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Hibernation Revived by Weak Magnetic Braking
2006-09-07
Cataclysmic variables undergo periodic nova explosions during which a finite mass of material is expelled on a short timescale. The system widens and, as a result, the mass-transfer rate drops. This state of hibernation may account for the variety of cataclysmic variable types observed in systems of similar mass and period. In the light of recent changes to the theory of nova ignition and magnetic braking we investigate whether hibernation remains a viable mechanism for creating cataclysmic variable diversity. We model the ratio of time spent as dwarf novae (DNe) to nova-like systems (NLs). Above a critical mass-transfer rate the system is NL and below it a DN. The dominant loss of angular momentum is by magnetic braking but the rate is uncertain. It is also uncertain what fraction of the mass accreted is expelled during the novae. We compare the models of the ratios against the period of the system for different magnetic braking rates and different ejected masses with the ratio of the number of observed NLs to DNe. We deduce that a rate of angular momentum loss a factor of ten smaller than that traditionally assumed is necessary if hibernation is to account for the observed ratios.
Mass transfer and the period gap of cataclysmic variables
1984-07-01
Three different explanations for the period gap of cataclysmic variables are investigated in some detail, and compared with the observations. The static picture is ruled out; strong continued magnetic braking is shown to be unlikely; disrupted magnetic braking is shown to provide a good explanation. A simple derivation is given for the magnetic braking of a star as a function of the magnetic-field strength and the wind mass flux. A field strength of >= 100 gauss and a wind of 10/sup -10/ Msub(solar mass) yr/sup -1/ are needed for the secondary of a cataclysmic variable to explain the braking. These values are rather high, but perhaps not unfeasible.
2008-01-01
ABSTRACT We apply population synthesis techniques to calculate the present-day number of two types of white-dwarf main-sequence star (WDMS) binaries within the cataclysmic variable 2 to 3 h period gap. The first are post-common envelope binaries with secondary stars that have masses Formula Not Shown (gPCEBs), such that they will commence mass transfer within the period gap. The second type are systems that were cataclysmic variables (CVs) at some point in their past, but detached once they evolved down in orbital period to 3 h as a consequence of disrupted magnetic braking, and are crossing the period gap via gravitational radiation detached cataclysmic variables (dCVs). Full population synthesis calculations are performed where we either assume constant, global values of the common envel...
Novae Crossing the Thermal Stability Line
1998-11-27
A method, based on the disc instability model, for testing the thermal stability of Cataclysmic Variables (CVs), is presented. It is shown that the border line between thermal stability and instability is crossed during some nova outbursts and decays, however it is not clear whether this is the general behaviour. We suggest two new evolutionary scenarios for short orbital period CVs. One of them is the analogy for the 'modified hibernation scenario' and the other is an extension of the ideas of Mukai and Naylor (1993) for long orbital period CVs. We conclude that the observations have not favoured one of the two models. Finally, we speculate the existence of a new type of nova - an AM CVn like nova.
2006-11-17
The population of non magnetic cataclysmic variables evolving under the influence of a circumbinary disk is investigated for systems above the upper edge of the period gap at orbital periods greater than 2.75hr. For a fractional mass input rate into the disk, corresponding to 3e-4 of the mass transfer rate, the model systems exhibit a bounce at orbital periods greater than 2.75hr. The simulations reveal that (1) some systems can exist as dwarf nova type systems throughout their lifetime, (2) dwarf nova type systems can evolve into nova-like systems as their mass transfer rate increases with increasing circumbinary disk mass, and (3) nova-like systems can evolve back into dwarf nova systems during their postbounce evolution to longer orbital periods. Among these subclasses, nova-like cataclysmic variables would be the best candidates to search for circumbinary disks at wavelengths greater than 10 micron. The theoretical orbital period distribution of our population synthesis model is in reasonable accord with the combined population of dwarf novae and nova-like systems above the period gap, suggesting the possibility that systems with unevolved donors need not detach and evolve below the period gap as in the disrupted magnetic braking model. The resulting population furthermore reveals the possible presence of systems with small mass ratios (a property of systems exhibiting superhump phenomena at long orbital periods) and a preference of O/Ne/Mg white dwarfs in dwarf nova systems in comparison to nova-like systems. The importance of observational bias in accounting for the differing populations is examined, and it is shown that an understanding of these effects is necessary in order to confront the theoretical distributions with the observed ones in a meaningful manner. (abridged)
Aims:The source AC Cnc is a nova-like cataclysmic variable containing a white-dwarf primary with a mass of 0.76 M? and a K2-type secondary with a mass of 0.77 M?. We intend to study its period changes and search for evidence of magnetic braking and unseen third body. Methods: The period changes were investigated based on the analysis of the O-C curve, which is formed by one new eclipse time together with the others compiled from the literature. Results: A cyclic change with a period of 16.2 yr was found to be superimposed on a long-term period decrease at a rate of dot{P}=-1.24(0.44){10-8} days/year. Conclusions: It is shown that the mechanism of magnetic activity-driven changes in the quadrupole momentum of the secondary star (Applegate's mechanism) does not explain it easily. This period oscillation was plausibly interpreted by a light-travel time effect caused by the presence of a cool M-type dwarf companion (M_3>0.097 M?) in a long orbit (16.2 yr) around the binary. Since the masses of both components are nearly the same, the mass transfer from the lobe-filling secondary to the primary is not efficient to cause the continuous period decrease. It may be strong evidence of an enhanced magnetic stellar wind from the K2-type component. If the Alfn radius of the cool secondary is the same as that of the Sun (i.e., RA = 15 R?), the mass-loss rate should be dot{M_2}=-1.65{10-10} M?/year. By using the enhanced mass loss proposed by Tout & Eggleton (1988), the mass-loss rate should be dot{M_2}=-1.18{10-9} M?/year. In this case, the Alfn radius is determined to be RA = 5.2 R?. However, the long-term decrease of the period may be only a part of a long-period (>100 yr) oscillation caused by the presence of an additional body. To check the conclusions, new precise times of light minimum will be required.
General Properties of Quiescent Novae
2002-06-26
The observed properties of novae before and after eruption are discussed. The distribution of orbital periods of novae shows a concentration near 3.2 h, which resembles that of magnetic cataclysmic variables, and there is some evidence that many of the novae themselves are magnetic near that orbital period. Desynchronisation of polars by nova eruptions can lead to an estimate (~2 x 10^3 y) for the time between eruptions for the strongly magnetic systems; this is much shorter than that found from other methods. The similarity of pre- and post-nova luminosities, at high rates of mass transfer, is ascribed to irradiation of the secondary producing a self-sustained high Mdot state. This slows cooling of the white dwarf after eruption, delays the onset of full scale dwarf nova outbursts in most systems, and delays any descent into a hibernation state of low rate of mass transfer.
K-BAND SPECTROSCOPY OF (PRE-)CATACLYSMIC VARIABLES: ARE SOME DONOR STARS REALLY CARBON POOR?
2010-01-01
We present a new sample of K-band spectral observations for cataclysmic variables (CVs): non-magnetic and magnetic as well as present-day and pre-CVs. The purpose of this diverse sample is to address the recent claim that the secondary stars in dwarf novae are carbon deficient, having become so through a far more evolved evolution than the current paradigm predicts. Our new observations, along with previous literature results, span a wide range of orbital period and CV type. In general, dwarf novae in which the secondary star is seen show weak to no CO absorption while polar and pre-CV donor stars appear to have normal CO absorption for their spectral type. However, this is not universal. The presence of normal looking CO absorption in the dwarf nova SS Aur and the hibernating CV QS Vir and a complete lack of CO absorption in the long-period polar V1309 Ori cloud the issue. A summary of ...
V405 Peg (RBS 1955): A Nearby, Low-Luminosity Cataclysmic Binary
2009-04-22
(Abridged). The cataclysmic binary V405 Peg, originally discovered as ROSAT Bright Source (RBS) 1955 (= 1RXS J230949.6+213523), shows a strong contribution from a late-type secondary star in its optical spectrum, which led Schwope et al. to suggest it to be among the nearest cataclysmic binaries. We present extensive optical observations of V405 Peg. Time-series spectroscopy shows the orbital period, Porb, to be 0.1776469(7) d (= 4.2635 hr), or 5.629 cycle/d. We classify the secondary as M3 - M4.5. Astrometry with the MDM 2.4m telescope gives a parallax 7.2 +- 1.1 milli-arcsec, and a relative proper motion of 58 mas/yr. Our best estimate of the distance yields d = 149 (+26, -20) pc. The secondary stars's radial velocity has K2 = 92 +- 3 km/s, indicating a fairly low orbital inclination if the masses are typical. Extensive I-band time-series observations in the show the system varying between a minimum brightness level of I = 14.14 and states of enhanced activity about 0.2 mag brighter. While the low-state shows an ellipsoidal modulation, an additional photometric modulation appears in the high state, with 0.1 mag amplitude and period 220-280 min. The frequency of this modulation appears to be stable for a month or so, but no single period was consistently detected from one observing season to the next. We estimate the system luminosity by combining optical measurements with the archival X-ray spectrum. The implied mass accretio n rate is orders of magnitudes below the predictions for the standard angular momentum loss above the period gap. The system may possibly belong to a largely undiscovered population of hibernating CVs.
Spectroscopic analysis of tremendous--outburst--nova candidates
2004-11-08
In the course of a long-term project investigating classical novae with large outburst amplitudes, we have performed optical spectroscopy of several old-nova candidates. We here present the spectra of the candidates V630 Sgr, XX Tau, CQ Vel, V842 Cen, and V529 Ori, that hitherto lacked such classification. While the first four show typical spectra for cataclysmic variables, and can thus be identified as such, V529 Ori is probably misclassified. Of special interest are the two systems XX Tau and V842 Cen, which show all signs for being low mass transfer systems. As such they can be used to judge the evolution scenarios for novae. In particular, given the rather young age of their outburst, it appears more likely that these systems are not on their way into hibernation, (i.e., cutting off mass transfer for a longer period of time), but are simply settling down towards their original configuration of comparatively low, but steady, mass transfer, such as for dwarf novae.
Response of Gut Microbiota to Fasting and Hibernation in Syrian Hamsters▿ †
2009-10-01
Although hibernating mammals wake occasionally to eat during torpor, this period represents a state of fasting. Fasting is known to alter the gut microbiota in nonhibernating mammals; therefore, hibernation...Full Text Available
Thermal stability and nova cycles in permanent superhump systems
2000-07-10
Archival data on permanent superhump systems are compiled to test the thermal stability of their accretion discs. We find that their discs are almost certainly thermally stable as expected. This result confirms Osaki's suggestion (1996) that permanent superhump systems form a new subclass of cataclysmic variables (CVs), with relatively short orbital periods and high mass transfer rates. We note that if the high accretion rates estimated in permanent superhump systems represent their mean secular values, then their mass transfer rates cannot be explained by gravitational radiation, therefore, either magnetic braking should be extrapolated to systems below the period gap or they must have mass transfer cycles. Alternatively, a new mechanism that removes angular momentum from CVs below the gap should be invoked. We suggest applying the nova cycle scenarios offered for systems above the period gap to the short orbital period CVs. Permanent superhumps have been observed in the two non-magnetic ex-novae with binary periods below the gap. Their post-nova magnitudes are brighter than their pre-outburst values. In one case (V1974 Cyg) it has been demonstrated that the pre-nova should have been a regular SU UMa system. Thus it is the first nova whose accretion disc was observed to change its thermal stability. If the superhumps in this system indicate persistent high mass transfer rates rather than a temporary change induced by irradiation from the hot post-nova white dwarf, it is the first direct evidence for mass transfer cycles in CVs. The proposed cycles are driven by the nova eruption.
The mass and radius of the M-dwarf in the short period eclipsing binary RR Caeli
2007-01-31
We present new photometry and spectroscopy of the eclipsing white dwarf - M-dwarf binary star RR Cae. We use timings of the primary eclipse from white-light photo-electric photometry to derive a new ephemeris for the eclipses. We find no evidence for any period change greater than Pdot/P ~ 5E-12 over a timescale of 10 years. We have measured the effective temperature of the white dwarf, T_WD, from an analysis of two high resolution spectra of RR Cae and find T_WD = (7540 +- 175)K. We estimate a spectral type of M4 for the companion from the same spectra. We have combined new spectroscopic orbits for the white dwarf and M-dwarf with an analysis of the primary eclipse and cooling models for helium white dwarfs to measure the mass and radius of the M-dwarf. The mass of the M-dwarf is (0.182 - 0.183) +- 0.013 Msun and the radius is (0.203 - 0.215) +- 0.013 Rsun, where the ranges quoted for these values reflect the range of white dwarf models used. In contrast to previous studies, which lacked a spectroscopic orbit for the white dwarf, we find that the mass and radius of the M-dwarf are normal for an M4 dwarf. The mass of the white dwarf is (0.440 +-0.022) Msun. With these revised masses and radii we find that RR Cae will become a cataclysmic variable star when the orbital period is reduced from its current value of 7.3 hours to 121 minutes by magnetic braking in 9-20 Gyr. We note that there is night-to-night variability of a few seconds in the timing of primary eclipse caused by changes to the shape of the primary eclipse. We speculate as to the possible causes of this phenomenon. (Abridged)
2005-10-11
We present results of high time resolution photometry of the eclipsing pre-cataclysmic variable NN Ser. We observed 13 primary eclipses of NN Ser using the high-speed CCD camera ULTRACAM and derived times of mid-eclipse, from fitting of light curve models, with uncertainties as low as 0.06 s. The observed rates of period change appear difficult to reconcile with any models of orbital period change. If the observed period change reflects an angular momentum loss, the average loss rate is consistent with the loss rates (via magnetic stellar wind braking) used in standard models of close binary evolution, which were derived from observations of much more massive cool stars. Observations of low-mass stars such as NN Ser's secondary predict rates of ~100 times lower than we observe. We show that magnetic activity-driven changes in the quadrupole moment of the secondary star (Applegate, 1992) fail to explain the period change by an order of magnitude on energetic grounds, but that a light travel time effect caused by the presence of a third body in a long (~ decades) orbit around the binary could account for the observed changes in the timings of NN Ser's mid-eclipses. We conclude that we have either observed a genuine angular momentum loss for NN Ser, in which case our observations pose serious difficulties for the theory of close binary evolution, or we have detected a previously unseen low-mass companion to the binary.
