity, loudness and spectral centroid are extracted in real-time and mapped...... to different visual cues that can be adapted to the circular widgets most often found in implementations of the stage metaphor. An initial evaluation suggests that while the visualisations are generally intuitive and provide information about activity of audio channels, they are not used directly. When...... implementing these kinds of dynamic graphical visualisations it is thus important to consider how intrusive they are compared to their usefulness in a real mixing context....

Gamma Ray Bursts-Afterglows and Counterparts

Science.gov (United States)

Fishman, Gerald J

1998-01-01

Several breakthrough discoveries were made last year of x-ray, optical and radio afterglows and counterparts to gamma-ray bursts, and a redshift has been associated with at least one of these. These discoveries were made possible by the fast, accurate gamma-ray burst locations of the BeppoSAX satellite. It is now generally believed that the burst sources are at cosmological distances and that they represent the most powerful explosions in the Universe. These observations also open new possibilities for the study of early star formation, the physics of extreme conditions and perhaps even cosmology. This session will concentrate on recent x-ray, optical and radio afterglow observations of gamma-ray bursts, associated redshift measurements, and counterpart observations. Several review and theory talks will also be presented, along with a summary of the astrophysical implications of the observations. There will be additional poster contributions on observations of gamma-ray burst source locations at wavelengths other than gamma rays. Posters are also solicited that describe new observational capabilities for rapid follow-up observations of gamma-ray bursts.

Teleportations of Mixed States and Multipartite Quantum States

Institute of Scientific and Technical Information of China (English)

YU Chang-Shui; WANG Ya-Hong; SONG He-Shan

2007-01-01

In this paper, we propose a protocol to deterministically teleport an unknown mixed state of qubit by utilizing a maximally bipartite entangled state of qubits as quantum channel. Ifa non-maximally entangled bipartite pure state is employed as quantum channel, the unknown mixed quantum state of qubit can be teleported with 1 - √1 - C2 probability, where C is the concurrence of the quantum channel. The protocol can also be generalized to teleport a mixed state of qudit or a multipartite mixed state. More important purpose is that, on the basis of the protocol, the teleportation of an arbitrary multipartite (pure or mixed) quantum state can be decomposed into the teleportation of each subsystem by employing separate entangled states as quantum channels. In the case of deterministic teleportation,Bob only needs to perform unitary transformations on his single particles in order to recover the initial teleported multipartite quantum state.

SGR J1550-5418 BURSTS DETECTED WITH THE FERMI GAMMA-RAY BURST MONITOR DURING ITS MOST PROLIFIC ACTIVITY

Energy Technology Data Exchange (ETDEWEB)

Van der Horst, A. J.; Finger, M. H. [Universities Space Research Association, NSSTC, Huntsville, AL 35805 (United States); Kouveliotou, C. [Space Science Office, VP62, NASA/Marshall Space Flight Center, Huntsville, AL 35812 (United States); Gorgone, N. M. [Connecticut College, New London, CT 06320 (United States); Kaneko, Y.; Goegues, E.; Lin, L. [Sabanc Latin-Small-Letter-Dotless-I University, Orhanl Latin-Small-Letter-Dotless-I -Tuzla, Istanbul 34956 (Turkey); Baring, M. G. [Department of Physics and Astronomy, Rice University, MS-108, P.O. Box 1892, Houston, TX 77251 (United States); Guiriec, S.; Bhat, P. N.; Chaplin, V. L.; Goldstein, A. [University of Alabama, Huntsville, CSPAR, Huntsville, AL 35805 (United States); Granot, J. [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Watts, A. L. [Astronomical Institute ' Anton Pannekoek' , University of Amsterdam, Postbus 94249, 1090 GE Amsterdam (Netherlands); Bissaldi, E.; Gruber, D. [Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse, Postfach 1312, 85748 Garching (Germany); Gehrels, N.; Harding, A. K. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Gibby, M. H.; Giles, M. M., E-mail: A.J.VanDerHorst@uva.nl [Jacobs Technology, Inc., Huntsville, AL (United States); and others

2012-04-20

We have performed detailed temporal and time-integrated spectral analysis of 286 bursts from SGR J1550-5418 detected with the Fermi Gamma-ray Burst Monitor (GBM) in 2009 January, resulting in the largest uniform sample of temporal and spectral properties of SGR J1550-5418 bursts. We have used the combination of broadband and high time-resolution data provided with GBM to perform statistical studies for the source properties. We determine the durations, emission times, duty cycles, and rise times for all bursts, and find that they are typical of SGR bursts. We explore various models in our spectral analysis, and conclude that the spectra of SGR J1550-5418 bursts in the 8-200 keV band are equally well described by optically thin thermal bremsstrahlung (OTTB), a power law (PL) with an exponential cutoff (Comptonized model), and two blackbody (BB) functions (BB+BB). In the spectral fits with the Comptonized model, we find a mean PL index of -0.92, close to the OTTB index of -1. We show that there is an anti-correlation between the Comptonized E{sub peak} and the burst fluence and average flux. For the BB+BB fits, we find that the fluences and emission areas of the two BB functions are correlated. The low-temperature BB has an emission area comparable to the neutron star surface area, independent of the temperature, while the high-temperature BB has a much smaller area and shows an anti-correlation between emission area and temperature. We compare the properties of these bursts with bursts observed from other SGR sources during extreme activations, and discuss the implications of our results in the context of magnetar burst models.

THE FIVE YEAR FERMI/GBM MAGNETAR BURST CATALOG

Energy Technology Data Exchange (ETDEWEB)

Collazzi, A. C. [SciTec, Inc., 100 Wall Street, Princeton, NJ 08540 (United States); Kouveliotou, C.; Horst, A. J. van der; Younes, G. A. [Department of Physics, The George Washington University, 725 21st Street NW, Washington, DC 20052 (United States); Kaneko, Y.; Göğüş, E. [Sabancı University, Orhanlı-Tuzla, İstanbul 34956 (Turkey); Lin, L. [François Arago Centre, APC, 10 rue Alice Domon et Léonie Duquet, F-75205 Paris (France); Granot, J. [Department of Natural Sciences, The Open University of Israel, 1 University Road, P.O. Box 808, Raanana 43537 (Israel); Finger, M. H. [Universities Space Research Association, NSSTC, 320 Sparkman Drive, Huntsville, AL 35805 (United States); Chaplin, V. L. [School of Medicine, Vanderbilt University, 1161 21st Avenue S, Nashville, TN 37232 (United States); Huppenkothen, D. [Center for Data Science, New York University, 726 Broadway, 7th Floor, New York, NY 10003 (United States); Watts, A. L. [Anton Pannekoek Institute, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam (Netherlands); Kienlin, A. von [Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany); Baring, M. G. [Department of Physics and Astronomy, Rice University, MS-108, P.O. Box 1892, Houston, TX 77251 (United States); Gruber, D. [Planetarium Südtirol, Gummer 5, I-39053 Karneid (Italy); Bhat, P. N. [CSPAR, University of Alabama in Huntsville, 320 Sparkman Drive, Huntsville, AL 35899 (United States); Gibby, M. H., E-mail: acollazzi@scitec.com [Jacobs Technology, Inc., Huntsville, AL (United States); and others

2015-05-15

Since launch in 2008, the Fermi Gamma-ray Burst Monitor (GBM) has detected many hundreds of bursts from magnetar sources. While the vast majority of these bursts have been attributed to several known magnetars, there is also a small sample of magnetar-like bursts of unknown origin. Here, we present the Fermi/GBM magnetar catalog, providing the results of the temporal and spectral analyses of 440 magnetar bursts with high temporal and spectral resolution. This catalog covers the first five years of GBM magnetar observations, from 2008 July to 2013 June. We provide durations, spectral parameters for various models, fluences, and peak fluxes for all the bursts, as well as a detailed temporal analysis for SGR J1550–5418 bursts. Finally, we suggest that some of the bursts of unknown origin are associated with the newly discovered magnetar 3XMM J185246.6+0033.7.

Hierarchic Analysis Method to Evaluate Rock Burst Risk

Directory of Open Access Journals (Sweden)

Ming Ji

2015-01-01

Full Text Available In order to reasonably evaluate the risk of rock bursts in mines, the factors impacting rock bursts and the existing grading criterion on the risk of rock bursts were studied. By building a model of hierarchic analysis method, the natural factors, technology factors, and management factors that influence rock bursts were analyzed and researched, which determined the degree of each factor’s influence (i.e., weight and comprehensive index. Then the grade of rock burst risk was assessed. The results showed that the assessment level generated by the model accurately reflected the actual risk degree of rock bursts in mines. The model improved the maneuverability and practicability of existing evaluation criteria and also enhanced the accuracy and science of rock burst risk assessment.

Observation of gamma-ray bursts with GINGA

International Nuclear Information System (INIS)

Murakami, Toshio; Fujii, Masami; Nishimura, Jun

1989-01-01

Gamma-ray Burst Detector System (GBD) on board the scientific satellite 'GINGA' which was launched on Feb. 5, 1987, was realized as an international cooperation between ISAS and LANL. It has recorded more than 40 Gamma-Ray Burst candidates during 20 months observation. Although many observational evidences were accumulated in past 20 years after the discovery of gamma-ray burst by LANL scientists, there are not enough evidence to determine the origin and the production mechanism of the gamma-ray burst. GBD consists of a proportional counter and a NaI scintillation counter so that it became possible to observe energy spectrum of the gamma-ray burst with high energy resolution over wide range of energy (1.5-380 keV) together with high time resolution. As the result of observation, the following facts are obtained: (1) A large fraction of observed gamma-ray bursts has a long X-ray tail after the harder part of gamma-ray emission has terminated. (2) Clear spectral absorption features with harmonic in energy was observed in some of the energy spectrum of gamma-ray bursts. These evidences support the hypothesis that the strongly magnetized neutron star is the origin of gamma-ray burst. (author)

Swift Burst Alert Telescope (BAT) Instrument Response

International Nuclear Information System (INIS)

Parsons, A.; Barthelmy, S.; Cummings, J.; Gehrels, N.; Hullinger, D.; Krimm, H.; Markwardt, C.; Tueller, J.; Fenimore, E.; Palmer, D.; Sato, G.; Takahashi, T.; Nakazawa, K.; Okada, Y.; Takahashi, H.; Suzuki, M.; Tashiro, M.

2004-01-01

The Burst Alert Telescope (BAT), a large coded aperture instrument with a wide field-of-view (FOV), provides the gamma-ray burst triggers and locations for the Swift Gamma-Ray Burst Explorer. In addition to providing this imaging information, BAT will perform a 15 keV - 150 keV all-sky hard x-ray survey based on the serendipitous pointings resulting from the study of gamma-ray bursts, and will also monitor the sky for transient hard x-ray sources. For BAT to provide spectral and photometric information for the gamma-ray bursts, the transient sources and the all-sky survey, the BAT instrument response must be determined to an increasingly greater accuracy. This paper describes the spectral models and the ground calibration experiments used to determine the BAT response to an accuracy suitable for gamma-ray burst studies

Prompt burst energetics experiments: fresh oxide/sodium series

International Nuclear Information System (INIS)

Reil, K.O.; Young, M.F.

1978-08-01

A series of in-pile experiments has been performed to provide information on thermal energy to work conversion under prompt burst excursion (PBE) conditions. These consisted of single pin tests using fresh uranium oxide or uranium carbide fuel in a capsule geometry, with either stagnant sodium or helium in the coolant channel. The experiments were irradiated with single or double pulses in the Annular Core Pulse Reactor (ACPR) to provide energy depositions up to 2900 J/g. This report covers the seven single and five double pulse UO 2 sodium-in tests. Experimental data includes pressure and linear motion transducer histories, measured work-energy conversion efficiencies, and post-irradiation examination. Analysis includes derived work-energy conversion efficiencies (up to 0.54%), pin failure modeling, hydrodynamic analysis of pressure pulse propagation in the channel, and piston stopping effects. Initial pressure events in the single pulse experiments appear to be dominated by fuel vapor pressure. Definite fuel-coolant interactions were observed in several experiments, including some that were coincident with stopping of the linear motion transducer piston, suggesting a possible triggering effect by the deceleration pressure

Dark gamma-ray bursts

Science.gov (United States)

Brdar, Vedran; Kopp, Joachim; Liu, Jia

2017-03-01

Many theories of dark matter (DM) predict that DM particles can be captured by stars via scattering on ordinary matter. They subsequently condense into a DM core close to the center of the star and eventually annihilate. In this work, we trace DM capture and annihilation rates throughout the life of a massive star and show that this evolution culminates in an intense annihilation burst coincident with the death of the star in a core collapse supernova. The reason is that, along with the stellar interior, also its DM core heats up and contracts, so that the DM density increases rapidly during the final stages of stellar evolution. We argue that, counterintuitively, the annihilation burst is more intense if DM annihilation is a p -wave process than for s -wave annihilation because in the former case, more DM particles survive until the supernova. If among the DM annihilation products are particles like dark photons that can escape the exploding star and decay to standard model particles later, the annihilation burst results in a flash of gamma rays accompanying the supernova. For a galactic supernova, this "dark gamma-ray burst" may be observable in the Čerenkov Telescope Array.

BURST AND OUTBURST CHARACTERISTICS OF MAGNETAR 4U 0142+61

Energy Technology Data Exchange (ETDEWEB)

Göğüş, Ersin; Chakraborty, Manoneeta; Kaneko, Yuki [Sabancı University, Orhanlı-Tuzla, İstanbul 34956 (Turkey); Lin, Lin [Department of Astronomy, Beijing Normal University, Beijing 100875 (China); Roberts, Oliver J. [School of Physics, University College Dublin, Stillorgan Road, Belfield, Dublin 4 (Ireland); Gill, Ramandeep; Granot, Jonathan [Department of Natural Sciences, The Open University of Israel, 1 University Road, P.O. Box 808, Ranana 43537 (Israel); Horst, Alexander J. van der; Kouveliotou, Chryssa; Younes, George [Department of Physics, The George Washington University, Washington, DC 20052 (United States); Watts, Anna L. [Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam (Netherlands); Baring, Matthew [Department of Physics and Astronomy, Rice University, MS-108, P.O. Box 1892, Houston, TX 77251 (United States); Huppenkothen, Daniela [Center for Data Science, New York University, 726 Broadway, 7th Floor, NY 10003 (United States)

2017-01-20

We have compiled the most comprehensive burst sample from magnetar 4U 0142+61, comprising 27 bursts from its three burst-active episodes in 2011, 2012 and the latest one in 2015 observed with Swift /Burst Alert Telescope and Fermi /Gamma-ray Burst Monitor. Bursts from 4U 0142+61 morphologically resemble typical short bursts from other magnetars. However, 4U 0142+61 bursts are less energetic compared to the bulk of magnetar bursts. We uncovered an extended tail emission following a burst on 2015 February 28, with a thermal nature, cooling over a timescale of several minutes. During this tail emission, we also uncovered pulse peak phase aligned X-ray bursts, which could originate from the same underlying mechanism as that of the extended burst tail, or an associated and spatially coincident but different mechanism.

Bursting synchronization in clustered neuronal networks

International Nuclear Information System (INIS)

Yu Hai-Tao; Wang Jiang; Deng Bin; Wei Xi-Le

2013-01-01

Neuronal networks in the brain exhibit the modular (clustered) property, i.e., they are composed of certain subnetworks with differential internal and external connectivity. We investigate bursting synchronization in a clustered neuronal network. A transition to mutual-phase synchronization takes place on the bursting time scale of coupled neurons, while on the spiking time scale, they behave asynchronously. This synchronization transition can be induced by the variations of inter- and intracoupling strengths, as well as the probability of random links between different subnetworks. Considering that some pathological conditions are related with the synchronization of bursting neurons in the brain, we analyze the control of bursting synchronization by using a time-periodic external signal in the clustered neuronal network. Simulation results show a frequency locking tongue in the driving parameter plane, where bursting synchronization is maintained, even in the presence of external driving. Hence, effective synchronization suppression can be realized with the driving parameters outside the frequency locking region. (interdisciplinary physics and related areas of science and technology)

Self-regulation of turbulence bursts and transport barriers

International Nuclear Information System (INIS)

Floriani, E; Ciraolo, G; Ghendrih, Ph; Sarazin, Y; Lima, R

2013-01-01

The interplay between turbulent bursts and transport barriers is analyzed with a simplified model of interchange turbulence in magnetically confined plasmas. The turbulent bursts spread into the transport barriers and, depending on the competing magnitude of the burst and stopping capability of the barrier, can burn through. Simulations of two models of transport barriers are presented: a hard barrier where interchange turbulence modes are stable in a prescribed region and a soft barrier with external plasma biasing. The response of the transport barriers to the non-linear perturbations of the turbulent bursts, addressed in a predator–prey approach, indicates that the barriers monitor an amplification factor of the turbulent bursts, with amplification smaller than one for most bursts and, in some cases, amplification factors that can significantly exceed unity. The weak barriers in corrugated profiles and magnetic structures, as well as the standard barriers, are characterized by these transmission properties, which then regulate the turbulent burst transport properties. The interplays of barriers and turbulent bursts are modeled as competing stochastic processes. For different classes of the probability density function (PDF) of these processes, one can predict the heavy tail properties of the bursts downstream from the barrier, either exponential for a leaky barrier, or with power laws for a tight barrier. The intrinsic probing of the transport barriers by the turbulent bursts thus gives access to the properties of the barriers. The main stochastic variables are the barrier width and the spreading distance of the turbulent bursts within the barrier, together with their level of correlation. One finds that in the case of a barrier with volumetric losses, such as radiation or particle losses as addressed in our present simulations, the stochastic model predicts a leaky behavior with an exponential PDF of escaping turbulent bursts in agreement with the simulation

The γ-ray burst-detection system of SPI

International Nuclear Information System (INIS)

Lichti, G.G.; Georgii, R.; Kienlin, A. von; Schoenfelder, V.; Wunderer, C.; Jung, H.-J.; Hurley, K.

2000-01-01

The determination of precise locations of γ-ray bursts is a crucial task of γ-ray astronomy. Although γ-ray burst locations can be obtained nowadays from single experiments (BATSE, COMPTEL, BeppoSax) the location of bursts via triangulation using the interplanetary network is still important because not all bursts will be located precisely enough by these single instruments. In order to get location accuracies down to arcseconds via triangulation one needs long baselines. At the beginning of the next decade several spacecrafts which explore the outer planetary system (the Mars-Surveyor-2001 Orbiter and probably Ulysses) will carry γ-ray burst instruments. INTEGRAL as a near-earth spacecraft is the ideal counterpart for these satellites. The massive anticoincidence shield of the INTEGRAL-spectrometer SPI allows the measurement of γ-ray bursts with a high sensitivity. Estimations have shown that with SPI some hundred γ-ray bursts per year on the 5σ level can be measured. This is equivalent to the BATSE sensitivity. We describe the γ-ray burst-detection system of SPI, present its technical features and assess the scientific capabilities

Balloon observation of gamma-ray burst

International Nuclear Information System (INIS)

Nishimura, Jun; Fujii, Masami; Yamagami, Takamasa; Oda, Minoru; Ogawara, Yoshiaki

1978-01-01

Cosmic gamma-ray burst is an interesting high energy astrophysical phenomenon, but the burst mechanism has not been well understood. Since 1975, long duration balloon flight has been conducted to search for gamma-ray bursts and to determine the source locations. A rotating cross-modulation collimator was employed to determine the locations of sources, and four NaI(Tl) scintillation counters were employed to detect hard X-ray with energy from 20 to 200 keV. The balloon light was performed at altitude of 8.3 mb from September 28, 1977, and the observation time of 79 hours was achieved. In this experiment, the monitor counter was not mounted. The count increase was observed at 16 h 22 m 31 s JST on October 1, 1977. The event disappeared after 1 sec. The total flux is estimated to be 1.6 x 10 -6 erg/cm 2 sec at the top of the atmosphere. When this event was observed, the solar-terrestrial environment was also quiet. Thus, this event was attributed to a small gamma-ray burst. Unfortunately, the duration of the burst was so short that the position of the burst source was not able to be determined. (Yoshimori, M.)

Frequency of fast, narrow γ-ray bursts

International Nuclear Information System (INIS)

Norris, J.P.; Maryland Univ., College Park; Cline, T.L.; Desai, U.D.; Teegarden, B.J.

1984-01-01

The paper describes the existence of two γ-ray burst populations detected by the ISEE-3 experiment. Data from the distribution of 123 Venera 13 and 14 events (60 detected by both spacecraft) also suggests two γ-ray burst populations in each experiment sample, the domains separated with a minimum near 1 or 2 s. The authors point out that the results of the Goddard ISEE-3 γ-ray burst spectrometer actually enhance the appearance of two burst populations suggested in the Venera data. (author)

Possible galactic origin of. gamma. -ray bursts

Energy Technology Data Exchange (ETDEWEB)

Manchanda, R K; Ramsden, D [Southampton Univ. (UK). Dept. of Physics

1977-03-31

It is stated that extragalactic models for the origin of non-solar ..gamma..-ray bursts include supernova bursts in remote galaxies, and the collapse of the cores of active stars, whilst galactic models are based on flare stars, thermonuclear explosions in neutron stars and the sudden accretion of cometary gas on to neutron stars. The acceptability of any of these models may be tested by the observed size spectrum of the ..gamma..-ray bursts. The extragalactic models predict a power law spectrum with number index -1.5, whilst for the galactic models the number index will be -1. Experimental data on ..gamma..-ray bursts is, however, still meagre, and so far only 44 confirmed events have been recorded by satellite-borne instruments. The number spectrum of the observed ..gamma..-ray bursts indicates that the observed distribution for events with an energy < 10/sup -4/ erg/cm/sup 2/ is flat; this makes the choice of any model completely arbitrary. An analysis of the observed ..gamma..-ray events is here presented that suggests very interesting possibilities for their origin. There appears to be a preferred mean energy for ..gamma..-ray bursts; some 90% of the recorded events show a mean energy between 5 x 10/sup -5/ and 5 x 10/sup -4/ erg/cm/sup 2/, contrary to the predicted characteristics of the number spectrum of various models. A remarkable similarity is found between the distribution of ..gamma..-ray bursts and that of supernova remnants, suggesting a genetic relationship between the two and the galactic origin of the ..gamma..-ray bursts, and the burst source could be identified with completely run down neutron stars, formed during supernova explosions.

Single K ATP channel opening in response to action potential firing in mouse dentate granule neurons.

Science.gov (United States)

Tanner, Geoffrey R; Lutas, Andrew; Martínez-François, Juan Ramón; Yellen, Gary

2011-06-08

ATP-sensitive potassium channels (K(ATP) channels) are important sensors of cellular metabolic state that link metabolism and excitability in neuroendocrine cells, but their role in nonglucosensing central neurons is less well understood. To examine a possible role for K(ATP) channels in modulating excitability in hippocampal circuits, we recorded the activity of single K(ATP) channels in cell-attached patches of granule cells in the mouse dentate gyrus during bursts of action potentials generated by antidromic stimulation of the mossy fibers. Ensemble averages of the open probability (p(open)) of single K(ATP) channels over repeated trials of stimulated spike activity showed a transient increase in p(open) in response to action potential firing. Channel currents were identified as K(ATP) channels through blockade with glibenclamide and by comparison with recordings from Kir6.2 knock-out mice. The transient elevation in K(ATP) p(open) may arise from submembrane ATP depletion by the Na(+)-K(+) ATPase, as the pump blocker strophanthidin reduced the magnitude of the elevation. Both the steady-state and stimulus-elevated p(open) of the recorded channels were higher in the presence of the ketone body R-β-hydroxybutyrate, consistent with earlier findings that ketone bodies can affect K(ATP) activity. Using perforated-patch recording, we also found that K(ATP) channels contribute to the slow afterhyperpolarization following an evoked burst of action potentials. We propose that activity-dependent opening of K(ATP) channels may help granule cells act as a seizure gate in the hippocampus and that ketone-body-mediated augmentation of the activity-dependent opening could in part explain the effect of the ketogenic diet in reducing epileptic seizures.

Throughput Estimation Method in Burst ACK Scheme for Optimizing Frame Size and Burst Frame Number Appropriate to SNR-Related Error Rate

Science.gov (United States)

Ohteru, Shoko; Kishine, Keiji

The Burst ACK scheme enhances effective throughput by reducing ACK overhead when a transmitter sends sequentially multiple data frames to a destination. IEEE 802.11e is one such example. The size of the data frame body and the number of burst data frames are important burst transmission parameters that affect throughput. The larger the burst transmission parameters are, the better the throughput under error-free conditions becomes. However, large data frame could reduce throughput under error-prone conditions caused by signal-to-noise ratio (SNR) deterioration. If the throughput can be calculated from the burst transmission parameters and error rate, the appropriate ranges of the burst transmission parameters could be narrowed down, and the necessary buffer size for storing transmit data or received data temporarily could be estimated. In this paper, we present a method that features a simple algorithm for estimating the effective throughput from the burst transmission parameters and error rate. The calculated throughput values agree well with the measured ones for actual wireless boards based on the IEEE 802.11-based original MAC protocol. We also calculate throughput values for larger values of the burst transmission parameters outside the assignable values of the wireless boards and find the appropriate values of the burst transmission parameters.

Gamma-Ray Bursts: 4th Huntsville Symposium. Proceedings

International Nuclear Information System (INIS)

Meegan, C.A.; Preece, R.D.; Koshut, T.M.

1998-01-01

These proceedings represent papers presented at the Fourth Huntsville Gamma-Ray Bursts Symposium held in September, 1997 in Huntsville, Alabama, USA. This conference occurred at a crucial time in the history of the gamma-ray burst research. In early 1997, 30 years after the detection of the first gamma-ray burst by the Vela satellites, counterparts to bursts were finally detected at optical and radio wavelengths. The symposium attracted about 200 scientists from 16 countries. Some of the topics discussed include gamma-ray burst spectra, x-ray observations, optical observations, radio observations, host galaxies, shocks and afterglows and models of gamma-ray bursts. There were 183 papers presented, out of these, 16 have been abstracted for the Energy Science and Technology database

X-ray echoes from gamma-ray bursts

International Nuclear Information System (INIS)

Dermer, C.D.; Hurley, K.C.; Hartmann, D.H.

1991-01-01

The identification of an echo of reflected radiation in time histories of gamma-ray burst spectra can provide important information about the existence of binary companions or accretion disks in gamma-ray burst systems. Because of the nature of Compton scattering, the spectrum of the echo will be attenuated at gamma-ray energies compared with the spectrum of the primary burst emission. The expected temporal and spectral signatures of the echo and a search for such echoes are described, and implications for gamma-ray burst models are discussed. 35 refs

A New Measurement of the Spectral Lag of Gamma-Ray Bursts and its Implications for Spectral Evolution Behaviors

Energy Technology Data Exchange (ETDEWEB)

Shao, Lang; Wang, Fu-Ri; Cheng, Ye-Hao; Zhang, Xi; Yu, Bang-Yao; Xi, Bao-Jia; Wang, Xue; Feng, Huan-Xue; Zhang, Meng, E-mail: lshao@hebtu.edu.cn [Department of Space Sciences and Astronomy, Hebei Normal University, Shijiazhuang 050024 (China); Zhang, Bin-Bin [Instituto de Astrofísica de Andalucá (IAA-CSIC), P.O. Box 03004, E-18080 Granada (Spain); Wu, Xue-Feng [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China); Xu, Dong [Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2017-08-01

We carry out a systematical study of the spectral lag properties of 50 single-pulsed gamma-ray bursts (GRBs) detected by the Fermi Gamma-Ray Burst Monitor. By dividing the light curves into multiple consecutive energy channels, we provide a new measurement of the spectral lag that is independent of energy channel selections. We perform a detailed statistical study of our new measurements. We find two similar power-law energy dependencies of both the pulse arrival time and pulse width. Our new results on the power-law indices would favor the relativistic geometric effects for the origin of spectral lag. However, a complete theoretical framework that can fully account for the diverse energy dependencies of both arrival time and pulse width revealed in this work is still lacking. We also study the spectral evolution behaviors of the GRB pulses. We find that a GRB pulse with negligible spectral lag would usually have a shorter pulse duration and would appear to have a “hardness-intensity tracking” behavior, and a GRB pulse with a significant spectral lag would usually have a longer pulse duration and would appear to have a “hard-to-soft” behavior.

Bs0 → Ds-α1+ (Ds- → φπ-, Ds- → K*0K-)-decay channel in the ATLAS Bs0-mixing studies

International Nuclear Information System (INIS)

Bannikov, A.V.; Shelkov, G.A.; Silagadze, Z.K.

1998-01-01

It is shown, using a track-level simulation, that the use of the D s - → K *0 K - - decay channel for D s - reconstruction, in addition with the previously studied D s - → φπ - mode, enables two fold gain in the ATLAS B s 0 -mixing signal statistics through B s 0 → D s - α 1 B s 0 -decay channel. A new modification of the amplitude fit method is suggested for the x s -determination

Gamma-ray burst observations: the present situation

International Nuclear Information System (INIS)

Vedrenne, G.

1984-01-01

Recent results in gamma ray burst investigations concerning the spectral variability on a short time scale, precise locations, and the discovery of optical flashes in gamma ray burst positions on archival plates are presented. The implications of optical and X-ray observations of gamma ray burst error boxes are also discussed. 72 references

Detecting pipe bursts by monitoring water demand

NARCIS (Netherlands)

Bakker, M.; Vreeburg, J.H.G.; Van der Roer, M.; Sperber, V.

2012-01-01

An algorithm which compares measured and predicted water demands to detect pipe bursts was developed and tested on three data sets of water demand and reported pipe bursts of three years. The algorithm proved to be able to detect bursts where the water loss exceeds 30% of the average water demand in

Fine structure in fast drift storm bursts

International Nuclear Information System (INIS)

McConnell, D.; Ellis, G.R.A.

1981-01-01

Recent observations with high time resolution of fast drift storm (FDS) solar bursts are described. A new variety of FDS bursts characterised by intensity maxima regularly placed in the frequency domain is reported. Possible interpretations of this are mentioned and the implications of the short duration of FDS bursts are discussed. (orig.)

Mosquito drinking with a burst in reserve: explaining behavior with a fluid mechanics model

Science.gov (United States)

Chatterjee, Souvick; Socha, Jake; Stremler, Mark

2014-03-01

Mosquitoes drink using a pair of in-line pumps in the head that draw liquid food through a long drinking channel, or proboscis. Experimental observations indicate two modes of drinking: a predominantly occurring continuous mode, in which the cibarial and pharyngeal pumps expand cyclically at a constant phase difference, and an isolated burst mode, in which the pharyngeal pump expansion is several orders of magnitude larger than in the continuous mode. We use a reduced order model of the fluid mechanics to hypothesize an explanation of this naturally occurring drinking behavior. Our model results show that the continuous mode is the more efficient mode in terms of energy expenditure, and the burst mode creates a large pressure difference across the proboscis. We speculate that the mosquito uses this pressure drop to clear blockages in the proboscis. We compared the two-pump system with one-pump configurations, as found in some other insects like butterflies, and show that the two pumps have unique roles in mosquito feeding.

Bursting neurons and ultrasound avoidance in crickets

Directory of Open Access Journals (Sweden)

Gary eMarsat

2012-07-01

Full Text Available Decision making in invertebrates often relies on simple neural circuits composed of only a few identified neurons. The relative simplicity of these circuits makes it possible to identify the key computation and neural properties underlying decisions. In this review, we summarize recent research on the neural basis of ultrasound avoidance in crickets, a response that allows escape from echolocating bats. The key neural property shaping behavioral output is high-frequency bursting of an identified interneuron, AN2, which carries information about ultrasound stimuli from receptor neurons to the brain. AN2's spike train consists of clusters of spikes –bursts– that may be interspersed with isolated, non-burst spikes. AN2 firing is necessary and sufficient to trigger avoidance steering but only high-rate firing, such as occurs in bursts, evokes this response. AN2 bursts are therefore at the core of the computation involved in deciding whether or not to steer away from ultrasound. Bursts in AN2 are triggered by synaptic input from nearly synchronous bursts in ultrasound receptors. Thus the population response at the very first stage of sensory processing –the auditory receptor- already differentiates the features of the stimulus that will trigger a behavioral response from those that will not. Adaptation, both intrinsic to AN2 and within ultrasound receptors, scales the burst-generating features according to the stimulus statistics, thus filtering out background noise and ensuring that bursts occur selectively in response to salient peaks in ultrasound intensity. Furthermore AN2’s sensitivity to ultrasound varies adaptively with predation pressure, through both developmental and evolutionary mechanisms. We discuss how this key relationship between bursting and the triggering of avoidance behavior is also observed in other invertebrate systems such as the avoidance of looming visual stimuli in locusts or heat avoidance in beetles.

AUTOMATIC RECOGNITION OF CORONAL TYPE II RADIO BURSTS: THE AUTOMATED RADIO BURST IDENTIFICATION SYSTEM METHOD AND FIRST OBSERVATIONS

International Nuclear Information System (INIS)

Lobzin, Vasili V.; Cairns, Iver H.; Robinson, Peter A.; Steward, Graham; Patterson, Garth

2010-01-01

Major space weather events such as solar flares and coronal mass ejections are usually accompanied by solar radio bursts, which can potentially be used for real-time space weather forecasts. Type II radio bursts are produced near the local plasma frequency and its harmonic by fast electrons accelerated by a shock wave moving through the corona and solar wind with a typical speed of ∼1000 km s -1 . The coronal bursts have dynamic spectra with frequency gradually falling with time and durations of several minutes. This Letter presents a new method developed to detect type II coronal radio bursts automatically and describes its implementation in an extended Automated Radio Burst Identification System (ARBIS 2). Preliminary tests of the method with spectra obtained in 2002 show that the performance of the current implementation is quite high, ∼80%, while the probability of false positives is reasonably low, with one false positive per 100-200 hr for high solar activity and less than one false event per 10000 hr for low solar activity periods. The first automatically detected coronal type II radio burst is also presented.

NICER Eyes on Bursting Stars

Science.gov (United States)

Kohler, Susanna

2018-03-01

What happens to a neutron stars accretion disk when its surface briefly explodes? A new instrument recently deployed at the International Space Station (ISS) is now watching bursts from neutron stars and reporting back.Deploying a New X-Ray MissionLaunch of NICER aboard a Falcon 9 rocket in June 2017. [NASA/Tony Gray]In early June of 2017, a SpaceX Dragon capsule on a Falcon 9 rocket launched on a resupply mission to the ISS. The pressurized interior of the Dragon contained the usual manifest of crew supplies, spacewalk equipment, and vehicle hardware. But the unpressurized trunk of the capsule held something a little different: the Neutron star Interior Composition Explorer (NICER).In the two weeks following launch, NICER was extracted from the SpaceX Dragon capsule and installed on the ISS. And by the end of the month, the instrument was already collecting its first data set: observations of a bright X-ray burst from Aql X-1, a neutron star accreting matter from a low-mass binary companion.Impact of BurstsNICERs goal is to provide a new view of neutron-star physics at X-ray energies of 0.212 keV a window that allows us to explore bursts of energy that neutron stars sometimes emit from their surfaces.Artists impression of an X-ray binary, in which a compact object accretes material from a companion star. [ESA/NASA/Felix Mirabel]In X-ray burster systems, hydrogen- and helium-rich material from a low-mass companion star piles up in an accretion disk around the neutron star. This material slowly funnels onto the neutron stars surface, forming a layer that gravitationally compresses and eventually becomes so dense and hot that runaway nuclear fusion ignites.Within seconds, the layer of material is burned up, producing a burst of emission from the neutron star that outshines even the inner regions of the hot accretion disk. Then more material funnels onto the neutron star and the process begins again.Though we have a good picture of the physics that causes these bursts

Impact of Bimodal Traffic on Latency in Optical Burst Switching Networks

Directory of Open Access Journals (Sweden)

Yuhua Chen

2008-01-01

Full Text Available This paper analyzes the impact of bimodal traffic composition on latency in optical burst switching networks. In particular, it studies the performance degradation to short-length packets caused by longer packets, both of which are part of a heterogeneous traffic model. The paper defines a customer satisfaction index for each of the classes of traffic, and a composite satisfaction index. The impact of higher overall utilization of the network as well as that of the ratio of the traffic mix on each of the customer satisfaction indices is specifically addressed.

Observation of cosmic gamma ray burst by Hinotori

International Nuclear Information System (INIS)

Okudaira, Kiyoaki; Yoshimori, Masato; Hirashima, Yo; Kondo, Ichiro.

1982-01-01

The solar gamma ray detecor (SGR) on Hinotori has no collimator, and the collimator of a hard X-ray monitor is not effective for gamma ray with energy more than 100 KeV. Accordingly, the detection system can detect cosmic gamma ray burst, and two bursts were observed. The first burst was detected on February 28, 1981, and the source of the burst was in the direction of 81 degree from Venus. The time profile and the spectrum were observed. In July 21, 1981, the second burst was detected. The time profile obtained with the SGR was compared with those of PVO (Pioneer Venus Orbiter) and LASL-ISEE. The time difference among the data of time profiles indicated that the source of the burst was not the sun. The spectrum was also measured. (Kato, T.)

Advances in gamma-ray burst astronomy

International Nuclear Information System (INIS)

Cline, T.L.; Desai, U.D.

1976-01-01

Work at Goddard is presently being carried out in three major areas of gamma-ray burst research: (1) A pair of simultaneously operating 0.8-m 2 burst detectors were successfully balloon-borne at locations 800 miles apart on 9 May, 1975, each to atmospheric depths of 3 to 4 g cm -2 , for a 20-h period of coincident data coverage. This experiment investigates the size spectrum of bursts in the 10 -7 to 10 -6 erg cm -2 size region where dozens of events per day are expected on a -1.5 index integral power-law extrapolation. Considerable separation in latitude was used to avoid possible atmospheric and auroral secondary effects. Its results are not yet available. (2) A deep-space burst detector, the first spacecraft instrument built specifically for gamma-ray burst studies, was recently successfully integrated into the Helios-B space probe. Its use at distances of up to 2 AU will make possible the first high-resolution directional study of gamma-ray burst source locations. Similar modifications to several other space vehicles are also being prepared. (3) The gamma-ray instrument on the IMP-7 satellite is presently the most sensitive burst detector still operating in orbit. Its results have shown that all measured event-average energy spectra are consistent with being alike. Using this characteristic spectrum to select IMP-7 candidate events of smaller size than those detected using other spacecraft in coincidence, a size spectrum is constructed which fits the -1.5 index power law down to 2.5 x 10 -5 erg cm -2 per event, at an occurrence rate of about once per month. (Auth.)