Can angular momentum loss cause the period change of NN Ser?
2009-04-16
NN Ser is a non mass-transferring pre-cataclysmic variable containing a white dwarf with a mass of $\\sim 0.5 M_{\\odot}$ and an M dwarf secondary star with a mass of $\\sim 0.2 M_{\\odot}$. Based on the data detected by the high-speed CCD camera ULTRACAM, it was observed that the orbital period of NN Ser is decreasing, which may be caused by a genuine angular momentum loss or the presence of a third body. However, neither gravitational radiation and magnetic braking can ideally account for the period change of NN Ser. In this Letter, we attempt to examine a feasible mechanism which can drain the angular momentum from NN Ser. We propose that a fossil circumbinary disk (CB disk) around the binary may have been established at the end of the common envelope phase, and the tidal torques caused by the gravitational interaction between the disk and the binary can efficiently extract the orbital angular momentum from the system. We find that only if M dwarf has an ultra-high wind loss rates of $\\sim 10^{-10} M_{\\odot} \\rm yr^{-1}$, and a large fraction ($\\delta\\sim 10 %$) of wind loss is fed into the CB disk, the loss rates of angular momentum via the CB disk can interpret the period change observed in NN Ser. Such a wind loss rate and $\\delta$-value seem to be incredible. Hence it seems that the presence of a third body in a long orbit around the binary might account for the changing period of NN Ser.
Seasonal differences in the feeding ecology and behavior of male edible dormice (Glis glis)
2009-01-01
Mammalian hibernators undergo dramatic seasonal changes of food intake and the use of their gastrointestinal tract. During several months of hibernation fat-storing hibernators do not use their intestinal tract for nutritional intake. However, during the rest of the year they have to increase their energy intake in order to compensate high reproductive investment and store sufficient body fat to survive the following hibernation period. Edible dormice (Glis glis) are obligate fat-storing hibernators which hibernate in Germany from September until June. Males incur high energetic costs during mating and as soon as reproduction is terminated they have to accumulate high quantities of fat to survive hibernation. In order to understand how fat-storing hibernators like edible dormice cope with ...
Hibernation in the tropics: lessons from a primate
2005-01-01
The Malagasy primate Cheirogaleus medius hibernates in tree holes for 7months, although ambient temperatures during hibernation rise above 30C in their natural environment. In a field study we show that during hibernation the body temperature of most lemurs fluctuates between about 10C and 30C, closely tracking the diurnal fluctuations of ambient temperature passively. These lemurs do not interrupt hibernation by spontaneous arousals, previously thought to be obligatory for all mammalian hibernators. However, some lemurs hibernate in large trees, which provide better thermal insulation. Their body temperature fluctuates only little around 25C, but they show regular arousals, as known from temperate and arctic hibernators. The results from this study demonstrate that maximum body ...
Cool Sex? Hibernation and Reproduction Overlap in the Echidna
During hibernation there is a slowing of all metabolic processes, and thus it is normally considered to be incompatible with reproduction. In Tasmania the egg-laying mammal, the echidna (Tachyglossus...Full Text Available
Ca induced hypothermia in a hibernator /Citellus beechyi/
Results of perfusion of excess Ca and Na into the hypothalamus of the hibernating ground squirrel Citellus beechyi are presented. The significant finding is that perfused excess Ca causes a reduction in core ...
Magnetic Brake Considerations for the High-T c Superconducting Maglev Vehicle System
2010-01-01
Levitation, guidance and driving/braking are three indispensable parts for a high temperature superconducting Maglev vehicle system. To maintain the advantage of a passive, non-contact levitation system, a magnetic brake based on a discontinuous permanent magnet guideway (PMG) is introduced. Its feasibility is verified by the experimental investigations on the behavior of a levitated bulk high temperature superconductor (HTSC) moving towards the broken-off PMG. When the bulk moves towards the broken-off PMG, a braking force will be generated to hold back the bulk due to the inhomogeneous field distribution. That is to say, this magnetic braking mechanism can act as a safe-protection function. The magnetic brake just makes use of the existing PMG, which is very simple with no extra componen...
K-BAND SPECTROSCOPY OF (PRE-)CATACLYSMIC VARIABLES: ARE SOME DONOR STARS REALLY CARBON POOR?
We present a new sample of K-band spectral observations for cataclysmic variables (CVs): non-magnetic and magnetic as well as present-day and pre-CVs. The purpose of this diverse sample is to address the recent claim that the secondary stars in dwarf novae are carbon deficient, having become so through a far more evolved evolution than the current paradigm predicts. Our new observations, along with previous literature results, span a wide range of orbital period and CV type. In general, dwarf novae in which the secondary star is seen show weak to no CO absorption while polar and pre-CV donor stars appear to have normal CO absorption for their spectral type. However, this is not universal. The presence of normal looking CO absorption in the dwarf nova SS Aur and the hibernating CV QS Vir and a complete lack of CO absorption in the long-period polar V1309 Ori cloud the issue. A summary of the literature pointing to non-solar abundances including enhanced N V/C IV ratios is presented. It appears that some CVs have non-solar abundance material accreting onto the white dwarf suggesting an evolved secondary star while for others CO emission in the accretion disk may play a role. However, the exact mechanism or combination of factors causing the CO absorption anomaly in CVs is not yet clear.
HS2237+8154: On the onset of mass transfer or entering the period gap?
2004-02-09
We report follow-up observations of a new white dwarf/red dwarf binary HS2237+8154, identified as a blue variable star from the Hamburg Quasar Survey. Ellipsoidal modulation observed in the R band as well as the Halpha radial velocity variations measured from time-resolved spectroscopy determine the orbital period to be Porb=178.10+-0.08min. The optical spectrum of HS2237+8154 is well described by a combination of a Teff=11500+-1500K white dwarf (assuming log g=8) and a dM3.5+-0.5 secondary star. The distance implied from the flux scaling factors of both stellar components is d=105+-25pc. Combining the constraints obtained from the radial velocity of the secondary and from the ellipsoidal modulation, we derive a binary inclination of i~50deg-70deg and stellar masses of Mwd=0.47-0.67Msun and Msec=0.2-0.4Msun. All observations imply that the secondary star must be nearly Roche-lobe filling. Consequently, HS2237+8154 may be either a pre-cataclysmic variable close to the start of mass transfer, or (considering its orbital period) a cataclysmic variable that terminated mass transfer and entered the period gap, or a hibernating nova.
Cataclysmic Variables and a Candidate Helium White Dwarf in the Globular Cluster NGC 6397
We have used HST/FOS to study faint UV stars in the core of the nearby globular cluster NGC 6397. We confirm the presence of a 4th cataclysmic variable (CV) in NGC 6397 (CV 4), and we use the photometry of Cool et al. (1998) to present evidence that CVs 1--4 all have faint disks and probably low accretion rates. By combining these results with new UV spectra of CV 1 and the published spectra of Grindlay et al. (1995) we present new evidence that CVs 1--3 may be DQ Her systems, and we show that CV 4 may either be a dwarf nova or another magnetic system. Another possibility is that the CVs could be old novae in hibernation between nova eruptions. We also present the first spectrum of a member of a new class of UV bright stars in NGC 6397. These faint, hot stars do not vary, unlike the CVs, and are thus denoted as ``non-flickerers'' (NFs). Like the CVs, their spatial concentration is strongly concentrated toward the cluster center. Using stellar atmosphere models we have determined log g = 6.25, and T_eff = 17,500 K for this NF. Using these line parameters and the luminosity of the NF we show that the NF spectrum is consistent with a helium WD having a mass of ~0.25 solar masses and an age between 0.1 and 0.5 Gyr (depending on the models used). The NF spectrum appears to be significantly Doppler shifted from the expected wavelength, suggesting the presence of a dark, massive companion, probably a carbon-oxygen WD.
Yearlong hibernation in a marsupial mammal
2007-01-01
Many mammals hibernate each year for about 6months in autumn and winter and reproduce during spring and summer when they are generally not in torpor. I tested the hypothesis that the marsupial pygmy-possum (Cercartetus nanus), an opportunistic nonseasonal hibernator with a capacity for substantial fattening, would continue to hibernate well beyond winter. I also quantified how long they were able to hibernate without access to food before their body fat stores were depleted. Pygmy-possums exhibited a prolonged hibernation season lasting on average for 310days. The longest hibernation season in one individual lasted for 367days. For much of this time, despite periodic arousals after torpor bouts of 12.5days, energy expenditure was reduced to only 2.5% of that predicted for act...
Angular Momentum Loss by Magnetic Braking and Gravitational Radiation in Relativistic Binary Stars
2008-11-05
Angular momentum loss (AML) mechanisms and dynamical evolution owing to magnetic braking and gravitational radiation in relativistic binary stars (RBS) are studied with use of physical parameters collected from the literature. We have calculated and compared AML time scales for the RBS with non-degenerate components and double degenerate (DD) systems.
Energy conservation in hibernating endotherms: Why suboptimal temperatures are optimal
2010-01-01
Many endotherms use facultative heterothermic responses of torpor or hibernation to conserve energy during periods of low energy availability. A common assumption when estimating winter energy budgets is that endotherms should hibernate at the ambient temperature (Ta) that minimizes torpid metabolic rate (TMR) and maximizes the duration of torpor bouts. However, previous studies of the energetic benefits of hibernation have assumed constant Ta within hibernacula. Here we use an individual-based energetic model to estimate overwinter energy expenditure of mammals hibernating at Tas that vary temporally. We show that, in accordance with the principles of Jenson's inequality, hibernators can conserve energy by selecting microclimates warmer than the single Ta value that minimizes TMR (Tmin). ...
Cardiac function adaptations in hibernating grizzly bears (Ursus arctos horribilis)
2010-01-01
Research on the cardiovascular physiology of hibernating mammals may provide insight into evolutionary adaptations; however, anesthesia used to handle wild animals may affect the cardiovascular parameters of interest. To overcome these potential biases, we investigated the functional cardiac phenotype of the hibernating grizzly bear (Ursus arctos horribilis) during the active, transitional and hibernating phases over a 4year period in conscious rather than anesthetized bears. The bears were captive born and serially studied from the age of 5months to 4years. Heart rate was significantly different from active (82.67.7beats/min) to hibernating states (17.82.8beats/min). There was no difference from the active to the hibernating state in diastolic and stroke volume param...
MAGNETIC BRAKING AND PROTOSTELLAR DISK FORMATION: AMBIPOLAR DIFFUSION
2009-01-01
It is established that the formation of rotationally supported disks during the main accretion phase of star formation is suppressed by a moderately strong magnetic field in the ideal MHD limit. Nonideal MHD effects are expected to weaken the magnetic braking, perhaps allowing the disk to reappear. We concentrate on one such effect, ambipolar diffusion, which enables the field lines to slip relative to the bulk neutral matter. We find that the slippage does not sufficiently weaken the braking to allow rotationally supported disks to form for realistic levels of cloud magnetization and cosmic ray ionization rate. In some cases, the magnetic braking is even enhanced. Only in dense cores with both exceptionally weak fields and unreasonably low ionization rate do such disks start to form in our simulations. We conclude that additional processes, such as Ohmic dissipation or Hall ...
2008-01-01
Specific features of the spatial distribution and localization of bats have been studied during their hibernation in artificial caves of Samarskaya Luka. The proportion of cave area occupied by bats varies from 70 to 93% in large caves (
2004-05-01
Objectives: To assess whether quantification of myocardial systolic velocities by pulsed wave tissue Doppler imaging can differentiate between stunned, hibernating, and scarred myocardium.Design:...Full Text Available
2008-12-01
Full Text Available.Reduced skeletal loading typically leads to bone loss because bone formation and bone resorption become unbalanced. Hibernation is a natural model of musculoskeletal disuse because hibernating animals greatly reduce weight-bearing activity, and therefore, they would be expected to lose bone. Some evidence suggests that small mammals like ground squirrels, bats, and hamsters do lose bone during hibernation, but the mechanism of bone loss is unclear. In contrast, hibernating bears maintain balanced bone remodeling and preserve bone structure and strength. Differences in the skeletal responses of bears and smaller mammals to hibernation may be due to differences in their hibernation patterns; smaller mammals may excrete calcium liberated from bone during periodic arousals throughout hibernation, leading to progressive bone loss over time, whereas bears may have evolved more sophisticated physiological processes to recycle calcium, prevent hypercalcemia, and maintain bone integrity. Investigating the roles of neural and hormonal control of bear bone metabolism could give valuable insight into translating the mechanisms that prevent disuse-induced bone loss in bears into novel therapies for treating osteoporosis.
Female Cantabrian bears and their young do not hibernate
2010-10-06
A team of Spanish scientists followed the brown bear population through the mountains of the Cantabrian Cordillera between 1998 and 2007 in order to find out about their hibernation habits, which had been questioned in ...
Bats Facing Regional Extinction From White-Nose Syndrome (7 of 9)
2010-08-05
Researcher conducting annual counts of hibernating bats. Biologists in New York first noticed a problem in 2007 when they discovered white fungus growing on hibernating bats and unusually high numbers of dead bats at ...
The DA+dMe eclipsing binary EC13471-1258: its cup runneth over...just
2003-07-08
EC13471-1258 is a detached eclipsing binary with Porb = 3h37m, comprising a DA white dwarf and a dMe dwarf. Total eclipses of the white dwarf lasting 14 min, and a large amplitude ellipsoidal variation are seen in the light curve. Flares from the dMe star occur regularly. Each star contributes roughly equal amounts of light at 5500 Ang. HST STIS spectra show strong Ly alpha with weak metal lines, and yield Teff = 14220 K, log g = 8.34, Z = 1/30th solar, K = 138 km/s and V sin i = 400 km/s for the white dwarf. Optical spectra yield the spectral type (M3.5-4.0), Teff = 3100 K, Z = solar, K = 266 km/s and V sin i = 140 km/s for the dMe star. The H alpha emission line comprises 2 or more components and implies that very weak mass transfer is occurring. The dynamical solution also implies that the dMe star just fills its Roche lobe. Accurate masses and radii for each star were derived: the dMe values favour the Clemens et al. (1998) mass-radius relation. The large rotational velocity of the white dwarf (400 km/s) suggests that the system has transferred mass in the past so that it is presently a hibernating cataclysmic variable. The metallicity contrast between the component stars provides an opportunity for tests of diffusion theory.
K-Band Spectroscopy of (Pre-)Cataclysmic Variables: Are Some Donor Stars Really Carbon Poor?
2010-02-19
We present a new sample of $K$-band spectral observations for CVs: non-magnetic and magnetic as well as present day and pre CVs. The purpose of this diverse sample is to address the recent claim that the secondary stars in dwarf novae are carbon deficient, having become so through a far more evolved evolution than the current paradigm predicts. Our new observations, along with previous literature results, span a wide range of orbital period and CV type. In general, dwarf novae in which the secondary star is seen show weak to no CO absorption while polar and pre-CV donor stars appear to have normal CO absorption for their spectral type. However, this is not universal. The presence of normal looking CO absorption in the dwarf nova SS Aur and the hibernating CV QS Vir and a complete lack of CO absorption in the long period polar V1309 Ori cloud the issue. A summary of the literature pointing to non-solar abundances including enhanced NV/CIV ratios is presented. It appears that some CVs have non-solar abundance material accreting onto the white dwarf suggesting an evolved secondary star while for others CO emission in the accretion disk may play a role. However, the exact mechanism or combination of factors causing the CO absorption anomaly in CVs is not yet clear.
Magnetic Braking and Protostellar Disk Formation: Ambipolar Diffusion
2008-09-23
It is established that the formation of rotationally supported disks during the main accretion phase of star formation is suppressed by a moderately strong magnetic field in the ideal MHD limit. Non-ideal MHD effects are expected to weaken the magnetic braking, perhaps allowing the disk to reappear. We concentrate on one such effect, ambipolar diffusion, which enables the field lines to slip relative to the bulk neutral matter. We find that the slippage does not sufficiently weaken the braking to allow rotationally supported disks to form for realistic levels of cloud magnetization and cosmic ray ionization rate; in some cases, the magnetic braking is even enhanced. Only in dense cores with both exceptionally weak fields and unreasonably low ionization rate do such disks start to form in our simulations. We conclude that additional processes, such as Ohmic dissipation or Hall effect, are needed to enable disk formation. Alternatively, the disk may form at late times when the massive envelope that anchors the magnetic brake is dissipated, perhaps by a protostellar wind.
1984-12-11
A hydraulic shock absorber of the dash pot kind for use with electrically conducting liquid such as sodium, has magnet means for electro magnetically braking a stream of liquid discharged from the cylinder. The shock absorber finds use in a liquid metal cooled nuclear reactor for arresting control rods.
2007-01-01
Understanding temperatures used by hibernating bats will aid conservation and management efforts for many species. A limestone mine with 71 km of passages, used as a hibernaculum by approximately 30,000 bats, was visited four times during a 6-year period. The mine had been surveyed and mapped; therefore, bats could be precisely located and temperatures (T s) of the entire hibernaculum ceiling accurately mapped. It was predicted that bats should hibernate between 5 and 10C to (1) use temperatures that allow a near minimal metabolic rate, (2) maximize the duration of hibernation bouts, (3) avoid more frequent and prolonged arousal at higher temperatures, (4) avoid cold and freezing temperatures that require an increase in metabolism and a decrease in duration of hibernation bouts or that c...
The oxygen-radiation effects on the conservation of radiation injuries during hibernation were studied in frogs exposed to 900 r in a nitrogen atmosphere. Preliminary data indicate morphological changes in the epithelium begin developing after the awakening. Moreover, the radiation injuries are not altered during hibernation but are slowed down, confirming the existence of a radiation conservation mechanism. Experimental studies of protective effects of hypoxia show different morphological changes in cornea epithelium during hibernation and after awakening. Administration of hypoxia during irradiation of hibernating animals was not effective while hypoxia admninistered in active animals at the moment of exposure showed positive results, also confirming the protective effects of hypoxia during the initial stages of radiation injury. (R.V.J.)
Rodent predation on hibernating peacock and small tortoiseshell butterflies
2008-01-01
Insects that hibernate as adults have a life span of almost a whole year. Hence, they must have extraordinary adaptations for adult survival. In this paper, we study winter survival in two butterflies that hibernate as adults and have multimodal anti-predator defencesthe peacock, Inachis io, which has intimidating eyespots that are effective against bird predation, and the small tortoiseshell, Aglais urticae, which does not have an effective secondary defence against birds. We assessed predation on wild butterflies hibernating in the attic of an unheated house, as well as survival of individually marked butterflies placed by hand on different sites in the attic. Our objectives were to assess (1) the number of butterflies that were killed during hibernation, (2) whether survival differed...
Progressive activation of paratrigeminal nucleus during entrance to hibernation
The paratrigeminal nucleus (Pa5) undergoes a progressive increase in its uptake of 2-({sup 14}C)deoxyglucose (2DG) relative to other brain structures during entrance to hibernation in the ground squirrel. This highly significant increase results in the Pa5 becoming the most highly labeled brain region during hibernation, even though it exhibits one of the lowest levels of 2DG uptake in the brain during the nonhibernating state. The progressive activation of the Pa5 observed during entrance is reversed during arousal from hibernation. These observations and the neuroanatomical projections of the Pa5 implicate this nucleus as playing a role in the entrance and maintenance of the hibernating state.
Progressive activation of paratrigeminal nucleus during entrance to hibernation
1988-07-01
The paratrigeminal nucleus (Pa5) undergoes a progressive increase in its uptake of 2-({sup 14}C)deoxyglucose (2DG) relative to other brain structures during entrance to hibernation in the ground squirrel. This highly significant increase results in the Pa5 becoming the most highly labeled brain region during hibernation, even though it exhibits one of the lowest levels of 2DG uptake in the brain during the nonhibernating state. The progressive activation of the Pa5 observed during entrance is reversed during arousal from hibernation. These observations and the neuroanatomical projections of the Pa5 implicate this nucleus as playing a role in the entrance and maintenance of the hibernating state.
Progressive activation of paratrigeminal nucleus during entrance to hibernation
1988-01-01
The paratrigeminal nucleus (Pa5) undergoes a progressive increase in its uptake of 2-[14C]deoxyglucose (2DG) relative to other brain structures during entrance to hibernation in the ground squirrel. This highly significant increase results in the Pa5 becoming the most highly labeled brain region during hibernation, even though it exhibits one of the lowest levels of 2DG uptake in the brain during the nonhibernating state. The progressive activation of the Pa5 observed during entrance is reversed during arousal from hibernation. These observations and the neuroanatomical projections of the Pa5 implicate this nucleus as playing a role in the entrance and maintenance of the hibernating state
2010-01-01
Ghrelin is a recently discovered hormone which has profound effects on food intake and lipogenesis in mammals. In all mammals studied thus far, plasma ghrelin concentrations are increased before a meal and decrease immediately following a meal; ghrelin levels increase with fasting. The golden-mantled ground squirrel Spermophilus lateralis (also known as Callospermophilus lateralis (see Helgen et al., 2009) is a diurnal hibernator which has a robust annual cycle of body mass gain and loss that is primarily controlled by food intake. We hypothesized that in spring, summer, and autumn, the endogenous ghrelin concentrations of hibernators would be similar to those of non-hibernators, but that during the winter hibernation season, plasma ghrelin concentrations would be low or undetectable. We f...
Hibernating bears as a model for preventing disuse osteoporosis
2006-01-01
The hibernating bear is an excellent model for disuse osteoporosis in humans because it is a naturally occurring large animal model. Furthermore, bears and humans have similar lower limb skeletal morphology, and bears walk plantigrade like humans. Black bears (Ursus americanus) may not develop disuse osteoporosis during long periods of disuse (i.e. hibernation) because they maintain osteoblastic bone formation during hibernation. As a consequence, bone volume, mineral content, porosity, and strength are not adversely affected by annual periods of disuse. In fact, cortical bone bending strength has been shown to increase with age in hibernating black bears without a significant change in porosity. Other animals require remobilization periods 2-3 times longer than the immobilization period t...
2009-01-01
Disuse typically causes an imbalance in bone formation and bone resorption, leading to losses of cortical and trabecular bone. In contrast, bears maintain balanced intracortical remodeling and prevent cortical bone loss during disuse (hibernation). Trabecular bone, however, is more detrimentally affected than cortical bone in other animal models of disuse. Here we investigated the effects of hibernation on bone remodeling, architectural properties, and mineral density of grizzly bear (Ursus arctos horribilis) and black bear (Ursus americanus) trabecular bone in several skeletal locations. There were no differences in bone volume fraction or tissue mineral density between hibernating and active bears or between pre- and post-hibernation bears in the ilium, distal femur, or calcaneus. Though...
Comparing hypothermia in the human and the black bear (Ursus americanus)
2010-01-01
Hearts of small hibernators can resist lethal arrhythmias seen in hypothermic non-hibernators. While studies have confirmed this in small mammals, there are no data on large hibernators in hypothermia. We present data on the effects of hypothermia on hearts of large hibernators, black bears. We compare the electrophysiologic changes the heart undergoes in hypothermia between black bears and humans while also considering data obtained from hibernating bears. Specifically, we compare heart rate (HR) and QT interval with core body temperature. The last part of the QT is the time during which the heart electrically repolarises and mechanically relaxes. During this time the heart is vulnerable to fibrillation. Animal hypothermia data were obtained using human EKG equipment on three black bears ...
UV emission as diagnostics for wind dynamics in cataclysmic variables
The International Ultraviolet Explorer (IUE) database was used to analyze the UV line shapes of cataclysmic variables (CV's). The standard reduction package at the IUE Regional Data Analysis Facility ...
Cataclysmic variables and related objects
This volume begins with an introductory chapter on general properties of cataclysmic variables. Chapters 2 through 5 of Part 1 are devoted to observations and interpretation of dwarf novae and nova-like stars. ...
Cataclysmic Variables as Synchrotron Sources?
Evidence is mounting that cataclysmic variables are weak sources of synchrotron emission. If true, it demonstrates that accretion powered interacting binaries produce such emission whether their primaries are white dwarfs, neutron stars, or black holes.
Cataclysmic Variables as Synchrotron Sources?
2008-01-01
Evidence is mounting that cataclysmic variables are weak sources of synchrotron emission. If true, it demonstrates that accretion powered interacting binaries produce such emission whether their primaries are white dwarfs, neutron stars, or black holes
Magnetic braking in ultracompact binaries
2010-06-22
Angular momentum loss in ultracompact binaries, such as the AM Canum Venaticorum stars, is usually assumed to be due entirely to gravitational radiation. Motivated by the outflows observed in ultracompact binaries, we investigate whether magnetically coupled winds could in fact lead to substantial additional angular momentum losses. We remark that the scaling relations often invoked for the relative importance of gravitational and magnetic braking do not apply, and instead use simple non-empirical expressions for the braking rates. In order to remove significant angular momentum, the wind must be tied to field lines anchored in one of the binary's component stars; uncertainties remain as to the driving mechanism for such a wind. In the case of white dwarf accretors, we find that magnetic braking can potentially remove angular momentum on comparable or even shorter timescales than gravitational waves over a large range in orbital period. We present such a solution for the 17-minute binary AM CVn itself which admits a cold white dwarf donor and requires that the accretor have surface field strength ~6E4 G. Such a field would not substantially disturb the accretion disk. Although the treatment in this paper is necessarily simplified, and many conditions must be met in order for a wind to operate as proposed, it is clear that magnetic braking cannot easily be ruled out as an important angular momentum sink. We finish by highlightin g observational tests that in the next few years will allow an assessment of the importance of magnetic braking.
Long-term optical and X-ray observations of the old novae DI Lacertae and V841 Ophiuchi
2000-08-29
We present an analysis of ground-based optical photometry and spectroscopy, and Rossi X-ray Timing Explorer X-ray observations of the old novae DI Lacertae and V841 Ophiuchi. Our optical photometry data (obtained with the automated photometry telescope RoboScope) comprise an almost decade-long light curve for each star, while the contemporaneous spectroscopy and X-ray observations repeatedly sampled each nova during separate intervals of ~45-55 d in length. The long-term optical light curves of both novae reveal quasiperiodic variability on typical time scales of ~30-50 d with amplitudes of dV ~ 0.4-0.8 mag. V841 Oph also displays a long-term, sinusoidal modulation of its optical light on a time scale of 3.5-5 yr. The optical spectra of these novae display quite different characteristics from each other, with DI Lac showing narrow Balmer emission cores situated in broad absorption troughs while V841 Oph exhibits strong single-peaked Balmer, He I and He II emission lines. We find little change between spectra obtained during different optical brightness states. The X-ray count rates for both novae were very low (< ~1.5 ct/s) and there was no reliable correlation between X-ray and optical brightness. The combined X-ray spectrum of DI Lac is best fit by a bremsstrahlung emission model (with kT ~ 4 keV and N_H < 1.8x10^22 cm^-3); the X-ray spectrum of V841 Oph is too weak to allow model fitting. We discuss the possible origin of variability in these old novae in terms of magnetic activity on the secondary star, dwarf nova type disk instabilities, and the ``hibernation'' scenario for cataclysmic variable stars.