Study on cosmic gamma bursts in the ''KONUS'' experiment

International Nuclear Information System (INIS)

Mazets, E.P.; Golenetskij, S.V.; Il'inskij, V.N.; Panov, V.N.; Aptekar', R.L.; Gur'yan, Yu.A.; Sokolov, I.A.; Sokolova, Z.Ya.; Kharitonova, T.V.

1979-01-01

Made are the investigations of cosmic gamma bursts with the help of the ''Konus'' apparatus, positioned on the ''Venera 11'' and ''Venera 12'' automatic interplanetary stations. 37 gamma bursts have been recorded in the energy range from 50 to 150 keV during the observation period from September to December 1978. Time profiles of bursts on 4, 9 and 24.11.1978 are presented. For the most events the time of burst increase and decrease constitute parts and units of seconds. Differential energy spectra are measured for all recorded bursts. In many cases the spectrum shape is similar to the grade one with the 1.5-2.3 index. In a graphical form built up are the integral distributions of gamma bursts appearence frequency in dependence on their intensity and maximum capacity in the burst peak. Galaxy coordinates of the 17-teen bursts, for which a simple localization is possible, are put on the celestial sphere map. The type of the integral distributions and the source distribution about the celestial sphere show that the gamma burst sources are whithin the Galaxy

A Novel QKD-based Secure Edge Router Architecture Design for Burst Confidentiality in Optical Burst Switched Networks

Science.gov (United States)

Balamurugan, A. M.; Sivasubramanian, A.

2014-06-01

The Optical Burst Switching (OBS) is an emergent result to the technology issue that could achieve a viable network in future. They have the ability to meet the bandwidth requisite of those applications that call for intensive bandwidth. The field of optical transmission has undergone numerous advancements and is still being researched mainly due to the fact that optical data transmission can be done at enormous speeds. The concept of OBS is still far from perfection facing issues in case of security threat. The transfer of optical switching paradigm to optical burst switching faces serious downfall in the fields of burst aggregation, routing, authentication, dispute resolution and quality of service (QoS). This paper proposes a framework based on QKD based secure edge router architecture design to provide burst confidentiality. The QKD protocol offers high level of confidentiality as it is indestructible. The design architecture was implemented in FPGA using diverse models and the results were taken. The results show that the proposed model is suitable for real time secure routing applications of the Optical burst switched networks.

Stimulus-dependent state transition between synchronized oscillation and randomly repetitive burst in a model cerebellar granular layer.

Directory of Open Access Journals (Sweden)

Takeru Honda

2011-07-01

Full Text Available Information processing of the cerebellar granular layer composed of granule and Golgi cells is regarded as an important first step toward the cerebellar computation. Our previous theoretical studies have shown that granule cells can exhibit random alternation between burst and silent modes, which provides a basis of population representation of the passage-of-time (POT from the onset of external input stimuli. On the other hand, another computational study has reported that granule cells can exhibit synchronized oscillation of activity, as consistent with observed oscillation in local field potential recorded from the granular layer while animals keep still. Here we have a question of whether an identical network model can explain these distinct dynamics. In the present study, we carried out computer simulations based on a spiking network model of the granular layer varying two parameters: the strength of a current injected to granule cells and the concentration of Mg²⁺ which controls the conductance of NMDA channels assumed on the Golgi cell dendrites. The simulations showed that cells in the granular layer can switch activity states between synchronized oscillation and random burst-silent alternation depending on the two parameters. For higher Mg²⁺ concentration and a weaker injected current, granule and Golgi cells elicited spikes synchronously (synchronized oscillation state. In contrast, for lower Mg²⁺ concentration and a stronger injected current, those cells showed the random burst-silent alternation (POT-representing state. It is suggested that NMDA channels on the Golgi cell dendrites play an important role for determining how the granular layer works in response to external input.

3rd Interplanetary Network Gamma-Ray Burst Website

Science.gov (United States)

Hurley, Kevin

1998-05-01

We announce the opening of the 3rd Interplanetary Network web site at http://ssl.berkeley.edu/ipn3/index.html This site presently has four parts: 1. A bibliography of over 3000 publications on gamma-ray bursts, 2. IPN data on all bursts triangulated up to February 1998, 3. A master list showing which spacecraft observed which bursts, 4. Preliminary IPN data on the latest bursts observed.

THE INTERPLANETARY NETWORK SUPPLEMENT TO THE BURST AND TRANSIENT SOURCE EXPERIMENT 5B CATALOG OF COSMIC GAMMA-RAY BURSTS

International Nuclear Information System (INIS)

Hurley, K.; Briggs, M. S.; Kippen, R. M.; Kouveliotou, C.; Fishman, G.; Meegan, C.; Cline, T.; Trombka, J.; McClanahan, T.; Boynton, W.; Starr, R.; McNutt, R.; Boer, M.

2011-01-01

We present Interplanetary Network localization information for 343 gamma-ray bursts observed by the Burst and Transient Source Experiment (BATSE) between the end of the 4th BATSE catalog and the end of the Compton Gamma-Ray Observatory (CGRO) mission, obtained by analyzing the arrival times of these bursts at the Ulysses, Near Earth Asteroid Rendezvous (NEAR), and CGRO spacecraft. For any given burst observed by CGRO and one other spacecraft, arrival time analysis (or t riangulation ) results in an annulus of possible arrival directions whose half-width varies between 11 arcsec and 21 0 , depending on the intensity, time history, and arrival direction of the burst, as well as the distance between the spacecraft. This annulus generally intersects the BATSE error circle, resulting in an average reduction of the area of a factor of 20. When all three spacecraft observe a burst, the result is an error box whose area varies between 1 and 48,000 arcmin 2 , resulting in an average reduction of the BATSE error circle area of a factor of 87.

Hydraulic jumps in a channel

DEFF Research Database (Denmark)

Bonn, D.; Andersen, Anders Peter; Bohr, Tomas

2009-01-01

We present a study of hydraulic jumps with flow predominantly in one direction, created either by confining the flow to a narrow channel with parallel walls or by providing an inflow in the form of a narrow sheet. In the channel flow, we find a linear height profile upstream of the jump as expected......'s mixing-length theory with a mixing length that is proportional to the height of the fluid layer. Using averaged boundary-layer equations, taking into account the friction with the channel walls and the eddy viscosity, the flow both upstream and downstream of the jump can be understood. For the downstream...... subcritical flow, we assume that the critical height is attained close to the channel outlet. We use mass and momentum conservation to determine the position of the jump and obtain an estimate which is in rough agreement with our experiment. We show that the averaging method with a varying velocity profile...

Thermal mixing of two miscible fluids in a T-shaped microchannel.

Science.gov (United States)

Xu, Bin; Wong, Teck Neng; Nguyen, Nam-Trung; Che, Zhizhao; Chai, John Chee Kiong

2010-10-01

In this paper, thermal mixing characteristics of two miscible fluids in a T-shaped microchannel are investigated theoretically, experimentally, and numerically. Thermal mixing processes in a T-shaped microchannel are divided into two zones, consisting of a T-junction and a mixing channel. An analytical two-dimensional model was first built to describe the heat transfer processes in the mixing channel. In the experiments, de-ionized water was employed as the working fluid. Laser induced fluorescence method was used to measure the fluid temperature field in the microchannel. Different combinations of flow rate ratios were studied to investigate the thermal mixing characteristics in the microchannel. At the T-junction, thermal diffusion is found to be dominant in this area due to the striation in the temperature contours. In the mixing channel, heat transfer processes are found to be controlled by thermal diffusion and convection. Measured temperature profiles at the T-junction and mixing channel are compared with analytical model and numerical simulation, respectively.

Low-Frequency Type III Bursts and Solar Energetic Particle Events

Science.gov (United States)

Gopalswamy, Nat; Makela, Pertti

2010-01-01

We analyzed the coronal mass ejections (CMEs), flares, and type 11 radio bursts associated with a set of six low frequency (15 min) normally used to define these bursts. All but one of the type III bursts was not associated with a type 11 burst in the metric or longer wavelength domains. The burst without type 11 burst also lacked a solar energetic particle (SEP) event at energies >25 MeV. The 1-MHz duration of the type III burst (28 min) is near the median value of type III durations found for gradual SEP events and ground level enhancement (GLE) events. Yet, there was no sign of SEP events. On the other hand, two other type III bursts from the same active region had similar duration but accompanied by WAVES type 11 bursts; these bursts were also accompanied by SEP events detected by SOHO/ERNE. The CMEs were of similar speeds and the flares are also of similar size and duration. This study suggests that the type III burst duration may not be a good indicator of an SEP event.

New decoding methods of interleaved burst error-correcting codes

Science.gov (United States)

Nakano, Y.; Kasahara, M.; Namekawa, T.

1983-04-01

A probabilistic method of single burst error correction, using the syndrome correlation of subcodes which constitute the interleaved code, is presented. This method makes it possible to realize a high capability of burst error correction with less decoding delay. By generalizing this method it is possible to obtain probabilistic method of multiple (m-fold) burst error correction. After estimating the burst error positions using syndrome correlation of subcodes which are interleaved m-fold burst error detecting codes, this second method corrects erasure errors in each subcode and m-fold burst errors. The performance of these two methods is analyzed via computer simulation, and their effectiveness is demonstrated.

Flash photoionization of gamma-ray burst environments

Science.gov (United States)

Band, David L.; Hartmann, Dieter H.

1992-01-01

The H-alpha line emission that a flash-photoionized region emits is calculated. Archival transients, as well as various theoretical predictions, suggest that there may be significant ionizing flux. The limits on the line flux which might be observable indicate that the density must be fairly high for the recombination radiation to be observable. The intense burst radiation is insufficient to melt the dust which will be present in such a dense medium. This dust may attenuate the observable line emission, but does not attenuate the ionizing radiation before it ionizes the neutral medium surrounding the burst source. The dust can also produce a light echo. If there are indeed gamma-ray bursts in dense clouds, then it is possible that the burst was triggered by Bondi-Hoyle accretion from the dense medium, although it is unlikely on statistical grounds that all bursts occur in clouds.

Long X-ray burst monitoring with INTEGRAL

DEFF Research Database (Denmark)

X-ray bursts are thermonuclear explosions on the surface of accreting neutron stars in low mass X-ray binary systems. In the frame of the INTEGRAL observational Key Programme over the Galactic Center a good number of the known X-ray bursters are frequently being monitored. An international...... collaboration lead by the JEM-X team at the Danish National Space Center has proposed to exploit the improved sensitivity of the INTEGRAL instruments to investigate the observational properties and physics up to high energies of exceptional burst events lasting between a few tens of minutes and several hours....... Of special interest are low luminosity bursting sources that exhibit X-ray bursts of very different durations allowing to study the transition from a hydrogen-rich bursting regime to a pure helium regime and from helium burning to carbon burning. I will present results obtained from INTEGRAL archive data...

Frequency chirping during a fishbone burst

International Nuclear Information System (INIS)

Marchenko, V.S.; Reznik, S.N.

2011-01-01

It is shown that frequency chirping during fishbone activity can be attributed to the reactive torque exerted on the plasma during the instability burst, which slows down plasma rotation inside the q = 1 surface and reduces the mode frequency in the lab frame. Estimates show that the peak value of this torque can exceed the neutral beam torque in modern tokamaks. The simple line-broadened quasilinear burst model (Berk et al 1995 Nucl. Fusion 35 1661), properly adapted for the fishbone case, is capable of reproducing the key features of the bursting mode. (letter)

Simulating X-ray bursts during a transient accretion event

Science.gov (United States)

Johnston, Zac; Heger, Alexander; Galloway, Duncan K.

2018-06-01

Modelling of thermonuclear X-ray bursts on accreting neutron stars has to date focused on stable accretion rates. However, bursts are also observed during episodes of transient accretion. During such events, the accretion rate can evolve significantly between bursts, and this regime provides a unique test for burst models. The accretion-powered millisecond pulsar SAX J1808.4-3658 exhibits accretion outbursts every 2-3 yr. During the well-sampled month-long outburst of 2002 October, four helium-rich X-ray bursts were observed. Using this event as a test case, we present the first multizone simulations of X-ray bursts under a time-dependent accretion rate. We investigate the effect of using a time-dependent accretion rate in comparison to constant, averaged rates. Initial results suggest that using a constant, average accretion rate between bursts may underestimate the recurrence time when the accretion rate is decreasing, and overestimate it when the accretion rate is increasing. Our model, with an accreted hydrogen fraction of X = 0.44 and a CNO metallicity of ZCNO = 0.02, reproduces the observed burst arrival times and fluences with root mean square (rms) errors of 2.8 h, and 0.11× 10^{-6} erg cm^{-2}, respectively. Our results support previous modelling that predicted two unobserved bursts and indicate that additional bursts were also missed by observations.

Review of GRANAT observations of gamma-ray bursts

DEFF Research Database (Denmark)

Terekhov, O.; Denissenko, D.; Sunyaev, R.

1995-01-01

The GRANAT observatory was launched into a high apogee orbit on 1 December, 1989. Three instruments onboard GRANAT - PHEBUS, WATCH and SIGMA are able to detect gamma-ray bursts in a very broad energy range from 6 keV up to 100 MeV. Over 250 gamma-ray bursts were detected. We discuss the results...... of the observations of the time histories and spectral evolution of the detected events provided by the different instruments in different energy ranges. Short Gamma-Ray Bursts ( 2 s) events. Evidence of the existence...... of four differently behaving componenents in gamma-ray burst spectra is discussed. Statistical properties of the gamma-ray burst sources based on the 5 years of observations with (∼ 10−6 erg/cm2) sensitivity as well as the results of high sensitivity (∼ 10−8 erg/cm2) search for Gamma-Ray Bursts within...

Near stellar sources of gamma-ray bursts

OpenAIRE

Luchkov, B. I.; Markin, P. D.

2012-01-01

Correlation analysis of gamma-ray burst coordinates and nearby stars, registered on 2008-2011, revealed 5 coincidences with angular accuracy better than 0.1 degree. The random probability is $7\\times 10^{-7}$, so evidencing that coincident stars are indeed gamma-ray burst sources. The proposed method should be continued in order to provide their share in common balance of cosmic gamma-ray bursts.

Measurement of the Shape of the Optical-IR Spectrum of Prompt Emission from Gamma-Ray Bursts

Science.gov (United States)

Grossan, Bruce; Kistaubayev, M.; Smoot, G.; Scherr, L.

2017-06-01

While the afterglow phase of gamma-ray bursts (GRBs) has been extensively measured, detections of prompt emission (i.e. during bright X-gamma emission) are more limited. Some prompt optical measurements are regularly made, but these are typically in a single wide band, with limited time resolution, and no measurement of spectral shape. Some models predict a synchrotron self-absorption spectral break somewhere in the IR-optical region. Measurement of the absorption frequency would give extensive information on each burst, including the electron Lorentz factor, the radius of emission, and more (Shen & Zhang 2008). Thus far the best prompt observations have been explained invoking a variety of models, but often with a non-unique interpretation. To understand this apparently heterogeneous behavior, and to reduce the number of possible models, it is critical to add data on the optical - IR spectral shape.Long GRB prompt X-gamma emission typically lasts ~40-80 s. The Swift BAT instrument rapidly measures GRB positions to within a few arc minutes and communicates them via the internet within a few seconds. We have measured the time for a fast-moving D=700 mm telescope to point and settle to be less than 9 s anywhere on the observable sky. Therefore, the majority of prompt optical-IR emission can be measured responding to BAT positions with this telescope. In this presentation, we describe our observing and science programs, and give our design for the Burst Simultaneous Three-channel Instrument (BSTI), which uses dichroics to send eparate bands to 3 cameras. Two EMCCD cameras, give high-time resolution in B and V; a third camera with a HgCdTe sensor covers H band, allowing us to study extinguished bursts. For a total exposure time of 10 s, we find a 5 sigma sensitivity of 21.3 and 20.3 mag in B and R for 1" seeing and Kitt Peak sky brightness, much fainter than typical previous prompt detections. We estimate 5 sigma H-band sensitivity for an IR optimized telescope to be

Role of mixed boundaries on flow in open capillary channels with curved air-water interfaces.

Science.gov (United States)

Zheng, Wenjuan; Wang, Lian-Ping; Or, Dani; Lazouskaya, Volha; Jin, Yan

2012-09-04

Flow in unsaturated porous media or in engineered microfluidic systems is dominated by capillary and viscous forces. Consequently, flow regimes may differ markedly from conventional flows, reflecting strong interfacial influences on small bodies of flowing liquids. In this work, we visualized liquid transport patterns in open capillary channels with a range of opening sizes from 0.6 to 5.0 mm using laser scanning confocal microscopy combined with fluorescent latex particles (1.0 μm) as tracers at a mean velocity of ∼0.50 mm s(-1). The observed velocity profiles indicate limited mobility at the air-water interface. The application of the Stokes equation with mixed boundary conditions (i.e., no slip on the channel walls and partial slip or shear stress at the air-water interface) clearly illustrates the increasing importance of interfacial shear stress with decreasing channel size. Interfacial shear stress emerges from the velocity gradient from the adjoining no-slip walls to the center where flow is trapped in a region in which capillary forces dominate. In addition, the increased contribution of capillary forces (relative to viscous forces) to flow on the microscale leads to increased interfacial curvature, which, together with interfacial shear stress, affects the velocity distribution and flow pattern (e.g., reverse flow in the contact line region). We found that partial slip, rather than the commonly used stress-free condition, provided a more accurate description of the boundary condition at the confined air-water interface, reflecting the key role that surface/interface effects play in controlling flow behavior on the nanoscale and microscale.

Carrier frequency offset estimation for an acoustic-electric channel using 16 QAM modulation

Science.gov (United States)

Cunningham, Michael T.; Anderson, Leonard A.; Wilt, Kyle R.; Chakraborty, Soumya; Saulnier, Gary J.; Scarton, Henry A.

2016-05-01

Acoustic-electric channels can be used to send data through metallic barriers, enabling communications where electromagnetic signals are ineffective. This paper considers an acoustic-electric channel that is formed by mounting piezoelectric transducers on metallic barriers that are separated by a thin water layer. The transducers are coupled to the barriers using epoxy and the barriers are positioned to axially-align the PZTs, maximizing energy transfer efficiency. The electrical signals are converted by the transmitting transducers into acoustic waves, which propagate through the elastic walls and water medium to the receiving transducers. The reverberation of the acoustic signals in these channels can produce multipath distortion with a significant delay spread that introduces inter-symbol interference (ISI) into the received signal. While the multipath effects can be severe, the channel does not change rapidly which makes equalization easier. Here we implement a 16-QAM system on this channel, including a method for obtaining accurate carrier frequency offset (CFO) estimates in the presence of the quasi-static multipath propagation. A raised-power approach is considered but found to suffer from excessive data noise resulting from the ISI. An alternative approach that utilizes a pilot tone burst at the start of a data packet is used for CFO estimation and found to be effective. The autocorrelation method is used to estimate the frequency of the received burst. A real-time prototype of the 16 QAM system that uses a Texas Instruments MSP430 microcontroller-based transmitter and a personal computer-based receiver is presented along with performance results.

Gamma-Ray Burst Host Galaxies Have "Normal" Luminosities.

Science.gov (United States)

Schaefer

2000-04-10

The galactic environment of gamma-ray bursts can provide good evidence about the nature of the progenitor system, with two old arguments implying that the burst host galaxies are significantly subluminous. New data and new analysis have now reversed this picture: (1) Even though the first two known host galaxies are indeed greatly subluminous, the next eight hosts have absolute magnitudes typical for a population of field galaxies. A detailed analysis of the 16 known hosts (10 with redshifts) shows them to be consistent with a Schechter luminosity function with R*=-21.8+/-1.0, as expected for normal galaxies. (2) Bright bursts from the Interplanetary Network are typically 18 times brighter than the faint bursts with redshifts; however, the bright bursts do not have galaxies inside their error boxes to limits deeper than expected based on the luminosities for the two samples being identical. A new solution to this dilemma is that a broad burst luminosity function along with a burst number density varying as the star formation rate will require the average luminosity of the bright sample (>6x1058 photons s-1 or>1.7x1052 ergs s-1) to be much greater than the average luminosity of the faint sample ( approximately 1058 photons s-1 or approximately 3x1051 ergs s-1). This places the bright bursts at distances for which host galaxies with a normal luminosity will not violate the observed limits. In conclusion, all current evidence points to gamma-ray burst host galaxies being normal in luminosity.

Cosmology and the Subgroups of Gamma-ray Bursts

Directory of Open Access Journals (Sweden)

A. Mészáros

2011-01-01

Full Text Available Both short and intermediate gamma-ray bursts are distributed anisotropically in the sky (Mészáros, A. et al. ApJ, 539, 98 (2000, Vavrek, R. et al. MNRAS, 391, 1 741 (2008. Hence, in the redshift range, where these bursts take place, the cosmological principle is in doubt. It has already been noted that short bursts should be mainly at redshifts smaller than one (Mészáros, A. et al. Gamma-ray burst: Sixth Huntsville Symp., AIP, Vol. 1 133, 483 (2009; Mészáros, A. et al. Baltic Astron., 18, 293 (2009. Here we show that intermediate bursts should be at redshifts up to three.

Type III Radio Burst Duration and SEP Events

Science.gov (United States)

Gopalswamy, N.; Makela, P.; Xie, H.

2010-01-01

Long-duration (>15 min), low-frequency (25 MeV. The 1-MHz duration of the type III burst (28 rein) is near the median value of type III durations found for gradual SEP events and ground level enhancement (GLE) events. Yet, there was no sign of SEP events. On the other hand, two other type III bursts from the same active region had similar duration but accompanied by WAVES type 11 bursts; these bursts were also accompanied by SEP events detected by SOHO/ERNE. This study suggests that the type III burst duration may not be a good indicator of an SEP event, consistent with the statistical study of Cliver and Ling (2009, ApJ ).

Eddington-limited X-Ray Bursts as Distance Indicators. I. Systematic Trends and Spherical Symmetry in Bursts from 4U 1728-34

Science.gov (United States)

Galloway, Duncan K.; Psaltis, Dimitrios; Chakrabarty, Deepto; Muno, Michael P.

2003-06-01

We investigate the limitations of thermonuclear X-ray bursts as a distance indicator for the weakly magnetized accreting neutron star 4U 1728-34. We measured the unabsorbed peak flux of 81 bursts in public data from the Rossi X-Ray Timing Explorer (RXTE). The distribution of peak fluxes was bimodal: 66 bursts exhibited photospheric radius expansion (presumably reaching the local Eddington limit) and were distributed about a mean bolometric flux of 9.2×10-8ergscm-2s-1, while the remaining (non-radius expansion) bursts reached 4.5×10-8ergscm-2s-1, on average. The peak fluxes of the radius expansion bursts were not constant, exhibiting a standard deviation of 9.4% and a total variation of 46%. These bursts showed significant correlations between their peak flux and the X-ray colors of the persistent emission immediately prior to the burst. We also found evidence for quasi-periodic variation of the peak fluxes of radius expansion bursts, with a timescale of ~=40 days. The persistent flux observed with RXTE/ASM over 5.8 yr exhibited quasi-periodic variability on a similar timescale. We suggest that these variations may have a common origin in reflection from a warped accretion disk. Once the systematic variation of the peak burst fluxes is subtracted, the residual scatter is only ~=3%, roughly consistent with the measurement uncertainties. The narrowness of this distribution strongly suggests that (1) the radiation from the neutron star atmosphere during radius expansion episodes is nearly spherically symmetric and (2) the radius expansion bursts reach a common peak flux that may be interpreted as a standard candle intensity. Adopting the minimum peak flux for the radius expansion bursts as the Eddington flux limit, we derive a distance for the source of 4.4-4.8 kpc (assuming RNS=10 km), with the uncertainty arising from the probable range of the neutron star mass MNS=1.4-2 Msolar.

Bursts from the very early universe

International Nuclear Information System (INIS)

Silk, J.; Stodolsky, L.

2006-01-01

Bursts of weakly interacting particles such as neutrinos or even more weakly interacting particles such as wimps and gravitons from the very early universe would offer a much deeper 'look back time' to early epochs than is possible with photons. We consider some of the issues related to the existence of such bursts and their detectability. Characterizing the burst rate by a probability P per Hubble four-volume we find, for events in the radiation-dominated era, that the natural unit of description is the present intensity of the CMB times P. The existence of such bursts would make the observation of phenomena associated with very early times in cosmology at least conceptually possible. One might even hope to probe the transplanckian epoch if complexes more weakly interacting than the graviton can exist. Other conceivable applications include the potential detectability of the formation of 'pocket universes' in a multiverse

Light Dawns on Dark Gamma-ray Bursts

Science.gov (United States)

2010-12-01

Gamma-ray bursts are among the most energetic events in the Universe, but some appear curiously faint in visible light. The biggest study to date of these so-called dark gamma-ray bursts, using the GROND instrument on the 2.2-metre MPG/ESO telescope at La Silla in Chile, has found that these gigantic explosions don't require exotic explanations. Their faintness is now fully explained by a combination of causes, the most important of which is the presence of dust between the Earth and the explosion. Gamma-ray bursts (GRBs), fleeting events that last from less than a second to several minutes, are detected by orbiting observatories that can pick up their high energy radiation. Thirteen years ago, however, astronomers discovered a longer-lasting stream of less energetic radiation coming from these violent outbursts, which can last for weeks or even years after the initial explosion. Astronomers call this the burst's afterglow. While all gamma-ray bursts [1] have afterglows that give off X-rays, only about half of them were found to give off visible light, with the rest remaining mysteriously dark. Some astronomers suspected that these dark afterglows could be examples of a whole new class of gamma-ray bursts, while others thought that they might all be at very great distances. Previous studies had suggested that obscuring dust between the burst and us might also explain why they were so dim. "Studying afterglows is vital to further our understanding of the objects that become gamma-ray bursts and what they tell us about star formation in the early Universe," says the study's lead author Jochen Greiner from the Max-Planck Institute for Extraterrestrial Physics in Garching bei München, Germany. NASA launched the Swift satellite at the end of 2004. From its orbit above the Earth's atmosphere it can detect gamma-ray bursts and immediately relay their positions to other observatories so that the afterglows could be studied. In the new study, astronomers combined Swift

Information transmission and recovery in neural communications channels

International Nuclear Information System (INIS)

Eguia, M. C.; Rabinovich, M. I.; Abarbanel, H. D. I.

2000-01-01

Biological neural communications channels transport environmental information from sensors through chains of active dynamical neurons to neural centers for decisions and actions to achieve required functions. These kinds of communications channels are able to create information and to transfer information from one time scale to the other because of the intrinsic nonlinear dynamics of the component neurons. We discuss a very simple neural information channel composed of sensory input in the form of a spike train that arrives at a model neuron, then moves through a realistic synapse to a second neuron where the information in the initial sensory signal is read. Our model neurons are four-dimensional generalizations of the Hindmarsh-Rose neuron, and we use a model of chemical synapse derived from first-order kinetics. The four-dimensional model neuron has a rich variety of dynamical behaviors, including periodic bursting, chaotic bursting, continuous spiking, and multistability. We show that, for many of these regimes, the parameters of the chemical synapse can be tuned so that information about the stimulus that is unreadable at the first neuron in the channel can be recovered by the dynamical activity of the synapse and the second neuron. Information creation by nonlinear dynamical systems that allow chaotic oscillations is familiar in their autonomous oscillations. It is associated with the instabilities that lead to positive Lyapunov exponents in their dynamical behavior. Our results indicate how nonlinear neurons acting as input/output systems along a communications channel can recover information apparently ''lost'' in earlier junctions on the channel. Our measure of information transmission is the average mutual information between elements, and because the channel is active and nonlinear, the average mutual information between the sensory source and the final neuron may be greater than the average mutual information at an earlier neuron in the channel. This

Mixed convection in a baffled grooved channel

Indian Academy of Sciences (India)

MS received 16 May 2014; revised 19 October 2014; accepted 06 November 2014. Abstract. In the present numerical work, flow structure and heat transfer charac- teristics are investigated in a baffled grooved channel, differentially heated from the sides. The baffle is placed vertically downward from the top wall of grooved ...

Probability density function modeling of scalar mixing from concentrated sources in turbulent channel flow

Science.gov (United States)

Bakosi, J.; Franzese, P.; Boybeyi, Z.

2007-11-01

Dispersion of a passive scalar from concentrated sources in fully developed turbulent channel flow is studied with the probability density function (PDF) method. The joint PDF of velocity, turbulent frequency and scalar concentration is represented by a large number of Lagrangian particles. A stochastic near-wall PDF model combines the generalized Langevin model of Haworth and Pope [Phys. Fluids 29, 387 (1986)] with Durbin's [J. Fluid Mech. 249, 465 (1993)] method of elliptic relaxation to provide a mathematically exact treatment of convective and viscous transport with a nonlocal representation of the near-wall Reynolds stress anisotropy. The presence of walls is incorporated through the imposition of no-slip and impermeability conditions on particles without the use of damping or wall-functions. Information on the turbulent time scale is supplied by the gamma-distribution model of van Slooten et al. [Phys. Fluids 10, 246 (1998)]. Two different micromixing models are compared that incorporate the effect of small scale mixing on the transported scalar: the widely used interaction by exchange with the mean and the interaction by exchange with the conditional mean model. Single-point velocity and concentration statistics are compared to direct numerical simulation and experimental data at Reτ=1080 based on the friction velocity and the channel half width. The joint model accurately reproduces a wide variety of conditional and unconditional statistics in both physical and composition space.

Relativistic motion in gamma-ray bursts

International Nuclear Information System (INIS)

Krolik, J.H.; Pier, E.A.

1991-01-01

Three fundamental problems affect models of gamma-ray bursts, i.e., the energy source, the ability of high-energy photons to escape the radiation region, and the comparative weakness of X-ray emission. It is indicated that relativistic bulk motion of the gamma-ray-emitting plasma generically provides a solution to all three of these problems. Results show that, if the plasma that produces gamma-ray bursts has a bulk relativistic velocity with Lorentz factor gamma of about 10, several of the most troubling problems having to do with gamma-ray bursts are solved. 42 refs

The Glycolytic Metabolite, Fructose-1,6-bisphosphate, Blocks Epileptiform Bursts by Attenuating Voltage-Activated Calcium Currents in Hippocampal Slices

Directory of Open Access Journals (Sweden)

Li-Rong Shao

2018-06-01

Full Text Available Manipulation of metabolic pathways (e.g., ketogenic diet (KD, glycolytic inhibition alters neural excitability and represents a novel strategy for treatment of drug-refractory seizures. We have previously shown that inhibition of glycolysis suppresses epileptiform activity in hippocampal slices. In the present study, we aimed to examine the role of a “branching” metabolic pathway stemming off glycolysis (i.e., the pentose-phosphate pathway, PPP in regulating seizure activity, by using a potent PPP stimulator and glycolytic intermediate, fructose-1,6-bisphosphate (F1,6BP. Employing electrophysiological approaches, we investigated the action of F1,6BP on epileptiform population bursts, intrinsic neuronal firing, glutamatergic and GABAergic synaptic transmission and voltage-activated calcium currents (ICa in the CA3 area of hippocampal slices. Bath application of F1,6BP (2.5–5 mM blocked epileptiform population bursts induced in Mg2+-free medium containing 4-aminopyridine, in ~2/3 of the slices. The blockade occurred relatively rapidly (~4 min, suggesting an extracellular mechanism. However, F1,6BP did not block spontaneous intrinsic firing of the CA3 neurons (when synaptic transmission was eliminated with DNQX, AP-5 and SR95531, nor did it significantly reduce AMPA or NMDA receptor-mediated excitatory postsynaptic currents (EPSCAMPA and EPSCNMDA. In contrast, F1,6BP caused moderate reduction (~50% in GABAA receptor-mediated current, suggesting it affects excitatory and inhibitory synapses differently. Finally and unexpectedly, F1,6BP consistently attenuated ICa by ~40% without altering channel activation or inactivation kinetics, which may explain its anticonvulsant action, at least in this in vitro seizure model. Consistent with these results, epileptiform population bursts in CA3 were readily blocked by the nonspecific Ca2+ channel blocker, CdCl2 (20 μM, suggesting that these bursts are calcium dependent. Altogether, these data

THE FERMI –GBM THREE-YEAR X-RAY BURST CATALOG

Energy Technology Data Exchange (ETDEWEB)

Jenke, P. A. [CSPAR, SPA University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Linares, M. [Instituto de Astrofísica de Canarias, c/Vía Láctea s/n, E-38205 La Laguna, Tenerife (Spain); Connaughton, V.; Camero-Arranz, A.; Finger, M. H. [Universities Space Research Association, Huntsville, AL 35805 (United States); Beklen, E. [Department of Physics, Suleyman Demirel University, 32260, Isparta (Turkey); Wilson-Hodge, C. A. [Marshall Space Flight Center, Huntsville, AL 35812 (United States)

2016-08-01

The Fermi Gamma-ray Burst Monitor (GBM) is an all-sky gamma-ray monitor well known in the gamma-ray burst (GRB) community. Although GBM excels in detecting the hard, bright extragalactic GRBs, its sensitivity above 8 keV and its all-sky view make it an excellent instrument for the detection of rare, short-lived Galactic transients. In 2010 March, we initiated a systematic search for transients using GBM data. We conclude this phase of the search by presenting a three-year catalog of 1084 X-ray bursts. Using spectral analysis, location, and spatial distributions we classified the 1084 events into 752 thermonuclear X-ray bursts, 267 transient events from accretion flares and X-ray pulses, and 65 untriggered gamma-ray bursts. All thermonuclear bursts have peak blackbody temperatures broadly consistent with photospheric radius expansion (PRE) bursts. We find an average rate of 1.4 PRE bursts per day, integrated over all Galactic bursters within about 10 kpc. These include 33 and 10 bursts from the ultra-compact X-ray binaries 4U 0614+09 and 2S 0918-549, respectively. We discuss these recurrence times and estimate the total mass ejected by PRE bursts in our Galaxy.

Discovery of the short gamma-ray burst GRB 050709.

Science.gov (United States)

Villasenor, J S; Lamb, D Q; Ricker, G R; Atteia, J-L; Kawai, N; Butler, N; Nakagawa, Y; Jernigan, J G; Boer, M; Crew, G B; Donaghy, T Q; Doty, J; Fenimore, E E; Galassi, M; Graziani, C; Hurley, K; Levine, A; Martel, F; Matsuoka, M; Olive, J-F; Prigozhin, G; Sakamoto, T; Shirasaki, Y; Suzuki, M; Tamagawa, T; Vanderspek, R; Woosley, S E; Yoshida, A; Braga, J; Manchanda, R; Pizzichini, G; Takagishi, K; Yamauchi, M

2005-10-06

Gamma-ray bursts (GRBs) fall into two classes: short-hard and long-soft bursts. The latter are now known to have X-ray and optical afterglows, to occur at cosmological distances in star-forming galaxies, and to be associated with the explosion of massive stars. In contrast, the distance scale, the energy scale and the progenitors of the short bursts have remained a mystery. Here we report the discovery of a short-hard burst whose accurate localization has led to follow-up observations that have identified the X-ray afterglow and (for the first time) the optical afterglow of a short-hard burst; this in turn led to the identification of the host galaxy of the burst as a late-type galaxy at z = 0.16 (ref. 10). These results show that at least some short-hard bursts occur at cosmological distances in the outskirts of galaxies, and are likely to be caused by the merging of compact binaries.

The Drift Burst Hypothesis

DEFF Research Database (Denmark)

Christensen, Kim; Oomen, Roel; Renò, Roberto

are an expected and regular occurrence in financial markets that can arise through established mechanisms such as feedback trading. At a theoretical level, we show how to build drift bursts into the continuous-time Itô semi-martingale model in such a way that the fundamental arbitrage-free property is preserved......, currencies and commodities. We find that the majority of identified drift bursts are accompanied by strong price reversals and these can therefore be regarded as “flash crashes” that span brief periods of severe market disruption without any material longer term price impacts....

Multiparameter Monitoring and Prevention of Fault-Slip Rock Burst

Directory of Open Access Journals (Sweden)

Shan-chao Hu

2017-01-01

Full Text Available Fault-slip rock burst is one type of the tectonic rock burst during mining. A detailed understanding of the precursory information of fault-slip rock burst and implementation of monitoring and early warning systems, as well as pressure relief measures, are essential to safety production in deep mines. This paper first establishes a mechanical model of stick-slip instability in fault-slip rock bursts and then reveals the failure characteristics of the instability. Then, change rule of mining-induced stress and microseismic signals before the occurrence of fault-slip rock burst are proposed, and multiparameter integrated early warning methods including mining-induced stress and energy are established. Finally, pressure relief methods targeting large-diameter boreholes and coal seam infusion are presented in accordance with the occurrence mechanism of fault-slip rock burst. The research results have been successfully applied in working faces 2310 of the Suncun Coal Mine, and the safety of the mine has been enhanced. These research results improve the theory of fault-slip rock burst mechanisms and provide the basis for prediction and forecasting, as well as pressure relief, of fault-slip rock bursts.

Turbulent mixed convection in vertical and inclined flat channels with aiding flows

Energy Technology Data Exchange (ETDEWEB)

Poskas, P.; Vilemas, J.; Adomaitis, J.E.; Bartkus, G.

1995-09-01

This paper presents an experimental study of turbulent mixed convection heat transfer for aiding flows in a vertical ({phi}=90{degrees}), inclined ({phi}=60{degrees},30{degrees}), and horizontal ({phi}=0{degrees}) flat channels with symmetrical heating and a ratio of height h to width b of about 1:10 and with length about 4 m (x/2h about 44). The study covered Re from 4x10{sup 3} to 5x10{sup 4} and Gr{sub q} from 5x10{sup 7}to 3x10{sup 10}. For the upper wall, a region of impaired heat transfer was found for all angular positions (from vertical to horizontal) and for bottom wall the augmentation of heat transfer in comparison to forced convection was revealed in the region of {phi}=0{degrees}-60{degrees}. Different characteristic buoyancy parameters were found for regions of impaired and enhanced heat transfer. General relations are suggested to predict the heat transfer for fully-developed-flow conditions and different angular positions.