Cool sex? Hibernation and reproduction overlap in the echidna.
During hibernation there is a slowing of all metabolic processes, and thus it is normally considered to be incompatible with reproduction. In Tasmania the egg-laying mammal, the echidna (Tachyglossus aculeatus) hibernates for several months before mating in mid-winter, and in previous studies we observed males with females that were still hibernating. We monitored the reproductive activity of radio-tracked echidnas by swabbing the reproductive tract for sperm while external temperature loggers provided information on the timing of hibernation. Additional information was provided by camera traps and ultrasound imaging. More than a third of the females found in mating groups were torpid, and the majority of these had mated. Some females re-entered deep torpor for extended periods after mating. Ultrasound examination showed a developing egg in the uterus of a female that had repeatedly re-entered torpor. The presence of fresh sperm in cloacal swabs taken from this female on three occasions after her presumed date of fertilization indicated she mated several times after being fertilized. The mating of males with torpid females is the result of extreme competition between promiscuous males, while re-entry into hibernation by pregnant females could improve the possibility of mating with a better quality male.
2008-01-01
Some hibernating animals are known to reduce muscle and bone loss associated with mechanical unloading during prolonged immobilisation, compared to humans. However, here we show that wild pregnant polar bears (Ursus maritimus) are the first known animals to avoid significant bone loss altogether, despite six months of continuous hibernation. Using serum biochemical markers of bone turnover, we showed that concentrations for bone resorption are not significantly increased as a consequence of hibernation in wild polar bears. This is in sharp contrast to previous studies on other hibernating species, where for example, black bears (Ursus americanus), show a 3–4 fold increase in serum bone resorption concentrations post-hibernation, and must compensate for this loss through rapid bone recovery on remobilisation, to avoid the risk of fracture. In further contrast to black bears, serum concentrations of bone formation markers were highly significantly increased in pregnant female polar bears compared to non-pregnant, thus non-hibernating females both prior to and after hibernation. However, bone formation concentrations in new mothers were significantly reduced compared to pre-hibernation concentrations. The de-coupling of bone turnover in favour of bone formation prior to hibernation, suggests that wild polar bears may posses a unique physiological mechanism for building bone in protective preparation against expected osteopenia associated with disuse, starvation, and hormonal drives to mobilise calcium for reproduction, during hibernation. Understanding this physiological mechanism could have profound implications for a natural solution for the prevention of osteoporosis in animals subjected to captivity with inadequate space for exercise, humans subjected to prolonged bed rest while recovering from illness, or astronauts exposed to antigravity during spaceflight.Alanda R. Lennox and Allen E. Goodship Publisher: Elsevier Science Contributor: School of Medical Science : Pathology Other identifier: Comparative Biochemistry and Physiology A-Molecular and Integrative Physiology, 2008; 149:203-208; 1095-6433; 0020084891; 10.1016/j.cbpa.2007.11.012 Language: en
2005-01-01
SummaryMetabolic depression, an adaptive biological process for energy preservation, is responsible for torpor, hibernation and estivation. We propose that a form of metabolic depression, and not mitochondrial dysfunction, is the process underlying the observed hypometabolism, state-dependent neurobiological changes and vegetative symptoms of major depression in humans. The process of metabolic depression is reactivated via differential gene expression in response to perceived adverse stimuli in predisposed persons. Behavior inhibition by temperament, anxiety disorders, genetic vulnerabilities, and early traumatic experiences predispose persons to depression. The proposed theory is supported by similarities in the presentation and neurobiology of hibernation in bears and major depression a...
1990-01-01
This paper provides a semi-popular account of the discovery that short-beaked echidnas, Tachyglossus aculeatus, hibernate. The discovery was made in Australian Alps, where echidnas with implanted temperature-sensitive transmitters were tracked through winter and found drop their body temperatures close to ambient temperature during winter, with arousals to normal body temperature (about 32oC) every couple of weeks. This is the same pattern shown in northern hemisphere hibernators such as marmots and ground squirrels, and suggests that the capacity for hibernation is an ancient rather than a very advanced characteristic. Coverage: 1990-01-01T00:00:00Z
Testing theoretical models of magnetic damping using an air track
2007-02-07
Magnetic braking is a long-established application of Lenz's law. A rigorous analysis of the laws governing this problem involves solving Maxwell's equations in a time-dependent situation. Approximate models have been developed to describe different experiences related to this phenomenon. In this paper we present a new method for the analysis of the magnetic braking using a magnet fixed to the glider of an air track. The forces acting on the glider, a result of the eddy currents, can be easily observed and measured. As a consequence of the air track inclination, the glider accelerates at the beginning, although it asymptotically tends towards a uniform rectilinear movement characterized by a terminal speed. This speed depends on the interaction between the magnetic field and the conductivity properties of the air track. Compared with previous related approaches, in our experimental setup the magnet fixed to the glider produces a magnetic braking force which acts continuously, rather than over a short period of time. The experimental results satisfactorily concur with the theoretical models adapted to this configuration.
Point X-ray Sources in Elliptical Galaxies
2005-09-18
We analyze the upper-end X-ray luminosity function (XLF) observed in elliptical galaxies for point sources. We propose that the observed XLF is dominated by transient BH systems in outburst and the XLF shape reflects the black hole (BH) mass spectrum among old X-ray transients. The BH mass spectrum -- XLF connection depends on a weighting factor that is related to the transient duty cycle and depends on the host-galaxy age, the BH mass and the donor type (main sequence, red giant, or white dwarf). We argue that the assumption of a constant duty cycle for all systems leads to results inconsistent with current observations. The type of dominant donors in the upper-end XLF depends on what type of magnetic braking operates: in the case of ``standard'' magnetic braking, BH X-ray binaries with red-giant donors dominate, and in the case of weaker magnetic braking prescriptions main sequence donors dominate.
Magnetic Braking and Protostellar Disk Formation: The Ideal MHD Limit
2007-09-05
Magnetic fields are usually considered dynamically important in star formation when the dimensionless mass-to-flux ratio is close to, or less than, unity (lambda~100, they merge together to form a more or less contiguous, rotationally supported disk. Even though the magnetic field in such a case is extremely weak on the scale of dense cores, it is amplified by collapse and differential rotation, to the extent that its pressure dominates the thermal pressure in both the disk and its surrounding region. For relatively strongly magnetized cores with lambda<~10, the disk formation is suppressed completely, as found previously. A new feature is that the mass accretion is highly episodic, due to reconnection of the accumulated magnetic field lines. For rotationally supported disks to appear during the protostellar mass accretion phase of star formation in dense cores with realistic field strengths, the powerful magnetic brake must be weakened, perhaps through nonideal MHD effects and/or protostellar winds. We discuss the possibility of observing a generic product of the magnetic braking, an extended circumstellar region that is supported by a combination of toroidal magnetic field and rotation - a "magnetogyrosphere".
Averting the magnetic braking catastrophe on small scales: disk formation due to Ohmic dissipation
2010-10-13
We perform axisymmetric resistive MHD calculations that demonstrate that centrifugal disks can indeed form around Class 0 objects despite magnetic braking. We follow the evolution of a prestellar core all the way to near-stellar densities and stellar radii. Under flux-freezing, the core is braked and disk formation is inhibited, while Ohmic dissipation renders magnetic braking ineffective within the first core. In agreement with observations that do not show evidence for large disks around Class 0 objects, the resultant disk forms in close proximity to the second core and has a radius of only $\\approx 10~R_{\\odot}$ early on. Disk formation does not require enhanced resistivity. We speculate that the disks can grow to the sizes observed around Class II stars over time under the influence of both Ohmic dissipation and ambipolar diffusion, as well as internal angular momentum redistribution.
The timing of hibernation in Tasmanian echidnas: why do they do it when they do?
2002-01-01
We investigated the patterns of hibernation and arousals in seven free-ranging echidnas Tachyglossus aculeatus setosus (two male, five female) in Tasmania using implanted temperature data loggers. All echidnas showed a 'classical' pattern of mammalian hibernation, with bouts of deep torpor interrupted by periodic arousals to euthermia (mean duration 1.04+/-0.05 (n=146). Torpor bout length increased as body temperature fell during the hibernation season, and became more variable as temperature rose again. Hibernation started in late summer (February 28+/-5 days, n=6) and males aroused just before the winter solstice (June 15+/-3 days, n=3), females that subsequently produced young aroused 40 days later (July 25+/-3, n=4) while females that did not produce young hibernated for a further two months (arousal Sept 27+/-5, n=7). We suggest that hibernation in Tasmanian echidnas can be divided into two phases, the first phase, marked by declining minimum body temperatures as ambient temperature falls, appears to be obligatory for all animals, while the second phase is 'optional' and is utilised to varying amounts by females. We suggest that early arousal and breeding is the favoured option for females in good condition, and that the ability to completely omit breeding in some years, and hibernate through to spring is an adaptation to an uncertain climate. Relation: Nicol, SC and Andersen, NA (2002) The timing of hibernation in Tasmanian echidnas: why do they do it when they do? Comparative Biochemistry and Physiology - Part B: Biochemistry & Molecular Biology, 131 (4). pp. 603-611. ISSN 1096-4959 Format: application/pdf
The hibernating stellar magnet
2008-09-24
Astronomers have discovered a most bizarre celestial object that emitted 40 visible-light flashes before disappearing again. It is most likely to be a missing link in the family of neutron stars, the first case of an ...
2004-01-01
The soil ecotoxicology literature has focused primarily on a few major taxa, to the neglect of other fossorial organisms such as amphibians. We selected cadmium (Cd) and the American toad (Bufo americanus) as a model contaminant and biological species to assess the impact of soil contamination on amphibian hibernation survival and post-hibernation condition. Soil sand composition (50, 70, 90%) and hydration (100, 150% water holding capacity (WHC)) were manipulated in addition to Cd concentration (0, 56, 165, 483 mug/g) to determine whether these soil properties affect toxicity. Soil Cd concentration significantly reduced survival and locomotor performance, and was correlated negatively with percent mass loss and positively with whole body Cd concentration. Higher sand content resulted in less mass loss and greater Cd uptake. Toads that were hibernated in ...
2004-01-01
Background: Hibernating myocardium is defined as a state of persistently impaired myocardial function at rest due to reduced coronary blood flow that can partially or completely be restored to normal if the myocardial oxygen supply/demand relationship is favorably altered. Percutaneous laser revascularization (PMR) is an emerging catheter-based technique that involves creating channels in the myocardium, directly through a percutaneous approach with a laser delivery system, and has been shown to reduce symptoms in patients with severe refractory angina. However, its effect on improving regional wall motion abnormalities in hibernating myocardium has not been clearly established. We sought to determine the effect of PMR using the Eclipse System (Cardiogenesis) on left ventricular function in a porcine model of hibernating myocardium. Methods: A model of ...
Physiological ecology of overwintering in hatchling turtles
2008-01-01
Temperate species of turtles hatch from eggs in late summer. The hatchlings of some species leave their natal nest to hibernate elsewhere on land or under water, whereas others usually remain inside the nest until spring; thus, post-hatching behavior strongly influences the hibernation ecology and physiology of this age class. Little is known about the habitats of and environmental conditions affecting aquatic hibernators, although laboratory studies suggest that chronically hypoxic sites are inhospitable to hatchlings. Field biologists have long been intrigued by the environmental conditions survived by hatchlings using terrestrial hibernacula, especially nests that ultimately serve as winter refugia. Hatchlings are unable to feed, although as metabolism is greatly reduced in hibernation,...
Hibernation in an Antarctic Fish: On Ice for Winter
Active metabolic suppression in anticipation of winter conditions has been demonstrated in species of mammals, birds, reptiles and amphibians, but not fish. This is because the reduction in metabolic...Full Text Available
Geographic variability of the life cycle in Pterostichus melanarius (Coleoptera, Carabidae)
2006-01-01
In Pterostichus melanarius, the seasonal dynamics of activity is characterized by two peaks (in mid-June-early July and in late July-mid-August). In southwestern Moldova, these peaks were registered twenty days later than in Moscow Province. In both regions, larvae and adults hibernate. Both hibernated immature adults and adults that had already bred before wintering start reproduction simultaneously. In hibernated immature individuals, the average number of eggs per female constituted 1.5 times that in the postgenerative females. In the steppe zone, the total number of eggs laid by immature females was closed to that laid by previously bred females, while in the southern taiga zone, hibernated immature females laid a greater number of eggs. In the steppe zone, females of a new generation ...
2008-01-01
Disuse uncouples bone formation from resorption, leading to increased porosity, decreased bone geometrical properties, and decreased bone mineral content which compromises bone mechanical properties and increases fracture risk. However, black bear bone properties are not adversely affected by aging despite annual periods of disuse (i.e., hibernation), which suggests that bears either prevent bone loss during disuse or lose bone and subsequently recover it at a faster rate than other animals. Here we show decreased cortical bone turnover during hibernation with balanced formation and resorption in grizzly bear femurs. Hibernating grizzly bear femurs were less porous and more mineralized, and did not demonstrate any changes in cortical bone geometry or whole bone mechanical properties compar...
2002-08-16
I outline the evidence pertinent to the connection between the nova explosion and mass transfer rates in CVs. I conclude that there is still insufficient evidence to decide whether or not such a connection exists.
2010-01-01
1. Protective coloration in insects may be aposematic or cryptic, and some species change defensive strategy between instars. In Sweden, the adult striated shieldbugs Graphosoma lineatum (Heteroptera: Pentatomidae) undergo a seasonal colour change from pale brown and black striation in the pre-hibernating adults, to red and black striation in the same post-hibernating individuals. To the human eye the pre-hibernating adults appear cryptic against the withered late summer vegetation, whereas the red and black post-hibernating adults appear aposematic. This suggests a possibility of a functional colour change. However, what is cryptic to the human eye is not necessarily cryptic to a potential predator. 2. Therefore we tested the effect of coloration in adult G. lineatum on their detectabilit...
2007-01-08
The collapse and fragmentation of initially filamentary, magnetic molecular clouds is calculated in three dimensions with a gravitational, radiative hydrodynamics code. The code includes magnetic field effects in an approximate manner: magnetic pressure, tension, braking, and ambipolar diffusion are all modelled. Three types of outcomes are observed: direct collapse and fragmentation into a multiple protostar system, periodic contraction and expansion without collapse, or periodic contraction and expansion leading eventually to collapse. While the models begin their evolution at rest except for the assumed solid-body rotation, they develop weakly supersonic velocity fields as a result of the rebounding prior to collapse. The models show that magnetically-supported clouds subject to magnetic braking can undergo dynamic collapse leading to protostellar fragmentation on scales of 10 AU to 100 AU, consistent with typical binary star separations.
Coaxial magnetic brakes using single-domain YBCO
2008-01-01
In coaxial magnetic brakes, the changing field produced by movement of a solenoidal magnet induces a current in the wall of a conductive tube. The interaction of the field and current leads to a repulsive force that slows the motion of the magnet. For brake applications that require high force density, melt-textured YBCO is a clear choice of material for the magnet because it can carry high currents at a given field and temperature, and is inherently capable of operating in persistent current mode. We present calculations of the performance of this type of brake as a function of magnet current density for catch tubes composed of aluminum and titanium. These results are validated with low speed (20 m/s) tests. Calculations indicate that melt-textured magnets can decelerate projectiles with a mass of 1 kg from 2000 m/s to rest in distances on the order of 10 m. This suggests that this type ...
New evolutionary scenarios for short orbital period CVs
1999-05-31
We suggest new evolutionary scenarios for non-magnetic short orbital period CVs. The first model is the analogy of the `hibernation scenario' or the `modern hibernation scenario'. The second one is an extension of Mukai and Naylor (1995) ideas. All models imply a tight connection between permanent superhump systems and classical novae. We highlight the significance of the observed evolution of V1974 Cyg, which might pose a major problem to Mukai and Naylor concept.
2010-01-01
The nocturnal dwarf lemurs of Madagascar (genus Cheirogaleus) are the only primates known to be obligate hibernators. Although the physiology of hibernation has been studied widely in the western, small-bodied species, Cheirogaleus medius, no direct evidence of hibernation, i.e., body temperature recordings, has been reported for any of the three recognized eastern dwarf lemur species. We present skin temperature data collected by external collar transmitters from two eastern dwarf lemur individuals (Cheirogaleus crossleyi) captured in the high-altitude forest of Tsinjoarivo, central-eastern Madagascar. Our study species is larger in body size than western dwarf lemurs and inhabits much colder environments. We present the first evidence of hibernation in an eastern dwarf lemur species, and...
Cold adaptations in animals; Teion to seibutsu
1996-02-05
This paper explains the relation between organisms and low temperature in three temperature regions divided by 0{degree}C with reference to protein and lipid, the constituents of an organism. At a low temperature somewhat higher than 0{degree}C, some mammals hibernate, and the hibernation of mammals has connection with protein. The results of recent researches clearly show that, when a chipmunk starts hibernating, four kinds of proteins having molecular weight of 20000-50000 disappear from his blood. At 0{degree}C, an insect has a reserve of special lipid as an energy source for the hibernation. Triacylglycerol which an insect utilizes as an energy source for the basal metabolism during the hibernation is a neutral lipid, which is also a main component of cooking oil and butter. In a temperature region lower than 0{degree}C, fishes in the polar regions hold nonfreezing proteins (glucoproteins), which have molecular weights of several thousands to several ten thousands, in the blood so as to prevent the water in the cells and blood does not freeze. 5 refs.
Winding workshop for the ISR low beta Superconducting Quadrupole Prototype
1975-10-01
From right to left one sees the wire spool with its electro-magnetic brake to ensure a constant tension of the superconducting wire, a pulley with a wire length recording and the winding machine. In front on the table a finished coil. In the back the heavy clamping tool. See also 7510213X, 7510213X.
Why Blue stragglers formed via collisions may not be rapid rotators
1993-01-01
We propose that the blue stragglers formed via collisions may not be rapid rotators due to magnetic braking during a Hayashi phase as they approach the main sequence. It is conceivable that just the envelopes of the blue stragglers are spun down, while their cores remain rapidly rotating. This would greatly extend the main-sequence lifetimes of the blue stragglers produced by collisions.
Why Blue stragglers formed via collisions may not be rapid rotators
1993-03-01
We propose that the blue stragglers formed via collisions may not be rapid rotators due to magnetic braking during a Hayashi phase as they approach the main sequence. It is conceivable that just the envelopes of the blue stragglers are spun down, while their cores remain rapidly rotating. This would greatly extend the main-sequence lifetimes of the blue stragglers produced by collisions.
Collapse and Fragmentation of Molecular Cloud Cores. X. Magnetic Braking of Prolate and Oblate Cores
2009-03-11
The collapse and fragmentation of initially prolate and oblate, magnetic molecular clouds is calculated in three dimensions with a gravitational, radiative hydrodynamics code. The code includes magnetic field effects in an approximate manner: magnetic pressure, tension, braking, and ambipolar diffusion are all modelled. The parameters varied for both the initially prolate and oblate clouds are the initial degree of central concentration of the radial density profile, the initial angular velocity, and the efficiency of magnetic braking (represented by a factor $f_{mb} = 10^{-4}$ or $10^{-3}$). The oblate cores all collapse to form rings that might be susceptible to fragmentation into multiple systems. The outcome of the collapse of the prolate cores depends strongly on the initial density profile. Prolate cores with central densities 20 times higher than their boundary densities collapse and fragment into binary or quadruple systems, whereas cores with central densities 100 times higher collapse to form single protostars embedded in bars. The inclusion of magnetic braking is able to stifle protostellar fragmentation in the latter set of models, as when identical models were calculated without magnetic braking (Boss 2002), those cores fragmented into binary protostars. These models demonstrate the importance of including magnetic fields in studies of protostellar collapse and fragmentation, and suggest that even when magnetic fie lds are included, fragmentation into binary and multiple systems remains as a possible outcome of protostellar collapse.
Two Types of Soft X-ray Spectra in Cataclysmic Variables
We present results of analyses of Chandra HETG soft X-ray spectra (Lambda = 1.5-25 A) of seven cataclysmic variables. We find that these spectra divide unambiguously into two distinct types. Spectra of the ...
Time variability studies of 5 cataclysmic variables
This grant supported the observations and analysis from the Japanese ASTRO-C x-ray satellite Ginga, as part of the Guest Investigator Program. Three cataclysmic variables were observed: BV Pup for 16.5 hours on ...
The missing link in the evolution of magnetic cataclysmic stars?
2007-09-14
An international team of astronomers might have discovered the missing link in the evolution of the so-called magnetic cataclysmic variable stars. They determined the spin and orbital periods of the binary star Paloma. ...
The hot white dwarf in the cataclysmic variable MV Lyrae
We have obtained the first far-ultraviolet spectrum of the novalike cataclysmic variable MV Lyrae using the Far Ultraviolet Spectroscopic Explorer. We also obtained contemporaneous optical light curves and spectra. ...
Soft x-ray emission from boundary layers in cataclysmic variables
This report lists the five papers published as a result of data obtained in connection with this grant: 'A Search for Boundary Layer Emission from Cataclysmic Variables using the ROSAT PSPC'; 'ROSAT ...
On the flickering of hot spots in cataclysmic variables
1987-01-01
A flickering point source inside a scattering cloud will have its higher flicker frequencies attenuated because of delays caused by multiple scattering of photons in the cloud. The effect of this on the flicker spectrum of a cataclysmic variable is considered.
IUE observations of cataclysmic variables
The four years of IUE operation have revealed that the ultraviolet region of the spectrum contributes a dominant share of the emerging energy from cataclysmic variables and provides important clues to the physical nature of these systems. The implications of the continuum flux distributions and line spectra for the determination of the accretion rates and mass loss rates are considered.
IUE observations of cataclysmic variables
1982-01-01
The four years of IUE operation have revealed that the ultraviolet region of the spectrum contributes a dominant share of the emerging energy from cataclysmic variables and provides important clues to the physical nature of these systems. The implications of the continuum flux distributions and line spectra for the determination of the accretion rates and mass loss rates are considered.
Far Ultraviolet Spectroscopic Explorer Spectroscopy of the Nova-Like Cataclysmic Variable BB Doradus
We present an analysis of the Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of the little-known southern nova-like cataclysmic variable, BB Doradus. The spectrum was obtained as part of our Cycle 8 FUSE survey ...
Far Ultraviolet Spectroscopic Explorer Spectroscopy of the Nova-Like Cataclysmic Variable BB Doradus
We present an analysis of the Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of the little-known southern nova-like cataclysmic variable, BB Doradus. The spectrum was obtained as part of our Cycle 8 FUSE survey of ...
A Beginner's Guide to Cataclysmic Variables
This site offers information concerned with a particular group of binary stars: a cataclysmic variable star system. This site describes what they are, how they interact, and interesting phenomenon related to them. It has very nice visuals and links at the bottom for more information.
Three unusual cataclysmic' variable stars
1983-02-24
Photometric and spectroscopic data are presented which enable definite classifications to be made of three cataclysmic variables already detected during an automated search. According to well defined criteria these form a complete sample of such objects. All these cataclysmic variables are very faint and two of them do not readily fit into any existing category.
Structure of cataclysmic variables
The cataclysmic variables are usually divided into the following four classes: novae; recurrent novae; dwarf novae, which are subclassified as U Geminorum stars or Z Camelopardalis stars; and novalike variables. Those observations that bear most directly on the structure of cataclysmic variables at minimum light are reviewed. Sections include: the basic model; masses; the structure of the disk; the rapid oscillations; and the source of the eruptions. 5 figs., 4 tables, 133 refs. (GHT)
Structure of cataclysmic variables
1976-01-01
The cataclysmic variables are usually divided into the following four classes: novae; recurrent novae; dwarf novae, which are subclassified as U Geminorum stars or Z Camelopardalis stars; and novalike variables. Those observations that bear most directly on the structure of cataclysmic variables at minimum light are reviewed. Sections include: the basic model; masses; the structure of the disk; the rapid oscillations; and the source of the eruptions. 5 figs., 4 tables, 133 refs. (GHT)
On the evidence for brown-dwarf secondary stars in cataclysmic variables
2002-11-21
We present the K-band spectrum of the cataclysmic variable LL And, obtained using NIRSPEC on Keck-II. The spectrum shows no evidence for the absorption features observed by Howell & Ciardi (2001), which these authors used to claim a detection of a brown-dwarf secondary star in LL And. In light of our new data, we review the evidence for brown-dwarf secondary stars in this and other cataclysmic variables.
Einstein x-ray observations of cataclysmic variables
Observations with the imaging x-ray detectors on the Einstein Observatory have led to a large increase in the number of low luminosity x-ray sources known to be associated with cataclysmic variable stars (CVs). The high sensitivity of the Einstein instrumentation has permitted study of their short timescale variability and spectra. The data are adding significantly to our knowledge of the accretion process in cataclysmic variables and forcing some revision in our ideas concerning the origin of the optical variability in these stars.
Einstein x-ray observations of cataclysmic variables
Observations with the imaging x-ray detectors on the Einstein Observatory have led to a large increase in the number of low luminosity x-ray sources known to be associated with cataclysmic variable stars (CVs). The high sensitivity of the Einstein instrumentation has permitted study of their short timescale variability and spectra. The data are adding significantly to our knowledge of the accretion process in cataclysmic variables and forcing some revision in our ideas concerning the origin of the optical variability in these stars.
Einstein x-ray observations of cataclysmic variables
1982-01-01
Observations with the imaging x-ray detectors on the Einstein Observatory have led to a large increase in the number of low luminosity x-ray sources known to be associated with cataclysmic variable stars (CVs). The high sensitivity of the Einstein instrumentation has permitted study of their short timescale variability and spectra. The data are adding significantly to our knowledge of the accretion process in cataclysmic variables and forcing some revision in our ideas concerning the origin of the optical variability in these stars.
Einstein X-ray observations of cataclysmic variables
Observations with the imaging X-ray detectors on the Einstein Observatory have led to a large increase in the number of low luminosity X-ray sources known to be associated with cataclysmic variable stars (CVs). The high sensitivity of the Einstein instrumentation has permitted study of their short timescale variability and spectra. The data are adding significantly to our knowledge of the accretion process in cataclysmic variables and forcing some revision in our ideas concerning the origin of the optical variability in these stars.
Einstein X-ray observations of cataclysmic variables
1982-01-01
Observations with the imaging X-ray detectors on the Einstein Observatory have led to a large increase in the number of low luminosity X-ray sources known to be associated with cataclysmic variable stars (CVs). The high sensitivity of the Einstein instrumentation has permitted study of their short timescale variability and spectra. The data are adding significantly to our knowledge of the accretion process in cataclysmic variables and forcing some revision in our ideas concerning the origin of the optical variability in these stars.
EUVE Observations of Nonmagnetic Cataclysmic Variables
The authors summarize EUVE's contribution to the study of the boundary layer emission of high accretion-rate nonmagnetic cataclysmic variables, especially the dwarf novae SS Cyg, U Gem, VW Hyi, and OY Car in outburst. They discuss the optical and EUV light curves of dwarf nova outbursts, the quasi-coherent oscillations of the EUV flux of SS Cyg, the EUV spectra of dwarf novae, and the future of EUV observations of cataclysmic variables.