Limits of the memory coefficient in measuring correlated bursts

Science.gov (United States)

Jo, Hang-Hyun; Hiraoka, Takayuki

2018-03-01

Temporal inhomogeneities in event sequences of natural and social phenomena have been characterized in terms of interevent times and correlations between interevent times. The inhomogeneities of interevent times have been extensively studied, while the correlations between interevent times, often called correlated bursts, are far from being fully understood. For measuring the correlated bursts, two relevant approaches were suggested, i.e., memory coefficient and burst size distribution. Here a burst size denotes the number of events in a bursty train detected for a given time window. Empirical analyses have revealed that the larger memory coefficient tends to be associated with the heavier tail of the burst size distribution. In particular, empirical findings in human activities appear inconsistent, such that the memory coefficient is close to 0, while burst size distributions follow a power law. In order to comprehend these observations, by assuming the conditional independence between consecutive interevent times, we derive the analytical form of the memory coefficient as a function of parameters describing interevent time and burst size distributions. Our analytical result can explain the general tendency of the larger memory coefficient being associated with the heavier tail of burst size distribution. We also find that the apparently inconsistent observations in human activities are compatible with each other, indicating that the memory coefficient has limits to measure the correlated bursts.

Relativistic effects in gamma-ray bursts

International Nuclear Information System (INIS)

Eriksen, Erik; Groen, Oeyvind

1999-01-01

According to recent models of the sources of gamma-ray bursts the extremely energetic emission is caused by shells expanding with ultrarelativistic velocity. With the recent identification of optical sources at the positions of some gamma-ray bursts these ''fireball'' models have acquired an actuality that invites to use them as a motivating application when teaching special relativity. We demonstrate several relativistic effects associated with these models which are very pronounced due to the great velocity of the shell. For example a burst lasting for a month in the rest frame of an element of the shell lasts for a few seconds only, in the rest frame of our detector. It is shown how the observed properties of a burst are modified by aberration and the Doppler effect. The apparent luminosity as a function of time is calculated. Modifications due to the motion of the star away from the observer are calculated. (Author)

Bursts from the very early universe

Energy Technology Data Exchange (ETDEWEB)

Silk, J. [Department of Physics, University of Oxford, Oxford OX1 3RH (United Kingdom); Stodolsky, L. [Max-Planck-Institut fuer Physik, Foehringer Ring 6, 80805 Munich (Germany)]. E-mail: les@mppmu.mpg.de

2006-07-27

Bursts of weakly interacting particles such as neutrinos or even more weakly interacting particles such as wimps and gravitons from the very early universe would offer a much deeper 'look back time' to early epochs than is possible with photons. We consider some of the issues related to the existence of such bursts and their detectability. Characterizing the burst rate by a probability P per Hubble four-volume we find, for events in the radiation-dominated era, that the natural unit of description is the present intensity of the CMB times P. The existence of such bursts would make the observation of pheno associated with very early times in cosmology at least conceptually possible. One might even hope to probe the transplanckian epoch if complexes more weakly interacting than the graviton can exist. Other conceivable applications include the potential detectability of the formation of 'pocket universes' in a multiverse.

Upgrading a marketing channels role

Directory of Open Access Journals (Sweden)

Tišma-Borota Ankica

2002-01-01

Full Text Available As one of the marketing mix instruments, marketing channels were usually behind other instruments (product, price and promotion. Many companies regarded marketing channels as something that was 'left' after more important strategies of price, product and promotion were created. In recent past, things have changed and marketing channels became more interesting for research. This change came as a result of change in global market functioning especially in competitive advantage, distributors' strength and increasing technology.

Different types of bursting calcium oscillations in non-excitable cells

International Nuclear Information System (INIS)

Perc, Matjaz; Marhl, Marko

2003-01-01

In the paper different types of bursting Ca 2+ oscillations are presented. We analyse bursting behaviour in four recent mathematical models for Ca 2+ oscillations in non-excitable cells. Separately, regular, quasi-periodic, and chaotic bursting Ca 2+ oscillations are classified into several subtypes. The classification is based on the dynamics of separated fast and slow subsystems, the so-called fast-slow burster analysis. For regular bursting Ca 2+ oscillations two types of bursting are specified: Point-Point and Point-Cycle bursting. In particular, the slow passage effect, important for the Hopf-Hopf and SubHopf-SubHopf bursting subtypes, is explained by local divergence calculated for the fast subsystem. Quasi-periodic bursting Ca 2+ oscillations can be found in only one of the four studied mathematical models and appear via a homoclinic bifurcation with a homoclinic torus structure. For chaotic bursting Ca 2+ oscillations, we found that bursting patterns resulting from the period doubling root to chaos considerably differ from those appearing via intermittency and have to be treated separately. The analysis and classification of different types of bursting Ca 2+ oscillations provides better insight into mechanisms of complex intra- and intercellular Ca 2+ signalling. This improves our understanding of several important biological phenomena in cellular signalling like complex frequency-amplitude signal encoding and synchronisation of intercellular signal transduction between coupled cells in tissue

Solar energetic particles and radio burst emission

Directory of Open Access Journals (Sweden)

Miteva Rositsa

2017-01-01

Full Text Available We present a statistical study on the observed solar radio burst emission associated with the origin of in situ detected solar energetic particles. Several proton event catalogs in the period 1996–2016 are used. At the time of appearance of the particle origin (flare and coronal mass ejection we identified radio burst signatures of types II, III and IV by inspecting dynamic radio spectral plots. The information from observatory reports is also accounted for during the analysis. The occurrence of solar radio burst signatures is evaluated within selected wavelength ranges during the solar cycle 23 and the ongoing 24. Finally, we present the burst occurrence trends with respect to the intensity of the proton events and the location of their solar origin.

Bright x-ray flares in gamma-ray burst afterglows.

Science.gov (United States)

Burrows, D N; Romano, P; Falcone, A; Kobayashi, S; Zhang, B; Moretti, A; O'brien, P T; Goad, M R; Campana, S; Page, K L; Angelini, L; Barthelmy, S; Beardmore, A P; Capalbi, M; Chincarini, G; Cummings, J; Cusumano, G; Fox, D; Giommi, P; Hill, J E; Kennea, J A; Krimm, H; Mangano, V; Marshall, F; Mészáros, P; Morris, D C; Nousek, J A; Osborne, J P; Pagani, C; Perri, M; Tagliaferri, G; Wells, A A; Woosley, S; Gehrels, N

2005-09-16

Gamma-ray burst (GRB) afterglows have provided important clues to the nature of these massive explosive events, providing direct information on the nearby environment and indirect information on the central engine that powers the burst. We report the discovery of two bright x-ray flares in GRB afterglows, including a giant flare comparable in total energy to the burst itself, each peaking minutes after the burst. These strong, rapid x-ray flares imply that the central engines of the bursts have long periods of activity, with strong internal shocks continuing for hundreds of seconds after the gamma-ray emission has ended.

Numerical and Experimental Study on Mixing Performances of Simple and Vortex Micro T-Mixers

Directory of Open Access Journals (Sweden)

Mubashshir Ahmad Ansari

2018-04-01

Full Text Available Vortex flow increases the interface area of fluid streams by stretching along with providing continuous stirring action to the fluids in micromixers. In this study, experimental and numerical analyses on a design of micromixer that creates vortex flow were carried out, and the mixing performance was compared with a simple micro T-mixer. In the vortex micro T-mixer, the height of the inlet channels is half of the height of the main mixing channel. The inlet channel connects to the main mixing channel (micromixer at the one end at an offset position in a fashion that creates vortex flow. In the simple micro T-mixer, the height of the inlet channels is equal to the height of the channel after connection (main mixing channel. Mixing of fluids and flow field have been analyzed for Reynolds numbers in a range from 1–80. The study has been further extended to planar serpentine microchannels, which were combined with a simple and a vortex T-junction, to evaluate and verify their mixing performances. The mixing performance of the vortex T-mixer is higher than the simple T-mixer and significantly increases with the Reynolds number. The design is promising for efficiently increasing mixing simply at the T-junction and can be applied to all micromixers.

Implications of fast radio bursts for superconducting cosmic strings

Energy Technology Data Exchange (ETDEWEB)

Yu, Yun-Wei [Institute of Astrophysics, Central China Normal University, 152 Luoyu Road, Wuhan 430079 (China); Cheng, Kwong-Sang [Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong (China); Shiu, Gary; Tye, Henry, E-mail: yuyw@phy.ccnu.edu.cn, E-mail: hrspksc@hku.hk, E-mail: shiu@ust.hk, E-mail: iastye@ust.hk [Department of Physics and Institute for Advanced Study, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong (China)

2014-11-01

Highly beamed, short-duration electromagnetic bursts could be produced by superconducting cosmic string (SCS) loops oscillating in cosmic magnetic fields. We demonstrated that the basic characteristics of SCS bursts such as the electromagnetic frequency and the energy release could be consistently exhibited in the recently discovered fast radio bursts (FRBs). Moreover, it is first showed that the redshift distribution of the FRBs can also be well accounted for by the SCS burst model. Such agreements between the FRBs and SCS bursts suggest that the FRBs could originate from SCS bursts and thus they could provide an effective probe to study SCSs. The obtained values of model parameters indicate that the loops generating the FRBs have a small length scale and they are mostly formed in the radiation-dominated cosmological epoch.

Implications of fast radio bursts for superconducting cosmic strings

International Nuclear Information System (INIS)

Yu, Yun-Wei; Cheng, Kwong-Sang; Shiu, Gary; Tye, Henry

2014-01-01

Highly beamed, short-duration electromagnetic bursts could be produced by superconducting cosmic string (SCS) loops oscillating in cosmic magnetic fields. We demonstrated that the basic characteristics of SCS bursts such as the electromagnetic frequency and the energy release could be consistently exhibited in the recently discovered fast radio bursts (FRBs). Moreover, it is first showed that the redshift distribution of the FRBs can also be well accounted for by the SCS burst model. Such agreements between the FRBs and SCS bursts suggest that the FRBs could originate from SCS bursts and thus they could provide an effective probe to study SCSs. The obtained values of model parameters indicate that the loops generating the FRBs have a small length scale and they are mostly formed in the radiation-dominated cosmological epoch

Neutrino bursts and gravitational waves experiments

Energy Technology Data Exchange (ETDEWEB)

Castagnoli, C; Galeotti, P; Saavedra, O [Consiglio Nazionale delle Ricerche, Turin (Italy). Lab. di Cosmo-Geofisica

1978-05-01

Several experiments have been performed in many countries to observe gravitational waves or neutrino bursts. Since their simultaneous emission may occur in stellar collapse, the authors evaluate the effect of neutrino bursts on gravitational wave antennas and suggest the usefulness of a time correlation among the different detectors.

On the performance of two-way multiuser mixed RF/FSO relay networks with opportunistic scheduling & asymmetric channel gains

KAUST Repository

Al-Eryani, Yasser F.; Salhab, Anas M.; Zummo, Salam A.; Alouini, Mohamed-Slim

2017-01-01

In this paper, the performance of two-way relaying (TWR) multiuser mixed radio frequency/free space optical (RF/FSO) relay networks with opportunistic user scheduling and asymmetric channel fading is studied. First, closed-form expressions for the exact outage probability, asymptotic (high signal-to-noise ration (SNR)) outage probability, and average ergodic channel capacity are derived assuming heterodyne detection (HD) scheme. Additionally, impacts of several system parameters including number of users, pointing errors, and atmospheric turbulence conditions on the overall network performance are investigated. All the theoretical results are validated by Monte-Carlo simulations. The results show that the TWR scheme almost doubles the network ergodic capacity compared to that of one-way relaying (OWR) scheme with the same outage performance. Additionally, the overall diversity order of the network is shown to be affected not only by the number of users, but it is also a function of the pointing error and atmospheric turbulence conditions.

On the performance of two-way multiuser mixed RF/FSO relay networks with opportunistic scheduling & asymmetric channel gains

KAUST Repository

Al-Eryani, Yasser F.

2017-07-20

In this paper, the performance of two-way relaying (TWR) multiuser mixed radio frequency/free space optical (RF/FSO) relay networks with opportunistic user scheduling and asymmetric channel fading is studied. First, closed-form expressions for the exact outage probability, asymptotic (high signal-to-noise ration (SNR)) outage probability, and average ergodic channel capacity are derived assuming heterodyne detection (HD) scheme. Additionally, impacts of several system parameters including number of users, pointing errors, and atmospheric turbulence conditions on the overall network performance are investigated. All the theoretical results are validated by Monte-Carlo simulations. The results show that the TWR scheme almost doubles the network ergodic capacity compared to that of one-way relaying (OWR) scheme with the same outage performance. Additionally, the overall diversity order of the network is shown to be affected not only by the number of users, but it is also a function of the pointing error and atmospheric turbulence conditions.

Broadband Spectral Investigations of Magnetar Bursts

Science.gov (United States)

Kırmızıbayrak, Demet; Şaşmaz Muş, Sinem; Kaneko, Yuki; Göğüş, Ersin

2017-09-01

We present our broadband (2-250 keV) time-averaged spectral analysis of 388 bursts from SGR J1550-5418, SGR 1900+14, and SGR 1806-20 detected with the Rossi X-ray Timing Explorer (RXTE) here and as a database in a companion web-catalog. We find that two blackbody functions (BB+BB), the sum of two modified blackbody functions (LB+LB), the sum of a blackbody function and a power-law function (BB+PO), and a power law with a high-energy exponential cutoff (COMPT) all provide acceptable fits at similar levels. We performed numerical simulations to constrain the best fitting model for each burst spectrum and found that 67.6% of burst spectra with well-constrained parameters are better described by the Comptonized model. We also found that 64.7% of these burst spectra are better described with the LB+LB model, which is employed in the spectral analysis of a soft gamma repeater (SGR) for the first time here, than with the BB+BB and BB+PO models. We found a significant positive lower bound trend on photon index, suggesting a decreasing upper bound on hardness, with respect to total flux and fluence. We compare this result with bursts observed from SGR and AXP (anomalous X-ray pulsar) sources and suggest that the relationship is a distinctive characteristic between the two. We confirm a significant anticorrelation between burst emission area and blackbody temperature, and find that it varies between the hot and cool blackbody temperatures differently than previously discussed. We expand on the interpretation of our results in the framework of a strongly magnetized neutron star.

Broadband Spectral Investigations of Magnetar Bursts

Energy Technology Data Exchange (ETDEWEB)

Kırmızıbayrak, Demet; Şaşmaz Muş, Sinem; Kaneko, Yuki; Göğüş, Ersin, E-mail: demetk@sabanciuniv.edu [Faculty of Engineering and Natural Sciences, Sabancı University, Orhanlı Tuzla, Istanbul 34956 (Turkey)

2017-09-01

We present our broadband (2–250 keV) time-averaged spectral analysis of 388 bursts from SGR J1550−5418, SGR 1900+14, and SGR 1806−20 detected with the Rossi X-ray Timing Explorer ( RXTE ) here and as a database in a companion web-catalog. We find that two blackbody functions (BB+BB), the sum of two modified blackbody functions (LB+LB), the sum of a blackbody function and a power-law function (BB+PO), and a power law with a high-energy exponential cutoff (COMPT) all provide acceptable fits at similar levels. We performed numerical simulations to constrain the best fitting model for each burst spectrum and found that 67.6% of burst spectra with well-constrained parameters are better described by the Comptonized model. We also found that 64.7% of these burst spectra are better described with the LB+LB model, which is employed in the spectral analysis of a soft gamma repeater (SGR) for the first time here, than with the BB+BB and BB+PO models. We found a significant positive lower bound trend on photon index, suggesting a decreasing upper bound on hardness, with respect to total flux and fluence. We compare this result with bursts observed from SGR and AXP (anomalous X-ray pulsar) sources and suggest that the relationship is a distinctive characteristic between the two. We confirm a significant anticorrelation between burst emission area and blackbody temperature, and find that it varies between the hot and cool blackbody temperatures differently than previously discussed. We expand on the interpretation of our results in the framework of a strongly magnetized neutron star.

Sources of type III solar microwave bursts

Directory of Open Access Journals (Sweden)

Zhdanov D.A.

2016-06-01

Full Text Available Microwave fine structures allow us to study plasma evolution in an energy release region. The Siberian Solar Radio Telescope (SSRT is a unique instrument designed to examine fine structures at 5.7 GHz. A complex analysis of data from RATAN-600, 4–8 GHz spectropolarimeter, and SSRT, simultaneously with EUV data, made it possible to localize sources of III type microwave bursts in August 10, 2011 event within the entire frequency band of burst occurrence, as well as to determine the most probable region of primary energy release. To localize sources of III type bursts from RATAN-600 data, an original method for data processing has been worked out. At 5.7 GHz, the source of bursts was determined along two coordinates, whereas at 4.5, 4.7, 4.9, 5.1, 5.3, 5.5, and 6.0 GHz, their locations were identified along one coordinate. The size of the burst source at 5.1 GHz was found to be maximum as compared to those at other frequencies.

Spectra of gamma-ray bursts at high energies

International Nuclear Information System (INIS)

Matz, S.M.

1986-01-01

Between 1980 February and 1983 August the Gamma-Ray Spectrometer (GRS) on the Solar Maximum Mission satellite (SMM) observed 71 gamma-ray bursts. These events form a representative subset of the class of classical gamma-ray bursts. Since their discovery more than 15 years ago, hundreds of gamma-ray bursts have been detected; however, most observations have been limited to an energy range of roughly 30 keV-1 MeV. The large sensitive area and spectral range of the GRS allow, for the first time, an investigation of the high energy (>1 MeV) behavior of a substantial number of gamma-ray bursts. It is found that high-energy emission is seen in a large fraction of all events and that the data are consistent with all bursts emitting to at least 5 MeV with no cut-offs. Further, no burst spectrum measured by GRS has a clear high-energy cut-off. The high-energy emission can be a significant part of the total burst energy on the average about 30% of the observed energy above 30 keV is contained in the >1 MeV photons. The fact that the observations are consistent with the presence of high-energy emission in all events implies a limit on the preferential beaming of high-energy photons, from any mechanism. Single-photon pair-production in a strong magnetic field produces such beaming; assuming that the low-energy emission is isotropic, the data imply an upper limit of 1 x 10 12 G on the typical magnetic field at burst radiation sites

Optimal unitary dilation for bosonic Gaussian channels

International Nuclear Information System (INIS)

Caruso, Filippo; Eisert, Jens; Giovannetti, Vittorio; Holevo, Alexander S.

2011-01-01

A general quantum channel can be represented in terms of a unitary interaction between the information-carrying system and a noisy environment. In this paper the minimal number of quantum Gaussian environmental modes required to provide a unitary dilation of a multimode bosonic Gaussian channel is analyzed for both pure and mixed environments. We compute this quantity in the case of pure environment corresponding to the Stinespring representation and give an improved estimate in the case of mixed environment. The computations rely, on one hand, on the properties of the generalized Choi-Jamiolkowski state and, on the other hand, on an explicit construction of the minimal dilation for arbitrary bosonic Gaussian channel. These results introduce a new quantity reflecting ''noisiness'' of bosonic Gaussian channels and can be applied to address some issues concerning transmission of information in continuous variables systems.

Powerful Radio Burst Indicates New Astronomical Phenomenon

Science.gov (United States)

2007-09-01

Astronomers studying archival data from an Australian radio telescope have discovered a powerful, short-lived burst of radio waves that they say indicates an entirely new type of astronomical phenomenon. Region of Strong Radio Burst Visible-light (negative greyscale) and radio (contours) image of Small Magellanic Cloud and area where burst originated. CREDIT: Lorimer et al., NRAO/AUI/NSF Click on image for high-resolution file ( 114 KB) "This burst appears to have originated from the distant Universe and may have been produced by an exotic event such as the collision of two neutron stars or the death throes of an evaporating black hole," said Duncan Lorimer, Assistant Professor of Physics at West Virginia University (WVU) and the National Radio Astronomy Observatory (NRAO). The research team led by Lorimer consists of Matthew Bailes of Swinburne University in Australia, Maura McLaughlin of WVU and NRAO, David Narkevic of WVU, and Fronefield Crawford of Franklin and Marshall College in Lancaster, Pennsylvania. The astronomers announced their findings in the September 27 issue of the online journal Science Express. The startling discovery came as WVU undergraduate student David Narkevic re-analyzed data from observations of the Small Magellanic Cloud made by the 210-foot Parkes radio telescope in Australia. The data came from a survey of the Magellanic Clouds that included 480 hours of observations. "This survey had sought to discover new pulsars, and the data already had been searched for the type of pulsating signals they produce," Lorimer said. "We re-examined the data, looking for bursts that, unlike the usual ones from pulsars, are not periodic," he added. The survey had covered the Magellanic Clouds, a pair of small galaxies in orbit around our own Milky Way Galaxy. Some 200,000 light-years from Earth, the Magellanic Clouds are prominent features in the Southern sky. Ironically, the new discovery is not part of these galaxies, but rather is much more distant

Ballerina - pirouettes in search of gamma bursts

DEFF Research Database (Denmark)

Brandt, Søren Kristian; Lund, Niels; Pedersen, Henrik

1999-01-01

The cosmological origin of gamma ray bursts has now been established with reasonable certainty, Many more bursts will need to be studied to establish the typical distance scale, and to map out the large diversity in properties which have been indicated by the first handful of events. We are propo...... are proposing Ballerina, a small satellite to provide accurate positions and new data on the gamma-ray bursts. We anticipate a detection rate an order of magnitude larger than obtained from Beppo-SAX....

12-lipoxygenase regulates hippocampal long-term potentiation by modulating L-type Ca2+ channels

Science.gov (United States)

DeCostanzo, Anthony J.; Voloshyna, Iryna; Rosen, Zev B.; Feinmark, Steven J.; Siegelbaum, Steven A.

2010-01-01

Although long-term potentiation (LTP) has been intensely studied, there is disagreement as to which molecules mediate and modulate LTP. This is partly due to the presence of mechanistically distinct forms of LTP that are induced by different patterns of stimulation and that depend on distinct Ca2+ sources. Here we report a novel role for the arachidonic acid-metabolizing enzyme 12-lipoxygenase (12-LO) in LTP at CA3-CA1 hippocampal synapses that is dependent on the pattern of tetanic stimulation. We find that 12-LO activity is required for the induction of LTP in response to a theta-burst stimulation (TBS) protocol, which depends on Ca2+ influx through both NMDA receptors and L-type voltage-gated Ca2+ channels. In contrast, LTP induced by 100 Hz tetanic stimulation, which requires Ca2+ influx through NMDA receptors but not L-type channels, does not require 12-LO. We find that 12-LO regulates LTP by enhancing postsynaptic somatodendritic Ca2+ influx through L-type channels during theta burst stimulation, an action exerted via 12(S)-HPETE, a downstream metabolite of 12-LO. These results help define the role of a long-disputed signaling enzyme in LTP. PMID:20130191

Large-conductance calcium-dependent potassium channels prevent dendritic excitability in neocortical pyramidal neurons.

Science.gov (United States)

Benhassine, Narimane; Berger, Thomas

2009-03-01

Large-conductance calcium-dependent potassium channels (BK channels) are homogeneously distributed along the somatodendritic axis of layer 5 pyramidal neurons of the rat somatosensory cortex. The relevance of this conductance for dendritic calcium electrogenesis was studied in acute brain slices using somatodendritic patch clamp recordings and calcium imaging. BK channel activation reduces the occurrence of dendritic calcium spikes. This is reflected in an increased critical frequency of somatic spikes necessary to activate the distal initiation zone. Whilst BK channels repolarise the somatic spike, they dampen it only in the distal dendrite. Their activation reduces dendritic calcium influx via glutamate receptors. Furthermore, they prevent dendritic calcium electrogenesis and subsequent somatic burst discharges. However, the time window for coincident somatic action potential and dendritic input to elicit dendritic calcium events is not influenced by BK channels. Thus, BK channel activation in layer 5 pyramidal neurons affects cellular excitability primarily by establishing a high threshold at the distal action potential initiation zone.

Beta burst dynamics in Parkinson's disease OFF and ON dopaminergic medication.

Science.gov (United States)

Tinkhauser, Gerd; Pogosyan, Alek; Tan, Huiling; Herz, Damian M; Kühn, Andrea A; Brown, Peter

2017-11-01

Exaggerated basal ganglia beta activity (13-35 Hz) is commonly found in patients with Parkinson's disease and can be suppressed by dopaminergic medication, with the degree of suppression being correlated with the improvement in motor symptoms. Importantly, beta activity is not continuously elevated, but fluctuates to give beta bursts. The percentage number of longer beta bursts in a given interval is positively correlated with clinical impairment in Parkinson's disease patients. Here we determine whether the characteristics of beta bursts are dependent on dopaminergic state. Local field potentials were recorded from the subthalamic nucleus of eight Parkinson's disease patients during temporary lead externalization during surgery for deep brain stimulation. The recordings took place with the patient quietly seated following overnight withdrawal of levodopa and after administration of levodopa. Beta bursts were defined by applying a common amplitude threshold and burst characteristics were compared between the two drug conditions. The amplitude of beta bursts, indicative of the degree of local neural synchronization, progressively increased with burst duration. Treatment with levodopa limited this evolution leading to a relative increase of shorter, lower amplitude bursts. Synchronization, however, was not limited to local neural populations during bursts, but also, when such bursts were cotemporaneous across the hemispheres, was evidenced by bilateral phase synchronization. The probability of beta bursts and the proportion of cotemporaneous bursts were reduced by levodopa. The percentage number of longer beta bursts in a given interval was positively related to motor impairment, while the opposite was true for the percentage number of short duration beta bursts. Importantly, the decrease in burst duration was also correlated with the motor improvement. In conclusion, we demonstrate that long duration beta bursts are associated with an increase in local and

Chimera states in bursting neurons

OpenAIRE

Bera, Bidesh K.; Ghosh, Dibakar; Lakshmanan, M.

2015-01-01

We study the existence of chimera states in pulse-coupled networks of bursting Hindmarsh-Rose neurons with nonlocal, global and local (nearest neighbor) couplings. Through a linear stability analysis, we discuss the behavior of stability function in the incoherent (i.e. disorder), coherent, chimera and multi-chimera states. Surprisingly, we find that chimera and multi-chimera states occur even using local nearest neighbor interaction in a network of identical bursting neurons alone. This is i...

US Army Nuclear Burst Detection System (NBDS)

International Nuclear Information System (INIS)

Glaser, R.F.

1980-07-01

The Nuclear Burst Detection System (NBDS) was developed to meet the Army requirements of an unattended, automatic nuclear burst reporting system. It provides pertinent data for battlefield commanders on a timely basis with high reliability

X-ray bursts from GX 17+2: a new approach

International Nuclear Information System (INIS)

Sztajno, M.; Langmeier, A.; Truemper, J.; Pietsch, W.; Paradijs, J. van; Lewin, W.H.G.; Massachusetts Inst. of Tech., Cambridge

1986-01-01

The detection of two X-ray bursts from GX 17+2 is reported; a short one (lasting about 10s), and a long one (which lasted about 5 min). These bursts reached a maximum intensity of only about 40 per cent above the persistent flux level. Like previous long bursts observed from GX 17+2 the long burst showed little softening during its decay, and it is difficult at first glance to classify it as either a type 1 or a type 2 burst. Following the recent results of two of the authors a time-dependent spectral analysis of these bursts has been made. (author)

Cosmic gamma-ray bursts

International Nuclear Information System (INIS)

Hurley, K.

1989-01-01

This paper reviews the essential aspects of the gamma-ray burst (GRB) phenomenon, with emphasis on the more recent results. GRBs are introduced by their time histories, which provide some evidence for a compact object origin. The energy spectra of bursts are presented and they are seen to demonstrate practically unambiguously that the origin of some GRBs involves neutron stars. Counterpart searches are reviewed briefly and the statistical properties of bursters treated. This paper presents a review of the three known repeating bursters (the Soft Gamma Repeaters). Extragalactic and galactic models are discussed and future prospects are assessed

Leader neurons in population bursts of 2D living neural networks

International Nuclear Information System (INIS)

Eckmann, J-P; Zbinden, Cyrille; Jacobi, Shimshon; Moses, Elisha; Marom, Shimon

2008-01-01

Eytan and Marom (2006 J. Neurosci. 26 8465-76) recently showed that the spontaneous bursting activity of rat neuron cultures includes 'first-to-fire' cells that consistently fire earlier than others. Here, we analyze the behavior of these neurons in long-term recordings of spontaneous activity of rat hippocampal and rat cortical neuron cultures from three different laboratories. We identify precursor events that may either subside ('aborted bursts') or can lead to a full-blown burst ('pre-bursts'). We find that the activation in the pre-burst typically has a first neuron ('leader'), followed by a localized response in its neighborhood. Locality is diminished in the bursts themselves. The long-term dynamics of the leaders is relatively robust, evolving with a half-life of 23-34 h. Stimulation of the culture alters the leader distribution, but the distribution stabilizes within about 1 h. We show that the leaders carry information about the identity of the burst, as measured by the signature of the number of spikes per neuron in a burst. The number of spikes from leaders in the first few spikes of a precursor event is furthermore shown to be predictive with regard to the transition into a burst (pre-burst versus aborted burst). We conclude that the leaders play a role in the development of the bursts and conjecture that they are part of an underlying sub-network that is excited first and then acts as a nucleation center for the burst

Analysis of Passive Mixing in a Serpentine Microchannel with Sinusoidal Side Walls

Directory of Open Access Journals (Sweden)

Muhammad Usman Javaid

2017-12-01

Full Text Available Sample mixing is difficult in microfluidic devices because of laminar flow. Micromixers are designed to ensure the optimal use of miniaturized devices. The present study aims to design a chaotic-advection-based passive micromixer with enhanced mixing efficiency. A serpentine-shaped microchannel with sinusoidal side walls was designed, and three cases, with amplitude to wavelength (A/λ ratios of 0.1, 0.15, and 0.2 were investigated. Numerical simulations were conducted using the Navier–Stokes equations, to determine the flow field. The flow was then coupled with the convection–diffusion equation to obtain the species concentration distribution. The mixing performance of sinusoidal walled channels was compared with that of a simple serpentine channel for Reynolds numbers ranging from 0.1 to 50. Secondary flows were observed at high Reynolds numbers that mixed the fluid streams. These flows were dominant in the proposed sinusoidal walled channels, thereby showing better mixing performance than the simple serpentine channel at similar or less mixing cost. Higher mixing efficiency was obtained by increasing the A/λ ratio.

Impulsive EUV bursts observed in C IV with OSO-8

International Nuclear Information System (INIS)

Grant Athay, R.; White, O.R.; Lites, B.W.

1980-01-01

Time sequences of profiles of the lambda 1548 line of C IV containing 51 EUV bursts observed in or near active regions are analyzed to determine the brightness. Doppler shift and line broadening characteristics of the bursts. The bursts have mean lifetimes of approximately 150s, and mean increases in brightness at burst maximum of four-fold as observed with a field of view of 2'' x 20''. Mean burst diameters are estimated to be 3'', or smaller. All but three of the bursts show Doppler shift with velocities sometimes exceeding 75 km s -1 ; 31 are dominated by red shifts and 17 are dominated by blue shifts. Approximately half of the latter group have red-shifted precursors. We interpret the bursts as prominence material, such as surges and coronal rain, moving through the field of view of the spectrometer. (orig.)

Multiparameter Monitoring and Prevention of Fault-Slip Rock Burst

OpenAIRE

Hu, Shan-chao; Tan, Yun-liang; Ning, Jian-guo; Guo, Wei-Yao; Liu, Xue-sheng

2017-01-01

Fault-slip rock burst is one type of the tectonic rock burst during mining. A detailed understanding of the precursory information of fault-slip rock burst and implementation of monitoring and early warning systems, as well as pressure relief measures, are essential to safety production in deep mines. This paper first establishes a mechanical model of stick-slip instability in fault-slip rock bursts and then reveals the failure characteristics of the instability. Then, change rule of mining-i...

PHYSICAL CONSTRAINTS ON FAST RADIO BURSTS

Energy Technology Data Exchange (ETDEWEB)

Luan, Jing; Goldreich, Peter, E-mail: jingluan@caltech.edu [California Institute of Technology, Pasadena, CA 91125 (United States)

2014-04-20

Fast radio bursts (FRBs) are isolated, ms radio pulses with dispersion measure (DM) of order 10{sup 3} pc cm{sup –3}. Galactic candidates for the DM of high latitude bursts detected at GHz frequencies are easily dismissed. DM from bursts emitted in stellar coronas are limited by free-free absorption and those from H II regions are bounded by the nondetection of associated free-free emission at radio wavelengths. Thus, if astronomical, FRBs are probably extragalactic. FRB 110220 has a scattering tail of ∼5.6 ± 0.1 ms. If the electron density fluctuations arise from a turbulent cascade, the scattering is unlikely to be due to propagation through the diffuse intergalactic plasma. A more plausible explanation is that this burst sits in the central region of its host galaxy. Pulse durations of order ms constrain the sizes of FRB sources implying high brightness temperatures that indicates coherent emission. Electric fields near FRBs at cosmological distances would be so strong that they could accelerate free electrons from rest to relativistic energies in a single wave period.

PHYSICAL CONSTRAINTS ON FAST RADIO BURSTS

International Nuclear Information System (INIS)

Luan, Jing; Goldreich, Peter

2014-01-01

Fast radio bursts (FRBs) are isolated, ms radio pulses with dispersion measure (DM) of order 10 3 pc cm –3 . Galactic candidates for the DM of high latitude bursts detected at GHz frequencies are easily dismissed. DM from bursts emitted in stellar coronas are limited by free-free absorption and those from H II regions are bounded by the nondetection of associated free-free emission at radio wavelengths. Thus, if astronomical, FRBs are probably extragalactic. FRB 110220 has a scattering tail of ∼5.6 ± 0.1 ms. If the electron density fluctuations arise from a turbulent cascade, the scattering is unlikely to be due to propagation through the diffuse intergalactic plasma. A more plausible explanation is that this burst sits in the central region of its host galaxy. Pulse durations of order ms constrain the sizes of FRB sources implying high brightness temperatures that indicates coherent emission. Electric fields near FRBs at cosmological distances would be so strong that they could accelerate free electrons from rest to relativistic energies in a single wave period

IDENTIFICATION OF BURSTING WATER MASER FEATURES IN ORION KL

International Nuclear Information System (INIS)

Hirota, Tomoya; Honma, Mareki; Kim, Mi Kyoung; Kobayashi, Hideyuki; Shibata, Katsunori M.; Tsuboi, Masato; Fujisawa, Kenta; Kawaguchi, Noriyuki; Imai, Hiroshi; Omodaka, Toshihiro; Shimoikura, Tomomi; Yonekura, Yoshinori

2011-01-01

In 2011 February, a burst event of the H 2 O maser in Orion KL (Kleinmann-Low object) has started after a 13 year silence. This is the third time such phenomena has been detected in Orion KL, followed by the events in 1979-1985 and 1998. We have carried out astrometric observations of the bursting H 2 O maser features in Orion KL with the VLBI Exploration of Radio Astrometry (VERA), a Japanese very long baseline interferometry network dedicated for astrometry. The total flux of the bursting feature at the local standard of rest (LSR) velocity of 7.58 km s -1 reaches 4.4 x 10 4 Jy in 2011 March. The intensity of the bursting feature is three orders of magnitude larger than that of the same velocity feature in the quiescent phase in 2006. Two months later, another new feature appears at the LSR velocity of 6.95 km s -1 in 2011 May, separated by 12 mas north of the 7.58 km s -1 feature. Thus, the current burst occurs at two spatially different features. The bursting masers are elongated along the northwest-southeast direction as reported in the previous burst in 1998. We determine the absolute positions of the bursting features for the first time ever with a submilliarcsecond (mas) accuracy. Their positions are coincident with the shocked molecular gas called the Orion Compact Ridge. We tentatively detect the absolute proper motions of the bursting features toward the southwest direction. It is most likely that the outflow from the radio source I or another young stellar object interacting with the Compact Ridge is a possible origin of the H 2 O maser burst.

Thalamic neuron models encode stimulus information by burst-size modulation

Directory of Open Access Journals (Sweden)

Daniel Henry Elijah

2015-09-01

Full Text Available Thalamic neurons have been long assumed to fire in tonic mode during perceptive states, and in burst mode during sleep and unconsciousness. However, recent evidence suggests that bursts may also be relevant in the encoding of sensory information. Here we explore the neural code of such thalamic bursts. In order to assess whether the burst code is generic or whether it depends on the detailed properties of each bursting neuron, we analyzed two neuron models incorporating different levels of biological detail. One of the models contained no information of the biophysical processes entailed in spike generation, and described neuron activity at a phenomenological level. The second model represented the evolution of the individual ionic conductances involved in spiking and bursting, and required a large number of parameters. We analyzed the models' input selectivity using reverse correlation methods and information theory. We found that n-spike bursts from both models transmit information by modulating their spike count in response to changes to instantaneous input features, such as slope, phase, amplitude, etc. The stimulus feature that is most efficiently encoded by bursts, however, need not coincide with one of such classical features. We therefore searched for the optimal feature among all those that could be expressed as a linear transformation of the time-dependent input current. We found that bursting neurons transmitted 6 times more information about such more general features. The relevant events in the stimulus were located in a time window spanning ~100 ms before and ~20 ms after burst onset. Most importantly, the neural code employed by the simple and the biologically realistic models was largely the same, implying that the simple thalamic neuron model contains the essential ingredients that account for the computational properties of the thalamic burst code. Thus, our results suggest the n-spike burst code is a general property of

Thalamic neuron models encode stimulus information by burst-size modulation.

Science.gov (United States)

Elijah, Daniel H; Samengo, Inés; Montemurro, Marcelo A

2015-01-01

Thalamic neurons have been long assumed to fire in tonic mode during perceptive states, and in burst mode during sleep and unconsciousness. However, recent evidence suggests that bursts may also be relevant in the encoding of sensory information. Here, we explore the neural code of such thalamic bursts. In order to assess whether the burst code is generic or whether it depends on the detailed properties of each bursting neuron, we analyzed two neuron models incorporating different levels of biological detail. One of the models contained no information of the biophysical processes entailed in spike generation, and described neuron activity at a phenomenological level. The second model represented the evolution of the individual ionic conductances involved in spiking and bursting, and required a large number of parameters. We analyzed the models' input selectivity using reverse correlation methods and information theory. We found that n-spike bursts from both models transmit information by modulating their spike count in response to changes to instantaneous input features, such as slope, phase, amplitude, etc. The stimulus feature that is most efficiently encoded by bursts, however, need not coincide with one of such classical features. We therefore searched for the optimal feature among all those that could be expressed as a linear transformation of the time-dependent input current. We found that bursting neurons transmitted 6 times more information about such more general features. The relevant events in the stimulus were located in a time window spanning ~100 ms before and ~20 ms after burst onset. Most importantly, the neural code employed by the simple and the biologically realistic models was largely the same, implying that the simple thalamic neuron model contains the essential ingredients that account for the computational properties of the thalamic burst code. Thus, our results suggest the n-spike burst code is a general property of thalamic neurons.

Coronal mass ejections and solar radio bursts

International Nuclear Information System (INIS)

Kundu, M.R.

1990-01-01

The properties of coronal mass ejection (CME) events and their radio signatures are discussed. These signatures are mostly in the form of type II and type IV burst emissions. Although type II bursts are temporally associated with CMEs, it is shown that there is no spatial relationship between them. Type II's associated with CMEs have in most cases a different origin, and they are not piston-driven by CMEs. Moving type IV and type II bursts can be associated with slow CMEs with speeds as low as 200 km/s, contrary to the earlier belief that only CMEs with speeds >400 km/s are associated with radio bursts. A specific event has been discussed in which the CME and type IV burst has nearly the same speed and direction, but the type II burst location was behind the CME and its motion was transverse. The speed and motion of the type II burst strongly suggest that the type II shock was decoupled from the CME and was probably due to a flare behind the limb. Therefore only the type IV source could be directly associated with the slow CME. The electrons responsble for the type IV emission could be produced in the flare or in the type II and then become trapped in a plasmoid associated with the CME. The reconnected loop could then move outwards as in the usual palsmoid model. Alternatively, the type IV emission could be interpreted as due to electrons produced by acceleration in wave turbulence driven by currents in the shock front driven by the CME. The lower-hybrid model Lampe and Papadopoulos (1982), which operates at both fast and slow mode shocks, could be applied to this situation. (author). 31 refs., 12 figs

Channel's Concurrence and Quantum Teleportation

Institute of Scientific and Technical Information of China (English)

LING Yin-Sheng

2005-01-01

Concurrence can measure the entanglement property of a system. If the channel is a pure state, positive concurrence state can afford the good performance in the teleportation process. If the channel ia a mixed state, positive concurrence state cannot assure the good performance in the teleportation. The conditions of the positive concurrence and the quantum teleportation in the Heisenberg spin ring is derived.

ARE ULTRA-LONG GAMMA-RAY BURSTS DIFFERENT?

Energy Technology Data Exchange (ETDEWEB)

Boër, M.; Gendre, B. [CNRS-ARTEMIS, Boulevard de l' Observatoire, CS 34229, 06304 Nice Cedex 4 (France); Stratta, G., E-mail: michel.boer@unice.fr [Università degli Studi di Urbino Carlo Bo, I-61029 Urbino (Italy)

2015-02-10

The discovery of a number of gamma-ray bursts (GRBs) with duration exceeding 1000 s has opened the debate on whether these bursts form a new class of sources, the so-called ultra-long GRBs, or if they are rather the tail of the distribution of the standard long GRB duration. Using the long GRB sample detected by Swift, we investigate the statistical properties of long GRBs and compare them with the ultra-long burst properties. We compute the burst duration of long GRBs using the start epoch of the so-called ''steep decay'' phase detected with Swift/XRT. We discuss also the differences observed in their spectral properties. We find that ultra-long GRBs are statistically different from the standard long GRBs with typical burst duration less than 100-500 s, for which a Wolf-Rayet star progenitor is usually invoked. Together with the presence of a thermal emission component we interpret this result as indication that the usual long GRB progenitor scenario cannot explain the extreme duration of ultra-long GRBs, their energetics, as well as the mass reservoir and size that can feed the central engine for such a long time.

Galactic distribution of X-ray burst sources

International Nuclear Information System (INIS)

Lewin, W.H.G.; Hoffman, J.A.; Doty, J.; Clark, G.W.; Swank, J.H.; Becker, R.H.; Pravdo, S.H.; Serlemitsos, P.J.

1977-01-01

It is stated that 18 X-ray burst sources have been observed to date, applying the following definition for these bursts - rise times of less than a few seconds, durations of seconds to minutes, and recurrence in some regular pattern. If single burst events that meet the criteria of rise time and duration, but not recurrence are included, an additional seven sources can be added. A sky map is shown indicating their positions. The sources are spread along the galactic equator and cluster near low galactic longitudes, and their distribution is different from that of the observed globular clusters. Observations based on the SAS-3 X-ray observatory studies and the Goddard X-ray Spectroscopy Experiment on OSO-9 are described. The distribution of the sources is examined and the effect of uneven sky exposure on the observed distribution is evaluated. It has been suggested that the bursts are perhaps produced by remnants of disrupted globular clusters and specifically supermassive black holes. This would imply the existence of a new class of unknown objects, and at present is merely an ad hoc method of relating the burst sources to globular clusters. (U.K.)

On Burst Detection and Prediction in Retweeting Sequence

Science.gov (United States)

2015-05-22

We conduct a comprehensive empirical analysis of a large microblogging dataset collected from the Sina Weibo and report our observations of burst...whether and how accurate we can predict bursts using classifiers based on the extracted features. Our empirical study of the Sina Weibo data shows the...feasibility of burst prediction using appropriately extracted features and classic classifiers. 1 Introduction Microblogging, such as Twitter and Sina

LAT Onboard Science: Gamma-Ray Burst Identification

International Nuclear Information System (INIS)

Kuehn, Frederick; Hughes, Richard; Smith, Patrick; Winer, Brian; Bonnell, Jerry; Norris, Jay; Ritz, Steven; Russell, James

2007-01-01

The main goal of the Large Area Telescope (LAT) onboard science program is to provide quick identification and localization of Gamma Ray Bursts (GRB) onboard the LAT for follow-up observations by other observatories. The GRB identification and localization algorithm will provide celestial coordinates with an error region that will be distributed via the Gamma ray burst Coordinate Network (GCN). We present results that show our sensitivity to bursts as characterized using Monte Carlo simulations of the GLAST observatory. We describe and characterize the method of onboard track determination and the GRB identification and localization algorithm. Onboard track determination is considerably different than in the on-ground case, resulting in a substantially altered point spread function. The algorithm contains tunable parameters which may be adjusted after launch when real bursts characteristics at very high energies have been identified

Gamma-ray burst polarimeter (GAP)

International Nuclear Information System (INIS)

Mihara, Tatehiro; Murakami, Toshio; Yonetoku, Daisuke; Gunji, Shuichi; Kubo, Shin

2013-01-01

The gamma-ray burst polarimeter (GAP: GAmma-ray burst Polarimeter), which had been almost handcrafted by scientists, has succeeded in working normally in interplanetary space, and in detecting the polarization of the gamma-ray from a mysterious astronomical object 'gamma-ray burst'. It is the first result of the detectors in the world exclusively aiming at detecting gamma-ray polarization. We mainly describe the hardware of our GAP equipment and show the method of preparing equipment to work in the cosmic space with a tight budget. The mechanical structure, the electronic circuits, the software on the equipment, the data analysis on the earth, and the scientific results gained by the observation just over one year, are presented after explaining the principle of gamma-ray polarization detection. Our design to protect equipment against mechanical shock and cosmic radiation may provide useful information for future preparation of compact satellite. (J.P.N.)

Multifrequency Observations of Gamma-Ray Burst

OpenAIRE

Greiner, J.

1995-01-01

Neither a flaring nor a quiescent counterpart to a gamma-ray burst has yet been convincingly identified at any wavelength region. The present status of the search for counterparts of classical gamma-ray bursts is given. Particular emphasis is put on the search for flaring counterparts, i.e. emission during or shortly after the gamma-ray emission.

THE INFLUENCE OF MAC BUFFER ON THE CONTENTION-BASED ACCESS SCHEME WITH BURSTING OPTION FOR IEEE 802.11E WIRELESS NETWORKS

Directory of Open Access Journals (Sweden)

S. SELVAKENNEDY

2006-12-01

Full Text Available Wireless LANs are increasingly being used for inelastic applications. Currently, there is little support for quality of service in the IEEE 802.11 MAC protocol, and IEEE task group E has defined the 802.11e MAC extension. Enhanced distributed channel access (EDCA is a contention-based scheme of the 802.11e standard. To allow a station to transmit more than one frame from a single contention, an optional feature known as controlled frame-bursting (CFB is introduced in the standard. In this paper, we initially performed an average analysis to determine a suitable burst duration limit. Then, a detailed evaluation and comparison of the EDCA protocol with the CFB option is carried out through simulation to quantify its performance gain. The impact of the MAC transmit buffer size is also incorporated. Accordingly, we have proposed a suitable approach to guide the configuration of the burst duration limit. It is demonstrated that an optimized CFB configuration allows the MAC protocol to achieve 30% more capacity than the basic EDCA scheme.

Dust reddening and extinction curves toward gamma-ray bursts at z > 4

Science.gov (United States)

Bolmer, J.; Greiner, J.; Krühler, T.; Schady, P.; Ledoux, C.; Tanvir, N. R.; Levan, A. J.

2018-01-01

Context. Dust is known to be produced in the envelopes of asymptotic giant branch (AGB) stars, the expanded shells of supernova (SN) remnants, and in situ grain growth within the interstellar medium (ISM), although the corresponding efficiency of each of these dust formation mechanisms at different redshifts remains a topic of debate. During the first Gyr after the Big Bang, it is widely believed that there was not enough time to form AGB stars in high numbers, hence the dust at this epoch is expected to be purely from SNe or subsequent grain growth in the ISM. The time period corresponding to z 5-6 is thus expected to display the transition from SN-only dust to a mixture of both formation channels as is generally recognized at present. Aims: Here we aim to use afterglow observations of gamma-ray bursts (GRBs) at redshifts larger than z > 4 to derive host galaxy dust column densities along their line of sight and to test if a SN-type dust extinction curve is required for some of the bursts. Methods: We performed GRB afterglow observations with the seven-channel Gamma-Ray Optical and Near-infrared Detector (GROND) at the 2.2 m MPI telescope in La Silla, Chile (ESO), and we combined these observations with quasi-simultaneous data gathered with the XRT telescope on board the Swift satellite. Results: We increase the number of measured AV values for GRBs at z > 4 by a factor of 2-3 and find that, in contrast to samples at mostly lower redshift, all of the GRB afterglows have a visual extinction of AV different scenarios. For the first time we also report a photometric redshift of zphot = 7.88-0.94+0.75 for GRB 100905A, making it one of the most distant GRBs known to date.

Gamma Ray Bursts and the Birth of Black Holes

Science.gov (United States)

Gehrels, Neil

2009-01-01

Black holes have been predicted since the 1940's from solutions of Einstein's general relativity field equation. There is strong evidence of their existence from astronomical observations, but their origin has remained an open question of great interest. Gamma-ray bursts may the clue. They are powerful explosions, visible to high redshift, and appear to be the birth cries of black holes. The Swift and Fermi missions are two powerful NASA observatories currently in orbit that are discovering how gamma-ray bursts work. Evidence is building that the long and short duration subcategories of GRBs have very different origins: massive star core collapse to a black hole for long bursts and binary neutron star coalescence to a black hole for short bursts. The similarity to Type II and Ia supernovae originating from young and old stellar progenitors is striking. Bursts are tremendously luminous and are providing a new tool to study the high redshift universe. One Swift burst at z=8.3 is the most distant object known in the universe. The talk will present the latest gamma-ray burst results from Swift and Fermi and will highlight what they are teaching us about black holes and jet outflows.

Observational properties of cosmic gamma-ray bursts

International Nuclear Information System (INIS)

Mazets, E.P.

1986-01-01

A brief overview of the major observational results obtained in gamma-ray burst studies is presented. Also discussed is to what extent the thermonuclear model, which appears at present to be the most plausible, can account for the observed properties of the bursts. The investigation of gamma-ray bursts should cover observations of the time histories of events, energy spectra, and their variablility, source localization, and inspection of the localization regions during the active and quiescent phases of the source in other wavelengths, as well as, evaluation of the statistical distributions of the data obtained

Heuristic burst detection method using flow and pressure measurements

NARCIS (Netherlands)

Bakker, M.; Vreeburg, J.H.G.; Roer, Van de M.; Rietveld, L.C.

2014-01-01

Pipe bursts in a drinking water distribution system lead to water losses, interruption of supply, and damage to streets and houses due to the uncontrolled water flow. To minimize the negative consequences of pipe bursts, an early detection is necessary. This paper describes a heuristic burst

IGR J17254-3257, a new bursting neutron star

DEFF Research Database (Denmark)

Chenevez, Jérôme; Falanga, M.; Kuulkers, E.

2007-01-01

Aims. The study of the observational properties of uncommonly long bursts from low luminosity sources is important when investigating the transition from a hydrogen - rich bursting regime to a pure helium regime and from helium burning to carbon burning as predicted by current burst theories. On ...

The development of a burst criterion for zircaloy fuel cladding under LOCA conditions

International Nuclear Information System (INIS)

Neitzel, H.J.; Rossinger, H.E.

1980-02-01

A burst criterion model, which assumes that deformation is controlled by steady-state creep, has been developed for a thin-walled cladding, in this case Zircaloy-4, subjected to a differential pressure and high temperature. The creep equation is integrated to obtain a burst time at the singularity of the strain. Once the burst time is known, the burst temperature and burst pressure can be calculated from the known temperature and pressure histories. A further relationship between burst stress and burst temperature is used to calculate the burst strain. Comparison with measured burst data shows good agreement between theory and experiment was found that, if the heating rate is constant, the burst temperature increases with decreasing stress, and that, if the stress level is constant, the burst temperature increases with increasing heating rate. It was also found that anisotropy alters the burst temperature and burst strain, and that test conditions in the α-Zr temperature range have no influence on the burst data. (auth)

Bursts generate a non-reducible spike-pattern code

Directory of Open Access Journals (Sweden)

Hugo G Eyherabide

2009-05-01

Full Text Available On the single-neuron level, precisely timed spikes can either constitute firing-rate codes or spike-pattern codes that utilize the relative timing between consecutive spikes. There has been little experimental support for the hypothesis that such temporal patterns contribute substantially to information transmission. Using grasshopper auditory receptors as a model system, we show that correlations between spikes can be used to represent behaviorally relevant stimuli. The correlations reflect the inner structure of the spike train: a succession of burst-like patterns. We demonstrate that bursts with different spike counts encode different stimulus features, such that about 20% of the transmitted information corresponds to discriminating between different features, and the remaining 80% is used to allocate these features in time. In this spike-pattern code, the "what" and the "when" of the stimuli are encoded in the duration of each burst and the time of burst onset, respectively. Given the ubiquity of burst firing, we expect similar findings also for other neural systems.

Internally consistent gamma ray burst time history phenomenology

International Nuclear Information System (INIS)

Cline, T.L.

1985-01-01

A phenomenology for gamma ray burst time histories is outlined. Order of their generally chaotic appearance is attempted, based on the speculation that any one burst event can be represented above 150 keV as a superposition of similarly shaped increases of varying intensity. The increases can generally overlap, however, confusing the picture, but a given event must at least exhibit its own limiting characteristic rise and decay times if the measurements are made with instruments having adequate temporal resolution. Most catalogued observations may be of doubtful or marginal utility to test this hypothesis, but some time histories from Helios-2, Pioneer Venus Orbiter and other instruments having one-to several-millisecond capabilities appear to provide consistency. Also, recent studies of temporally resolved Solar Maximum Mission burst energy spectra are entirely compatible with this picture. The phenomenology suggested here, if correct, may assist as an analytic tool for modelling of burst processes and possibly in the definition of burst source populations

What can NuSTAR do for X-ray bursts?

DEFF Research Database (Denmark)

Chenevez, Jérôme; Tomsick, John; Chakrabarty, Deepto

2012-01-01

burning are ejected in the burst expansion wind. We have investigated the possibility of observing with NuSTAR some X-ray bursters selected for their high burst rate and trend to exhibit so-called superexpansion bursts. Our main ambition is to detect the photoionization edges associated with the ejected...

Covert Channels and Simple Timed Mix-Firewalls

National Research Council Canada - National Science Library

Newman, Richard

2004-01-01

Traditional methods for evaluating the amount of anonymity afforded by various Mix configurations have depended on either measuring the size of the set of possible senders of a particular message (anonymity set size...

Measurement of turbulent flow in a narrow open channel

Directory of Open Access Journals (Sweden)

Sarkar Sankar

2016-09-01

Full Text Available The paper presents the experimental results of turbulent flow over hydraulically smooth and rough beds. Experiments were conducted in a rectangular flume under the aspect ratio b/h = 2 (b = width of the channel 0.5 m, and h = flow depth 0.25 m for both the bed conditions. For the hydraulically rough bed, the roughness was created by using 3/8″ commercially available angular crushed stone chips; whereas sand of a median diameter d50 = 1.9 mm was used as the bed material for hydraulically smooth bed. The three-dimensional velocity components were captured by using a Vectrino (an acoustic Doppler velocimeter. The study focuses mainly on the turbulent characteristics within the dip that were observed towards the sidewall (corner of the channel where the maximum velocity occurs below the free-surface. It was also observed that the nondimensional Reynolds shear stress changes its sign from positive to negative within the dip. The quadrant plots for the turbulent bursting shows that the signs of all the bursting events change within the dip. Below the dip, the probability of the occurrence of sweeps and ejections are more than that of inward and outward interactions. On the other hand, within the dip, the probability of the occurrence of the outward and inward interactions is more than that of sweeps and ejections.

Effect of wear on the burst strength of l-80 steel casing

International Nuclear Information System (INIS)

Irawan, S; Bharadwaj, A M; Temesgen, B; Karuppanan, S; Abdullah, M Z B

2015-01-01

Casing wear has recently become one of the areas of research interest in the oil and gas industry especially in extended reach well drilling. The burst strength of a worn out casing is one of the significantly affected mechanical properties and is yet an area where less research is done The most commonly used equations to calculate the resulting burst strength after wear are Barlow, the initial yield burst, the full yield burst and the rupture burst equations. The objective of this study was to estimate casing burst strength after wear through Finite Element Analysis (FEA). It included calculation and comparison of the different theoretical bursts pressures with the simulation results along with effect of different wear shapes on L-80 casing material. The von Misses stress was used in the estimation of the burst pressure. The result obtained shows that the casing burst strength decreases as the wear percentage increases. Moreover, the burst strength value of the casing obtained from the FEA has a higher value compared to the theoretical burst strength values. Casing with crescent shaped wear give the highest burst strength value when simulated under nonlinear analysis. (paper)

Bubble bursting at an interface

Science.gov (United States)

Kulkarni, Varun; Sajjad, Kumayl; Anand, Sushant; Fezzaa, Kamel

2017-11-01

Bubble bursting is crucial to understanding the life span of bubbles at an interface and more importantly the nature of interaction between the bulk liquid and the outside environment from the point of view of chemical and biological material transport. The dynamics of the bubble as it rises from inside the liquid bulk to its disappearance on the interface after bursting is an intriguing process, many aspects of which are still being explored. In our study, we make detailed high speed imaging measurements to examine carefully the hole initiation and growth in bursting bubbles that unearth some interesting features of the process. Previous analyses available in literature are revisited based on our novel experimental visualizations. Using a combination of experiments and theory we investigate the role of various forces during the rupturing process. This work aims to further our current knowledge of bubble dynamics at an interface with an aim of predicting better the bubble evolution from its growth to its eventual integration with the liquid bulk.

On the mechanism of TBA block of the TRPV1 channel.

Science.gov (United States)

Oseguera, Andrés Jara; Islas, León D; García-Villegas, Refugio; Rosenbaum, Tamara

2007-06-01

The transient receptor potential vanilloid 1 (TRPV1) channel is a nonselective cation channel activated by capsaicin and responsible for thermosensation. To date, little is known about the gating characteristics of these channels. Here we used tetrabutylammonium (TBA) to determine whether this molecule behaves as an ion conduction blocker in TRPV1 channels and to gain insight into the nature of the activation gate of this protein. TBA belongs to a family of classic potassium channel blockers that have been widely used as tools for determining the localization of the activation gate and the properties of the pore of several ion channels. We found TBA to be a voltage-dependent pore blocker and that the properties of block are consistent with an open-state blocker, with the TBA molecule binding to multiple open states, each with different blocker affinities. Kinetics of channel closure and burst-length analysis in the presence of blocker are consistent with a state-dependent blocking mechanism, with TBA interfering with closing of an activation gate. This activation gate may be located cytoplasmically with respect to the binding site of TBA ions, similar to what has been observed in potassium channels. We propose an allosteric model for TRPV1 activation and block by TBA, which explains our experimental data.

The development of a burst criterion for Zircaloy fuel cladding under LOCA conditions

International Nuclear Information System (INIS)

Neitzel, H.J.; Rosinger, H.E.

1980-10-01

A burst criterion model, which assumes that deformation is controlled by steady-state creep, has been developed for a thin-walled cladding, in this case Zircaloy-4, subjected to a differential pressure and high temperature. The creep equation is integrated to obtain a burst time at the singularity of the strain. Once that urst time is known, the burst temperature and burst pressure can be calculated from the known temperature and pressure histories. A further relationship between burst stress and burst temperature is used to calculate the burst strain. Comparison with measured burst data shows good agreement between theory and experiment. It was found that, if the heating rate is constant, the burst temperature increases with decreasing stress, and that, if the stress level is constant, the burst temperature increases with increasing heating rate. It was also found that anisotropy alters the burst temperature and burst strain, and that thest conditions in the α-Zr temperature range have no influence on the burst data. (orig.) [de

Stimulus-dependent modulation of spike burst length in cat striate cortical cells.

Science.gov (United States)

DeBusk, B C; DeBruyn, E J; Snider, R K; Kabara, J F; Bonds, A B

1997-07-01

Burst activity, defined by groups of two or more spikes with intervals of cats. Bursting varied broadly across a population of 507 simple and complex cells. Half of this population had > or = 42% of their spikes contained in bursts. The fraction of spikes in bursts did not vary as a function of average firing rate and was stationary over time. Peaks in the interspike interval histograms were found at both 3-5 ms and 10-30 ms. In many cells the locations of these peaks were independent of firing rate, indicating a quantized control of firing behavior at two different time scales. The activity at the shorter time scale most likely results from intrinsic properties of the cell membrane, and that at the longer scale from recurrent network excitation. Burst frequency (bursts per s) and burst length (spikes per burst) both depended on firing rate. Burst frequency was essentially linear with firing rate, whereas burst length was a nonlinear function of firing rate and was also governed by stimulus orientation. At a given firing rate, burst length was greater for optimal orientations than for nonoptimal orientations. No organized orientation dependence was seen in bursts from lateral geniculate nucleus cells. Activation of cortical contrast gain control at low response amplitudes resulted in no burst length modulation, but burst shortening at optimal orientations was found in responses characterized by supersaturation. At a given firing rate, cortical burst length was shortened by microinjection of gamma-aminobutyric acid (GABA), and bursts became longer in the presence of N-methyl-bicuculline, a GABA(A) receptor blocker. These results are consistent with a model in which responses are reduced at nonoptimal orientations, at least in part, by burst shortening that is mediated by GABA. A similar mechanism contributes to response supersaturation at high contrasts via recruitment of inhibitory responses that are tuned to adjacent orientations. Burst length modulation can serve

Supernova sheds light on gamma-ray bursts

CERN Multimedia

2003-01-01

On 29 March the HETE-II satellite detected the most violent explosion in the universe to date - an enormous burst of gamma rays. Observers across the world recorded and studied the event. It appears to prove that gamma ray bursts originate in supernovae (1 page)

Observation of L-bursts of Jupiter decameter waves

International Nuclear Information System (INIS)

Imai, Kazumasa; Tomisawa, Ichiro

1978-01-01

The Jupiter decameter waves are the only information source which can be obtained on the earth for the investigation of dynamics concerning the generation of plasma waves in the magnetosphere of Jupiter. The emission of Jupiter decameter waves is modulated by the satellite Io considerably. It is observed that the emission of decameter waves fluctuated much in course of time. The duration time of bursts is 1 to 10 sec and 1 to 50 msec for L-bursts and S-bursts, respectively. The simultaneous observations were conducted at two locations from August, 1977, and at three locations from December, 1977, for searching the source of L-bursts. The relation between the appearance frequency of L-bursts and S-bursts and Io phase and system 3 longitude is explained. The observation points were Sugadaira, Chofu and Toyokawa, The minimum detectable flux density by the wave receiving network is 10 -21 W/m 2 .Hz. Concerning the observed results, the locations of observed events on the Io phase and the system 3 longitude are shown. The analytical results on the L-bursts of the main source and the early source are explained, taking ten events. The analysed dynamic cross-correlation and the spectrum analysis of the decameter intensity are shown. The relation between the origin and the emission mechanism was investigated, considering the observed data and the evaluation mentioned above for the main source and early source, and the clue was obtained to solve the riddle of emission mechanism. (Nakai, Y.)

Detection of gamma-ray bursts from Andromeda

International Nuclear Information System (INIS)

Bulik, Tomasz; Coppi, Paolo S.; Lamb, Donald Q.

1996-01-01

If gamma-ray bursts originate in a corona around the Milky Way, it should also be possible to detect them from a similar corona around Andromeda. Adopting a simple model of high velocity neutron star corona, we evaluate the ability of instruments on existing missions to detect an excess of bursts toward Andromeda. We also calculate the optimal properties of an instrument designed to detect such an excess. We find that if the bursts radiate isotropically, an experiment with a sampling distance d max > or approx. 500 kpc could detect a significant excess of bursts in the direction of Andromeda in a few years of observation. If the radiation is beamed along the neutron star's direction of motion, an experiment with d max > or approx. 800 kpc would detect such an excess in a similar amount of time, provided that the width of the beam is greater than 10 deg. Lack of an excess toward Andromeda would therefore be compelling evidence that the bursts are cosmological in origin if made by an instrument at least 50 times more sensitive than BATSE, given current constraints on Galactic corona models. Comparisons with detailed dynamical calculations of the spatial distribution of high velocity neutron stars in the coronae around the Milky Way and Andromeda confirm these conclusions

Scientific Applications Performance Evaluation on Burst Buffer

KAUST Repository

Markomanolis, George S.

2017-10-19

Parallel I/O is an integral component of modern high performance computing, especially in storing and processing very large datasets, such as the case of seismic imaging, CFD, combustion and weather modeling. The storage hierarchy includes nowadays additional layers, the latest being the usage of SSD-based storage as a Burst Buffer for I/O acceleration. We present an in-depth analysis on how to use Burst Buffer for specific cases and how the internal MPI I/O aggregators operate according to the options that the user provides during his job submission. We analyze the performance of a range of I/O intensive scientific applications, at various scales on a large installation of Lustre parallel file system compared to an SSD-based Burst Buffer. Our results show a performance improvement over Lustre when using Burst Buffer. Moreover, we show results from a data hierarchy library which indicate that the standard I/O approaches are not enough to get the expected performance from this technology. The performance gain on the total execution time of the studied applications is between 1.16 and 3 times compared to Lustre. One of the test cases achieved an impressive I/O throughput of 900 GB/s on Burst Buffer.

Physical characterization of the Skua fast burst assembly

International Nuclear Information System (INIS)

Paternoster, R.; Bounds, J.; Sanchez, R.; Miko, D.

1994-01-01

In this paper we discuss the system design and ongoing efforts to characterize the machine physics and operating properties of the Skua fast burst assembly. The machine is currently operating up to prompt critical while we await approval for super-prompt burst operations. Efforts have centered on characterizing neutron kinetic properties, comparing calculated and measured temperature coefficients and power distributions, improving the burst reproducibility, examining the site-wide dose characteristics, and fitting the machine with cooling and filtration systems

The influence of turbulent bursting on sediment resuspension under unidirectional currents

Directory of Open Access Journals (Sweden)

S. Salim

2017-07-01

Full Text Available Laboratory experiments were conducted in an open channel flume with a flat sandy bed to examine the role of turbulence on sediment resuspension. An acoustic Doppler velocimeter (ADV was used to measure the instantaneous three-dimensional velocity components and acoustic backscatter as a proxy to suspended sediment concentration. Estimates of sediment transport assume that there is a mean critical velocity that needs to be exceeded before sediment transport is initiated. This approach does not consider the turbulent flow field that may initiate sediment resuspension through event-based processes such as the bursting phenomenon. In this paper, laboratory measurements were used to examine the sediment resuspension processes below and above the mean critical velocity. The results within a range above and below the measured mean critical velocity suggested that (1 the contribution of turbulent bursting events remained identical in both experimental conditions, (2 ejection and sweep events contributed more to the total sediment flux than up-acceleration and down-deceleration events, and (3 wavelet transform revealed a correlation between the momentum and sediment flux in both test conditions. Such similarities in conditions above and below the measured mean critical velocity highlight the need to re-evaluate the accuracy of a single time-averaged mean critical velocity for the initiation of sediment entrainment.

Multi-Index Monitoring and Evaluation on Rock Burst in Yangcheng Mine

Directory of Open Access Journals (Sweden)

Yunliang Tan

2015-01-01

Full Text Available Based on the foreboding information monitoring of the energy released in the developing process of rock burst, prediction system for rock burst can be established. By using microseismic method, electromagnetic radiation method, and drilling bits method, rock burst in Yangcheng Mine was monitored, and a system of multi-index monitoring and evaluation on rock burst was established. Microseismic monitoring and electromagnetic radiation monitoring were early warning method, and drilling bits monitoring was burst region identification method. There were three identifying indexes: silence period in microseismic monitoring, rising period of the intensity, and rising period of pulse count in electromagnetic radiation monitoring. If there is identified burst risk in the workface, drilling bits method was used to ascertain the burst region, and then pressure releasing methods were carried out to eliminate the disaster.

DO THE FERMI GAMMA-RAY BURST MONITOR AND SWIFT BURST ALERT TELESCOPE SEE THE SAME SHORT GAMMA-RAY BURSTS?

International Nuclear Information System (INIS)

Burns, Eric; Briggs, Michael S.; Connaughton, Valerie; Zhang, Bin-Bin; Lien, Amy; Goldstein, Adam; Pelassa, Veronique; Troja, Eleonora

2016-01-01

Compact binary system mergers are expected to generate gravitational radiation detectable by ground-based interferometers. A subset of these, the merger of a neutron star with another neutron star or a black hole, are also the most popular model for the production of short gamma-ray bursts (GRBs). The Swift Burst Alert Telescope (BAT) and the Fermi Gamma-ray Burst Monitor (GBM) trigger on short GRBs (SGRBs) at rates that reflect their relative sky exposures, with the BAT detecting 10 per year compared to about 45 for GBM. We examine the SGRB populations detected by Swift BAT and Fermi GBM. We find that the Swift BAT triggers on weaker SGRBs than Fermi GBM, providing they occur close to the center of the BAT field of view, and that the Fermi GBM SGRB detection threshold remains flatter across its field of view. Overall, these effects combine to give the instruments the same average sensitivity, and account for the SGRBs that trigger one instrument but not the other. We do not find any evidence that the BAT and GBM are detecting significantly different populations of SGRBs. Both instruments can detect untriggered SGRBs using ground searches seeded with time and position. The detection of SGRBs below the on-board triggering sensitivities of Swift BAT and Fermi GBM increases the possibility of detecting and localizing the electromagnetic counterparts of gravitational wave (GW) events seen by the new generation of GW detectors

DO THE FERMI GAMMA-RAY BURST MONITOR AND SWIFT BURST ALERT TELESCOPE SEE THE SAME SHORT GAMMA-RAY BURSTS?

Energy Technology Data Exchange (ETDEWEB)

Burns, Eric; Briggs, Michael S. [University of Alabama in Huntsville, 320 Sparkman Drive, Huntsville, AL 35805 (United States); Connaughton, Valerie [Universities Space Research Association, Science and Technology Institute, 320 Sparkman Drive, Huntsville, AL 35805 (United States); Zhang, Bin-Bin [Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35899 (United States); Lien, Amy [Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Goldstein, Adam [NASA Postdoctoral Program, Space Science Office, VP62, NASA/Marshall Space Flight Center, Huntsville, AL 35812 (United States); Pelassa, Veronique [Smithsonian Astrophysical Observatory, P.O. Box 97, Amado, AZ 85645 (United States); Troja, Eleonora, E-mail: eb0016@uah.edu [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2016-02-20

Compact binary system mergers are expected to generate gravitational radiation detectable by ground-based interferometers. A subset of these, the merger of a neutron star with another neutron star or a black hole, are also the most popular model for the production of short gamma-ray bursts (GRBs). The Swift Burst Alert Telescope (BAT) and the Fermi Gamma-ray Burst Monitor (GBM) trigger on short GRBs (SGRBs) at rates that reflect their relative sky exposures, with the BAT detecting 10 per year compared to about 45 for GBM. We examine the SGRB populations detected by Swift BAT and Fermi GBM. We find that the Swift BAT triggers on weaker SGRBs than Fermi GBM, providing they occur close to the center of the BAT field of view, and that the Fermi GBM SGRB detection threshold remains flatter across its field of view. Overall, these effects combine to give the instruments the same average sensitivity, and account for the SGRBs that trigger one instrument but not the other. We do not find any evidence that the BAT and GBM are detecting significantly different populations of SGRBs. Both instruments can detect untriggered SGRBs using ground searches seeded with time and position. The detection of SGRBs below the on-board triggering sensitivities of Swift BAT and Fermi GBM increases the possibility of detecting and localizing the electromagnetic counterparts of gravitational wave (GW) events seen by the new generation of GW detectors.

Frequency dependent characteristics of solar impulsive radio bursts

International Nuclear Information System (INIS)

Das, T.K.; Das Gupta, M.K.

1983-01-01

An investigation was made of the impulsive radio bursts observed in the frequency range 0.245 to 35 GHz. Important results obtained are: (i) Simple type 1 bursts with intensities 0 to 10 f.u. and simple type 2 bursts with intensities 10 to 500 f.u. are predominant in the frequency ranges 1.415 to 4.995 GHz and 4.995 to 8.8 GHz, respectively; (ii) With maxima around 2.7 GHz and 4 GHz for the first and second types respectively, the durations of the radio bursts decrease gradually both towards lower and higher frequencies; (iii) As regards occurrences, the first type dominates in the southern solar hemisphere peaking around 8.8 GHz, whereas the second type favours the north with no well-defined maximum in any frequency; (iv) Both types prefer the eastern hemisphere, the peak occurrences being around 8.8 GHz and 5 GHz for the two successive types, respectively; (c) The spectra of impulsive radio bursts are generally of the inverted U-type with the maximum emission intensity between 5 and 15 GHz. (author)

Ion burst event in the earth's dayside magnetosheath

International Nuclear Information System (INIS)

Paschalidis, N.P.; Krimigis, S.M.; Sibeck, D.G.; McEntire, R.W.; Zanetti, L.J.; Sarris, E.T.; Christon, S.P.

1991-01-01

The MEPA instrument on the AMPTE/CCE Spacecraft provided ion angular distributions as rapidly as every 6 sec for H, He, and O at energies of 10 keV to 2 MeV in the dayside magnetosheath within 8.75 R E , the CCE apogee. In this report the authors discuss a burst of energetic particles in the subsolar magnetosheath and its association with rapid changes in the local magnetic field direction in such a way that the magnetic field connected the spacecraft to the magnetopause during the enhancement. They find that magnetosheath angular distributions outside the burst peaked at 90 degree pitch angles, whereas during the burst they exhibited field aligned streaming either parallel or antiparallel to the magnetic field combined with a clear earthward gradient. The clear earthward gradients at E ≥ 10 KeV, the streaming, and the slope change in the burst-time magnetosheath spectrum at ∼10 KeV suggest magnetospheric source for the burst-time ≥ 10 KeV ions and heated solar wind for E < 10 KeV

Fuzzy correlations of gamma-ray bursts

International Nuclear Information System (INIS)

Hartmann, D.H.; Linder, E.V.; Blumenthal, G.R.

1991-01-01

The origin of gamma-ray bursts is not known, both in the sense of the nature of the source emitting the radiation and literally, the position of the burst on the sky. Lacking unambiguously identified counterparts in any wavelength band studied to date, statistical approaches are required to determine the burster distance scale. Angular correlation analysis is one of the most powerful tools in this regard. However, poor detector resolution gives large localization errors, effectively beam smearing the positions. The resulting fuzzy angular correlation function is investigated and the generic isotropization that smearing induces on any intrinsic clustering is discussed. In particular, the extent to which gamma-ray burst observations by the BATSE detector aboard the Gamma-Ray Observatory might recover an intrinsic source correlation is investigated. 16 refs

Accelerating Science with the NERSC Burst Buffer Early User Program

Energy Technology Data Exchange (ETDEWEB)

Bhimji, Wahid [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Bard, Debbie [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Romanus, Melissa [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Rutgers Univ., New Brunswick, NJ (United States); Paul, David [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Ovsyannikov, Andrey [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Friesen, Brian [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Bryson, Matt [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Correa, Joaquin [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Lockwood, Glenn K. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Tsulaia, Vakho [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Byna, Suren [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Farrell, Steve [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Gursoy, Doga [Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS); Daley, Chris [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Beckner, Vince [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Van Straalen, Brian [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Trebotich, David [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Tull, Craig [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Weber, Gunther H. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Wright, Nicholas J. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Antypas, Katie [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Prabhat, none [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

2016-01-01

NVRAM-based Burst Buffers are an important part of the emerging HPC storage landscape. The National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory recently installed one of the first Burst Buffer systems as part of its new Cori supercomputer, collaborating with Cray on the development of the DataWarp software. NERSC has a diverse user base comprised of over 6500 users in 700 different projects spanning a wide variety of scientific computing applications. The use-cases of the Burst Buffer at NERSC are therefore also considerable and diverse. We describe here performance measurements and lessons learned from the Burst Buffer Early User Program at NERSC, which selected a number of research projects to gain early access to the Burst Buffer and exercise its capability to enable new scientific advancements. To the best of our knowledge this is the first time a Burst Buffer has been stressed at scale by diverse, real user workloads and therefore these lessons will be of considerable benefit to shaping the developing use of Burst Buffers at HPC centers.

Early detection of preferential channeling in reverse electrodialysis

NARCIS (Netherlands)

Vermaas, David; Saakes, Michel; Nijmeijer, Dorothea C.