EUVE Observations of Nonmagnetic Cataclysmic Variables
The authors summarize EUVE's contribution to the study of the boundary layer emission of high accretion-rate nonmagnetic cataclysmic variables, especially the dwarf novae SS Cyg, U Gem, VW Hyi, and OY Car in outburst. They discuss the optical and EUV light curves of dwarf nova outbursts, the quasi-coherent oscillations of the EUV flux of SS Cyg, the EUV spectra of dwarf novae, and the future of EUV observations of cataclysmic variables.
EUVE Observations of Nonmagnetic Cataclysmic Variables
2001-09-05
The authors summarize EUVE's contribution to the study of the boundary layer emission of high accretion-rate nonmagnetic cataclysmic variables, especially the dwarf novae SS Cyg, U Gem, VW Hyi, and OY Car in outburst. They discuss the optical and EUV light curves of dwarf nova outbursts, the quasi-coherent oscillations of the EUV flux of SS Cyg, the EUV spectra of dwarf novae, and the future of EUV observations of cataclysmic variables.
1985-04-01
The present state of understanding of the cause of stellar explosions in novae and related systems is examined. Two physical phenomena unique to cataclysmic variables are the occurrence of a cool, Roche-lobe filling binary component with a compact companion, and a rotationally supported accretion disc about this compact companion. The conceptual advances that cataclysmic variables have contributed to the understanding of these astrophysical structures, largely through tests based on eruption behaviour in dwarf novae and symbiotic variables, are reviewed. The distinctly different conditions of classical nova explosions are briefly explored.
A Study of White Dwarfs in the Solar Neighbourhood
2003-01-01
The aim of this thesis is to revisit the properties of white dwarf stars in the Solar neighbourhood (distance > 100 pc), in particular their magnetic fields, the occurrence of binarity and their space density. This thesis presents observations and analysis of a sample of white dwarfs from the southern hemisphere. Over 80 objects were observed spectroscopically, and 65 of these were also observed with a spectropolarimeter. Many of the white dwarfs observed belong to the Solar neighbourhood, and can be used to study the star formation and evolution in this region. Our spectropolarimetric measurements helped constrain the fraction of magnetic white dwarfs in the Solar neighbourhood. Combining data from different surveys, I found a higher fraction of these objects in the relatively old local population than in other younger selections such as the Palomar-Green survey which suggests magnetic field evolution in white dwarfs, or different sets of progenitors. The progenitors of magnetic white dwarfs have been assumed to be Ap and Bp stars, however I find that the properties and number of Ap and Bp stars would only explain white dwarfs with magnetic fields larger than 100 MG. The number of known white dwarfs is believed to be complete to about 13 pc, however the sample is certainly incomplete to 20 pc from the Sun. To identify new white dwarfs in the Solar neighbourhood, some possibly magnetic or in binaries, numerous candidate white dwarfs from the Revised NLTT catalogue have been observed, which resulted in the discovery of 13 new white dwarfs, with 4 of these having a distance that places them within 20 pc of the Sun. The candidates were selected using a V − J reduced-proper-motion diagram and optical-infrared diagram. A total of 417 white dwarf candidates were selected, 200 of these have already been spectroscopically confirmed as white dwarfs. Spectroscopic confirmation is required for the remaining 217 candidates, many of these are likely to belong to the Solar neighbourhood. Four close binaries consisting of a white dwarf and a cool companion were also observed, for which atmospheric and orbital parameters were obtained. The photometry for two of these binary systems, BPM 71214 and EC 13471-1258 shows that the secondary stars are filling their Roche lobes, and combined with their orbital parameters, these systems are very good candidates for hibernating novae. The time of their previous interaction or the extent of this interaction are unknown. The two other binary systems, BPM 6502 and EUVE J0720-31.7 are post-common envelope binaries. BPM 6502 is not expected to interact within a Hubble time, however EUVE J0720-31 is expected to become a cataclysmic variable within a Hubble time. The atmospheric parameters of the white dwarfs were determined using model atmosphere codes which were modified for the present study to include convective energy transfer, self-broadening and Lyman satellite features. Publisher: Murdoch University Language: en Rights: http://www.murdoch.edu.au/goto/CopyrightNotice; Copyright Adela Kawka
Winter activity of Australian tree-roosting bats: influence of temperature and climatic patterns
2008-01-01
Abstract Many bats hibernate to overcome a critical energy shortage in winter. However, unlike strictly seasonal hibernators, bats sometimes alternate prolonged torpor bouts with increased activity coinciding with periods of mild weather. Winter activity may be especially common in hibernating tree-roosting bats because they are less insulated from external conditions than cave-roosting species and must also leave their roosts to drink, socialize or mate. To test this hypothesis, I measured the activity of a community of tree-roosting bats by recording echolocation calls at four sites on 18 nights throughout winter in south-eastern Australia. I also measured insect activity using light traps at each site. I recorded some bat activity on most nights, typically at dusk. Greater bat and insec...
Peculiarities of RBCs resistance to acid hemolysis in hibernating mammals
2008-01-01
The binding of acids and alkalis, formed in tissues by metabolism, along with oxygen and CO2 transport are recognise as the principal functions of red blood cells (RBCs). Decreases in internal environment pH may result in activation of potential endogenous cytotoxic metabolites, OH and oxidant formation and, as a consequence, result in oxidative damage of cell membrane leading to hemolysis. The characteristics of acid hemolysis in hibernating mammals have been determined in this study. Parameters of HCl-hemolysis, such as the average time for RBC hemolysis and the population distribution of the response, have been investigated. Measurements were performed within 405C temperature range. The resistance of hibernator RBCs to increased acidity, determined according to the acid hemolys...
Hibernation metabolism of mammalia (marmota menzeri kaschk) and reptiles (testudo horsfieldi gray)
2001-01-01
It has been revealed that, upon hypnosis resulting from the winter hibernation, the content of glucose in the blood of mammals (Marmota menzberi Kaschk.) and reptiles( Testudo horsfieldi Gray) has decreased whereas the components of the lipid exchange and the activity of the enzyme alanin and aspartate transaminase have increased, the changes observed being more pronounced in the tortoise than in marmote. On a level of the intact organism in vitro, over the 30 fold and 100 fold decrease of gas oxygen exchange takes place in marmots and tortoises, respectively upon the body temperature decreases as low as 4-5 degree Celsius as a result of winter hibernation. At a mitochondrial level, a decrease in the bio energetic parameters by 4-6 times with a prevailing inhibition of succinate oxidation was recorded in marmots and by 3 times in tortoises in the state of hypo biosis, which ...
2003-01-01
Objective: To establish the chronic low-flow myocardial hibernation animal model in pigs, and to assess the diagnostic value for myocardial hibernation by using various imaging methods. Methods: A total of 13 miniswine (30-40 kg) were used. All animals underwent general anesthesia and orotracheal intubation while the animals were mechanically ventilated. Under sterile conditions, left ventriculography and coronary angiography were performed by introduction of catheter into the right femoral artery. Further, a left anterolateral thoracotomy was performed in the third intercostal space. The proximal LCX was dissected free to allow placement of an ameroid constrictor. More than 1 month later, left ventriculography and coronary angiography were performed again, followed by cine-MRI at rest and during stress with low-dose of dobutamine ...
Activity following arousal in winter in North American vespertilionid bats:
2006-01-01
ABSTRACT Many bat species hibernate to conserve energy during winter and like all hibernators they commonly arouse. During these arousals, some bats may undertake activities away from the hibernation site. Systematic ecological studies of the frequency and purpose of winter activity in temperate zone bats of North America are rare and much of the literature involves observations of single individuals or unmarked populations. We review the available literature on winter activity among North American vespertilionid bats to highlight the paucity of data on this subject and to stimulate future research. Due to the lack of repeated, systematic studies on most North American species, the conclusions drawn are general or pertain only to parts of the geographical range of any species. We suggest t...
Constraints on the source of lunar cataclysm impactors
2010-01-01
Multiple impact basins formed on the Moon about 3.8 Gyr ago in what is known as the lunar cataclysm or Late Heavy Bombardment. Many workers currently interpret the lunar cataclysm as an impact spike primarily caused by main-belt asteroids destabilized by delayed planetary migration. We show that morphologically fresh (class 1) craters on the lunar highlands were mostly formed during the brief tail of the cataclysm, as they have absolute crater number density similar to that of the Orientale basin and ejecta blanket. The connection between class 1 craters and the cataclysm is supported by the similarity of their size-frequency distribution to that of stratigraphically-identified Imbrian craters. Majority of lunar craters younger than the Imbrium basin (including class 1 craters) thus record...
Constraints on the Source of Lunar Cataclysm Impactors
2009-12-10
Multiple impact basins formed on the Moon about 3.8 Gyr ago in what is known as the lunar cataclysm or late heavy bombardment. Many workers currently interpret the lunar cataclysm as an impact spike primarily caused by main-belt asteroids destabilized by delayed planetary migration. We show that morphologically fresh (class 1) craters on the lunar highlands were mostly formed during the brief tail of the cataclysm, as they have absolute crater number density similar to that of the Orientale basin and ejecta blanket. The connection between class 1 craters and the cataclysm is supported by the similarity of their size-frequency distribution to that of stratigraphically-identified Imbrian craters. Majority of lunar craters younger than the Imbrium basin (including class 1 craters) thus record the size-frequency distribution of the lunar cataclysm impactors. This distribution is much steeper than that of main-belt asteroids. We argue that the projectiles bombarding the Moon at the time of the cataclysm could not have been main-belt asteroids ejected by purely gravitational means.
Cataclysmic variables and related objects
1983-01-01
The periods of cataclysmic variable stars are considered along with photometric and spectroscopic observations of the cataclysmic variable AC Cancri, recent spectroscopy of X-ray sources and systems related to cataclysmic variables, orbital solutions for WZ Sagittae during quiescence, spectra of symbiotic stars, and the formation of optical CNO emission lines in cataclysmic variables. Attention is given to infrared spectra of nova dust shells, evolutionary models for SNI progenitor stars, the physical conditions inside white dwarfs and type I supernovae, the energy distribution of hard X-ray emitting cataclysmic variables, time dependence in accretion onto magnetic white dwarfs, polarized radiation from AM Herculis stars, and radio emission and synchronization. Other topics discussed are related to X-ray emission from cataclysmic variables, mass loss associated with X-ray bursts of neutron stars, and fast oscillations in variable X-ray sources and X-ray bursters.
Concept Mapping Assessment of Media Assisted Learning in Interdisciplinary Science Education
Acquisition of conceptual knowledge is a central aim in science education. In this study we monitored an interdisciplinary hypermedia assisted learning unit on hibernation and thermodynamics based on cooperative learning. We used concept
An estimated ten million Americans have osteoporosis, an age-related disease in which the bones gradually become brittle and weak. Now, scientists are looking to animals for clues on how to combat this condition. This resource describes the study of sustaining bone strength of hibernating bears.
Endocannabinoid signalling: has it got rhythm?
2010-01-01
Endogenous cannabinoid signalling is widespread throughout the body, and considerable evidence supports its modulatory role in many fundamental physiological processes. The daily and seasonal cycles of the relationship of the earth and sun profoundly affect the terrestrial environment. Terrestrial species have adapted to these cycles in many ways, most well studied are circadian rhythms and hibernation. The purpose of this review was to examine literature support for three hypotheses: (i) endocannabinoid signalling exhibits brain region-specific circadian rhythms; (ii) endocannabinoid signalling modulates the rhythm of circadian processes in mammals; and (iii) changes in endocannabinoid signalling contribute to the state of hibernation. The results of two novel studies are presented. First...
Active and hibernating turbulence in minimal channel flow of Newtonian and polymeric fluids
2010-04-30
Turbulent channel flow of drag-reducing polymer solutions is simulated in minimal flow geometries. Even in the Newtonian limit, we find intervals of "hibernating" turbulence that display many features of the universal maximum drag reduction (MDR) asymptote observed in polymer solutions: weak streamwise vortices, nearly nonexistent streamwise variations and a mean velocity gradient that quantitatively matches experiments. As viscoelasticity increases, the frequency of these intervals also increases, while the intervals themselves are unchanged, leading to flows that increasingly resemble MDR.
General Relativistic Simulations of Slowly and Differentially Rotating Magnetized Neutron Stars
2006-09-22
We present long-term (~10^4 M) axisymmetric simulations of differentially rotating, magnetized neutron stars in the slow-rotation, weak magnetic field limit using a perturbative metric evolution technique. Although this approach yields results comparable to those obtained via nonperturbative (BSSN) evolution techniques, simulations performed with the perturbative metric solver require about 1/4 the computational resources at a given resolution. This computational efficiency enables us to observe and analyze the effects of magnetic braking and the magnetorotational instability (MRI) at very high resolution. Our simulations demonstrate that (1) MRI is not observed unless the fastest-growing mode wavelength is resolved by more than about 10 gridpoints; (2) as resolution is improved, the MRI growth rate converges, but due to the small-scale turbulent nature of MRI, the maximum growth amplitude increases, but does not exhibit convergence, even at the highest resolution; and (3) independent of resolution, magnetic braking drives the star toward uniform rotation as energy is sapped from differential rotation by winding magnetic fields.
Disk Formation Enabled by Enhanced Resistivity
2010-06-07
Disk formation in magnetized cloud cores is hindered by magnetic braking. Previous work has shown that for realistic levels of core magnetization, the magnetic field suppresses the formation of rotationally supported disks during the protostellar mass accretion phase of low-mass star formation both in the ideal MHD limit and in the presence of ambipolar diffusion for typical rates of cosmic ray ionization. Additional effects, such as ohmic dissipation, the Hall effect, and protostellar outflow, are needed to weaken the magnetic braking and enable the formation of persistent, rotationally supported, protostellar disks. In this paper, we first demonstrate that the classic microscopic resistivity is not large enough to enable disk formation by itself. We then experiment with a set of enhanced values for the resistivity in the range $\\eta=10^{17}$--$10^{22}$ cm^2/s. We find that a value of order $10^{19}$ cm^2/s is needed to enable the formation of a 100 AU-scale Keplerian disk; the value depends somewhat on the degree of core magnetization. The required resistivity is a few orders of magnitude larger than the classic microscopic values. Whether it can be achieved naturally during protostellar collapse remains to be determined.
A Model of Magnetic Braking of Solar Rotation That Satisfies Observational Constraints
2010-02-12
The model of magnetic braking of solar rotation considered by Charbonneau & MacGregor (1993) has been modified so that it is able to reproduce for the first time the rotational evolution of both the fastest and slowest rotators among solar-type stars in open clusters of different ages, without coming into conflict with other observational constraints, such as the time evolution of the atmospheric Li abundance in solar twins and the thinness of the solar tachocline. This new model assumes that rotation-driven turbulent diffusion, which is thought to amplify the viscosity and magnetic diffusivity in stellar radiative zones, is strongly anisotropic with the horizontal components of the transport coefficients strongly dominating over those in the vertical direction. Also taken into account is the poloidal field decay that helps to confine the width of the tachocline at the solar age. The model's properties are investigated by numerically solving the azimuthal components of the coupled momentum and magnetic induction equations in two dimensions using a finite element method
2005-06-20
We propose that the shape of the upper-end X-ray luminosity function observed in elliptical galaxies for point sources is a footprint of the black-hole (BH) mass spectrum among old X-ray transients formed in the galaxies. We show that this underlying BH mass spectrum is modified by a weighting factor that is related to the transient duty cycle and it generally depends on the BH mass and XRB donor type (main-sequence, red-giant, or white-dwarf donors). A duty cycle that depends on the binary mass-transfer rate relative to the critical rate for transient behavior is most probably favored. We also find that the derived BH mass spectrum slope depends on the strength of angular momentum loss due to magnetic braking for main-sequence donors. More specifically, we find that, for ``standard'' magnetic braking, BH XRBs with red-giant donors dominate the upper-end XLF; for weaker magnetic braking prescriptions main-sequence donors are found to be dominant. In both cases the BH mass spectrum has a differential slope of ~2.5 and an upper BH mass cut-off at ~20 Msun is needed to understand the very brightest of the BH XRBs in elliptical galaxies. We expect that our result will help to constrain binary population synthesis models and the adopted relations between black holes and the masses of their progenitors.
Magnetic Braking in Differentially Rotating, Relativistic Stars
2003-12-01
We study the magnetic braking and viscous damping of differential rotation in incompressible, uniform density stars in general relativity. Differentially rotating stars can support significantly more mass in equilibrium than nonrotating or uniformly rotating stars. The remnant of a binary neutron star merger or supernova core collapse may produce such a "hypermassive" neutron star. Although a hypermassive neutron star may be stable on a dynamical timescale, magnetic braking and viscous damping of differential rotation will ultimately alter the equilibrium structure, possibly leading to delayed catastrophic collapse. Here we consider the slow-rotation, weak-magnetic field limit in which E_rot << E_mag << W, where E_rot is the rotational kinetic energy, E_mag is the magnetic energy, and W is the gravitational binding energy of the star. We assume the system to be axisymmetric and solve the MHD equations in both Newtonian gravitation and general relativity. Toroidal magnetic fields are generated whenever the angular velocity varies along the initial poloidal field lines. We find that the toroidal fields and angular velocities oscillate independently along each poloidal field line, which enables us to transform the original 2+1 equations into 1+1 form and solve them along each field line independently. The incoherent oscillations on different field lines stir up turbulent-like motion in tens of Alfven timescales ("phase mixing"). In the presence of viscosity, the stars eventually are driven to uniform rotation, with the energy contained in the initial differential rotation going into heat. Our evolution calculations serve as qualitative guides and benchmarks for future, more realistic MHD simulations in full 3+1 general relativity.
Effect of Magnetic Braking on the Circumstellar Disk Formation in a Strongly Magnetized Cloud
2010-09-14
Using resistive magnetohydrodynamics simulation, we investigate circumstellar disk formation in a strongly magnetized cloud. As the initial state, an isolated cloud core embedded in a low-density interstellar medium with a uniform magnetic field is adopted. The cloud evolution is calculated until almost all gas inside the initial cloud falls onto either the circumstellar disk or a protostar, and a part of the gas is ejected into the interstellar medium by the protostellar outflow driven by the circumstellar disk. In the early main accretion phase, the disk size is limited to \\sim 10 AU because the angular momentum of the circumstellar disk is effectively transferred by both magnetic braking and the protostellar outflow. In the later main accretion phase, however, the circumstellar disk grows rapidly and exceeds 100 AU by the end of the main accretion phase. This rapid growth of the circumstellar disk is caused by the depletion of the infalling envelope, while magnetic braking is effective when the infalling envelope is more massive than the circumstellar disk. The infalling envelope cannot brake the circumstellar disk when the latter is more massive than the former. In addition, the protostellar outflow weakens and disappears in the later main accretion phase, because the outflow is powered by gas accretion onto the circumstellar disk. Although the circumstellar disk formed in a magnetized cloud is considerably smaller than tha t in an unmagnetized cloud, a circumstellar disk exceeding 100 AU can form even in a strongly magnetized cloud.
X-ray and optical measurements of the cataclysmic variable CH UMa
1982-10-01
A program to identify optical counterparts of X-ray sources discovered with the Einstein Observatory has resulted in an independent identification of Ch UMa as a cataclysmic variable. Spectrophotometric observations made with the Intensified Image Dissector Scanner on the 2.1-m telescope at KPNO revealed an emission line spectrum from a msub(b) of the order of 15 mag object similar to the spectra of cataclysmic variables. A subsequent search of the Harvard photographic plate collection revealed outbursts of 4 mag in amplitude.
ULTRACAM photometry of eclipsing cataclysmic variable stars
The accurate determination of the masses of cataclysmic variable stars is critical to our understanding of their origin, evolution and behaviour. Observations of cataclysmic variables also afford an excellent opportunity to constrain theoretical physical models of the accretion discs housed in these systems. In particular, the brightness distributions of the accretion discs of eclipsing systems can be mapped at a spatial resolution unachievable in any other astrophysical situation. This thesis addresses both of these important topics via the analysis of the light curves of six eclipsing dwarf novae, obtained using ULTRACAM, a novel high-speed imaging photometer.
The masses of cataclysmic variables - a statistical approach
1990-03-01
A statistical analysis of the eclipse durations in eclipsing cataclysmic variables is used to obtain information on the mass ratio (q=M{sub 2}/M{sub 1}) for cataclysmic variables, using the assumption that the orbits are randomly oriented in space. For nine systems below the period gap (P0.13 d) the mean value is q=0.65{plus minus}0.12. However, the latter value may be too small because of selection effects in inclination. (author).
The fainter the better: cataclysmic variable stars from the SDSS
2008-10-28
The Sloan Digital Sky Survey has identified a total of 212 cataclysmic variables, most of which are fainter than 18th magnitude. This is the deepest and most populous homogeneous sample of cataclysmic variables to date, and we are undertaking a project to characterise this population. We have found that the SDSS sample is dominated by a great ``silent majority'' of old and faint CVs. We detect, for the first time, a population spike at the minimum period of 80 minutes which has been predicted by theoretical studies for over a decade.
The fainter the better: Cataclysmic variable stars from the Sloan Digital Sky Survey
2009-01-01
The Sloan Digital Sky Survey has identified a total of 212 cataclysmic variables, most of which are fainter than 18th magnitude. This is the deepest and most populous homogeneous sample of cataclysmic variables to date, and we are undertaking a project to characterise this population. We have found that the SDSS sample is dominated by a great 'silent majority' of old and faint CVs. We detect, for the first time, a population spike at the minimum period of 80 min which has been predicted by theoretical studies for over a decade
Spectrophotometry of the recently discovered cataclysmic variable CPD-48/sup 0/ 1577
1983-07-01
First optical spectrophotometric observations of the recently discovered cataclysmic variable CPD -48/sup 0/ 1577 are presented. The spectra show strong Balmer absorption troughs with superimposed emissions, as well as HeI, HeII and CIII - NIII emission features, with complex profile structures. From radial velocity measurements a preliminary value of the orbital period of 0.187 +- 0.003 day is derived. The place of CPD -48/sup 0/ 1577 among the cataclysmic variables is briefly discussed.
Dynamical mass transfer in cataclysmic binaries
1987-10-01
When a binary comes into contact and mass transfer begins, orbital angular momentum is stored in the accretion disk until the disk couples tidally to the binary system. Taam and McDermott (1987) have suggested that this leads to unstable dynamical mass transfer in many cataclysmic variables in which mass transfer would otherwise be stable, and that it explains the gap between 2 and 3 h in the orbital period distribution of these systems. Here the consequences of this hypothesis for the evolution of cataclysmic binaries are explored. It is found that systems coming into contact longward of the period gap undergo one or more episodes of dynamical mass transfer. 16 references.
Dust in nova system - thoughts in transition
1983-06-01
The evidence for the presence of dust around cataclysmic variables is reviewed with particular emphasis on classical novae. Two general models - rapid grain formation and pre-existing grains - for infrared development of novae are critically discussed and relevant observations of other cataclysmic variables that have some bearing on these models are described. It may be premature to opt for either model at this stage and further observations which may provide more evidence are suggested. An understanding of dust formation in cataclysmics - by whatever mechanism - could provide valuable information about several important astrophysical processes.
CCD time-resolved photometry of faint cataclysmic variables. IV
Time-resolved CCD photometry in V, B, and the near-IR has been obtained, with average time-series length of 3 hours, for 15 certified or candidate cataclysmic-variable faint stars. Orbital periods are found in three of the stars, and nine others are noted to exhibit evidence leading toward confirmation of cataclysmic-variable status. The characteristics of PG 0917+342 and PG 2240+193 are as yet unclear. 23 refs.
CCD time-resolved photometry of faint cataclysmic variables. IV
1991-03-01
Time-resolved CCD photometry in V, B, and the near-IR has been obtained, with average time-series length of 3 hours, for 15 certified or candidate cataclysmic-variable faint stars. Orbital periods are found in three of the stars, and nine others are noted to exhibit evidence leading toward confirmation of cataclysmic-variable status. The characteristics of PG 0917+342 and PG 2240+193 are as yet unclear. 23 refs.
CCD time-resolved photometry of faint cataclysmic variables. IV
1991-01-01
Time-resolved CCD photometry in V, B, and the near-IR has been obtained, with average time-series length of 3 hours, for 15 certified or candidate cataclysmic-variable faint stars. Orbital periods are found in three of the stars, and nine others are noted to exhibit evidence leading toward confirmation of cataclysmic-variable status. The characteristics of PG 0917+342 and PG 2240+193 are as yet unclear. 23 refs
Evolution of magnetic cataclysmic variables
Computations of the secular evolution of magnetic cataclismic variables under different hypotheses are used to study their period distribution. King et al.'s (1985) suggestion that the distribution of magnetic cataclysmic variables is well explained when they evolve in the same way as nonmagnetic cataclysmic systems, is confirmed for magnetic moments lying in the range 10 to the 33rd-34th G cu cm. The propeller mechanism proposed by Schmidt et al. (1986) is shown to be efficient in bringing the white-dwarf spin near synchronism with the orbital motion, and it is suggested that the period gap in all cataclysmic variables is due to the cessation of the secondary's stellar wind at approximately 3 hr periods. 32 references.
Evolution of magnetic cataclysmic variables
1987-05-01
Computations of the secular evolution of magnetic cataclismic variables under different hypotheses are used to study their period distribution. King et al.'s (1985) suggestion that the distribution of magnetic cataclysmic variables is well explained when they evolve in the same way as nonmagnetic cataclysmic systems, is confirmed for magnetic moments lying in the range 10 to the 33rd-34th G cu cm. The propeller mechanism proposed by Schmidt et al. (1986) is shown to be efficient in bringing the white-dwarf spin near synchronism with the orbital motion, and it is suggested that the period gap in all cataclysmic variables is due to the cessation of the secondary's stellar wind at approximately 3 hr periods. 32 references.
The final merger of two black holes releases a tremendous amount of energy, more than the combined light from all the stars in the visible universe. This energy is emitted in the form of gravitational waves, and observing ...
Cataclysmic variables from the Calan-Tololo Survey - II. Spectroscopic periods
2010-01-01
ABSTRACT In this second paper on cataclysmic variables detected in the Calan-Tololo Survey we present time-resolved spectroscopy for the remaining eight systems without a measured orbital period. We derive orbital periods for all of these systems, where we find two objects with periods above the period gap and six systems with periods shorter than 2 h. We discuss the spectroscopic results and do not find any specific general reason why the period could not be determined from photometry. This does imply that to study the period distribution of a large sample of cataclysmic variables phase-resolved spectroscopy is required. We also looked at the general results for the cataclysmic variables in the Calan-Tololo Survey (CTS). Our main objective was to search for the (very) short-period catacly...
2010-05-31
In this lecture the basic theory of accretion disks is reviewed, with emphasis on aspects relevant for X-ray binaries and Cataclysmic Variables. The text gives a general introduction as well as a selective discussion of a number of more recent topics.