2014-01-01

Membrane applications often experience fouling, which prevent uniform flow distribution through the feed water compartments, i.e. preferential channeling may occur. This research shows the effect of preferential channeling on energy generation from mixing salt water and fresh water using reverse

Beyond initiation-limited translational bursting: the effects of burst size distributions on the stability of gene expression

KAUST Repository

Kuwahara, Hiroyuki

2015-11-04

A main source of gene expression noise in prokaryotes is translational bursting. It arises from efficient translation of mRNAs with low copy numbers, which makes the production of protein copies highly variable and pulsatile. To obtain analytical solutions, previous models to capture this noise source had to assume translation to be initiation-limited, representing the burst size by a specific type of a long-tail distribution. However, there is increasing evidence suggesting that the initiation is not the rate-limiting step in certain settings, for example, under stress conditions. Here, to overcome the limitations imposed by the initiation-limited assumption, we present a new analytical approach that can evaluate biological consequences of the protein burst size with a general distribution. Since our new model can capture the contribution of other factors to the translational noise, it can be used to analyze the effects of gene expression noise in more general settings. We used this new model to analytically analyze the connection between the burst size and the stability of gene expression processes in various settings. We found that the burst size with different distributions can lead to quantitatively and qualitatively different stability characteristics of protein abundance and can have non-intuitive effects. By allowing analysis of how the stability of gene expression processes changes based on various distributions of translational noise, our analytical approach is expected to enable deeper insights into the control of cell fate decision-making, the evolution of cryptic genetic variations, and fine-tuning of gene circuits.

The sample of INTEGRAL SPI-ACS gamma-ray bursts

International Nuclear Information System (INIS)

Rau, A.; Kienlin, A. von; Licht, G.G.; Hurley, K.

2005-01-01

The anti-coincidence system of the spectrometer on board INTEGRAL is operated as a nearly omni directional gamma-ray burst detector above ∼ 75 KeV. During the elapsed mission time 324 burst candidates were detected. As part of the 3rd Interplanetary Network of gamma-ray detectors the cosmic origin of 115 burst was confirmed. Here we present a preliminary analysis of the SPI-ACS gamma-ray burst sample. In particular we discuss the origin of a significant population of short events (duration < 0.2 s) and a possible method for a flux calibration of the data

Coupled hydro-neutronic calculations for fast burst reactor accidents

International Nuclear Information System (INIS)

Paternoster, R.; Kimpland, R.; Jaegers, P.; McGhee, J.

1994-01-01

Methods are described for determining the fully coupled neutronic/hydrodynamic response of fast burst reactors (FBR) under disruptive accident conditions. Two code systems, PAD (1 -D Lagrangian) and NIKE-PAGOSA (3-D Eulerian) were used to accomplish this. This is in contrast to the typical methodology that computes these responses by either single point kinetics or in a decoupled manner. This methodology is enabled by the use of modem supercomputers (CM-200). Two examples of this capability are presented: an unreflected metal fast burst assembly, and a reflected fast burst assembly typical of the Skua or SPR-III class of fast burst reactor

Separation of Particles in Channels Rotary Engine

Directory of Open Access Journals (Sweden)

Zyatikov Pavel

2015-01-01

Full Text Available The article considers the separation of particles in channels with different relative length. It is shown that the intensity of turbulence at the inlet section of the channel varies considerably in its length. The dependence of the turbulence damping along the channel expressing by fraction of the distance is shown. The ratio of the particle separation efficiency out the gas flow in the rotor channel is defined. The values of particle separation efficiency in the channel for the angle α=π/4 in turbulent aerosol flow is shows, including without mixing the particles.

Gamma Ray Burst Discoveries by the Swift Mission

Science.gov (United States)

Gehrels, Neil

2006-01-01

Gamma-ray bursts are among the most fascinating occurrences in the cosmos. They are thought to be the birth cries of black holes throughout the universe. The NASA swift mission is an innovative new multiwavelength observatory designed to determine the origin of bursts and use them to probe the early Universe. Swift is now in orbit since November 20, 2004 and all hardware is performing well. A new-technology wide-field gamma-ray camera is detecting a hundred bursts per year. sensitive narrow-field X-ray and uv/optical telescopes, built in collaboration with UK and Italian partners, are pointed at the burst location in 50-100 sec by an autonomously controlled "swift" spacecraft. For each burst, arcsec positions are determined and optical/UV/X-ray/gamma-ray spectrophotometry performed. Information is also rapidly sent to the ground to a team of more than 50 observers at telescopes around the world. The first year of findings from the mission will be presented. There has been a break-through in the longstanding mystery of short GRBs; they appear to be caused by merging neutron stars. High redshift bursts have been detected leading to a better understanding of star formation rates and distant galaxy environments. GRBs have been found with giant X-ray flares occurring in their afterglow.

Gamma Ray Burst Discoveries by the Swift Mission

Science.gov (United States)

Gehrels, Neil

2006-04-01

Gamma-ray bursts are among the most fascinating occurrences in the cosmos. They are thought to be the birth cries of black holes throughout the universe. The NASA Swift mission is an innovative new multiwavelength observatory designed to determine the origin of bursts and use them to probe the early Universe. Swift is now in orbit since November 20, 2004 and all hardware is performing well. A new-technology wide-field gamma-ray camera is detecting a hundred bursts per year. Sensitive narrow-field X-ray and UV/optical telescopes, built in collaboration with UK and Italian partners, are pointed at the burst location in 50-100 sec by an autonomously controlled ``swift'' spacecraft. For each burst, arcsec positions are determined and optical/UV/X-ray/gamma-ray spectrophotometry performed. Information is also rapidly sent to the ground to a team of more than 50 observers at telescopes around the world. The first year of findings from the mission will be presented. There has been a break-through in the long-standing mystery of short GRBs; they appear to be caused by merging neutron stars. High redshift bursts have been detected leading to a better understanding of star formation rates and distant galaxy environments. GRBs have been found with giant X-ray flares occurring in their afterglow.

Recent achievements in the field of gamma-ray bursts

International Nuclear Information System (INIS)

Lu Tan; Dai Zigao

2001-01-01

Recent progresses in the field of gamma-ray bursts is briefly introduced. Gamma-ray bursts are the most energetic explosion since the Big Bang of the universe. Within a few tens of seconds, the energy released in gamma-ray bursts could be several hundred times larger than that released form the sun in its whole life (about 10 billion years). The authors will first briefly discuss the observational facts, based on which the authors will discuss the standard fireball model, the dynamical behavior and evolution of gamma-ray bursts and their afterglows. Then, various observational phenomena that contradict the standard model are given and the importance of these post-standard effects are pointed out. The questions related to the energy source of gamma-ray bursts are still unanswered, and other important questions also remain to be solved

Probing Intrinsic Properties of Short Gamma-Ray Bursts with Gravitational Waves.

Science.gov (United States)

Fan, Xilong; Messenger, Christopher; Heng, Ik Siong

2017-11-03

Progenitors of short gamma-ray bursts are thought to be neutron stars coalescing with their companion black hole or neutron star, which are one of the main gravitational wave sources. We have devised a Bayesian framework for combining gamma-ray burst and gravitational wave information that allows us to probe short gamma-ray burst luminosities. We show that combined short gamma-ray burst and gravitational wave observations not only improve progenitor distance and inclination angle estimates, they also allow the isotropic luminosities of short gamma-ray bursts to be determined without the need for host galaxy or light-curve information. We characterize our approach by simulating 1000 joint short gamma-ray burst and gravitational wave detections by Advanced LIGO and Advanced Virgo. We show that ∼90% of the simulations have uncertainties on short gamma-ray burst isotropic luminosity estimates that are within a factor of two of the ideal scenario, where the distance is known exactly. Therefore, isotropic luminosities can be confidently determined for short gamma-ray bursts observed jointly with gravitational waves detected by Advanced LIGO and Advanced Virgo. Planned enhancements to Advanced LIGO will extend its range and likely produce several joint detections of short gamma-ray bursts and gravitational waves. Third-generation gravitational wave detectors will allow for isotropic luminosity estimates for the majority of the short gamma-ray burst population within a redshift of z∼1.

Spatial-temporal variation of low-frequency earthquake bursts near Parkfield, California

Science.gov (United States)

Wu, Chunquan; Guyer, Robert; Shelly, David R.; Trugman, D.; Frank, William; Gomberg, Joan S.; Johnson, P.

2015-01-01

Tectonic tremor (TT) and low-frequency earthquakes (LFEs) have been found in the deeper crust of various tectonic environments globally in the last decade. The spatial-temporal behaviour of LFEs provides insight into deep fault zone processes. In this study, we examine recurrence times from a 12-yr catalogue of 88 LFE families with ∼730 000 LFEs in the vicinity of the Parkfield section of the San Andreas Fault (SAF) in central California. We apply an automatic burst detection algorithm to the LFE recurrence times to identify the clustering behaviour of LFEs (LFE bursts) in each family. We find that the burst behaviours in the northern and southern LFE groups differ. Generally, the northern group has longer burst duration but fewer LFEs per burst, while the southern group has shorter burst duration but more LFEs per burst. The southern group LFE bursts are generally more correlated than the northern group, suggesting more coherent deep fault slip and relatively simpler deep fault structure beneath the locked section of SAF. We also found that the 2004 Parkfield earthquake clearly increased the number of LFEs per burst and average burst duration for both the northern and the southern groups, with a relatively larger effect on the northern group. This could be due to the weakness of northern part of the fault, or the northwesterly rupture direction of the Parkfield earthquake.

Arachidonic acid triggers an oxidative burst in leukocytes

Directory of Open Access Journals (Sweden)

Pompeia C.

2003-01-01

Full Text Available The change in cellular reducing potential, most likely reflecting an oxidative burst, was investigated in arachidonic acid- (AA stimulated leukocytes. The cells studied included the human leukemia cell lines HL-60 (undifferentiated and differentiated into macrophage-like and polymorphonuclear-like cells, Jurkat and Raji, and thymocytes and macrophages from rat primary cultures. The oxidative burst was assessed by nitroblue tetrazolium reduction. AA increased the oxidative burst until an optimum AA concentration was reached and the burst decreased thereafter. In the leukemia cell lines, optimum concentration ranged from 200 to 400 µM (up to 16-fold, whereas in rat cells it varied from 10 to 20 µM. Initial rates of superoxide generation were high, decreasing steadily and ceasing about 2 h post-treatment. The continuous presence of AA was not needed to stimulate superoxide generation. It seems that the NADPH oxidase system participates in AA-stimulated superoxide production in these cells since the oxidative burst was stimulated by NADPH and inhibited by N-ethylmaleimide, diphenyleneiodonium and superoxide dismutase. Some of the effects of AA on the oxidative burst may be due to its detergent action. There apparently was no contribution of other superoxide-generating systems such as xanthine-xanthine oxidase, cytochromes P-450 and mitochondrial electron transport chain, as assessed by the use of inhibitors. Eicosanoids and nitric oxide also do not seem to interfere with the AA-stimulated oxidative burst since there was no systematic effect of cyclooxygenase, lipoxygenase or nitric oxide synthase inhibitors, but lipid peroxides may play a role, as indicated by the inhibition of nitroblue tetrazolium reduction promoted by tocopherol.

Molecular mechanism of voltage sensing in voltage-gated proton channels

Science.gov (United States)

Rebolledo, Santiago; Perez, Marta E.

2013-01-01

Voltage-gated proton (Hv) channels play an essential role in phagocytic cells by generating a hyperpolarizing proton current that electrically compensates for the depolarizing current generated by the NADPH oxidase during the respiratory burst, thereby ensuring a sustained production of reactive oxygen species by the NADPH oxidase in phagocytes to neutralize engulfed bacteria. Despite the importance of the voltage-dependent Hv current, it is at present unclear which residues in Hv channels are responsible for the voltage activation. Here we show that individual neutralizations of three charged residues in the fourth transmembrane domain, S4, all reduce the voltage dependence of activation. In addition, we show that the middle S4 charged residue moves from a position accessible from the cytosolic solution to a position accessible from the extracellular solution, suggesting that this residue moves across most of the membrane electric field during voltage activation of Hv channels. Our results show for the first time that the charge movement of these three S4 charges accounts for almost all of the measured gating charge in Hv channels. PMID:23401575

The velocities of type II solar radio bursts

International Nuclear Information System (INIS)

Tlamicha, A.; Karlicky, M.

1976-01-01

A list is presented of type II radio bursts identified at Ondrejov between January 1973 and December 1974 in the frequency range of the dynamic spectrum 70 to 810 MHz. The velocities of shock waves in the individual cases of type II bursts are given using the fourfold Newkirk model. Some problems associated with type II radio bursts and with the propagation of the shock wave into the interplanetary space and into the region of the Earth are also discussed. (author)

The LASL gamma-ray burst astronomy program

International Nuclear Information System (INIS)

Klebesadel, R.W.; Evans, W.D.; Laros, J.G.

1981-01-01

Gamma-ray burst observations performed by LASL began with the identification and initial report of the phenomenon from data acquired by the Vela satellites. The Vela instruments have recorded responses to 73 gamma-ray bursts over a ten-year interval, and are continuing to contribute toward these observations. Similar instrumentation was included aboard the NRL SOLRAD 11 spacecraft. These performed well but suffered an early demise. Recently, the LASL gamma-ray burst astronomy program has been enhanced through the implementation of experiments aboard the Pioneer Venus Orbiter and ISEF-C spacecraft. Both of these experiments are continuing to contribute data vital to trigonometric directional analyses. (orig.)

Slow Bursting Neurons of Mouse Cortical Layer 6b Are Depolarized by Hypocretin/Orexin and Major Transmitters of Arousal.

Science.gov (United States)

Wenger Combremont, Anne-Laure; Bayer, Laurence; Dupré, Anouk; Mühlethaler, Michel; Serafin, Mauro

2016-01-01

Neurons firing spontaneously in bursts in the absence of synaptic transmission have been previously recorded in different layers of cortical brain slices. It has been suggested that such neurons could contribute to the generation of alternating UP and DOWN states, a pattern of activity seen during slow-wave sleep. Here, we show that in layer 6b (L6b), known from our previous studies to contain neurons highly responsive to the wake-promoting transmitter hypocretin/orexin (hcrt/orx), there is a set of neurons, endowed with distinct intrinsic properties, which displayed a strong propensity to fire spontaneously in rhythmic bursts. In response to small depolarizing steps, they responded with a delayed firing of action potentials which, upon higher depolarizing steps, invariably inactivated and were followed by a depolarized plateau potential and a depolarizing afterpotential. These cells also displayed a strong hyperpolarization-activated rectification compatible with the presence of an I h current. Most L6b neurons with such properties were able to fire spontaneously in bursts. Their bursting activity was of intrinsic origin as it persisted not only in presence of blockers of ionotropic glutamatergic and GABAergic receptors but also in a condition of complete synaptic blockade. However, a small number of these neurons displayed a mix of intrinsic bursting and synaptically driven recurrent UP and DOWN states. Most of the bursting L6b neurons were depolarized and excited by hcrt/orx through a direct postsynaptic mechanism that led to tonic firing and eventually inactivation. Similarly, they were directly excited by noradrenaline, histamine, dopamine, and neurotensin. Finally, the intracellular injection of these cells with dye and their subsequent Neurolucida reconstruction indicated that they were spiny non-pyramidal neurons. These results lead us to suggest that the propensity for slow rhythmic bursting of this set of L6b neurons could be directly impeded by hcrt

Data quality studies for burst analysis of Virgo data acquired during Weekly Science Runs

International Nuclear Information System (INIS)

Acernese, F; Amico, P; Alshourbagy, M

2007-01-01

Virgo started collecting science data during weekends in order to not interfere with commissioning activities. The goal of Weekly Science Runs is to ease the transition between commissioning periods and data taking periods, in addition to providing data sets exploiting the stationary behavior of the detector. The detection of gravitational wave (GW) bursts emitted by core collapse of supernovae is one of the most difficult tasks for the GW community due to the fact that there are uncertainties in the exact shape of the waveforms, as we do not have complete models. A major task for this kind of detection effort is the cleaning of the event triggers found by the detection pipelines, namely the removal of accidental transient signals due to noise source events. In order to clean our data from false GW events, we need to define a strategy for data quality cut and veto of auxiliary and environmental monitoring channels. In this paper we report on the analysis we performed on data acquired during Weekly Science Runs to explore and define the data quality cut and veto studies for burst analysis

Inhibition of NMDARs in the nucleus reticularis of the thalamus produces delta frequency bursting

Directory of Open Access Journals (Sweden)

Yuchun Zhang

2009-11-01

Full Text Available Injection of NMDAR antagonist into the thalamus can produce delta frequency EEG oscillations in the thalamocortical system. It is surprising that an antagonist of an excitatory neurotransmitter should trigger such activity, and the mechanism is unknown. One hypothesis is that the antagonist blocks excitation of GABAergic cells, thus producing disinhibition. To test this hypothesis, we investigated the effect of NMDAR antagonist (APV on cells of the nucleus reticularis (nRT in rat brain slices, a thalamic nucleus that can serve as a pacemaker for thalamocortical delta oscillations and that is composed entirely of GABAergic neurons. We found, unexpectedly, that nRT cells are hyperpolarized by APV. This occurs because these cells have an unusual form of NMDAR (probably NR2C that contributes inward current at resting potential in response to ambient glutamate. The hyperpolarization produced by APV is sufficient to deinactivate T-type calcium channels, and these trigger rhythmic bursting at delta frequency. The APV-induced delta frequency bursting is abolished by dopamine D2 receptor antagonist, indicating that dopamine and NMDAR antagonist work synergistically to stimulate delta frequency bursting. Our results have significant implications concerning the electrophysiological basis of schizophrenia and bring together the NMDAR hypofunction, dopamine, and GABA theories of the disease. Our results suggest that NMDAR hypofunction and dopamine work synergistically on the GABAergic cells of the nRT to generate the delta frequency EEG oscillations, a thalamocortical dysrhythmia (TCD in the awake state that is an established abnormality in schizophrenia.

Gamma ray bursts observed with WATCH‐EURECA

DEFF Research Database (Denmark)

Brandt, Søren; Lund, Niels; Castro-Tirado, A. J.

1994-01-01

The WATCH wide field x‐ray monitor has the capability of independently locating bright Gamma Ray Bursts to 1° accuracy. We report the preliminary positions of 12 Gamma Ray Bursts observed with the WATCH monitor flown on the ES spacecraft EURECA during its 11 month mission. Also the recurrence...

Gamma ray bursts: Current status of observations and theory

International Nuclear Information System (INIS)

Meegan, C.A.

1990-04-01

Gamma ray bursts display a wide range of temporal and spectral characteristics, but typically last several seconds and emit most of their energy in a low energy, gamma ray region. The burst sources appear to be isotropically distributed on the sky. Several lines of evidence suggest magnetic neutron stars as sources for bursts. A variety of energy sources and emission mechanisms are proposed

Infrared and X-ray bursts from the rapid burster

International Nuclear Information System (INIS)

Apparao, K.M.V.; Chitre, S.M.

1979-01-01

Studies on sudden bursts from the cosmic X-ray sources are reported. The processes occuring from the rise in luminosity of an x-ray source to its collapse are described. Records of the x-ray burst from the globular cluster NGC 6624 and the 'Rapid Burster' are shown. The Infra-red bursts from the Rapid Burster are also explained. (A.K.)

THE SECOND SWIFT BURST ALERT TELESCOPE GAMMA-RAY BURST CATALOG

International Nuclear Information System (INIS)

Sakamoto, T.; Baumgartner, W. H.; Cummings, J. R.; Krimm, H. A.; Barthelmy, S. D.; Gehrels, N.; Markwardt, C. B.; Parsons, A. M.; Tueller, J.; Fenimore, E. E.; Palmer, D. M.; Sato, G.; Stamatikos, M.; Ukwatta, T. N.; Zhang, B.

2011-01-01

We present the second Swift Burst Alert Telescope (BAT) catalog of gamma-ray bursts (GRBs), which contains 476 bursts detected by the BAT between 2004 December 19 and 2009 December 21. This catalog (hereafter the BAT2 catalog) presents burst trigger time, location, 90% error radius, duration, fluence, peak flux, time-averaged spectral parameters, and time-resolved spectral parameters measured by the BAT. In the correlation study of various observed parameters extracted from the BAT prompt emission data, we distinguish among long-duration GRBs (L-GRBs), short-duration GRBs (S-GRBs), and short-duration GRBs with extended emission (S-GRBs with E.E.) to investigate differences in the prompt emission properties. The fraction of L-GRBs, S-GRBs, and S-GRBs with E.E. in the catalog are 89%, 8%, and 2%, respectively. We compare the BAT prompt emission properties with the BATSE, BeppoSAX, and HETE-2 GRB samples. We also correlate the observed prompt emission properties with the redshifts for the GRBs with known redshift. The BAT T 90 and T 50 durations peak at 70 s and 30 s, respectively. We confirm that the spectra of the BAT S-GRBs are generally harder than those of the L-GRBs. The time-averaged spectra of the BAT S-GRBs with E.E. are similar to those of the L-GRBs. Whereas, the spectra of the initial short spikes of the S-GRBs with E.E. are similar to those of the S-GRBs. We show that the BAT GRB samples are significantly softer than the BATSE bright GRBs and that the time-averaged E obs peak of the BAT GRBs peaks at 80 keV, which is significantly lower energy than those of the BATSE sample, which peak at 320 keV. The time-averaged spectral properties of the BAT GRB sample are similar to those of the HETE-2 GRB samples. By time-resolved spectral analysis, we find that only 10% of the BAT observed photon indices are outside the allowed region of the synchrotron shock model. We see no obvious observed trend in the BAT T 90 and the observed spectra with redshifts. The T 90

On the Nature of the Gamma-ray Bursts

Directory of Open Access Journals (Sweden)

Kyung-Ai Hong

1987-12-01

Full Text Available Review of the γ-ray burst phenomena are presented. History of the γ-ray bursts, characteristics, and three radiation mechanisms of thermal bremsstrahlung, thermal synchrotron, and inverse Compton scattering processes are considered.

Unusual X-ray burst profiles from 4U/MXB 1636-53

Science.gov (United States)

Sztajno, M.; Truemper, J.; Pietsch, W.; Van Paradijs, J.; Stollman, G.

1985-01-01

During a one day Exosat observation eight X-ray bursts from 4U/MXB 1636-53 are observed. Four of these were very unusual. Their peak fluxes were relatively low, and they showed a distinct double peak in their bolometric flux profiles. These new double-peaked bursts are unexplained by presently available models of X-ray bursts. It is possible that the energy release in these bursts proceeds in two 'steps'. The burst profiles are not the result of an expansion and subsequent contraction of the photosphere of the neutron star. Thus, they are very different from previously observed bursts which do show a double peak in certain energy ranges but not in their bolometric flux profiles; these are satisfactorily explained in terms of photospheric radius expansion and contraction. The anticorrelation between the apparent blackbody radius and blackbody temperature is discussed in terms of the nonPlanckian character of burst spectra and it is concluded that the model calculations reported by London, Taam, and Howard in 1984 give a reasonable first-order description of the observed apparent radius changes in X-ray bursts.

Pre-experiment testing of the Multi Channel Systems 16-channel preamplifier CPA16

International Nuclear Information System (INIS)

Patin, J B; Stoyer, M A; Moody, K J; Friensehner, A V

2003-01-01

The 16-channel preamplifier model CPA16 from Multi Channel Systems was studied. The CPA16 preamplifier/amplifier module is a candidate to be used as the preamplifiers and amplifiers for the focal plane detectors of the Mass Analyzer of Super Heavy Atoms (MASHA). The equipment used to test the CPA16, the results of testing the CPA16 with a pulser, a mixed 229 Th/ 148 Gd source and a 252 Cf source, and a summary of the results will be presented

DETECTING THE SUPERNOVA BREAKOUT BURST IN TERRESTRIAL NEUTRINO DETECTORS

International Nuclear Information System (INIS)

Wallace, Joshua; Burrows, Adam; Dolence, Joshua C.

2016-01-01

We calculate the distance-dependent performance of a few representative terrestrial neutrino detectors in detecting and measuring the properties of the ν e breakout burst light curve in a Galactic core-collapse supernova. The breakout burst is a signature phenomenon of core collapse and offers a probe into the stellar core through collapse and bounce. We examine cases of no neutrino oscillations and oscillations due to normal and inverted neutrino-mass hierarchies. For the normal hierarchy, other neutrino flavors emitted by the supernova overwhelm the ν e signal, making a detection of the breakout burst difficult. For the inverted hierarchy (IH), some detectors at some distances should be able to see the ν e breakout burst peak and measure its properties. For the IH, the maximum luminosity of the breakout burst can be measured at 10 kpc to accuracies of ∼30% for Hyper-Kamiokande (Hyper-K) and ∼60% for the Deep Underground Neutrino Experiment (DUNE). Super-Kamiokande (Super-K) and Jiangmen Underground Neutrino Observatory (JUNO) lack the mass needed to make an accurate measurement. For the IH, the time of the maximum luminosity of the breakout burst can be measured in Hyper-K to an accuracy of ∼3 ms at 7 kpc, in DUNE to ∼2 ms at 4 kpc, and JUNO and Super-K can measure the time of maximum luminosity to an accuracy of ∼2 ms at 1 kpc. Detector backgrounds in IceCube render a measurement of the ν e breakout burst unlikely. For the IH, a measurement of the maximum luminosity of the breakout burst could be used to differentiate between nuclear equations of state

Rock Burst Mechanics: Insight from Physical and Mathematical Modelling

Directory of Open Access Journals (Sweden)

J. Vacek

2008-01-01

Full Text Available Rock burst processes in mines are studied by many groups active in the field of geomechanics. Physical and mathematical modelling can be used to better understand the phenomena and mechanisms involved in the bursts. In the present paper we describe both physical and mathematical models of a rock burst occurring in a gallery of a coal mine.For rock bursts (also called bumps to occur, the rock has to possess certain particular rock burst properties leading to accumulation of energy and the potential to release this energy. Such materials may be brittle, or the rock burst may arise at the interfacial zones of two parts of the rock, which have principally different material properties (e.g. in the Poíbram uranium mines.The solution is based on experimental and mathematical modelling. These two methods have to allow the problem to be studied on the basis of three presumptions:· the solution must be time dependent,· the solution must allow the creation of cracks in the rock mass,· the solution must allow an extrusion of rock into an open space (bump effect. 

On burst-and-coast swimming performance in fish-like locomotion

International Nuclear Information System (INIS)

Chung, M-H

2009-01-01

Burst-and-coast swimming performance in fish-like locomotion is studied via two-dimensional numerical simulation. The numerical method used is the collocated finite-volume adaptive Cartesian cut-cell method developed previously. The NACA00xx airfoil shape is used as an equilibrium fish-body form. Swimming in a burst-and-coast style is computed assuming that the burst phase is composed of a single tail-beat. Swimming efficiency is evaluated in terms of the mass-specific cost of transport instead of the Froude efficiency. The effects of the Reynolds number (based on the body length and burst time), duty cycle and fineness ratio (the body length over the largest thickness) on swimming performance (momentum capacity and the mass-specific cost of transport) are studied quantitatively. The results lead to a conclusion consistent with previous findings that a larval fish seldom swims in a burst-and-coast style. Given mass and swimming speed, a fish needs the least cost if it swims in a burst-and-coast style with a fineness ratio of 8.33. This energetically optimal fineness ratio is larger than that derived from the simple hydromechanical model proposed in literature. The calculated amount of energy saving in burst-and-coast swimming is comparable with the real-fish estimation in the literature. Finally, the predicted wake-vortex structures of both continuous and burst-and-coast swimming are biologically relevant.

On burst-and-coast swimming performance in fish-like locomotion.

Science.gov (United States)

Chung, M-H

2009-09-01

Burst-and-coast swimming performance in fish-like locomotion is studied via two-dimensional numerical simulation. The numerical method used is the collocated finite-volume adaptive Cartesian cut-cell method developed previously. The NACA00xx airfoil shape is used as an equilibrium fish-body form. Swimming in a burst-and-coast style is computed assuming that the burst phase is composed of a single tail-beat. Swimming efficiency is evaluated in terms of the mass-specific cost of transport instead of the Froude efficiency. The effects of the Reynolds number (based on the body length and burst time), duty cycle and fineness ratio (the body length over the largest thickness) on swimming performance (momentum capacity and the mass-specific cost of transport) are studied quantitatively. The results lead to a conclusion consistent with previous findings that a larval fish seldom swims in a burst-and-coast style. Given mass and swimming speed, a fish needs the least cost if it swims in a burst-and-coast style with a fineness ratio of 8.33. This energetically optimal fineness ratio is larger than that derived from the simple hydromechanical model proposed in literature. The calculated amount of energy saving in burst-and-coast swimming is comparable with the real-fish estimation in the literature. Finally, the predicted wake-vortex structures of both continuous and burst-and-coast swimming are biologically relevant.

Characteristics of shock-associated fast-drift kilometric radio bursts

Science.gov (United States)

Macdowall, R. J.; Kundu, M. R.; Stone, R. G.

1987-01-01

The existence of a class of fast-drift, shock-associated (SA), kilometric radio bursts which occur at the time of metric type II emission and which are not entirely the kilometric continuation of metric type III bursts has been reported previously (Cane et al., 1981). In this paper unambiguous SA event criteria are established for the purpose of statistically comparing SA events with conventional kilometric type III bursts. Applying these criteria to all long-duration, fast-drift bursts observed by the ISEE-3 spacecraft during a 28-month interval, it is found that more than 70 percent of the events satisfying the criteria are associated with the radio signatures of coronal shocks. If a given event is associated with a metric type II or type IV burst, it is 13 times more likely to satisfy the SA criteria than an event associated only with metric type III activity.

Essays on Online and Multi-Channel Marketing

OpenAIRE

Zhang, Lingling

2016-01-01

Firms increasingly adopt online and multi-channel marketing strategies to reach and persuade consumers. Therefore, designing an effective marketing mix is critical to their success. The aim of my dissertation is to understand the strategy behind firms’ channel choices and assess marketing effectiveness. It consists of three large-scale empirical studies examining several important aspects of online and multi-channel marketing. My first essay focuses on the business-to-business (B2B) inte...

Gamma-ray bursts observed by the watch experiment

DEFF Research Database (Denmark)

Lund, Niels; Brandt, Søren; Castro-Tirado, A. J.

1991-01-01

After two years in orbit the WATCH instruments on the GRANAT space observatory have localized seven gamma burst sources with better than 1° accuracy. In several cases, follow‐up observations with Schmidt telescopes have been made within a few days. Some of the bursts have also been detected...... by the distant space probes PVO and ULYSSES and there are, therefore, good prospects for obtaining much improved positions using the burst arrival times. The existence of the almost concurrent Schmidt plates could then become particularly interesting....

Gamma-ray burst theory after Swift.

Science.gov (United States)

Piran, Tsvi; Fan, Yi-Zhong

2007-05-15

Afterglow observations in the pre-Swift era confirmed to a large extend the relativistic blast wave model for gamma-ray bursts (GRBs). Together with the observations of properties of host galaxies and the association with (type Ic) SNe, this has led to the generally accepted collapsar origin of long GRBs. However, most of the afterglow data was collected hours after the burst. The X-ray telescope and the UV/optical telescope onboard Swift are able to slew to the direction of a burst in real time and record the early broadband afterglow light curves. These observations, and in particular the X-ray observations, resulted in many surprises. While we have anticipated a smooth transition from the prompt emission to the afterglow, many observed that early light curves are drastically different. We review here how these observations are changing our understanding of GRBs.

Interaction function of coupled bursting neurons

International Nuclear Information System (INIS)

Shi Xia; Zhang Jiadong

2016-01-01

The interaction functions of electrically coupled Hindmarsh–Rose (HR) neurons for different firing patterns are investigated in this paper. By applying the phase reduction technique, the phase response curve (PRC) of the spiking neuron and burst phase response curve (BPRC) of the bursting neuron are derived. Then the interaction function of two coupled neurons can be calculated numerically according to the PRC (or BPRC) and the voltage time course of the neurons. Results show that the BPRC is more and more complicated with the increase of the spike number within a burst, and the curve of the interaction function oscillates more and more frequently with it. However, two certain things are unchanged: ϕ = 0, which corresponds to the in-phase synchronization state, is always the stable equilibrium, while the anti-phase synchronization state with ϕ = 0.5 is an unstable equilibrium. (paper)

Type III bursts in interplanetary space - Fundamental or harmonic?

Science.gov (United States)

Dulk, G. A.; Steinberg, J. L.; Hoang, S.

1984-01-01

ISEE-3 spacecraft observation of 120 relatively simple, isolated bursts in the 30-1980 kHz range are the basis of the present study of Type III bursts in the solar wind. Several characteristics are identified for many of these bursts which imply that the mode of emission changes from predominantly fundamental plasma radiation during the rise phase to predominantly second harmonic during decay. The fundamental emission begins in time coincidence with the start of Langmuir waves, confirming the conventional belief in these waves' causation of Type III bursts. Attention is given to the characteristics of fundamental components, by comparison to harmonics, at km-wavelengths.

A polarized fast radio burst at low Galactic latitude

OpenAIRE

Petroff, E.; Kasliwal, M.; Ravi, V.

2017-01-01

We report on the discovery of a new fast radio burst (FRB), FRB 150215, with the Parkes radio telescope on 2015 February 15. The burst was detected in real time with a dispersion measure (DM) of 1105.6 ± 0.8 pc cm^(−3), a pulse duration of 2.8 ^(+1.2)_(−0.5)ms, and a measured peak flux density assuming that the burst was at beam centre of 0.7 ^(+0.2)_(−0.1) Jy. The FRB originated at a Galactic longitude and latitude of 24.66°, 5.28° and 25° away from the Galactic Center. The burst was found t...

Phase-locking of bursting neuronal firing to dominant LFP frequency components.

Science.gov (United States)

Constantinou, Maria; Elijah, Daniel H; Squirrell, Daniel; Gigg, John; Montemurro, Marcelo A

2015-10-01

Neuronal firing in the hippocampal formation relative to the phase of local field potentials (LFP) has a key role in memory processing and spatial navigation. Firing can be in either tonic or burst mode. Although bursting neurons are common in the hippocampal formation, the characteristics of their locking to LFP phase are not completely understood. We investigated phase-locking properties of bursting neurons using simulations generated by a dual compartmental model of a pyramidal neuron adapted to match the bursting activity in the subiculum of a rat. The model was driven with stochastic input signals containing a power spectral profile consistent with physiologically relevant frequencies observed in LFP. The single spikes and spike bursts fired by the model were locked to a preferred phase of the predominant frequency band where there was a peak in the power of the driving signal. Moreover, the preferred phase of locking shifted with increasing burst size, providing evidence that LFP phase can be encoded by burst size. We also provide initial support for the model results by analysing example data of spontaneous LFP and spiking activity recorded from the subiculum of a single urethane-anaesthetised rat. Subicular neurons fired single spikes, two-spike bursts and larger bursts that locked to a preferred phase of either dominant slow oscillations or theta rhythms within the LFP, according to the model prediction. Both power-modulated phase-locking and gradual shift in the preferred phase of locking as a function of burst size suggest that neurons can use bursts to encode timing information contained in LFP phase into a spike-count code. Copyright © 2015 The Authors. Published by Elsevier Ireland Ltd.. All rights reserved.

Observations of the highest energy gamma-rays from gamma-ray bursts

International Nuclear Information System (INIS)

Dingus, Brenda L.

2001-01-01

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile new ground based detectors with sensitivity to gamma-ray bursts are beginning operation, and one recently reported evidence for TeV emission from a burst

Barbed channels enhance unidirectional connectivity between neuronal networks cultured on multi electrode arrays

Science.gov (United States)

le Feber, Joost; Postma, Wybren; de Weerd, Eddy; Weusthof, Marcel; Rutten, Wim L. C.

2015-01-01

Cultured neurons on multi electrode arrays (MEAs) have been widely used to study various aspects of neuronal (network) functioning. A possible drawback of this approach is the lack of structure in these networks. At the single cell level, several solutions have been proposed to enable directed connectivity, and promising results were obtained. At the level of connected sub-populations, a few attempts have been made with promising results. First assessment of the designs' functionality, however, suggested room for further improvement. We designed a two chamber MEA aiming to create a unidirectional connection between the networks in both chambers (“emitting” and “receiving”). To achieve this unidirectionality, all interconnecting channels contained barbs that hindered axon growth in the opposite direction (from receiving to emitting chamber). Visual inspection showed that axons predominantly grew through the channels in the promoted direction. This observation was confirmed by spontaneous activity recordings. Cross-correlation between the signals from two electrodes inside the channels suggested signal propagation at ≈2 m/s from emitting to receiving chamber. Cross-correlation between the firing patterns in both chambers indicated that most correlated activity was initiated in the emitting chamber, which was also reflected by a significantly lower fraction of partial bursts (i.e., a one-chamber-only burst) in the emitting chamber. Finally, electrical stimulation in the emitting chamber induced a fast response in that chamber, and a slower response in the receiving chamber. Stimulation in the receiving chamber evoked a fast response in that chamber, but no response in the emitting chamber. These results confirm the predominantly unidirectional nature of the connecting channels from emitting to receiving chamber. PMID:26578869

Barbed channels enhance unidirectional connectivity between neuronal networks cultured on multi electrode arrays.

Directory of Open Access Journals (Sweden)

Joost eLe Feber

2015-11-01

Full Text Available Cultured neurons on multi electrode arrays (MEAs have been widely used to study various as-pects of neuronal (network functioning. A possible drawback of this approach is the lack of structure in these networks. At the single cell level, several solutions have been proposed to ena-ble directed connectivity, and promising results were obtained. At the level of connected sub-populations, a few attempts have been made with promising results. First assessment of the de-signs’ functionality, however, suggested room for further improvement.We designed a two chamber MEA aiming to create a unidirectional connection between the net-works in both chambers (‘emitting’ and ‘receiving’. To achieve this unidirectionality, all inter-connecting channels contained barbs that hindered axon growth in the opposite direction (from receiving to emitting chamber. Visual inspection showed that axons predominantly grew through the channels in the promoted direction . This observation was confirmed by spontaneous activity recordings. Cross-correlation between the signals from two electrodes inside the channels suggested signal propagation at ≈2 m/s from emitting to receiving chamber. Cross-correlation between the firing patterns in both chambers indicated that most correlated activity was initiated in the emitting chamber, which was also reflected by a significantly lower fraction of partial bursts (e. a one-chamber-only burst in the emitting chamber. Finally, electrical stimulation in the emitting chamber induced a fast response in that chamber, and a slower response in the receiving chamber. Stimulation in the receiving chamber evoked a fast response in that chamber, but no response in the emitting chamber. These results confirm the predominantly unidirectional nature of the connecting channels from emitting to receiving chamber.

Stress Effects on Stop Bursts in Five Languages

Directory of Open Access Journals (Sweden)

Marija Tabain

2016-11-01

Full Text Available This study examines the effects of stress on the stop burst in five languages differing in number of places of articulation, as reflected in burst duration, spectral centre of gravity, and ­spectral standard deviation. The languages studied are English (three places of articulation /p t k/, the Indonesian language Makasar (four places /p t c k/, and the Central Australian languages ­Pitjantjatjara, Warlpiri (both five places /p t ʈ c k/, and Arrernte (six places /p t̪ t ʈ c k/. We find that languages differ in how they manifest stress on the consonant, with Makasar not ­showing any effect of stress at all, and Warlpiri showing an effect on burst duration, but not on the ­spectral measures. For the other languages, the velar /k/ has a “darker” quality (i.e., lower spectral centre of gravity, and/or a less diffuse spectrum (i.e., lower standard deviation under stress; while the alveolar /t/ has a “lighter” quality under stress. In addition, the dental /t̪/ has a more diffuse spectrum under stress. We suggest that this involves enhancement of the features [grave] and [diffuse] under stress, with velars being [+grave] and [–diffuse], alveolars being [–grave], and dentals being [+diffuse]. We discuss the various possible spectral effects of enhancement of these features. Finally, in the languages with five or six places of articulation, the stop burst is longer only for the palatal /c/ and the velar /k/, which have intrinsically long burst durations, and not for the anterior coronals /t̪ t ʈ/, which have intrinsically short burst durations. We suggest that in these systems, [burst duration] is a feature that separates these two groups of consonants.

Fermi/GBM Observations of SGRJ0501 + 4516 Bursts

Science.gov (United States)

Lin, Lin; Kouveliotou, Chryssa; Baring, Matthew G.; van der Horst, Alexander J.; Guiriec, Sylvain; Woods, Peter M.; Goegues, Ersin; Kaneko, Yuki; Scargle, Jeffrey; Granot, Jonathan;

Polarization of a periodic solar microwave burst

Energy Technology Data Exchange (ETDEWEB)

Kaufmann, P [Universidade Mackenzie, Sao Paulo (Brazil). Centro de Radio-Astronomia e Astrofisica

1976-09-01

No fluctuations in polarization have been found during a 7 GHz solar burst showing 17s periodic pulses in intensity. Polarization effects can be produced by the propagation media in the active centre, which are not affected directly by the burst source, but situated more deeply than the observed heights at that microwave frequency.

The host galaxy of a fast radio burst.

Science.gov (United States)

Keane, E F; Johnston, S; Bhandari, S; Barr, E; Bhat, N D R; Burgay, M; Caleb, M; Flynn, C; Jameson, A; Kramer, M; Petroff, E; Possenti, A; van Straten, W; Bailes, M; Burke-Spolaor, S; Eatough, R P; Stappers, B W; Totani, T; Honma, M; Furusawa, H; Hattori, T; Morokuma, T; Niino, Y; Sugai, H; Terai, T; Tominaga, N; Yamasaki, S; Yasuda, N; Allen, R; Cooke, J; Jencson, J; Kasliwal, M M; Kaplan, D L; Tingay, S J; Williams, A; Wayth, R; Chandra, P; Perrodin, D; Berezina, M; Mickaliger, M; Bassa, C

2016-02-25

In recent years, millisecond-duration radio signals originating in distant galaxies appear to have been discovered in the so-called fast radio bursts. These signals are dispersed according to a precise physical law and this dispersion is a key observable quantity, which, in tandem with a redshift measurement, can be used for fundamental physical investigations. Every fast radio burst has a dispersion measurement, but none before now have had a redshift measurement, because of the difficulty in pinpointing their celestial coordinates. Here we report the discovery of a fast radio burst and the identification of a fading radio transient lasting ~6 days after the event, which we use to identify the host galaxy; we measure the galaxy's redshift to be z = 0.492 ± 0.008. The dispersion measure and redshift, in combination, provide a direct measurement of the cosmic density of ionized baryons in the intergalactic medium of ΩIGM = 4.9 ± 1.3 per cent, in agreement with the expectation from the Wilkinson Microwave Anisotropy Probe, and including all of the so-called 'missing baryons'. The ~6-day radio transient is largely consistent with the radio afterglow of a short γ-ray burst, and its existence and timescale do not support progenitor models such as giant pulses from pulsars, and supernovae. This contrasts with the interpretation of another recently discovered fast radio burst, suggesting that there are at least two classes of bursts.

CaV3.1 isoform of T-type calcium channels supports excitability of rat and mouse ventral tegmental area neurons.

Science.gov (United States)

Tracy, Matthew E; Tesic, Vesna; Stamenic, Tamara Timic; Joksimovic, Srdjan M; Busquet, Nicolas; Jevtovic-Todorovic, Vesna; Todorovic, Slobodan M

2018-03-23

Recent data have implicated voltage-gated calcium channels in the regulation of the excitability of neurons within the mesolimbic reward system. While the attention of most research has centered on high voltage L-type calcium channel activity, the presence and role of the low voltage-gated T-type calcium channel (T-channels) has not been well explored. Hence, we investigated T-channel properties in the neurons of the ventral tegmental area (VTA) utilizing wild-type (WT) rats and mice, Ca V 3.1 knock-out (KO) mice, and TH-eGFP knock-in (KI) rats in acute horizontal brain slices of adolescent animals. In voltage-clamp experiments, we first assessed T-channel activity in WT rats with characteristic properties of voltage-dependent activation and inactivation, as well as characteristic crisscrossing patterns of macroscopic current kinetics. T-current kinetics were similar in WT mice and WT rats but T-currents were abolished in Ca V 3.1 KO mice. In ensuing current-clamp experiments, we observed the presence of hyperpolarization-induced rebound burst firing in a subset of neurons in WT rats, as well as dopaminergic and non-dopaminergic neurons in TH-eGFP KI rats. Following the application of a pan-selective T-channel blocker TTA-P2, rebound bursting was significantly inhibited in all tested cells. In a behavioral assessment, the acute locomotor increase induced by a MK-801 (Dizocilpine) injection in WT mice was abolished in Ca V 3.1 KO mice, suggesting a tangible role for 3.1 T-type channels in drug response. We conclude that pharmacological targeting of Ca V 3.1 isoform of T-channels may be a novel approach for the treatment of disorders of mesolimbic reward system. Copyright © 2018. Published by Elsevier Ltd.

Burst Test Qualification Analysis of DWPF Canister-Plug Weld

International Nuclear Information System (INIS)

Gupta, N.K.; Gong, Chung.

1995-02-01

The DWPF canister closure system uses resistance welding for sealing the canister nozzle and plug to ensure leak tightness. The welding group at SRTC is using the burst test to qualify this seal weld in lieu of the shear test in ASME B ampersand PV Code, Section IX, paragraph QW-196. The burst test is considered simpler and more appropriate than the shear test for this application. Although the geometry, loading and boundary conditions are quite different in the two tests, structural analyses show similarity in the failure mode of the shear test in paragraph QW-196 and the burst test on the DWPF canister nozzle Non-linear structural analyses are performed using finite element techniques to study the failure mode of the two tests. Actual test geometry and realistic stress strain data for the 304L stainless steel and the weld material are used in the analyses. The finite element models are loaded until failure strains are reached. The failure modes in both tests are shear at the failure points. Based on these observations, it is concluded that the use of a burst test in lieu of the shear test for qualifying the canister-plug weld is acceptable. The burst test analysis for the canister-plug also yields the burst pressures which compare favorably with the actual pressure found during burst tests. Thus, the analysis also provides an estimate of the safety margins in the design of these vessels

X-Ray Spectral Characteristics of Ginga Gamma-Ray Bursts

International Nuclear Information System (INIS)

Strohmayer, T.E.; Fenimore, E.E.; Murakami, T.; Yoshida, A.

1998-01-01

We have investigated the spectral characteristics of a sample of bright gamma-ray bursts detected with the gamma-ray burst sensors aboard the satellite Ginga. This instrument employed a proportional and scintillation counter to provide sensitivity to photons in the 2 endash 400 keV region and as such provided a unique opportunity to characterize the largely unexplored X-ray properties of gamma-ray bursts. The photon spectra of the Ginga bursts are well described by a low-energy slope, a bend energy, and a high-energy slope. In the energy range where they can be compared, this result is consistent with burst spectral analyses obtained from the BATSE experiment aboard the Compton Gamma-Ray Observatory. However, below 20 keV we find evidence for a positive spectral number index in approximately 40% of our burst sample, with some evidence for a strong rolloff at lower energies in a few events. There is a correlation (Pearson's r = -0.62) between the low-energy slope and the bend energy. We find that the distribution of spectral bend energies extends below 10 keV. There has been some concern in cosmological models of gamma-ray bursts (GRBs) that the bend energy covers only a small dynamic range. Our result extends the observed dynamic range, and, since we observe bend energies down to the limit of our instrument, perhaps observations have not yet limited the range. The Ginga trigger range was virtually the same as that of BATSE, yet we find a different range of fit parameters. One possible explanation might be that GRBs have two break energies, one often in the 50 endash 500 keV range and the other near 5 keV. Both BATSE and Ginga fit with only a single break energy, so BATSE tends to find breaks near the center of its energy range, and we tend to find breaks in our energy range. The observed ratio of energy emitted in the X-rays relative to the gamma rays can be much larger than a few percent and, in fact, is sometimes larger than unity. The average for our 22 bursts

BACODINE/3rd Interplanetary Network burst localization

International Nuclear Information System (INIS)

Hurley, K.; Barthelmy, S.; Butterworth, P.; Cline, T.; Sommer, M.; Boer, M.; Niel, M.; Kouveliotou, C.; Fishman, G.; Meegan, C.

1996-01-01

Even with only two widely separated spacecraft (Ulysses and GRO), 3rd Interplanetary Network (IPN) localizations can reduce the areas of BATSE error circles by two orders of magnitude. Therefore it is useful to disseminate them as quickly as possible following BATSE bursts. We have implemented a system which transmits the light curves of BACODINE/BATSE bursts directly by e-mail to UC Berkeley immediately after detection. An automatic e-mail parser at Berkeley watches for these notices, determines the Ulysses crossing time window, and initiates a search for the burst data on the JPL computer as they are received. In ideal cases, it is possible to retrieve the Ulysses data within a few hours of a burst, generate an annulus of arrival directions, and e-mail it out to the astronomical community by local nightfall. Human operators remain in this loop, but we are developing a fully automated routine which should remove them, at least for intense events, and reduce turn-around times to an absolute minimum. We explain the current operations, the data types used, and the speed/accuracy tradeoffs

Fine Tuning of CaV1.3 Ca2+ channel properties in adult inner hair cells positioned in the most sensitive region of the Gerbil Cochlea.

Directory of Open Access Journals (Sweden)

Valeria Zampini

Full Text Available Hearing relies on faithful signal transmission by cochlear inner hair cells (IHCs onto auditory fibres over a wide frequency and intensity range. Exocytosis at IHC ribbon synapses is triggered by Ca(2+ inflow through Ca(V1.3 (L-type Ca(2+ channels. We investigated the macroscopic (whole-cell and elementary (cell-attached properties of Ca(2+ currents in IHCs positioned at the middle turn (frequency ∼ 2 kHz of the adult gerbil cochlea, which is their most sensitive hearing region. Using near physiological recordings conditions (body temperature and a Na(+ based extracellular solution, we found that the macroscopic Ca(2+ current activates and deactivates very rapidly (time constant below 1 ms and inactivates slowly and only partially. Single-channel recordings showed an elementary conductance of 15 pS, a sub-ms latency to first opening, and a very low steady-state open probability (Po: 0.024 in response to 500-ms depolarizing steps at ∼-18 mV. The value of Po was significantly larger (0.06 in the first 40 ms of membrane depolarization, which corresponds to the time when most Ca(2+ channel openings occurred clustered in bursts (mean burst duration: 19 ms. Both the Po and the mean burst duration were smaller than those previously reported in high-frequency basal IHCs. Finally, we found that middle turn IHCs are likely to express about 4 times more Ca(2+ channels per ribbon than basal cells. We propose that middle-turn IHCs finely-tune Ca(V1.3 Ca(2+ channel gating in order to provide reliable information upon timing and intensity of lower-frequency sounds.

Fine Tuning of CaV1.3 Ca2+ channel properties in adult inner hair cells positioned in the most sensitive region of the Gerbil Cochlea.

Science.gov (United States)

Zampini, Valeria; Johnson, Stuart L; Franz, Christoph; Knipper, Marlies; Holley, Matthew C; Magistretti, Jacopo; Russo, Giancarlo; Marcotti, Walter; Masetto, Sergio

2014-01-01

Hearing relies on faithful signal transmission by cochlear inner hair cells (IHCs) onto auditory fibres over a wide frequency and intensity range. Exocytosis at IHC ribbon synapses is triggered by Ca(2+) inflow through Ca(V)1.3 (L-type) Ca(2+) channels. We investigated the macroscopic (whole-cell) and elementary (cell-attached) properties of Ca(2+) currents in IHCs positioned at the middle turn (frequency ∼ 2 kHz) of the adult gerbil cochlea, which is their most sensitive hearing region. Using near physiological recordings conditions (body temperature and a Na(+) based extracellular solution), we found that the macroscopic Ca(2+) current activates and deactivates very rapidly (time constant below 1 ms) and inactivates slowly and only partially. Single-channel recordings showed an elementary conductance of 15 pS, a sub-ms latency to first opening, and a very low steady-state open probability (Po: 0.024 in response to 500-ms depolarizing steps at ∼-18 mV). The value of Po was significantly larger (0.06) in the first 40 ms of membrane depolarization, which corresponds to the time when most Ca(2+) channel openings occurred clustered in bursts (mean burst duration: 19 ms). Both the Po and the mean burst duration were smaller than those previously reported in high-frequency basal IHCs. Finally, we found that middle turn IHCs are likely to express about 4 times more Ca(2+) channels per ribbon than basal cells. We propose that middle-turn IHCs finely-tune Ca(V)1.3 Ca(2+) channel gating in order to provide reliable information upon timing and intensity of lower-frequency sounds.

A stability analysis of ventilated boiling channels

International Nuclear Information System (INIS)

Taleyarkhan, R.P.; Podowski, M.Z.; Lahey, R.T. Jr.

1986-01-01

A mathematical model has been developed for the linear stability analysis of a system of ventilated parallel boiling channels. This model accounts for subcooled boiling, an arbitrary heat flux distribution, distributed and local hydraulic losses, heated wall dynamics, slip flow, turbulent mixing and arbitrary flow paths for transverse ventilation. The digital computer program MAZDA-NF was written for numerical evaluation of the mathematical model. Comparison of MAZDA-NF results with those obtained form both a closed form analytical solution and experiment, showed good agreement. A parametric study revealed that such phenomena as subcooled boiling, the transverse coupling between channels (due to cross-flow and mixing) and power skewing can have a significant impact on predicted stability margins. An analysis of an advanced BWR fuel, of the ASEA-ATOM SVEA design, has indicated that transverse ventilation may considerably improve channel stability. (orig.)

Gamma-ray bursts from black hole accretion disks

International Nuclear Information System (INIS)

Strong, I.B.

1975-01-01

The suggestion was first made more than a year ago that gamma-ray bursts might originate in the neighborhood of black holes, based on some rather circumstantial evidence linking Cygnus X-1, the prime black-hole candidate, with two of the then-known gamma-ray bursts. Since then additional evidence makes the idea still more plausible. The evidence is summarized briefly, a physical model for production of gamma-ray bursts is given, and several of the more interesting consequences of such an origin are pointed out. (orig.) [de

Gamma-ray bursts

CERN Document Server

Wijers, Ralph A M J; Woosley, Stan

2012-01-01

Cosmic gamma ray bursts (GRBs) have fascinated scientists and the public alike since their discovery in the late 1960s. Their story is told here by some of the scientists who participated in their discovery and, after many decades of false starts, solved the problem of their origin. Fourteen chapters by active researchers in the field present a detailed history of the discovery, a comprehensive theoretical description of GRB central engine and emission models, a discussion of GRB host galaxies and a guide to how GRBs can be used as cosmological tools. Observations are grouped into three sets from the satellites CGRO, BeppoSAX and Swift, and followed by a discussion of multi-wavelength observations. This is the first edited volume on GRB astrophysics that presents a fully comprehensive review of the subject. Utilizing the latest research, Gamma-ray Bursts is an essential desktop companion for graduate students and researchers in astrophysics.

V/V(max) test applied to SMM gamma-ray bursts

Science.gov (United States)

Matz, S. M.; Higdon, J. C.; Share, G. H.; Messina, D. C.; Iadicicco, A.

1992-01-01

We have applied the V/V(max) test to candidate gamma-ray bursts detected by the Gamma-Ray Spectrometer (GRS) aboard the SMM satellite to examine quantitatively the uniformity of the burst source population. For a sample of 132 candidate bursts identified in the GRS data by an automated search using a single uniform trigger criterion we find average V/V(max) = 0.40 +/- 0.025. This value is significantly different from 0.5, the average for a uniform distribution in space of the parent population of burst sources; however, the shape of the observed distribution of V/V(max) is unusual and our result conflicts with previous measurements. For these reasons we can currently draw no firm conclusion about the distribution of burst sources.

Signal Based Mixing Analysis for the magnetohydrodynamic mode reconstruction from homodyne microwave reflectometry

International Nuclear Information System (INIS)

Ejiri, Akira; Sakakibara, Satoru; Kawahata, Kazuo.

1995-03-01

A new method 'Signal Based Mixing Analysis', to extract the components which are coherent to a certain reference signal from a noisy signal, has been developed. The method is applied to homodyne microwave reflectometry to reconstruct the radial structure of a magnetohydrodynamic (MHD) mode in heliotron/torsatron Compact Helical System (CHS) [K. Matsuoka et al. Plasma Phys. Control. Nuclear Fusion Research 1988 Vol. 2, IAEA, Vienna 411 (1989)]. In CHS plasmas, MHD fluctuations measured with magnetic probes show bursts, in which the amplitude and frequency quasi-periodically vary. The signal based mixing analysis uses a set of functions which have the same amplitude and the harmonic frequency as those of the magnetic fluctuations. The product (mixing) of the signal of reflectometer and the functions yields the amplitude and phase of the coherent components. When the plasma density gradually increases, the measuring position moves radially outward. Thus, the radial structure of MHD modes can be obtained by this method. The analysis indicates several peaks and nodes inside the resonance surface of the MHD mode. In addition, the structure does not propagate radially during a burst. (author)

Ablation of silicon with bursts of femtosecond laser pulses

Science.gov (United States)

Gaudiuso, Caterina; Kämmer, Helena; Dreisow, Felix; Ancona, Antonio; Tünnermann, Andreas; Nolte, Stefan

2016-03-01

We report on an experimental investigation of ultrafast laser ablation of silicon with bursts of pulses. The pristine 1030nm-wavelength 200-fs pulses were split into bursts of up to 16 sub-pulses with time separation ranging from 0.5ps to 4080ps. The total ablation threshold fluence was measured depending on the burst features, finding that it strongly increases with the number of sub-pulses for longer sub-pulse delays, while a slowly increasing trend is observed for shorter separation time. The ablation depth per burst follows two different trends according to the time separation between the sub-pulses, as well as the total threshold fluence. For delays shorter than 4ps it decreases with the number of pulses, while for time separations longer than 510ps, deeper craters were achieved by increasing the number of subpulses in the burst, probably due to a change of the effective penetration depth.

A polarized fast radio burst at low Galactic latitude

Science.gov (United States)

Petroff, E.; Burke-Spolaor, S.; Keane, E. F.; McLaughlin, M. A.; Miller, R.; Andreoni, I.; Bailes, M.; Barr, E. D.; Bernard, S. R.; Bhandari, S.; Bhat, N. D. R.; Burgay, M.; Caleb, M.; Champion, D.; Chandra, P.; Cooke, J.; Dhillon, V. S.; Farnes, J. S.; Hardy, L. K.; Jaroenjittichai, P.; Johnston, S.; Kasliwal, M.; Kramer, M.; Littlefair, S. P.; Macquart, J. P.; Mickaliger, M.; Possenti, A.; Pritchard, T.; Ravi, V.; Rest, A.; Rowlinson, A.; Sawangwit, U.; Stappers, B.; Sullivan, M.; Tiburzi, C.; van Straten, W.; ANTARES Collaboration; Albert, A.; André, M.; Anghinolfi, M.; Anton, G.; Ardid, M.; Aubert, J.-J.; Avgitas, T.; Baret, B.; Barrios-Martí, J.; Basa, S.; Bertin, V.; Biagi, S.; Bormuth, R.; Bourret, S.; Bouwhuis, M. C.; Bruijn, R.; Brunner, J.; Busto, J.; Capone, A.; Caramete, L.; Carr, J.; Celli, S.; Chiarusi, T.; Circella, M.; Coelho, J. A. B.; Coleiro, A.; Coniglione, R.; Costantini, H.; Coyle, P.; Creusot, A.; Deschamps, A.; de Bonis, G.; Distefano, C.; di Palma, I.; Donzaud, C.; Dornic, D.; Drouhin, D.; Eberl, T.; El Bojaddaini, I.; Elsässer, D.; Enzenhöfer, A.; Felis, I.; Fusco, L. A.; Galatà, S.; Gay, P.; Geißelsöder, S.; Geyer, K.; Giordano, V.; Gleixner, A.; Glotin, H.; Grégoire, T.; Gracia-Ruiz, R.; Graf, K.; Hallmann, S.; van Haren, H.; Heijboer, A. J.; Hello, Y.; Hernández-Rey, J. J.; Hößl, J.; Hofestädt, J.; Hugon, C.; Illuminati, G.; James, C. W.; de Jong, M.; Jongen, M.; Kadler, M.; Kalekin, O.; Katz, U.; Kießling, D.; Kouchner, A.; Kreter, M.; Kreykenbohm, I.; Kulikovskiy, V.; Lachaud, C.; Lahmann, R.; Lefèvre, D.; Leonora, E.; Lotze, M.; Loucatos, S.; Marcelin, M.; Margiotta, A.; Marinelli, A.; Martínez-Mora, J. A.; Mathieu, A.; Mele, R.; Melis, K.; Michael, T.; Migliozzi, P.; Moussa, A.; Mueller, C.; Nezri, E.; Pǎvǎlaş, G. E.; Pellegrino, C.; Perrina, C.; Piattelli, P.; Popa, V.; Pradier, T.; Quinn, L.; Racca, C.; Riccobene, G.; Roensch, K.; Sánchez-Losa, A.; Saldaña, M.; Salvadori, I.; Samtleben, D. F. E.; Sanguineti, M.; Sapienza, P.; Schnabel, J.; Seitz, T.; Sieger, C.; Spurio, M.; Stolarczyk, Th.; Taiuti, M.; Tayalati, Y.; Trovato, A.; Tselengidou, M.; Turpin, D.; Tönnis, C.; Vallage, B.; Vallée, C.; van Elewyck, V.; Vivolo, D.; Vizzoca, A.; Wagner, S.; Wilms, J.; Zornoza, J. D.; Zúñiga, J.; H.E.S.S. Collaboration; Abdalla, H.; Abramowski, A.; Aharonian, F.; Ait Benkhali, F.; Akhperjanian, A. G.; Andersson, T.; Angüner, E. O.; Arrieta, M.; Aubert, P.; Backes, M.; Balzer, A.; Barnard, M.; Becherini, Y.; Tjus, J. Becker; Berge, D.; Bernhard, S.; Bernlöhr, K.; Blackwell, R.; Böttcher, M.; Boisson, C.; Bolmont, J.; Bordas, P.; Bregeon, J.; Brun, F.; Brun, P.; Bryan, M.; Bulik, T.; Capasso, M.; Casanova, S.; Cerruti, M.; Chakraborty, N.; Chalme-Calvet, R.; Chaves, R. C. G.; Chen, A.; Chevalier, J.; Chrétien, M.; Colafrancesco, S.; Cologna, G.; Condon, B.; Conrad, J.; Cui, Y.; Davids, I. D.; Decock, J.; Degrange, B.; Deil, C.; Devin, J.; Dewilt, P.; Dirson, L.; Djannati-Ataï, A.; Domainko, W.; Donath, A.; Drury, L. O'c.; Dubus, G.; Dutson, K.; Dyks, J.; Edwards, T.; Egberts, K.; Eger, P.; Ernenwein, J.-P.; Eschbach, S.; Farnier, C.; Fegan, S.; Fernandes, M. V.; Fiasson, A.; Fontaine, G.; Förster, A.; Funk, S.; Füßling, M.; Gabici, S.; Gajdus, M.; Gallant, Y. A.; Garrigoux, T.; Giavitto, G.; Giebels, B.; Glicenstein, J. F.; Gottschall, D.; Goyal, A.; Grondin, M.-H.; Hadasch, D.; Hahn, J.; Haupt, M.; Hawkes, J.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hervet, O.; Hinton, J. A.; Hofmann, W.; Hoischen, C.; Holler, M.; Horns, D.; Ivascenko, A.; Jacholkowska, A.; Jamrozy, M.; Janiak, M.; Jankowsky, D.; Jankowsky, F.; Jingo, M.; Jogler, T.; Jouvin, L.; Jung-Richardt, I.; Kastendieck, M. A.; Katarzyński, K.; Kerszberg, D.; Khélifi, B.; Kieffer, M.; King, J.; Klepser, S.; Klochkov, D.; Kluźniak, W.; Kolitzus, D.; Komin, Nu.; Kosack, K.; Krakau, S.; Kraus, M.; Krayzel, F.; Krüger, P. P.; Laffon, H.; Lamanna, G.; Lau, J.; Lees, J.-P.; Lefaucheur, J.; Lefranc, V.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J.-P.; Leser, E.; Lohse, T.; Lorentz, M.; Liu, R.; López-Coto, R.; Lypova, I.; Marandon, V.; Marcowith, A.; Mariaud, C.; Marx, R.; Maurin, G.; Maxted, N.; Mayer, M.; Meintjes, P. J.; Meyer, M.; Mitchell, A. M. W.; Moderski, R.; Mohamed, M.; Mohrmann, L.; Morâ, K.; Moulin, E.; Murach, T.; de Naurois, M.; Niederwanger, F.; Niemiec, J.; Oakes, L.; O'Brien, P.; Odaka, H.; Öttl, S.; Ohm, S.; Ostrowski, M.; Oya, I.; Padovani, M.; Panter, M.; Parsons, R. D.; Pekeur, N. W.; Pelletier, G.; Perennes, C.; Petrucci, P.-O.; Peyaud, B.; Piel, Q.; Pita, S.; Poon, H.; Prokhorov, D.; Prokoph, H.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raab, S.; Reimer, A.; Reimer, O.; Renaud, M.; Reyes, R. De Los; Rieger, F.; Romoli, C.; Rosier-Lees, S.; Rowell, G.; Rudak, B.; Rulten, C. B.; Sahakian, V.; Salek, D.; Sanchez, D. A.; Santangelo, A.; Sasaki, M.; Schlickeiser, R.; Schulz, A.; Schüssler, F.; Schwanke, U.; Schwemmer, S.; Settimo, M.; Seyffert, A. S.; Shafi, N.; Shilon, I.; Simoni, R.; Sol, H.; Spanier, F.; Spengler, G.; Spies, F.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Stinzing, F.; Stycz, K.; Sushch, I.; Tavernet, J.-P.; Tavernier, T.; Taylor, A. M.; Terrier, R.; Tibaldo, L.; Tiziani, D.; Tluczykont, M.; Trichard, C.; Tuffs, R.; Uchiyama, Y.; Walt, D. J. Van Der; van Eldik, C.; van Rensburg, C.; van Soelen, B.; Vasileiadis, G.; Veh, J.; Venter, C.; Viana, A.; Vincent, P.; Vink, J.; Voisin, F.; Völk, H. J.; Vuillaume, T.; Wadiasingh, Z.; Wagner, S. J.; Wagner, P.; Wagner, R. M.; White, R.; Wierzcholska, A.; Willmann, P.; Wörnlein, A.; Wouters, D.; Yang, R.; Zabalza, V.; Zaborov, D.; Zacharias, M.; Zanin, R.; Zdziarski, A. A.; Zech, A.; Zefi, F.; Ziegler, A.; Żywucka, N.

2017-08-01

We report on the discovery of a new fast radio burst (FRB), FRB 150215, with the Parkes radio telescope on 2015 February 15. The burst was detected in real time with a dispersion measure (DM) of 1105.6 ± 0.8 pc cm-3, a pulse duration of 2.8^{+1.2}_{-0.5} ms, and a measured peak flux density assuming that the burst was at beam centre of 0.7^{+0.2}_{-0.1} Jy. The FRB originated at a Galactic longitude and latitude of 24.66°, 5.28° and 25° away from the Galactic Center. The burst was found to be 43 ± 5 per cent linearly polarized with a rotation measure (RM) in the range -9 < RM < 12 rad m-2 (95 per cent confidence level), consistent with zero. The burst was followed up with 11 telescopes to search for radio, optical, X-ray, γ-ray and neutrino emission. Neither transient nor variable emission was found to be associated with the burst and no repeat pulses have been observed in 17.25 h of observing. The sightline to the burst is close to the Galactic plane and the observed physical properties of FRB 150215 demonstrate the existence of sight lines of anomalously low RM for a given electron column density. The Galactic RM foreground may approach a null value due to magnetic field reversals along the line of sight, a decreased total electron column density from the Milky Way, or some combination of these effects. A lower Galactic DM contribution might explain why this burst was detectable whereas previous searches at low latitude have had lower detection rates than those out of the plane.

Diagnostics from three rising submillimeter bursts

International Nuclear Information System (INIS)

Zhou, Ai-Hua; Li, Jian-Ping; Wang, Xin-Dong

2016-01-01

In this paper we investigate three novel rising submillimeter (THz) bursts that occurred sequentially in Super Active Region NOAA 10486. The average rising rate of the flux density above 200 GHz is only 20 sfu GHz −1 (corresponding to spectral index α of 1.6) for the THz spectral components of the 2003 October 28 and November 4 bursts, but it attained values of 235 sfu GHz −1 (α = 4.8) in the 2003 November 2 burst. The steeply rising THz spectrum can be produced by a population of highly relativistic electrons with a low-energy cutoff of 1 MeV, but it only requires a low-energy cutoff of 30 keV for the two slowly rising THz bursts, via gyrosynchrotron (GS) radiation based on our numerical simulations of burst spectra in the magnetic dipole field case. The electron density variation is much larger in the THz source than in the microwave (MW) source. It is interesting that the THz source radius decreased by 20%–50% during the decay phase for the three events, but the MW source increased by 28% for the 2003 November 2 event. In the paper we will present a formula that can be used to calculate the energy released by ultrarelativistic electrons, taking the relativistic correction into account for the first time. We find that the energy released by energetic electrons in the THz source exceeds that in the MW source due to the strong GS radiation loss in the THz range, although the modeled THz source area is 3–4 orders smaller than the modeled MW source one. The total energies released by energetic electrons via the GS radiation in radio sources are estimated, respectively, to be 5.2 × 10 33 , 3.9 × 10 33 and 3.7 × 10 32 erg for the October 28, November 2 and 4 bursts, which are 131, 76 and 4 times as large as the thermal energies of 2.9 × 10 31 , 2.1 × 10 31 and 5.2 × 10 31 erg estimated from soft X-ray GOES observations. (paper)

Fast Radio Burst/Gamma-Ray Burst Cosmography

Science.gov (United States)

Gao, He; Li, Zhuo; Zhang, Bing

2014-06-01

Recently, both theoretical arguments and observational evidence suggested that a small fraction of fast radio bursts (FRBs) could be associated with gamma-ray bursts (GRBs). If such FRB/GRB association systems are commonly detected in the future, the combination of dispersion measures (DM) derived from FRBs and redshifts derived from GRBs makes these systems a plausible tool to conduct cosmography. We quantify uncertainties in deriving the redshift-dependent DM_{IGM} as a function of z and test how well dark energy models can be constrained with Monte Carlo simulations. We show that with several tens of FRB/GRB systems potentially detected in a decade or so, one may reach reasonable constraints on wCDM models. When combined with Type Ia supernova (SN Ia) data, unprecedented constraints on the dark energy equation of state may be achieved, thanks to the prospects of detecting FRB/GRB systems at relatively high redshifts. The ratio between the mean value \\lt {DM_IGM} (z)\\gt and luminosity distance (D L(z)) is insensitive to dark energy models. This gives the prospect of applying SN Ia data to calibrate \\lt {DM_IGM} (z)\\gt using a relatively small sample of FRB/GRB systems, allowing a reliable constraint on the baryon inhomogeneity distribution as a function of redshift. The methodology developed in this paper can also be applied if the FRB redshifts can be measured by other means. Some caveats of putting this method into practice are also discussed.

Fast radio burst/gamma-ray burst cosmography

International Nuclear Information System (INIS)

Gao, He; Zhang, Bing; Li, Zhuo

2014-01-01

Recently, both theoretical arguments and observational evidence suggested that a small fraction of fast radio bursts (FRBs) could be associated with gamma-ray bursts (GRBs). If such FRB/GRB association systems are commonly detected in the future, the combination of dispersion measures (DM) derived from FRBs and redshifts derived from GRBs makes these systems a plausible tool to conduct cosmography. We quantify uncertainties in deriving the redshift-dependent DM IGM as a function of z and test how well dark energy models can be constrained with Monte Carlo simulations. We show that with several tens of FRB/GRB systems potentially detected in a decade or so, one may reach reasonable constraints on wCDM models. When combined with Type Ia supernova (SN Ia) data, unprecedented constraints on the dark energy equation of state may be achieved, thanks to the prospects of detecting FRB/GRB systems at relatively high redshifts. The ratio between the mean value and luminosity distance (D L (z)) is insensitive to dark energy models. This gives the prospect of applying SN Ia data to calibrate using a relatively small sample of FRB/GRB systems, allowing a reliable constraint on the baryon inhomogeneity distribution as a function of redshift. The methodology developed in this paper can also be applied if the FRB redshifts can be measured by other means. Some caveats of putting this method into practice are also discussed.

Fast radio burst/gamma-ray burst cosmography

Energy Technology Data Exchange (ETDEWEB)

Gao, He; Zhang, Bing [Department of Physics and Astronomy, University of Nevada Las Vegas, NV 89154 (United States); Li, Zhuo, E-mail: gaohe@physics.unlv.edu, E-mail: zhang@physics.unlv.edu, E-mail: zhuo.li@pku.edu.cn [Department of Astronomy, School of Physics, Peking University, Beijing 100871 (China)

2014-06-20

Recently, both theoretical arguments and observational evidence suggested that a small fraction of fast radio bursts (FRBs) could be associated with gamma-ray bursts (GRBs). If such FRB/GRB association systems are commonly detected in the future, the combination of dispersion measures (DM) derived from FRBs and redshifts derived from GRBs makes these systems a plausible tool to conduct cosmography. We quantify uncertainties in deriving the redshift-dependent DM{sub IGM} as a function of z and test how well dark energy models can be constrained with Monte Carlo simulations. We show that with several tens of FRB/GRB systems potentially detected in a decade or so, one may reach reasonable constraints on wCDM models. When combined with Type Ia supernova (SN Ia) data, unprecedented constraints on the dark energy equation of state may be achieved, thanks to the prospects of detecting FRB/GRB systems at relatively high redshifts. The ratio between the mean value and luminosity distance (D {sub L}(z)) is insensitive to dark energy models. This gives the prospect of applying SN Ia data to calibrate using a relatively small sample of FRB/GRB systems, allowing a reliable constraint on the baryon inhomogeneity distribution as a function of redshift. The methodology developed in this paper can also be applied if the FRB redshifts can be measured by other means. Some caveats of putting this method into practice are also discussed.

Detection of pseudo gamma-ray bursts of long duration

International Nuclear Information System (INIS)

Frontera, F.; Fuligni, F.; Morelli, E.; Pizzichini, G.; Ventura, G.

1981-01-01

It is known that the counting rate of both Na I and Cs I hard X-ray detectors can have intense enhancements of brief (< 1 s) duration, which appear like very short cosmic gamma-ray bursts but probably are due to phosphorescence in the detector itself. Unfortunately, this problem is not limited to short bursts. We present here three much longer (up to 80 s) pseudo-gamma-ray bursts observed during a transatlantic balloon flight. We conclude that detections of gamma-ray bursts (and probably also of hard X-ray source flares) based only on a rate increase by a single scintillator should always be confirmed by at least one other instrument. (orig.)

A Fast Radio Burst Host Galaxy

OpenAIRE

Keane, E. F.; Johnston, S.; Bhandari, S.; Barr, E.; Bhat, N. D. R.; Burgay, M.; Caleb, M.; Flynn, C.; Jameson, A.; Kramer, M.; Petroff, E.; Possenti, A.; van Straten, W.; Bailes, M.; Burke-Spolaor, S.

2016-01-01

In recent years, millisecond duration radio signals originating from distant galaxies appear to have been discovered in the so-called Fast Radio Bursts. These signals are dispersed according to a precise physical law and this dispersion is a key observable quantity which, in tandem with a redshift measurement, can be used for fundamental physical investigations. While every fast radio burst has a dispersion measurement, none before now have had a redshift measurement, due to the difficulty in...

COSMOLOGICAL IMPLICATIONS OF FAST RADIO BURST/GAMMA-RAY BURST ASSOCIATIONS

Energy Technology Data Exchange (ETDEWEB)

Deng, Wei; Zhang, Bing, E-mail: deng@physics.unlv.edu, E-mail: zhang@physics.unlv.edu [Department of Physics and Astronomy, University of Nevada Las Vegas, Las Vegas, NV 89154 (United States)

2014-03-10

If a small fraction of fast radio bursts (FRBs) are associated with gamma-ray bursts (GRBs), as recently suggested by Zhang, the combination of redshift measurements of GRBs and dispersion measure (DM) measurements of FRBs opens a new window to study cosmology. At z < 2 where the universe is essentially fully ionized, detections of FRB/GRB pairs can give an independent measurement of the intergalactic medium portion of the baryon mass fraction, Ω {sub b} f {sub IGM}, of the universe. If a good sample of FRB/GRB associations are discovered at higher redshifts, the free electron column density history can be mapped, which can be used to probe the reionization history of both hydrogen and helium in the universe. We apply our formulation to GRBs 101011A and 100704A that each might have an associated FRB, and constrained Ω {sub b} f {sub IGM} to be consistent with the value derived from other methods. The methodology developed here is also applicable, if the redshifts of FRBs not associated with GRBs can be measured by other means.

COSMOLOGICAL IMPLICATIONS OF FAST RADIO BURST/GAMMA-RAY BURST ASSOCIATIONS

International Nuclear Information System (INIS)

Deng, Wei; Zhang, Bing

2014-01-01

If a small fraction of fast radio bursts (FRBs) are associated with gamma-ray bursts (GRBs), as recently suggested by Zhang, the combination of redshift measurements of GRBs and dispersion measure (DM) measurements of FRBs opens a new window to study cosmology. At z < 2 where the universe is essentially fully ionized, detections of FRB/GRB pairs can give an independent measurement of the intergalactic medium portion of the baryon mass fraction, Ω b f IGM , of the universe. If a good sample of FRB/GRB associations are discovered at higher redshifts, the free electron column density history can be mapped, which can be used to probe the reionization history of both hydrogen and helium in the universe. We apply our formulation to GRBs 101011A and 100704A that each might have an associated FRB, and constrained Ω b f IGM to be consistent with the value derived from other methods. The methodology developed here is also applicable, if the redshifts of FRBs not associated with GRBs can be measured by other means

Frequency Chirping during a Fishbone Burst

Energy Technology Data Exchange (ETDEWEB)

Marchenko, V.; Reznik, S., E-mail: march@kinr.kiev.ua [Institute for Nuclear Research, Kyiv (Ukraine)

2012-09-15

Full text: It is shown that gradual (more than a factor of two, in some cases - down to zero in the lab frame) reduction of the mode frequency (the so called frequency chirping) can be attributed to the reactive torque exerted on the plasma during the fishbone instability burst, which slows down the plasma rotation inside the q = 1 surface and reduces the mode frequency in the lab frame, while frequency in the plasma frame remains constant. This torque arises due to imbalance between the power transfered to the mode by energeric ions and the power of the mode dissipation by thermal species. Estimates show that the peak value of this torque exceeds the neutral beam torque in modern tokamaks and in ITER. The line-broadened quasilinear burst model, properly adapted for the fishbone case, is capable of reproducing the key features of the bursting mode. (author)

Gamma-Ray Bursts: A Radio Perspective

Directory of Open Access Journals (Sweden)

Poonam Chandra

2016-01-01

Full Text Available Gamma-ray bursts (GRBs are extremely energetic events at cosmological distances. They provide unique laboratory to investigate fundamental physical processes under extreme conditions. Due to extreme luminosities, GRBs are detectable at very high redshifts and potential tracers of cosmic star formation rate at early epoch. While the launch of Swift and Fermi has increased our understanding of GRBs tremendously, many new questions have opened up. Radio observations of GRBs uniquely probe the energetics and environments of the explosion. However, currently only 30% of the bursts are detected in radio bands. Radio observations with upcoming sensitive telescopes will potentially increase the sample size significantly and allow one to follow the individual bursts for a much longer duration and be able to answer some of the important issues related to true calorimetry, reverse shock emission, and environments around the massive stars exploding as GRBs in the early Universe.

Imaging assessment of vertebral burst fracture

International Nuclear Information System (INIS)

Ding Jianlin; Liang Lihua; Wang Yujia

2006-01-01

Objective: To investigate the diagnostic value of radiography, CT and MRI in diagnosis of vertebral burst fracture. Methods: 51 patients with vertebral burst fracture were evaluated with X-ray, CT and MRI, including 3 cases in cervical vertebra, 18 cases in thoracic vertebra, and 30 cases in lumbar vertebra. The imaging features were comparatively studied. Results: Radiography showed decreased height of the vertebral body, increased antero-posterior diameter and the transverse diameter, and/or the widened interpedicle distance, the inter-spinous distance, as well as the bony fragment inserted into the vertebral canal in 28 cases(54.90%). X-ray findings similar to the compression fracture were revealed in 20 cases(39.21%). And missed diagnosis was made in 3 cases (5.88%). CT clearly demon-strated the vertebral body vertically or transversely burst crack in 49 cases (96.07%); bony fragment inserted into the vertebral canal and narrowed vertebral canal in 35 cases(68. 62% ); fracture of spinal appendix in 22 cases(43.14%). Meanwhile MRI showed abnormal signals within the spinal cord in 35 cases (68.62%),injured intervertebral disk in 29 cases(56.86% ), extradural hematoma in 12 cases(23.52% ) and torn posterior longitudinal ligament in 6 cases (11.76%). Conclusions: Radiography is the routine examination, while with limited diagnostic value in vertebral burst fracture. These patients who have nervous symptoms with simple compression fracture or unremarkable on X-ray should receive the CT or MRI examination. CT is better than MRI in demonstrating the fracture and the displaced bony fragment, while MRI is superior to CT in showing nervous injuries. CT and MRI will provide comprehensive information guiding clinical treatment of vertebral burst fracture. (authors)

Bursting of a bubble confined in between two plates

Science.gov (United States)

Murano, Mayuko; Kimono, Natsuki; Okumura, Ko

2015-11-01

Rupture of liquid thin films, driven by surface tension, has attracted interests of scientists for many years. It is also a daily phenomenon familiar to everyone in the form of the bursting of soap films. In recent years, many studies in confined geometries (e.g. in a Hele-Shaw cell) have revealed physical mechanisms of the dynamics of bubbles and drops. As for a liquid film sandwiched in between another liquid immiscible to the film liquid in the Hele-Shaw cell, it is reported that the thin film bursts at a constant speed and the speed depends on the viscosity of the surrounding liquid when the film is less viscous, although a rim is not formed at the bursting tip; this is because the circular symmetry of the hole in the bursting film is lost. Here, we study the bursting speed of a thin film sandwiched between air instead of the surrounding liquid in the Hele-Shaw cell to seek different scaling regimes. By measuring the bursting velocity and the film thickness of an air bubble with a high speed camera, we have found a new scaling law in viscous regime. This research was partly supported by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan).

A POSSIBLE CONNECTION BETWEEN FAST RADIO BURSTS AND GAMMA-RAY BURSTS

International Nuclear Information System (INIS)

Zhang, Bing

2014-01-01

The physical nature of fast radio bursts (FRBs), a new type of cosmological transient discovered recently, is not known. It has been suggested that FRBs can be produced when a spinning supra-massive neutron star loses centrifugal support and collapses to a black hole. Here, we suggest that such implosions can happen in supra-massive neutron stars shortly (hundreds to thousands of seconds) after their births, and an observational signature of such implosions may have been observed in the X-ray afterglows of some long and short gamma-ray bursts (GRBs). Within this picture, a small fraction of FRBs would be physically connected to GRBs. We discuss possible multi-wavelength electromagnetic signals and gravitational wave signals that might be associated with FRBs, and propose an observational campaign to unveil the physical nature of FRBs. In particular, we strongly encourage a rapid radio follow-up observation of GRBs starting from 100 s after a GRB trigger

DEPENDENCE OF X-RAY BURST MODELS ON NUCLEAR REACTION RATES

Energy Technology Data Exchange (ETDEWEB)

Cyburt, R. H.; Keek, L.; Schatz, H. [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824 (United States); Amthor, A. M. [Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837 (United States); Heger, A.; Meisel, Z.; Smith, K. [Joint Institute for Nuclear Astrophysics (JINA), Michigan State University, East Lansing, MI 48824 (United States); Johnson, E. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)

2016-10-20

X-ray bursts are thermonuclear flashes on the surface of accreting neutron stars, and reliable burst models are needed to interpret observations in terms of properties of the neutron star and the binary system. We investigate the dependence of X-ray burst models on uncertainties in (p, γ ), ( α , γ ), and ( α , p) nuclear reaction rates using fully self-consistent burst models that account for the feedbacks between changes in nuclear energy generation and changes in astrophysical conditions. A two-step approach first identified sensitive nuclear reaction rates in a single-zone model with ignition conditions chosen to match calculations with a state-of-the-art 1D multi-zone model based on the Kepler stellar evolution code. All relevant reaction rates on neutron-deficient isotopes up to mass 106 were individually varied by a factor of 100 up and down. Calculations of the 84 changes in reaction rate with the highest impact were then repeated in the 1D multi-zone model. We find a number of uncertain reaction rates that affect predictions of light curves and burst ashes significantly. The results provide insights into the nuclear processes that shape observables from X-ray bursts, and guidance for future nuclear physics work to reduce nuclear uncertainties in X-ray burst models.

Postillumination burst of carbon dioxide in crassalacean Acid metabolism plants.

Science.gov (United States)

Crews, C E; Vines, H M; Black, C C

1975-04-01

Immediately following exposure to light, a postillumination burst of CO(2) has been detected in Crassulacean acid metabolism plants. A detailed study with pineapple (Ananas comosus) leaves indicates that the postillumination burst changes its amplitude and kinetics during the course of a day. In air, the postillumination burst in pineapple leaves generally is exhibited as two peaks. The postillumination burst is sensitive to atmospheric CO(2) and O(2) concentrations as well as to the light intensity under which plants are grown. We propose that the CO(2) released in the first postillumination burst peak is indicative of photorespiration since it is sensitive to either O(2) or CO(2) concentration while the second CO(2) evolution peak is likely due to decarboxylation of organic acids involved in Crassulacean acid metabolism.In marked contrast to other higher plants, the postillumination burst in Crassulacean acid metabolism plants can be equal to or greater than the rate of photosynthesis. Photosynthesis in pineapple leaves also varies throughout a day. Both photosynthesis and the postillumination burst have a daily variation which apparently is a complex function of degree of leaf acidity, growth light intensity, ambient gas phase, and the time a plant has been exposed to a given gas.

Amplitude damping for single-qubit system with single-qubit mixed-state environment

International Nuclear Information System (INIS)

Jung, Eylee; Hwang, Mi-Ra; Ju, You Hwan; Park, D K; Kim, Hungsoo; Kim, Min-Soo; Son, Jin-Woo

2008-01-01

We study a generalized amplitude damping channel when environment is initially in the single-qubit mixed state. Representing the affine transformation of the generalized amplitude damping by a three-dimensional volume, we plot explicitly the volume occupied by the channels simulatable by a single-qubit mixed-state environment. As expected, this volume is embedded in the total volume by the channels which is simulated by a two-qubit enviroment. The volume ratio is approximately 0.08 which is much smaller than 3/8, the volume ratio for generalized depolarizing channels

Burst mode trigger of STEREO in situ measurements

Science.gov (United States)

Jian, L. K.; Russell, C. T.; Luhmann, J. G.; Curtis, D.; Schroeder, P.

2013-06-01

Since the launch of the STEREO spacecraft, the in situ instrument suites have continued to modify their burst mode trigger in order to optimize the collection of high-cadence magnetic field, solar wind, and suprathermal electron data. This report reviews the criteria used for the burst mode trigger and their evolution with time. From 2007 to 2011, the twin STEREO spacecraft observed 236 interplanetary shocks, and 54% of them were captured by the burst mode trigger. The capture rate increased remarkably with time, from 30% in 2007 to 69% in 2011. We evaluate the performance of multiple trigger criteria and investigate why some of the shocks were missed by the trigger. Lessons learned from STEREO are useful for future missions, because the telemetry bandwidth needed to capture the waveforms of high frequency but infrequent events would be unaffordable without an effective burst mode trigger.

Empirical Constraints on the Origin of Fast Radio Bursts: Volumetric Rates and Host Galaxy Demographics as a Test of Millisecond Magnetar Connection

Science.gov (United States)

Nicholl, M.; Williams, P. K. G.; Berger, E.; Villar, V. A.; Alexander, K. D.; Eftekhari, T.; Metzger, B. D.

2017-07-01

The localization of the repeating fast radio burst (FRB) 121102 to a low-metallicity dwarf galaxy at z = 0.193, and its association with a luminous quiescent radio source, suggests the possibility that FRBs originate from magnetars, formed by the unusual supernovae that occur in such galaxies. We investigate this possibility via a comparison of magnetar birth rates, the FRB volumetric rate, and host galaxy demographics. We calculate average volumetric rates of possible millisecond magnetar production channels, such as superluminous supernovae (SLSNe), long and short gamma-ray bursts (GRBs), and general magnetar production via core-collapse supernovae (CCSNe). For each channel, we also explore the expected host galaxy demographics using their known properties. We determine for the first time the number density of FRB emitters (the product of their volumetric birth rate and lifetime), {R}{FRB}τ ≈ {10}4 Gpc-3, assuming that FRBs are predominantly emitted from repetitive sources similar to FRB 121102 and adopting a beaming factor of 0.1. By comparing rates, we find that production via rare channels (SLSNe, GRBs) implies a typical FRB lifetime of ˜30-300 years, in good agreement with other lines of argument. The total energy emitted over this time is consistent with the available energy stored in the magnetic field. On the other hand, any relation to magnetars produced via normal CCSNe leads to a very short lifetime of ˜0.5 years, in conflict with both theory and observation. We demonstrate that due to the diverse host galaxy distributions of the different progenitor channels, many possible sources of FRB birth can be ruled out with ≲ 10 host galaxy identifications. Conversely, targeted searches of galaxies that have previously hosted decades-old SLSNe and GRBs may be a fruitful strategy for discovering new FRBs and related quiescent radio sources, and determining the nature of their progenitors.

Multi-Index Monitoring and Evaluation on Rock Burst in Yangcheng Mine

OpenAIRE

Tan, Yunliang; Yin, Yanchun; Gu, Shitan; Tian, Zhiwei

2015-01-01

Based on the foreboding information monitoring of the energy released in the developing process of rock burst, prediction system for rock burst can be established. By using microseismic method, electromagnetic radiation method, and drilling bits method, rock burst in Yangcheng Mine was monitored, and a system of multi-index monitoring and evaluation on rock burst was established. Microseismic monitoring and electromagnetic radiation monitoring were early warning method, and drilling bits moni...

An origin for short gamma-ray bursts unassociated with current star formation.

Science.gov (United States)

Barthelmy, S D; Chincarini, G; Burrows, D N; Gehrels, N; Covino, S; Moretti, A; Romano, P; O'Brien, P T; Sarazin, C L; Kouveliotou, C; Goad, M; Vaughan, S; Tagliaferri, G; Zhang, B; Antonelli, L A; Campana, S; Cummings, J R; D'Avanzo, P; Davies, M B; Giommi, P; Grupe, D; Kaneko, Y; Kennea, J A; King, A; Kobayashi, S; Melandri, A; Meszaros, P; Nousek, J A; Patel, S; Sakamoto, T; Wijers, R A M J

2005-12-15

Two short (gamma-ray bursts (GRBs) have recently been localized and fading afterglow counterparts detected. The combination of these two results left unclear the nature of the host galaxies of the bursts, because one was a star-forming dwarf, while the other was probably an elliptical galaxy. Here we report the X-ray localization of a short burst (GRB 050724) with unusual gamma-ray and X-ray properties. The X-ray afterglow lies off the centre of an elliptical galaxy at a redshift of z = 0.258 (ref. 5), coincident with the position determined by ground-based optical and radio observations. The low level of star formation typical for elliptical galaxies makes it unlikely that the burst originated in a supernova explosion. A supernova origin was also ruled out for GRB 050709 (refs 3, 31), even though that burst took place in a galaxy with current star formation. The isotropic energy for the short bursts is 2-3 orders of magnitude lower than that for the long bursts. Our results therefore suggest that an alternative source of bursts--the coalescence of binary systems of neutron stars or a neutron star-black hole pair--are the progenitors of short bursts.

Soudan 2 muons in coincidence with BATSE bursts

International Nuclear Information System (INIS)

DeMuth, D.M.; Marshak, M.L.; Wagner, G.L.

1994-01-01

We explore the possibilities of statistically significant temporal and spatial coincidences between underground muons at Soudan 2 and Gamma Ray Bursts at the GRO-BATSE detector. Our search uses data from the April 91 to March 92 BATSE burst catalog to seek correlations within a 100 second window of coincidence. Sixteen of 180 BATSE triggers have temporally and spatially coincident muons in the Soudan 2 detector. We estimate the chance probability of each coincidence assuming the null hypothesis on the basis of a study of the multiplicities of spatially coincident muons observed over a two day period centered on the time of burst

Bursting Smoke as an Infrared Countermeasure

OpenAIRE

Amarjit Singh; P. J. Kamale; S. A. Joshi; L. K. Bankar

1998-01-01

This paper describes the experimental setup for the evaluation of bursting smoke for anti-infrared role using SR-5000 spectroradiometer and a source of IR radiation (8-13 micrometer) using cadmium-mercury-telluride (CMI) detector cooled by liquid nitrogen. The particle size and shape of the powders used in the bursting smokes were determined microscopically using Carl Zeiss Jena Neophot- 21. Highest attenuation of 97 -lOO percent was produced for about 12 s using a mixture of bronze fl...

Nature of gamma-ray burst sources

International Nuclear Information System (INIS)

Ventura, J.

1983-01-01

Observational evidence suggests that gamma ray bursts have a local galactic origin involving neutron stars. In this light we make a critical review of physics of the thermonuclear runaway model placing emphasis on self-consistency. We further show that some of the proposed models can be observationally excluded in the light of existing data from the Einstein Observatory. The possibility of gamma bursts arising in low mass binaries is finally discussed in the light of evolutionary scenarios leading to low luminosity systems

Bursting oscillations, bifurcation and synchronization in neuronal systems

Energy Technology Data Exchange (ETDEWEB)

Wang Haixia [School of Science, Nanjing University of Science and Technology, Nanjing 210094 (China); Wang Qingyun, E-mail: drwangqy@gmail.com [Department of Dynamics and Control, Beihang University, Beijing 100191 (China); Lu Qishao [Department of Dynamics and Control, Beihang University, Beijing 100191 (China)

2011-08-15

Highlights: > We investigate bursting oscillations and related bifurcation in the modified Morris-Lecar neuron. > Two types of fast-slow bursters are analyzed in detail. > We show the properties of some crucial bifurcation points. > Synchronization transition and the neural excitability are explored in the coupled bursters. - Abstract: This paper investigates bursting oscillations and related bifurcation in the modified Morris-Lecar neuron. It is shown that for some appropriate parameters, the modified Morris-Lecar neuron can exhibit two types of fast-slow bursters, that is 'circle/fold cycle' bursting and 'subHopf/homoclinic' bursting with class 1 and class 2 neural excitability, which have different neuro-computational properties. By means of the analysis of fast-slow dynamics and phase plane, we explore bifurcation mechanisms associated with the two types of bursters. Furthermore, the properties of some crucial bifurcation points, which can determine the type of the burster, are studied by the stability and bifurcation theory. In addition, we investigate the influence of the coupling strength on synchronization transition and the neural excitability in two electrically coupled bursters with the same bursting type. More interestingly, the multi-time-scale synchronization transition phenomenon is found as the coupling strength varies.

Spikes matter for phase-locked bursting in inhibitory neurons

Science.gov (United States)

Jalil, Sajiya; Belykh, Igor; Shilnikov, Andrey

2012-03-01

We show that inhibitory networks composed of two endogenously bursting neurons can robustly display several coexistent phase-locked states in addition to stable antiphase and in-phase bursting. This work complements and enhances our recent result [Jalil, Belykh, and Shilnikov, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.81.045201 81, 045201(R) (2010)] that fast reciprocal inhibition can synchronize bursting neurons due to spike interactions. We reveal the role of spikes in generating multiple phase-locked states and demonstrate that this multistability is generic by analyzing diverse models of bursting networks with various fast inhibitory synapses; the individual cell models include the reduced leech heart interneuron, the Sherman model for pancreatic beta cells, and the Purkinje neuron model.

Polarimetry of the Fast Radio Burst Source FRB121102

Science.gov (United States)

Michilli, Daniele; Seymour, Andrew; Hessels, Jason W. T.; Spitler, Laura; Gajjar, Vishal; Archibald, Anne; Bower, Geoffrey C.; Chatterjee, Shami; Cordes, Jim; Gourdji, Kelly; Heald, George; Kaspi, Victoria; Law, Casey; Sobey, Charlotte

2018-01-01

Fast radio bursts (FRBs) are millisecond-duration radio flashes of presumably extragalactic origin. FRB121102 is the only FRB known to repeat and the only one with a precise localization. It is co-located with a persistent radio source inside a star-forming region in a dwarf galaxy at z=0.2. While the persistent source is compatible with either a low-luminosity accreting black hole or a very energetic nebula and supernova remnant, the source of the bursts is still a mystery. We present new bursts from FRB121102 detected at relatively high radio frequencies of ~5GHz. These observations allow us to investigate the polarization properties of the bursts, placing new constraints on the environment of FRB121102.

Recent results from the gamma-ray burst studies in the KONUS experiment

International Nuclear Information System (INIS)

Mazets, E.P.; Golenetskii, S.V.

1981-01-01

Observations of 85 gamma bursts by the KONUS instruments on the Venera 11 and Venera 12 spacecraft in the period September 1978 to May 1979 inclusive have provided proof of a galactic localization of the gamma-burst sources based on an analysis of the log N-log S plot and the revealed anisotropy in the angular distribution of sources over the celestial sphere. Evaluation of the energy released in the sources yields 10 40 -10 41 erg. There apparently exist several types of gamma bursts differing in time profile, duration and shape of their energy spectrum. In some cases, extensive evolution of the energy spectrum is observed during a burst. The discovery of a flaring X-ray pulsar in Dorado has provided the first observational evidence for a connection of gamma bursts with neutron stars. Repeated short bursts from this source have revealed for the first time the recurrent features of this phenomenon. Repeated bursts have been detected from one more source in the short burst class. The data obtained thus far impose a number of restrictions on the applicability of many theoretical suggestions concerning the nature of the gamma bursts. The most plausible model for the gamma-burst source appears to be a binary with a neutron star with strongly non-stationary accretion involving, possibly, non-stationary thermonuclear fusion of matter falling onto the surface of a degenerate star. (orig.)

FAST TCP over optical burst switched networks: Modeling and stability analysis

KAUST Repository

Shihada, Basem; El-Ferik, Sami; Ho, Pin-Han

2013-01-01

congestion-control mechanism in bufferless Optical Burst Switched Networks (OBS). The paper first shows that random burst contentions are essential to stabilize the network, but cause throughput degradation in FAST TCP flows when a burst with all the packets

Very high-energy gamma rays from gamma-ray bursts.

Science.gov (United States)

Chadwick, Paula M

2007-05-15

Very high-energy (VHE) gamma-ray astronomy has undergone a transformation in the last few years, with telescopes of unprecedented sensitivity having greatly expanded the source catalogue. Such progress makes the detection of a gamma-ray burst at the highest energies much more likely than previously. This paper describes the facilities currently operating and their chances for detecting gamma-ray bursts, and reviews predictions for VHE gamma-ray emission from gamma-ray bursts. Results to date are summarized.

FPGA Implementation of Burst-Mode Synchronization for SOQSPK-TG

Science.gov (United States)

2014-06-01

is normalized to π. The proposed burst-mode architecture is written in VHDL and verified using Modelsim. The VHDL design is implemented on a Xilinx...Document Number: SET 2014-0043 412TW-PA-14298 FPGA Implementation of Burst-Mode Synchronization for SOQSPK-TG June 2014 Final Report Test...To) 9/11 -- 8/14 4. TITLE AND SUBTITLE FPGA Implementation of Burst-Mode Synchronization for SOQSPK-TG 5a. CONTRACT NUMBER: W900KK-11-C-0032 5b

High sensitivity neutron bursts detecting system

International Nuclear Information System (INIS)

Shyam, A.; Kaushik, T.C.; Srinivasan, M.; Kulkarni, L.V.

1993-01-01

Technique and instrumentation to detect multiplicity of fast neutrons, emitted in sharp bursts, has been developed. A bank of 16 BF 3 detectors, in an appropriate thermalising assembly, efficiency ∼ 16%, is used to detect neutron bursts. The output from this setup, through appropriate electronics, is divided into two paths. The first is directly connected to a computer controlled scalar. The second is connected to another similar scalar through a delay time unit (DTU). The DTU design is such that once it is triggered by a count pulse than it does not allow any counts to be recorded for a fixed dead time set at ∼ 100 μs. The difference in counts recorded directly and through DTU gives the total number of neutrons produced in bursts. This setup is being used to study lattice cracking, anomalous effects in solid deuterium systems and various reactor physics experiments. (author). 3 refs., 1 fig

A New Clue in the Mystery of Fast Radio Bursts

Science.gov (United States)

Kohler, Susanna

2017-06-01

The origin of the mysterious fast radio bursts has eluded us for more than a decade. With the help of a particularly cooperative burst, however, scientists may finally be homing in on the answer to this puzzle.A Burst RepeatsThe host of FRB 121102 is placed in context in this Gemini image. [Gemini Observatory/AURA/NSF/NRC]More than 20 fast radio bursts rare and highly energetic millisecond-duration radio pulses have been observed since the first was discovered in 2007. FRB 121102, however, is unique in its behavior: its the only one of these bursts to repeat. The many flashes observed from FRB 121102 allowed us for the first time to follow up on the burst and hunt for its location.Earlier this year, this work led to the announcement that FRB 121102s host galaxy has been identified: a dwarf galaxy located at a redshift of z = 0.193 (roughly 3 billion light-years away). Now a team of scientists led by Cees Bassa (ASTRON, the Netherlands Institute for Radio Astronomy) has performed additional follow-up to learn more about this host and what might be causing the mysterious flashes.Hubble observation of the host galaxy. The object at the bottom right is a reference star. The blue ellipse marks the extended diffuse emission of the galaxy, the red circle marks the centroid of the star-forming knot, and the white cross denotes the location of FRB 121102 ad the associated persistent radio source. [Adapted from Bassa et al. 2017]Host ObservationsBassa and collaborators used the Hubble Space Telescope, the Spitzer Space Telecsope, and the Gemini North telecsope in Hawaii to obtain optical, near-infrared, and mid-infrared observations of FRB 121102s host galaxy.The authors determined that the galaxy is a dim, irregular, low-metallicity dwarf galaxy. Its resolved, revealing a bright star-forming region roughly 4,000 light-years across in the galaxys outskirts. Intriguingly, the persistent radio source associated with FRB 121102 falls directly within that star-forming knot

Plane waves and structures in turbulent channel flow

Science.gov (United States)

Sirovich, L.; Ball, K. S.; Keefe, L. R.

1990-01-01

A direct simulation of turbulent flow in a channel is analyzed by the method of empirical eigenfunctions (Karhunen-Loeve procedure, proper orthogonal decomposition). This analysis reveals the presence of propagating plane waves in the turbulent flow. The velocity of propagation is determined by the flow velocity at the location of maximal Reynolds stress. The analysis further suggests that the interaction of these waves appears to be essential to the local production of turbulence via bursting or sweeping events in the turbulent boundary layer, with the additional suggestion that the fast acting plane waves act as triggers.

Quasi-periodic Radio Bursts Associated with Fast-mode Waves near a Magnetic Null Point

Energy Technology Data Exchange (ETDEWEB)

Kumar, Pankaj [Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Nakariakov, Valery M. [Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, CV4 7AL (United Kingdom); Cho, Kyung-Suk, E-mail: pankaj.kumar@nasa.gov [Korea Astronomy and Space Science Institute (KASI), Daejeon, 305-348 (Korea, Republic of)

2017-08-01

This paper presents an observation of quasi-periodic rapidly propagating waves observed in the Atmospheric Image Assembly (AIA) 171/193 Å channels during the impulsive phase of an M1.9 flare that occurred on 2012 May 7. The instant period was found to decrease from 240 to 120 s, and the speed of the wavefronts was in the range of ∼664–1416 km s{sup −1}. Almost simultaneously, quasi-periodic bursts with similar instant periods, ∼70 and ∼140 s, occur in the microwave emission and in decimetric type IV and type III radio bursts, and in the soft X-ray emission. The magnetic field configuration of the flare site was consistent with a breakout topology, i.e., a quadrupolar field along with a magnetic null point. The quasi-periodic rapidly propagating wavefronts of the EUV emission are interpreted as a fast magnetoacoustic wave train. The observations suggest that the fast-mode waves are generated during the quasi-periodic magnetic reconnection in the cusp region above the flare arcade loops. For the first time, we provide evidence of a tadpole wavelet signature at about 70–140 s in decimetric (245/610 MHz) radio bursts, along with the direct observation of a coronal fast-mode wave train in EUV. In addition, at AIA 131/193 Å we observed quasi-periodic EUV disturbances with periods of 95 and 240 s propagating downward at apparent speeds of 172–273 km s{sup −1}. The nature of these downward propagating disturbances is not revealed, but they could be connected to magnetoacoustic waves or periodically shrinking loops.

Quasi-periodic Radio Bursts Associated with Fast-mode Waves near a Magnetic Null Point

International Nuclear Information System (INIS)

Kumar, Pankaj; Nakariakov, Valery M.; Cho, Kyung-Suk

2017-01-01

This paper presents an observation of quasi-periodic rapidly propagating waves observed in the Atmospheric Image Assembly (AIA) 171/193 Å channels during the impulsive phase of an M1.9 flare that occurred on 2012 May 7. The instant period was found to decrease from 240 to 120 s, and the speed of the wavefronts was in the range of ∼664–1416 km s −1 . Almost simultaneously, quasi-periodic bursts with similar instant periods, ∼70 and ∼140 s, occur in the microwave emission and in decimetric type IV and type III radio bursts, and in the soft X-ray emission. The magnetic field configuration of the flare site was consistent with a breakout topology, i.e., a quadrupolar field along with a magnetic null point. The quasi-periodic rapidly propagating wavefronts of the EUV emission are interpreted as a fast magnetoacoustic wave train. The observations suggest that the fast-mode waves are generated during the quasi-periodic magnetic reconnection in the cusp region above the flare arcade loops. For the first time, we provide evidence of a tadpole wavelet signature at about 70–140 s in decimetric (245/610 MHz) radio bursts, along with the direct observation of a coronal fast-mode wave train in EUV. In addition, at AIA 131/193 Å we observed quasi-periodic EUV disturbances with periods of 95 and 240 s propagating downward at apparent speeds of 172–273 km s −1 . The nature of these downward propagating disturbances is not revealed, but they could be connected to magnetoacoustic waves or periodically shrinking loops.

Study on Monitoring Rock Burst through Drill Pipe Torque

Directory of Open Access Journals (Sweden)

Zhonghua Li

2015-01-01

Full Text Available This paper presents a new method to identify the danger of rock burst from the response of drill pipe torque during drilling process to overcome many defects of the conventional volume of drilled coal rubble method. It is based on the relationship of rock burst with coal stress and coal strength. Through theoretic analysis, the change mechanism of drill pipe torque and the relationship of drill pipe torque with coal stress, coal strength, and drilling speed are investigated. In light of the analysis, a new device for testing drill pipe torque is developed and a series of experiments is performed under different conditions; the results show that drill pipe torque linearly increases with the increase of coal stress and coal strength; the faster the drilling speed, the larger the drill pipe torque, and vice versa. When monitoring rock burst by drill pipe torque method, the index of rock burst is regarded as a function in which coal stress index and coal strength index are principal variables. The results are important for the forecast of rock burst in coal mine.

Analysis of Burst Observations by GLAST's LAT Detector

International Nuclear Information System (INIS)

Band, David L.; Digel, Seth W.

2004-01-01

Analyzing data from GLAST's Large Area Telescope (LAT) will require sophisticated techniques. The PSF and effective area are functions of both photon energy and the position in the field-of-view. During most of the mission the observatory will survey the sky continuously, and thus, the LAT will detect each count from a source at a different detector orientation; each count requires its own response function! The likelihood as a function of celestial position and photon energy will be the foundation of the standard analysis techniques. However, the 20 MeV-300 GeV emission at the time of the ∼ 100 keV burst emission (timescale of ∼ 10 s) can be isolated and analyzed because essentially no non-burst counts are expected within a PSF radius of the burst location during the burst. Both binned and unbinned (in energy) spectral fitting will be possible. Longer timescale afterglow emission will require the likelihood analysis that will be used for persistent sources

Analyses of resource reservation schemes for optical burst switching networks

Science.gov (United States)

Solanska, Michaela; Scholtz, Lubomir; Ladanyi, Libor; Mullerova, Jarmila

2017-12-01

With growing demands of Internet Protocol services for transmission capacity and speed, the Optical Burst Switching presents the solution for future high-speed optical networks. Optical Burst Switching is a technology for transmitting large amounts of data bursts through a transparent optical switching network. To successfully transmit bursts over OBS network and reach the destination node, resource reservation schemes have to be implemented to allocate resources and configure optical switches for that burst at each node. The one-way resource reservation schemes and the performance evaluation of reservation schemes are presented. The OBS network model is performed using OMNeT++ simulation environment. During the reservation of network resources, the optical cross-connect based on semiconductor optical amplifier is used as the core node. Optical switches based on semiconductor optical amplifiers are a promising technology for high-speed optical communication networks.

On the Directivity of Low-Frequency Type IV Radio Bursts

Science.gov (United States)

Gopalswamy, N.; Akiyama, S.; Makela, P.; Yashiro, S.; Cairns, I. H.

2016-01-01

An intense type IV radio burst was observed by the STEREO Behind (STB) spacecraft located about 144 deg. behind Earth. The burst was associated with a large solar eruption that occurred on the backside of the Sun (N05E151) close to the disk center in the STB view. The eruption was also observed by the STEREO Ahead (STA) spacecraft (located at 149 deg. ahead of Earth) as an eruption close to the west limb (N05W60) in that view. The type IV burst was complete in STB observations in that the envelope reached the lowest frequency and then receded to higher frequencies. The burst was partial viewed from STA, revealing only the edge coming down to the lowest frequency. The type IV burst was not observed at all near Earth because the source was 61 deg. behind the east limb. The eruption was associated with a low-frequency type II burst observed in all three views, although it was not very intense. Solar energetic particles were also observed at both STEREOs and at SOHO, suggesting that the shock was much extended, consistent with the very high speed of the CME (2048 km/s). These observations suggest that the type IV emission is directed along a narrow cone above the flare site. We confirm this result statistically using the type IV bursts of solar cycle 23.

A study of the temporal and spectral characteristics of gamma ray bursts

International Nuclear Information System (INIS)

Norris, J.

1983-05-01

Gamma-ray burst data obtained from the ISEE-3 Gamma Ray Burst Spectrometer and the Solar Maximum Mission's Hard X-ray Burst Spectrometer (HXRBS) were analyzed to yield information on burst temporal and spectral characteristics. A Monte Carlo approach was used to simulate the HXRBS response to candidate spectral models. At energies above about 100 keV, the spectra are well fit by exponential forms. At lower energies, 30 keV to 60 keV, depressions below the model continua are apparent in some bursts. The depressions are not instrumental or data-reduction artifacts. The event selection criterion of the ISEE-3 experiment is based on the time to accumulate a present number of photons rather than the photon count per unit time and is consequently independent of event duration for a given burst intensity, unlike most conventional systems. As a result, a significantly greater percentage of fast, narrow events have been detected. The ratio of count rates from two ISEE-3 detectors indicates that bursts with durations or aprox. one second have much softer spectra than longer bursts

Results of using engineering and technological measures for rock burst prevention. [USSR

Energy Technology Data Exchange (ETDEWEB)

Kulikov, A P; Nechaev, A V; Khmara, O I

1980-01-01

The paper evaluates methods for rock burst forecasting and rock burst prevention used in the Donbass, Kuzbass, Karaganda and Pechora basins. Forecasting methods are based on measuring the initial velocity of gas flow from test boreholes and/or quantity ratio of drillings leaving a test borehole and monitoring seismoacoustic signals. Number of working faces at which each of the methods for rock burst forecasting is used is given. Methods for rock burst prevention are comparatively evaluated: explosive fracturing of rocks in seam roof or seam floor, fluid injection (water and surfactants), drilling destressing boreholes, cutting destressing slots using cutting machines or water jets, mining protective coal seams first for reducing rock burst hazard in protected coal seams, using narrow web coal cutter loaders, remote control of coal cutters at working faces with extremely high rock burst hazard, using mining schemes which reduce rock burst hazards (e.g. long pillar mining system). From 1976 to 1979 number of rock bursts in underground coal mines in the USSR decreased by 5 times in comparison to the period 1961 to 1965. (3 refs.) (In Russian)

High repetition rate burst-mode spark gap

International Nuclear Information System (INIS)

Faltens, A.; Reginato, L.; Hester, R.; Chesterman, A.; Cook, E.; Yokota, T.; Dexter, W.

1978-01-01

Results are presented on the design and testing of a pressurized gas blown spark gap switch capable of high repetition rates in a burst mode of operation. The switch parameters which have been achieved are as follows: 220-kV, 42-kA, a five pulse burst at 1-kHz, 12-ns risetime, 2-ns jitter at a pulse width of 50-ns

Precise outage analysis of mixed RF/unified-FSO DF relaying with HD and 2 IM-DD channel models

KAUST Repository

Al-Ebraheemy, Omer Mahmoud S.

2017-07-20

This paper derives and analyzes the outage probability of mixed radio frequency (RF)/unified free space optical (FSO) dual-hop decode-and-forward (DF) relaying scheme, where heterodyne detection (HD) and intensity modulation-direct detection (IM-DD) are considered for FSO detection. In doing that, we correctly utilize, for the first time to the best of our knowledge, a precise channel capacity result for the IM-DD channel. Moreover, this is the first time that not only the (IM-DD input-independent) but also the (IM-DD cost-dependent) AWGN channel is considered in such system analysis. This work assumes that the first hop (RF link) follows Naka-gami-m fading, while the second hop (FSO link) follows Málaga (M) turbulence with pointing error. These fading and turbulence models include other ones (such as Rayleigh fading and Gamma-Gamma turbulence) as special cases, so our analysis can be considered as a generalized one from both RF and FSO fading models point of view. Additionally, the system outage probability is investigated asymptotically in high signal-to-noise ratio (SNR) regime, where a new non-reported diversity order and coding gain analysis are shown. Interestingly, we find that in the FSO hop, based on SNR, the HD or IM-DD cost-dependent results in a same diversity order which is twice the one of IM-DD input-independent. However, based on transmitted power all these FSO detectors result in a same diversity order. Furthermore, we offer simulation results which confirm the derived exact and asymptotic expressions.

Precise outage analysis of mixed RF/unified-FSO DF relaying with HD and 2 IM-DD channel models

KAUST Repository

Al-Ebraheemy, Omer Mahmoud S.; Salhab, Anas M.; Chaaban, Anas; Zummo, Salam A.; Alouini, Mohamed-Slim

2017-01-01

This paper derives and analyzes the outage probability of mixed radio frequency (RF)/unified free space optical (FSO) dual-hop decode-and-forward (DF) relaying scheme, where heterodyne detection (HD) and intensity modulation-direct detection (IM-DD) are considered for FSO detection. In doing that, we correctly utilize, for the first time to the best of our knowledge, a precise channel capacity result for the IM-DD channel. Moreover, this is the first time that not only the (IM-DD input-independent) but also the (IM-DD cost-dependent) AWGN channel is considered in such system analysis. This work assumes that the first hop (RF link) follows Naka-gami-m fading, while the second hop (FSO link) follows Málaga (M) turbulence with pointing error. These fading and turbulence models include other ones (such as Rayleigh fading and Gamma-Gamma turbulence) as special cases, so our analysis can be considered as a generalized one from both RF and FSO fading models point of view. Additionally, the system outage probability is investigated asymptotically in high signal-to-noise ratio (SNR) regime, where a new non-reported diversity order and coding gain analysis are shown. Interestingly, we find that in the FSO hop, based on SNR, the HD or IM-DD cost-dependent results in a same diversity order which is twice the one of IM-DD input-independent. However, based on transmitted power all these FSO detectors result in a same diversity order. Furthermore, we offer simulation results which confirm the derived exact and asymptotic expressions.

The many phases of gamma-ray burst afterglows

NARCIS (Netherlands)

Leventis, K.

2013-01-01

Gamma-ray bursts are the brightest sources in the universe. Their afterglows have been observed for about 15 years now, and their study has greatly advanced our understanding of these, mysterious until recently, events. In a way, gamma-ray bursts can be seen as huge cosmic bombs which convert

Connecting protein and mRNA burst distributions for stochastic models of gene expression

International Nuclear Information System (INIS)

Elgart, Vlad; Jia, Tao; Fenley, Andrew T; Kulkarni, Rahul

2011-01-01

The intrinsic stochasticity of gene expression can lead to large variability in protein levels for genetically identical cells. Such variability in protein levels can arise from infrequent synthesis of mRNAs which in turn give rise to bursts of protein expression. Protein expression occurring in bursts has indeed been observed experimentally and recent studies have also found evidence for transcriptional bursting, i.e. production of mRNAs in bursts. Given that there are distinct experimental techniques for quantifying the noise at different stages of gene expression, it is of interest to derive analytical results connecting experimental observations at different levels. In this work, we consider stochastic models of gene expression for which mRNA and protein production occurs in independent bursts. For such models, we derive analytical expressions connecting protein and mRNA burst distributions which show how the functional form of the mRNA burst distribution can be inferred from the protein burst distribution. Additionally, if gene expression is repressed such that observed protein bursts arise only from single mRNAs, we show how observations of protein burst distributions (repressed and unrepressed) can be used to completely determine the mRNA burst distribution. Assuming independent contributions from individual bursts, we derive analytical expressions connecting means and variances for burst and steady-state protein distributions. Finally, we validate our general analytical results by considering a specific reaction scheme involving regulation of protein bursts by small RNAs. For a range of parameters, we derive analytical expressions for regulated protein distributions that are validated using stochastic simulations. The analytical results obtained in this work can thus serve as useful inputs for a broad range of studies focusing on stochasticity in gene expression

The Fermi Gamma-ray Burst Monitor Instrument

International Nuclear Information System (INIS)

Bhat, P. N.; Briggs, M. S.; Connaughton, V.; Paciesas, W. S.; Preece, R. D.; Meegan, C. A.; Lichti, G. G.; Diehl, R.; Greiner, J.; Kienlin, A. von; Fishman, G. J.; Kouveliotou, C.; Kippen, R. M.

2009-01-01

The Fermi Gamma-ray Space Telescope launched on June 11, 2008 carries two experiments onboard--the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). The primary mission of the GBM instrument is to support the LAT in observing γ-ray bursts (GRBs) by providing low-energy measurements with high temporal and spectral resolution as well as rapid burst locations over a large field-of-view (≥8 sr). The GBM will complement the LAT measurements by observing GRBs in the energy range 8 keV to 40 MeV, the region of the spectral turnover in most GRBs. The GBM detector signals are processed by the onboard digital processing unit (DPU). We describe some of the hardware features of the DPU and its expected limitations during intense triggers.

Localised Microwave Bursts During ELMs on MAST

Directory of Open Access Journals (Sweden)

Freethy Simon

2015-01-01

Full Text Available Bursts of microwave emission are observed during ELM events on the Mega Ampère Spherical Tokamak. In agreement with observations on other machines, these bursts are up to 3 orders of magnitude more intense than the thermal background, but are electron cyclotron in nature. The peak in microwave emission is ~20μ before the peak in midplane Dα emission. Using the Synthetic Aperture Microwave Imaging radiometer, we are able to demonstrate that these bursts are often highly spatially localised and preferentially occur at the tokamak midplane. It is hypothesised that the localisation is a result of Doppler resonance broadening for electron Bernstein waves and the high perpendicular electron energies could be the result of pitch angle scattering in high collisionality regions of the plasma.

Stage- vs. Channel-strip Metaphor

DEFF Research Database (Denmark)

Gelineck, Steven; Korsgaard, Dannie Michael; Büchert, Morten

2015-01-01

This study compares the stage metaphor and the channel strip metaphor in terms of performance. Traditionally, music mixing consoles employ a channels strip control metaphor for adjusting parameters such as volume and panning of each track. An alternative control metaphor, the so-called stage meta...... is surprisingly similar and thus we are not able to detect any significant difference in performance between the two interfaces. Qualitative data however, suggests that the stage metaphor is largely favoured for its intuitive interaction - confirming earlier studies....

BudBurst Buddies: A New Tool for Engaging the Youngest Citizen Scientists

Science.gov (United States)

Gardiner, L. S.; Henderson, S.; Ward, D.

2010-12-01

BudBurst Buddies (www.budburstbuddies.org) introduces elementary school age children to the science of observing plants and the timing of phenological (life cycle) events. BudBurst Buddies is a new part of the Project BudBurst national citizen science initiative (www.budburst.org), which allows individuals to engage in the scientific process, contributing to a better understanding of climate change while increasing public awareness of phenology and the impacts of climate change on plants. As a first step towards engaging the next generation of citizen scientists, BudBurst Buddies provides the opportunity for children to gain experience with scientific research and increases awareness of how plants change throughout the year. Children can participate in BudBurst Buddies on their own, with their families, or in formal or informal education settings. Each child who participates creates a journal about a plant of his or her choosing, makes observations of the plant over the growing season and submits findings online, earning an official BudBurst Buddies certificate. An online storybook for kids tells how two children, Lily and Sage, observed plants in their neighborhood and became BudBurst Buddies. This presentation will provide an overview of the BudBurst Buddies newly developed resources. BudBurst Buddies is a part of Project BudBurst, a national citizen science program coordinated by the National Ecological Observatory Network (NEON) and the Chicago Botanic Garden. Funding for this resource was provided by NEON, NSF, NASA, and the National Geographic Education Foundation.

MODELING EXTRAGALACTIC EXTINCTION THROUGH GAMMA-RAY BURST AFTERGLOWS

Energy Technology Data Exchange (ETDEWEB)

Zonca, Alberto; Mulas, Giacomo; Casu, Silvia; Aresu, Giambattista [INAF—Osservatorio Astronomico di Cagliari, Via della Scienza 5, I-09047 Selargius (Italy); Cecchi-Pestellini, Cesare, E-mail: azonca@oa-cagliari.inaf.it, E-mail: gmulas@oa-cagliari.inaf.it, E-mail: silvia@oa-cagliari.inaf.it, E-mail: garesu@oa-cagliari.inaf.it, E-mail: cecchi-pestellini@astropa.inaf.it [INAF—Osservatorio Astronomico di Palermo, P.za Parlamento 1, I-90134 Palermo (Italy)

2016-09-20

We analyze extragalactic extinction profiles derived through gamma-ray burst afterglows, using a dust model specifically constructed on the assumption that dust grains are not immutable but respond, time-dependently, to the local physics. Such a model includes core-mantle spherical particles of mixed chemical composition (silicate core, sp{sup 2}, and sp{sup 3} carbonaceous layers), and an additional molecular component in the form of free-flying polycyclic aromatic hydrocarbons. We fit most of the observed extinction profiles. Failures occur for lines of sight, presenting remarkable rises blueward of the bump. We find a tendency for the carbon chemical structure to become more aliphatic with the galactic activity, and to some extent with increasing redshifts. Moreover, the contribution of the molecular component to the total extinction is more important in younger objects. The results of the fitting procedure (either successes and failures) may be naturally interpreted through an evolutionary prescription based on the carbon cycle in the interstellar medium of galaxies.

The CaV2.3 R-type voltage-gated Ca2+ channel in mouse sleep architecture.

Science.gov (United States)

Siwek, Magdalena Elisabeth; Müller, Ralf; Henseler, Christina; Broich, Karl; Papazoglou, Anna; Weiergräber, Marco

2014-05-01

Voltage-gated Ca(2+) channels (VGCCs) are key elements in mediating thalamocortical rhythmicity. Low-voltage activated (LVA) CaV 3 T-type Ca(2+) channels have been related to thalamic rebound burst firing and to generation of non-rapid eye movement (NREM) sleep. High-voltage activated (HVA) CaV 1 L-type Ca(2+) channels, on the opposite, favor the tonic mode of action associated with higher levels of vigilance. However, the role of the HVA Non-L-type CaV2.3 Ca(2+) channels, which are predominantly expressed in the reticular thalamic nucleus (RTN), still remains unclear. Recently, CaV2.3(-/-) mice were reported to exhibit altered spike-wave discharge (SWD)/absence seizure susceptibility supported by the observation that CaV2.3 mediated Ca(2+) influx into RTN neurons can trigger small-conductance Ca(2+)-activated K(+)-channel type 2 (SK2) currents capable of maintaining thalamic burst activity. Based on these studies we investigated the role of CaV2.3 R-type Ca(2+) channels in rodent sleep. The role of CaV2.3 Ca(2+) channels was analyzed in CaV2.3(-/-) mice and controls in both spontaneous and artificial urethane-induced sleep, using implantable video-EEG radiotelemetry. Data were analyzed for alterations in sleep architecture using sleep staging software and time-frequency analysis. CaV2.3 deficient mice exhibited reduced wake duration and increased slow-wave sleep (SWS). Whereas mean sleep stage durations remained unchanged, the total number of SWS epochs was increased in CaV2.3(-/-) mice. Additional changes were observed for sleep stage transitions and EEG amplitudes. Furthermore, urethane-induced SWS mimicked spontaneous sleep results obtained from CaV2.3 deficient mice. Quantitative Real-time PCR did not reveal changes in thalamic CaV3 T-type Ca(2+) channel expression. The detailed mechanisms of SWS increase in CaV2.3(-/-) mice remain to be determined. Low-voltage activated CaV2.3 R-type Ca(2+) channels in the thalamocortical loop and extra

Probing the Cosmic Gamma-Ray Burst Rate with Trigger Simulations of the Swift Burst Alert Telescope

Science.gov (United States)

Lien, Amy; Sakamoto, Takanori; Gehrels, Neil; Palmer, David M.; Barthelmy, Scott D.; Graziani, Carlo; Cannizzo, John K.

2013-01-01

The gamma-ray burst (GRB) rate is essential for revealing the connection between GRBs, supernovae and stellar evolution. Additionally, the GRB rate at high redshift provides a strong probe of star formation history in the early universe. While hundreds of GRBs are observed by Swift, it remains difficult to determine the intrinsic GRB rate due to the complex trigger algorithm of Swift. Current studies of the GRB rate usually approximate the Swift trigger algorithm by a single detection threshold. However, unlike the previously own GRB instruments, Swift has over 500 trigger criteria based on photon count rate and additional image threshold for localization. To investigate possible systematic biases and explore the intrinsic GRB properties, we develop a program that is capable of simulating all the rate trigger criteria and mimicking the image threshold. Our simulations show that adopting the complex trigger algorithm of Swift increases the detection rate of dim bursts. As a result, our simulations suggest bursts need to be dimmer than previously expected to avoid over-producing the number of detections and to match with Swift observations. Moreover, our results indicate that these dim bursts are more likely to be high redshift events than low-luminosity GRBs. This would imply an even higher cosmic GRB rate at large redshifts than previous expectations based on star-formation rate measurements, unless other factors, such as the luminosity evolution, are taken into account. The GRB rate from our best result gives a total number of 4568 +825 -1429 GRBs per year that are beamed toward us in the whole universe.

Method of separation of celestial gamma-ray bursts from solar flares

International Nuclear Information System (INIS)

Chuang, K.W.; White, R.S.; Klebesadel, R.W.; Laros, J.G.

1991-01-01

We recently discovered 217 ''new'' celestial gamma-ray burst candidates from the ''new'' burst search of the PVO real time data base. 1 The burst search covered the time period from September 1978 to July 1988. Sixty were confirmed by at lest on other spacecraft, e.g., ISEE-3, V-11, V-12, etc. None triggered the PVO high time resolution memory. In this paper we describe a new algorithm based ont eh relationship between time width T w and hardness ratio HR, to distinguish cosmic gamma-ray bursts from solar flares without knowing the directions of the events. The criteria for identification as a gamma-ray burst candidate are: If T ww ≤a then HR≥bT w , or T w >a then HR>c. Otherwise, the event is a solar flare candidate. Here, a, b, and c are parameter which differ for different gamma-ray burst detectors. For PVO, a=18.8 s, b=(1.38/18.8) s -1 , and c=1.38. This algorithm was tested with 83 triggered and 60 nontriggered confirmed gamma-ray burst and 30 confirmed solar flares from PVO

Coherifying quantum channels

Science.gov (United States)

Korzekwa, Kamil; Czachórski, Stanisław; Puchała, Zbigniew; Życzkowski, Karol

2018-04-01

Is it always possible to explain random stochastic transitions between states of a finite-dimensional system as arising from the deterministic quantum evolution of the system? If not, then what is the minimal amount of randomness required by quantum theory to explain a given stochastic process? Here, we address this problem by studying possible coherifications of a quantum channel Φ, i.e., we look for channels {{{Φ }}}{ \\mathcal C } that induce the same classical transitions T, but are ‘more coherent’. To quantify the coherence of a channel Φ we measure the coherence of the corresponding Jamiołkowski state J Φ. We show that the classical transition matrix T can be coherified to reversible unitary dynamics if and only if T is unistochastic. Otherwise the Jamiołkowski state {J}{{Φ }}{ \\mathcal C } of the optimally coherified channel is mixed, and the dynamics must necessarily be irreversible. To assess the extent to which an optimal process {{{Φ }}}{ \\mathcal C } is indeterministic we find explicit bounds on the entropy and purity of {J}{{Φ }}{ \\mathcal C }, and relate the latter to the unitarity of {{{Φ }}}{ \\mathcal C }. We also find optimal coherifications for several classes of channels, including all one-qubit channels. Finally, we provide a non-optimal coherification procedure that works for an arbitrary channel Φ and reduces its rank (the minimal number of required Kraus operators) from {d}2 to d.

Elastic-plastic failure analysis of pressure burst tests of thin toroidal shells

International Nuclear Information System (INIS)

Jones, D.P.; Holliday, J.E.; Larson, L.D.

1998-07-01

This paper provides a comparison between test and analysis results for bursting of thin toroidal shells. Testing was done by pressurizing two toroidal shells until failure by bursting. An analytical criterion for bursting is developed based on good agreement between structural instability predicted by large strain-large displacement elastic-plastic finite element analysis and observed burst pressure obtained from test. The failures were characterized by loss of local stability of the membrane section of the shells consistent with the predictions from the finite element analysis. Good agreement between measured and predicted burst pressure suggests that incipient structural instability as calculated by an elastic-plastic finite element analysis is a reasonable way to calculate the bursting pressure of thin membrane structures

BALLERINA - Pirouettes in search of gamma burst sources

International Nuclear Information System (INIS)

Brandt, Soeren; Lund, Niels

1999-01-01

The cosmological origin of gamma-ray bursts (GRBs) has now been established with reasonable certainty. Many more bursts will need to be studied to establish the typical distance scale, and to map out the large variability in properties, which have been indicated by the first handful of events. We are proposing BALLERINA, a small satellite to provide accurate gamma burst positions at a rate an order of magnitude larger than from Beppo-SAX. On the experimental side, it remains a challenge to ensure the earliest detection of the X-ray afterglow. The mission proposed here allows for the first time systematic studies of the soft X-ray emission in the time interval from only a few minutes after the onset of the burst to a few hours later. In addition to positions of GRBs with accuracy better than 1'reported to the ground within a few minutes of the burst, essential for follow-up work, BALLERINA will on its own provide observations in an uncharted region of parameter space. Secondary objectives of the BALLERINA mission includes observations of the earliest phases of the outbursts of X-ray novae and other X-ray transients. BALLERINA is one of four missions currently under study for the Danish Small Satellite Program. The selection will be announced in 1999 for a planned launch in 2002-2003

Heating of aluminum by SPR-III burst

International Nuclear Information System (INIS)

Judd, S.V.

1987-01-01

Real time temperature measurements were made on an aluminum cylinder exposed to radiation bursts at SPR-III at neutron levels from 10 11 cm -2 to 4.5 x 10 14 cm -2 . Precision thermistors and high speed A/D converters were used to measure temperature with .0025 degree C resolution at 20ms intervals following the burst. Temperature data is presented as a function of neutron fluence

Detection Techniques of Microsecond Gamma-Ray Bursts Using Ground-based Telescopes

International Nuclear Information System (INIS)

Krennrich, F.; Le Bohec, S.; Weekes, T. C.

2000-01-01

Gamma-ray observations above 200 MeV are conventionally made by satellite-based detectors. The EGRET detector on the Compton Gamma Ray Observatory has provided good sensitivity for the detection of bursts lasting for more than 200 ms. Theoretical predictions of high-energy gamma-ray bursts produced by quantum mechanical decay of primordial black holes (Hawking) suggest the emission of bursts on shorter timescales. The final stage of a primordial black hole results in a burst of gamma rays, peaking around 250 MeV and lasting for 1/10 of a microsecond or longer depending on particle physics. In this work we show that there is an observational window using ground-based imaging Cerenkov detectors to measure gamma-ray burst emission at energies E>200 MeV. This technique, with a sensitivity for bursts lasting nanoseconds to several microseconds, is based on the detection of multiphoton-initiated air showers. (c) (c) 2000. The American Astronomical Society

FAST TCP over optical burst switched networks: Modeling and stability analysis

KAUST Repository

Shihada, Basem

2013-04-01

FAST TCP is important for promoting data-intensive applications since it can cleverly react to both packet loss and delay for detecting network congestion. This paper provides a continuous time model and extensive stability analysis of FAST TCP congestion-control mechanism in bufferless Optical Burst Switched Networks (OBS). The paper first shows that random burst contentions are essential to stabilize the network, but cause throughput degradation in FAST TCP flows when a burst with all the packets from a single round is dropped. Second, it shows that FAST TCP is vulnerable to burst delay and fails to detect network congestion due to the little variation of round-trip time, thus unstable. Finally it shows that introducing extra delays by implementing burst retransmission stabilizes FAST TCP over OBS. The paper proves that FAST TCP is not stable over barebone OBS. However, it is locally, exponentially, and asymptotically stable over OBS with burst retransmission.

Project BudBurst: Continental-scale citizen science for all seasons

Science.gov (United States)

Henderson, S.; Newman, S. J.; Ward, D.; Havens-Young, K.; Alaback, P.; Meymaris, K.

2011-12-01

Project BudBurst's (budburst.org) recent move to the National Ecological Observatory Network (NEON) has benefitted both programs. NEON has been able to use Project BudBurst as a testbed to learn best practices, network with experts in the field, and prototype potential tools for engaging people in continental-scale ecology as NEON develops its citizen science program. Participation in Project BudBurst has grown significantly since the move to NEON. Project BudBurst is a national citizen science initiative designed to engage the public in observations of phenological (plant life cycle) events that raise awareness of climate change, and create a cadre of informed citizen scientists. Citizen science programs such as Project BudBurst provide the opportunity for students and interested laypersons to actively participate in scientific research. Such programs are important not only from an educational perspective, but because they also enable scientists to broaden the geographic and temporal scale of their observations. The goals of Project BudBurst are to 1) increase awareness of phenology as an area of scientific study; 2) Increase awareness of the impacts of changing climates on plants at a continental-scale; and 3) increase science literacy by engaging participants in the scientific process. From its 2008 launch in February, this on-line educational and data-entry program, engaged participants of all ages and walks of life in recording the timing of the leafing and flowering of wild and cultivated species found across the continent. Thus far, thousands of participants from all 50 states have submitted data. This presentation will provide an overview of Project BudBurst and will report on the results of the 2010 field campaign and discuss plans to expand Project BudBurst in 2012 including the use of mobile phones applications for data collection and reporting from the field. Project BudBurst is co-managed by the National Ecological Observatory Network and the Chicago

Identification of an HV 1 voltage-gated proton channel in insects.

Science.gov (United States)

Chaves, Gustavo; Derst, Christian; Franzen, Arne; Mashimo, Yuta; Machida, Ryuichiro; Musset, Boris

2016-04-01

The voltage-gated proton channel 1 (HV 1) is an important component of the cellular proton extrusion machinery and is essential for charge compensation during the respiratory burst of phagocytes. HV 1 has been identified in a wide range of eukaryotes throughout the animal kingdom, with the exception of insects. Therefore, it has been proposed that insects do not possess an HV 1 channel. In the present study, we report the existence of an HV 1-type proton channel in insects. We searched insect transcriptome shotgun assembly (TSA) sequence databases and found putative HV 1 orthologues in various polyneopteran insects. To confirm that these putative HV 1 orthologues were functional channels, we studied the HV 1 channel of Nicoletia phytophila (NpHV 1), an insect of the Zygentoma order, in more detail. NpHV 1 comprises 239 amino acids and is 33% identical to the human voltage-gated proton channel 1. Patch clamp measurements in a heterologous expression system showed proton selectivity, as well as pH- and voltage-dependent gating. Interestingly, NpHV 1 shows slightly enhanced pH-dependent gating compared to the human channel. Mutations in the first transmembrane segment at position 66 (Asp66), the presumed selectivity filter, lead to a loss of proton-selective conduction, confirming the importance of this aspartate residue in voltage-gated proton channels. Nucleotide sequence data have been deposited in the GenBank database under accession number KT780722. © 2016 Federation of European Biochemical Societies.

Burst Mode Composite Photography for Dynamic Physics Demonstrations

Science.gov (United States)

Lincoln, James

2018-01-01

I am writing this article to raise awareness of burst mode photography as a fun and engaging way for teachers and students to experience physics demonstration activities. In the context of digital photography, "burst mode" means taking multiple photographs per second, and this is a feature that now comes standard on most digital…

Laser carved micro-crack channels in paper-based dilution devices.

Science.gov (United States)

Liu, Qian; Xu, Chaoping; Liang, Heng

2017-12-01

We developed novel laser carved micro-crack (LCC) paper-based channels to significantly accelerate the liquid flow without an external pump. For the aqueous solutions they increased the flow velocity 59 times in 16% laser power-8 micro-cracks-LCC channel compared with it in solely-printed channels. All experimental data from both LCC and solely-printed channels were well-fitted by the time-distance quadratic trinomial that we developed on laser power and micro-crack number. We designed and fabricated T-junction microstructures of LCCs. Further, the microfluidic paper-based analytical device (μPAD) of LCC on dye mixing gradient and pH gradient were developed with the characteristics, fast self-acting transportation and high-performance mixing of liquid flows. In the dye mixing gradient the time cost was reduced from 2355s in the solely-printed one to only 123s in the five-stage of this LCC-μPAD. It was useful for quick and long-distance transferences through the multiple units of μPADs. Certainly, this LCC-μPAD was inexpensive, disposable, portable and applicable to resource-limited environments. Copyright © 2017 Elsevier B.V. All rights reserved.

Reliability of COPVs Accounting for Margin of Safety on Design Burst

Science.gov (United States)

Murthy, Pappu L.N.

2012-01-01

In this paper, the stress rupture reliability of Carbon/Epoxy Composite Overwrapped Pressure Vessels (COPVs) is examined utilizing the classic Phoenix model and accounting for the differences between the design and the actual burst pressure, and the liner contribution effects. Stress rupture life primarily depends upon the fiber stress ratio which is defined as the ratio of stress in fibers at the maximum expected operating pressure to actual delivered fiber strength. The actual delivered fiber strength is calculated using the actual burst pressures of vessels established through burst tests. However, during the design phase the actual burst pressure is generally not known and to estimate the reliability of the vessels calculations are usually performed based upon the design burst pressure only. Since the design burst is lower than the actual burst, this process yields a much higher value for the stress ratio and consequently a conservative estimate for the reliability. Other complications arise due to the fact that the actual burst pressure and the liner contributions have inherent variability and therefore must be treated as random variables in order to compute the stress rupture reliability. Furthermore, the model parameters, which have to be established based on stress rupture tests of subscale vessels or coupons, have significant variability as well due to limited available data and hence must be properly accounted for. In this work an assessment of reliability of COPVs including both parameter uncertainties and physical variability inherent in liner and overwrap material behavior is made and estimates are provided in terms of degree of uncertainty in the actual burst pressure and the liner load sharing.

Chemistry in Microfluidic Channels

Science.gov (United States)

Chia, Matthew C.; Sweeney, Christina M.; Odom, Teri W.

2011-01-01

General chemistry introduces principles such as acid-base chemistry, mixing, and precipitation that are usually demonstrated in bulk solutions. In this laboratory experiment, we describe how chemical reactions can be performed in a microfluidic channel to show advanced concepts such as laminar fluid flow and controlled precipitation. Three sets of…

Different Types of X-Ray Bursts from GRS 1915+105 and Their Origin

Science.gov (United States)

Yadav, J. S.; Rao, A. R.; Agrawal, P. C.; Paul, B.; Seetha, S.; Kasturirangan, K.

1999-06-01

We report X-ray observations of the Galactic X-ray transient source GRS 1915+105 with the pointed proportional counters of the Indian X-ray Astronomy Experiment (IXAE) onboard the Indian satellite IRS-P3, which show remarkable richness in temporal variability. The observations were carried out on 1997 June 12-29 and August 7-10, in the energy range of 2-18 keV and revealed the presence of very intense X-ray bursts. All the observed bursts have a slow exponential rise, a sharp linear decay, and broadly can be put in two classes: irregular and quasi-regular bursts in one class, and regular bursts in the other. The regular bursts are found to have two distinct timescales and to persist over extended durations. There is a strong correlation between the preceding quiescent time and the burst duration for the quasi-regular and irregular bursts. No such correlation is found for the regular bursts. The ratio of average flux during the burst time to the average flux during the quiescent phase is high and variable for the quasi-regular and irregular bursts, while it is low and constant for the regular bursts. We present a comprehensive picture of the various types of bursts observed in GRS 1915+105 in the light of the recent theories of advective accretion disks. We suggest that the peculiar bursts that we have seen are characteristic of the change of state of the source. The source can switch back and forth between the low-hard state and the high-soft state near critical accretion rates in a very short timescale, giving rise to the irregular and quasi-regular bursts. The fast timescale for the transition of the state is explained by invoking the appearance and disappearance of the advective disk in its viscous timescale. The periodicity of the regular bursts is explained by matching the viscous timescale with the cooling timescale of the postshock region. A test of the model is presented using the publicly available 13-60 keV RXTE/PCA data for irregular and regular bursts

Distribution channels of insurance and reinsurance services

Directory of Open Access Journals (Sweden)

Njegomir Vladimir

2007-01-01

Full Text Available Insurance and reinsurance industry is famous for its traditionalism, that is uninventiveness and neglecting of marketing as business concept and function and by doing so, neglecting opportunities for optimal combination of different distribution channels. However, having in mind Drucker's thesis that only marketing and innovations produce results and that everything else are costs, that applies to all businesses including insurance and reinsurance companies, it is clear that they need to change their way of managing business. Keeping current and attracting new customers, by using optimal combination of marketing mix elements and within its scope by creating optimal mix of distribution channels, as business requirement and objective of insurance and reinsurance companies with strong marketing orientation that leads them to fulfillment of primary objective of their existence - making profit, is becoming specially emphasized with opening of domestic insurance and reinsurance market to foreign competitors with long history of gaining high level of customers' loyalty. Besides that, issues of successful distribution channels' management of insurance and reinsurance services are not treated holistically in domestic literature. Distribution channels of insurance and reinsurance services, as this study shows, are of critical importance for business success of insurance and reinsurance companies.

Classifying LISA gravitational wave burst signals using Bayesian evidence

International Nuclear Information System (INIS)

Feroz, Farhan; Graff, Philip; Hobson, Michael P; Lasenby, Anthony; Gair, Jonathan R

2010-01-01

We consider the problem of characterization of burst sources detected by the Laser Interferometer Space Antenna (LISA) using the multi-modal nested sampling algorithm, MultiNest. We use MultiNest as a tool to search for modelled bursts from cosmic string cusps, and compute the Bayesian evidence associated with the cosmic string model. As an alternative burst model, we consider sine-Gaussian burst signals, and show how the evidence ratio can be used to choose between these two alternatives. We present results from an application of MultiNest to the last round of the Mock LISA Data Challenge, in which we were able to successfully detect and characterize all three of the cosmic string burst sources present in the release data set. We also present results of independent trials and show that MultiNest can detect cosmic string signals with signal-to-noise ratio (SNR) as low as ∼7 and sine-Gaussian signals with SNR as low as ∼8. In both cases, we show that the threshold at which the sources become detectable coincides with the SNR at which the evidence ratio begins to favour the correct model over the alternative.

BudBurst Buddies: Introducing Young Citizen Scientists to Plants and Environmental Change

Science.gov (United States)

Ward, D.; Gardiner, L. S.; Henderson, S.

2011-12-01

As part of Project BudBurst, the BudBurst Buddies recently moved to the National Ecological Network (NEON) as part of its Education and Public Engagement efforts. The BudBurst Buddies (www.budburstbuddies.org) were created to engage elementary school age children in the science of observing plants and the timing of phenological (life cycle) events. BudBurst Buddies is a part of the Project BudBurst national citizen science initiative (www.budburst.org), which allows individuals to engage in the scientific process, contributing to a better understanding of climate change while increasing public awareness of phenology and the impacts of climate change on plants. As a first step towards engaging the next generation of citizen scientists, BudBurst Buddies provides the opportunity for children to gain experience with scientific research and increases awareness of how plants change throughout the year. Hundreds of young students have participated in the inaugural year of BudBurst Buddies. Children can participate in BudBurst Buddies on their own, with their families, or in formal or informal education settings. The program was recently highlighted by education staff at the New York Hall of Science and numerous classrooms have been implementing this resource as part of their curriculum. Each child who participates creates a journal about a plant of his or her choosing, makes observations of the plant over the growing season and submits findings online, earning an official BudBurst Buddies certificate. An online storybook for kids tells how two children, Lily and Sage, observed plants in their neighborhood and became BudBurst Buddies. This presentation will provide an overview of the BudBurst Buddies resources including a new implementation guide and will also share feedback from the first year of implementation.

Ca2+ and voltage dependence of cardiac ryanodine receptor channel block by sphingosylphosphorylcholine.

Science.gov (United States)

Yasukochi, Midori; Uehara, Akira; Kobayashi, Sei; Berlin, Joshua R

2003-03-01

The effect of sphingosylphosphorylcholine (SPC) on the cytoplasmic Ca(2+) and voltage dependence of channel gating by cardiac ryanodine receptors (RyR) was examined in lipid bilayer experiments. Micromolar concentrations of the lysosphingolipid SPC added to cis solutions rapidly and reversibly decreased the single-channel open probability (P(o)) of reconstituted RyR channels. The SPC-induced decrease in P(o) was marked by an increase in mean closed time and burst-like channel gating. Gating kinetics during intraburst periods were unchanged from those observed in the absence of the sphingolipid, although SPC induced a long-lived closed state that appeared to explain the observed decrease in channel P(o). SPC effects were observed over a broad range of cis [Ca(2+)] but were not competitive with Ca(2+). Interestingly, the sphingolipid-induced, long-lived closed state displayed voltage-dependent kinetics, even though other channel gating kinetics were not sensitive to voltage. Assuming SPC effects represent channel blockade, these results suggest that the blocking rate is independent of voltage whereas the unblocking rate is voltage dependent. Together, these results suggest that SPC binds directly to the cytoplasmic side of the RyR protein in a location in or near the membrane dielectric, but distinct from cytoplasmic Ca(2+) binding sites on the protein.

Solar Flares, Type III Radio Bursts, Coronal Mass Ejections, and Energetic Particles

Science.gov (United States)

Cane, Hilary V.; Erickson, W. C.; Prestage, N. P.; White, Nicholas E. (Technical Monitor)

2002-01-01

In this correlative study between greater than 20 MeV solar proton events, coronal mass ejections (CMEs), flares, and radio bursts it is found that essentially all of the proton events are preceded by groups of type III bursts and all are preceded by CMEs. These type III bursts (that are a flare phenomenon) usually are long-lasting, intense bursts seen in the low-frequency observations made from space. They are caused by streams of electrons traveling from close to the solar surface out to 1 AU. In most events the type III emissions extend into, or originate at, the time when type II and type IV bursts are reported (some 5 to 10 minutes after the start of the associated soft X-ray flare) and have starting frequencies in the 500 to approximately 100 MHz range that often get lower as a function of time. These later type III emissions are often not reported by ground-based observers, probably because of undue attention to type II bursts. It is suggested to call them type III-1. Type III-1 bursts have previously been called shock accelerated (SA) events, but an examination of radio dynamic spectra over an extended frequency range shows that the type III-1 bursts usually start at frequencies above any type II burst that may be present. The bursts sometimes continue beyond the time when type II emission is seen and, furthermore, sometimes occur in the absence of any type II emission. Thus the causative electrons are unlikely to be shock accelerated and probably originate in the reconnection regions below fast CMEs. A search did not find any type III-1 bursts that were not associated with CMEs. The existence of low-frequency type III bursts proves that open field lines extend from within 0.5 radius of the Sun into the interplanetary medium (the bursts start above 100 MHz, and such emission originates within 0.5 solar radius of the solar surface). Thus it is not valid to assume that only closed field lines exist in the flaring regions associated with CMEs and some

Operational experiences with automated acoustic burst classification by neural networks

International Nuclear Information System (INIS)

Olma, B.; Ding, Y.; Enders, R.

1996-01-01

Monitoring of Loose Parts Monitoring System sensors for signal bursts associated with metallic impacts of loose parts has proved as an useful methodology for on-line assessing the mechanical integrity of components in the primary circuit of nuclear power plants. With the availability of neural networks new powerful possibilities for classification and diagnosis of burst signals can be realized for acoustic monitoring with the online system RAMSES. In order to look for relevant burst signals an automated classification is needed, that means acoustic signature analysis and assessment has to be performed automatically on-line. A back propagation neural network based on five pre-calculated signal parameter values has been set up for identification of different signal types. During a three-month monitoring program of medium-operated check valves burst signals have been measured and classified separately according to their cause. The successful results of the three measurement campaigns with an automated burst type classification are presented. (author)

The voice conveys specific emotions: evidence from vocal burst displays.

Science.gov (United States)

Simon-Thomas, Emiliana R; Keltner, Dacher J; Sauter, Disa; Sinicropi-Yao, Lara; Abramson, Anna

2009-12-01

Studies of emotion signaling inform claims about the taxonomic structure, evolutionary origins, and physiological correlates of emotions. Emotion vocalization research has tended to focus on a limited set of emotions: anger, disgust, fear, sadness, surprise, happiness, and for the voice, also tenderness. Here, we examine how well brief vocal bursts can communicate 22 different emotions: 9 negative (Study 1) and 13 positive (Study 2), and whether prototypical vocal bursts convey emotions more reliably than heterogeneous vocal bursts (Study 3). Results show that vocal bursts communicate emotions like anger, fear, and sadness, as well as seldom-studied states like awe, compassion, interest, and embarrassment. Ancillary analyses reveal family-wise patterns of vocal burst expression. Errors in classification were more common within emotion families (e.g., 'self-conscious,' 'pro-social') than between emotion families. The three studies reported highlight the voice as a rich modality for emotion display that can inform fundamental constructs about emotion.

Participants Provide Mixed Reports about Learning from Channel One.

Science.gov (United States)

Barrett, Janice M.

1998-01-01

Investigates Channel One's educational benefits to teachers and students. Finds benefits are a student-heightened interest in geography, current events, and pop quizzes; and disadvantages are the commercials, superficial programming, intrusion into the school day, lack of integration into the curriculum, and limited availability of the equipment…

Imaging spectroscopy of type U and J solar radio bursts with LOFAR

Science.gov (United States)

Reid, Hamish A. S.; Kontar, Eduard P.

2017-10-01

Context. Radio U-bursts and J-bursts are signatures of electron beams propagating along magnetic loops confined to the corona. The more commonly observed type III radio bursts are signatures of electron beams propagating along magnetic loops that extend into interplanetary space. Given the prevalence of solar magnetic flux to be closed in the corona, why type III bursts are more frequently observed than U-bursts or J-bursts is an outstanding question. Aims: We use Low-Frequency Array (LOFAR) imaging spectroscopy between 30-80 MHz of low-frequency U-bursts and J-bursts, for the first time, to understand why electron beams travelling along coronal loops produce radio emission less often. Radio burst observations provide information not only about the exciting electron beams but also about the structure of large coronal loops with densities that are too low for standard extreme ultraviolet (EUV) or X-ray analysis. Methods: We analysed LOFAR images of a sequence of two J-bursts and one U-burst. The different radio source positions were used to model the spatial structure of the guiding magnetic flux tube and then deduce the energy range of the exciting electron beams without the assumption of a standard density model. We also estimated the electron density along the magnetic flux rope and compared it to coronal models. Results: The radio sources infer a magnetic loop that is 1 solar radius in altitude with the highest frequency sources starting around 0.6 solar radii. Electron velocities were found between 0.13 c and 0.24 c with the front of the electron beam travelling faster than the back of the electron beam. The velocities correspond to energy ranges within the beam from 0.7-11 keV to 0.7-43 keV. The density along the loop is higher than typical coronal density models and the density gradient is smaller. Conclusions: We found that a more restrictive range of accelerated beam and background plasma parameters can result in U-bursts or J-bursts, causing type III

Relationship between type III-V radio and hard X-ray bursts

International Nuclear Information System (INIS)

Stewart, R.T.

1978-01-01

Type III-V radio bursts are found to be closely associated with impulsive hard X-ray bursts. Probably 0.1% to 1% of the fast electrons in the X-ray source region escape to heights >0.1 solar radii in the corona and excite the type III-V burst. (Auth.)

Flow Reversal of Fully-Developed Mixed MHD Convection in Vertical Channels

International Nuclear Information System (INIS)