1RXS J180834.7+101041 is a new cataclysmic variable with non-uniform disc
2010-10-04
Results of photometric and spectroscopic investigations of the recently discovered disc cataclysmic variable star 1RXS J180834.7+101041 are presented. Emission spectra of the system show broad double peaked hydrogen and helium emission lines. Doppler maps for the hydrogen lines demonstrate strongly non-uniform emissivity distribution in the disc, similar to that found in IP Peg. It means that the system is a new cataclysmic variable with a spiral density wave in the disc. Masses of the components (M_WD = 0.8 +/- 0.22 M_sun and M_RD = 0.14 +/- 0.02 M_sun), and the orbit inclination (i = 78 +/- 1.5 deg) were estimated using the various well-known relations for cataclysmic variables.
Objectives: To assess whether quantification of myocardial systolic velocities by pulsed wave tissue Doppler imaging can differentiate between stunned, hibernating, and scarred myocardium.Design: Observational study.Setting: Tertiary referral centre.Patients: 70 patients with reduced left ventricular function caused by chronic coronary artery disease.Methods: Pulsed wave tissue Doppler imaging was done close to the mitral annulus at rest and during low dose dobutamine; systolic ejection velocity (Vs) and the difference in Vs between low dose dobutamine and the resting value (ΔVs) were assessed using a six segment model. Assessment of perfusion (with Tc-99m-tetrofosmin SPECT) and glucose utilisation (by 18F-fluorodeoxyglucose SPECT) was used to classify dysfunctional regions (by resting cross sectional echocardiography) as stunned, hibernating, or scarred.Results: 253 of 420 regions (60%) were dysfunctional. Of these, 132 (52%) were classified as stunned, 25 (10%) as hibernating, and 96 (38%) as scarred. At rest, Vs in stunned, hibernating, and scar tissue was, respectively, 6.3 (1.8), 6.6 (2.2), and 5.5 (1.5) cm/s (p = 0.001 by ANOVA). There was a gradual decline in Vs during low dose dobutamine infusion between stunned, hibernating, and scar tissue (8.3 (2.6) v 7.8 (1.5) v 6.8 (1.9) cm/s, p < 0.001 by ANOVA). ΔVs was higher in stunned (2.1 (1.9) cm/s) than in hibernating (1.2 (1.4) cm/s, p < 0.05) or scarred regions (1.3 (1.2) cm/s, p = 0.001).Conclusions: Quantitative tissue Doppler imaging showed a gradual reduction in regional velocities between stunned, hibernating, and scarred myocardium. Dobutamine induced contractile reserve was higher in stunned regions than in hibernating and scarred myocardium, reflecting different severities of myocardial damage.
Organ arrest, protection and preservation: natural hibernation to cardiac surgery
2004-01-01
Cardiac surgery continues to be limited by an inability to achieve complete myocardial protection from ischemia-reperfusion injury. This paper considers the following questions: (1) what lessons can be learned from mammalian hibernators to improve current methods of human myocardial arrest, protection and preservation? and (2) can the human heart be pharmacologically manipulated during acute global ischemia to act more like the heart of a hibernating mammal? After reviewing the major entropy-slowing strategies of hibernation, a major player identified in the armortarium is maintenance of the membrane potential. The resting membrane potential of the hibernator's heart appears to be maintained close to its pre-torpid state of around −85 mV. In open-heart surgery, 99% of all surgical heart arrest solutions (cardioplegia) employ high potassium (>16 mM) which depolarises the membrane voltage from −85 to around −50 mV. However, depolarising potassium cardioplegia has been increasingly linked to myocyte and microvascular damage leading to functional loss during reperfusion. Our recent work has been borrowed from hibernation biology and is focused on a very different arrest strategy which ‘clamps’ the membrane near its resting potential and depresses O2 consumption from baseline by about 90%. The new ‘polarising’ cardioplegia incorporates adenosine and lidocaine (AL) as the arresting combination, not high potassium. Studies in the isolated rat heart show that AL cardioplegia delivered at 37 °C can arrest the heart for up to 4 h with 70–80% recovery of the cardiac output, 85–100% recovery of heart rate, systolic pressure and rate-pressure product and 70–80% of baseline coronary flows. Only 14% of hearts arrested with crystalloid St. Thomas' solution No. 2 cardioplegia survived after 4 h. In conclusion, maintenance of the myocardial membrane potential near or close to its resting state appears to be an important feature of the hibernator's heart that may find great utility in surgical arrest and cellular preservation strategies. Identifying and safely turning ‘off’ and ‘on’ the entropy-slowing genes to down-regulate the hibernator's heart and applying this to human organs and tissues remains a major challenge for future genomics and proteomics. Publisher: Elsevier Format: application/pdf Other identifier: Dobson, Geoffrey P. (2004) Organ arrest, protection and preservation: natural hibernation to cardiac surgery. Comparative Biochemistry and Physiology-Part B: biochemistry & molecular biology, 139 (3). pp. 469-485. ISSN 1879-1107
Accumulated evidence has suggested that increased endogenous opioid activities may facilitate the onset of hibernation either directly or possibly through modulation of other neurotransmitter systems. The seasonal change of (D-Ala{sup 2}, D-Leu{sup 5})-enkephalin (DADLE), a {delta} receptor agonist, in modulating K{sup +}-induced ({sup 3}H)-5-hydroxytryptamine (5-HT) release from the hippocampal and hypothalamic slices of euthermic and hibernating Richardsons' ground squirrels was therefore investigated. DADLE had no effect on 5-HT release in the hypothalamic slices but elicited a dose-related inhibition on ({sup 3}H)-5-HT release from the hippocampal slices of the euthermic ground squirrel. The inhibitory effect of DADLE was completely reversed by naloxone, but not by tetrodotoxin. In contrast, DADLE failed to alter the K{sup +}-induced 5-HT release from the hippocampal slices of the hibernating ground squirrel. This state-dependent reduction in responsiveness to an opioid is consistent with the hypothesis that enhanced endogenous opioid activity in the hibernating phase could lead to down regulation of the opioid receptors and minimize its inhibition on hippocampal serotonergic activity. A high 5-HT activity would inhibit midbrain reticular activating system indirectly through non-serotonergic fibers, which in turn facilitate the onset or maintenance of hibernation.
1990-01-01
Accumulated evidence has suggested that increased endogenous opioid activities may facilitate the onset of hibernation either directly or possibly through modulation of other neurotransmitter systems. The seasonal change of (D-Ala{sup 2}, D-Leu{sup 5})-enkephalin (DADLE), a {delta} receptor agonist, in modulating K{sup +}-induced ({sup 3}H)-5-hydroxytryptamine (5-HT) release from the hippocampal and hypothalamic slices of euthermic and hibernating Richardsons' ground squirrels was therefore investigated. DADLE had no effect on 5-HT release in the hypothalamic slices but elicited a dose-related inhibition on ({sup 3}H)-5-HT release from the hippocampal slices of the euthermic ground squirrel. The inhibitory effect of DADLE was completely reversed by naloxone, but not by tetrodotoxin. In contrast, DADLE failed to alter the K{sup +}-induced 5-HT release from the hippocampal slices of the hibernating ground squirrel. This state-dependent reduction in responsiveness to an opioid is consistent with the hypothesis that enhanced endogenous opioid activity in the hibernating phase could lead to down regulation of the opioid receptors and minimize its inhibition on hippocampal serotonergic activity. A high 5-HT activity would inhibit midbrain reticular activating system indirectly through non-serotonergic fibers, which in turn facilitate the onset or maintenance of hibernation.
Daily metabolism was calculated from food consumption in pocket mice, Perognathus longimembris, at 8/sup 0/C, 18/sup 0/C, and 31/sup 0/C. At temperatures below thermal neutrality for this species, daily metabolism was related to the amount of time the mice spent in torpor. Ambient temperature has no net effect on the minimum energy expenditure during a typical 5-mo hibernation season. Once an animal has accumulated a food store of approximately 130 g of millet seeds, it has the minimum energy necessary to hibernate at any environmental temperature. Such temperature compensation results from the complex effects of temperature on (1) the ratio of time of euthermy to time of torpor, (2) the energetic cost per hour of torpor, (3) the energetic cost per hour of euthermy, and (4) the energetic cost of arousal from torpor. The amount of time spent in torpor was inversely dependent on the food supply, indicating that euthermia is preferred even during the hibernation season. Mice also maximize the time of euthermia by selecting high environmental temperatures at all times of the year. Torpor probably occurs naturally only during the winter when the highest temperatures available to the mice are below thermal neutrality. The maximization of the time of euthermia reduces the chances of freezing during hibernation and enhances the animal's ability to excape from predators.
Reproduction By Echidnas In A Cold Climate
1992-01-01
Echidnas are known to breed in July-August, so the discovery in 1987 that echidnas in Kosciusko National Park spend the winter in hibernation raised questions about when (and if) breeding occurs in this region. Continued radiotelemetry observations during 1988 and 1989 showed, however, that breeding occurred throughout the study area, even above the winter snowline at 1750m. Larger, sexually mature animals aroused from hibernation in time to breed in the normal July-August breeding season. Smaller, presumably younger individuals, however, hibernated much longer, well into the spring. Reproductive behaviour showed differences from previously published observations. We saw no 'trains' prior to mating - pairs formed and mated almost immediately after arousal from hibernation. Also, mating occurred within the shelter of a retreat rather than above ground. Further, we saw no sign of mothers carrying their young in the pouch, early rearing occurring instead in a purpose-built nursing burrow. Females were occupied with reproduction-related activities throughout their active season, mating on exit from hibernation and weaning the young just prior to re-entry. Whether they can accommodate these energetic costs annually, or whether breeding may be biannual or even less frequent remains unknown. Contributor: Augee, M. L. Coverage: 1992-01-01T00:00:00Z
During the hibernation season, mammalian hibernators alternate between prolonged bouts of torpor with a reduced body temperature (Tb) and short arousals with a return to euthermy. Evidence is presented here to show that this metabolic-and also physiological and neuroanatomical-rhythm is controlled by a clock, the torpor-arousal (TA) clock. The temperature dependence of torpor bout duration in 3 species of Spermophilus (published data) may be described by assuming that the TA clock is a circadian clock (probably not the suprachiasmatic clock) that has lost its temperature compensation. This loss might result either from a permanent deletion, or more likely from a seasonal epigenetic control at the level of the clock gene machinery. This hypothesis was verified over the full Tb range on published data from 5 other species (a monotreme, a marsupial, and 3 placental mammals). In a hibernation season, instantaneous subjective time of the putative TA clock was summated over each torpor bout. For each animal, torpor bout length (TBL) was accurately predicted as a constant fraction of a subjective day, for actual durations in astronomical time varying between 4 and 13 to 20 days. The resulting temperature dependence of the interval between arousals predicts that energy expenditure over the hibernation season will be minimal when Tb is as low as possible without eliciting cold thermogenesis.
X-ray Variability of the Magnetic Cataclysmic Variable V1432 Aql and the Seyfert Galaxy NGC 6814
V1432 Aquilae (=RX J1940.2-1025) is the X-ray bright, eclipsing magnetic cataclysmic variable approximately 37 (sup) away from the Seyfert galaxy, NGC 6814. Due to a 0.3% difference between the orbital (12116.3 s) and ...
White dwarfs and neutron stars in globular cluster X-ray sources
1983-02-17
It is predicted that globular clusters contain at least as many cataclysmic variables, which contain white dwarfs, as bright X-ray sources, which contain neutron stars. The consequences of the frequent formation of temporarily bound triple systems (resonance scattering) are examined including; the extra enhancement of neutron star capture with respect to white dwarf capture, the considerable probability of actual collisions between stars, and the presence of cataclysmic variables in the outer regions of globular clusters.
UV observations of Cataclysmic Variables
2009-01-01
Cataclysmic Variables are the most abundant population of galactic compact interacting binaries. They represent test objects to improve our knowledge of accretion theory as well as evolution of low-mass close binary systems. The UV domain represents a key range, linking the high energy emission to that of the optical domain, to understand the complex interplay of accretion and outflow processes, as well as to infer the physical status of the accreting primaries. Some of the major results and future needs in this range are discussed.
The winds of cataclysmic variables
1994-02-16
The authors present an observational and theoretical review of the winds of cataclysmic variables (CVs). Specifically, they consider the related problems of the geometry and mass-loss rate of the winds of CVs, their ionization state and variability, and the results from studies of eclipsing CVs. Finally, they consider the properties of accretion disk wind models. Some of these models predict substantial angular momentum loss, which could affect both disk structure and binary evolution.
The EUV emission of cataclysmic variables
1989-07-01
Approximately half the luminosity of a typical cataclysmic variable may emerge as an optically thick component peaking in the EUV. Observations of this component are important for understanding the energetics and accretion rates of CV's in general, as well as for understanding the physics of the accretion process. The nature of the turbulent boundary layers and winds of disk accretors and the heating of the white dwarfs by accretion are among the problems which can be addressed by observations in the EUV. 46 refs., 2 figs.
Short-timescale variability in cataclysmic binaries
1982-01-01
Rapid variability, including flickering and pulsations, has been detected in cataclysmic binaries at optical and x-ray frequencies. In the case of the novalike variable TT Arietis, simultaneous observations reveal that the x-ray and optical flickering activity is strongly correlated, while short period pulsations are observed that occur at the same frequencies in both wavelength bands.
Evolution of the white dwarf mass and spin in cataclysmic variables
1991-01-01
We consider the spin-up of the white dwarf in non-magnetic cataclysmic variables (CVs) during secular evolution. If this is unresisted, CVs are quenched as boundary-layer emitters once the binary period has decreased by approx 1 hr. Angular momentum loss in nova explosions may, however, prevent the star reaching breakup. If the explosions remove (1 + epsilon) x the mass accreted between outbursts, values 0.5
In the latest in our series of papers on XMM-Newton and ground-based optical follow-up of new candidate magnetic cataclysmic variables (mCVs) found in the Sloan Digital Sky Survey, we report classifications of ...
In the latest in our series of papers on XMM-Newton and ground-based optical follow-up of new candidate magnetic cataclysmic variables (mCVs) found in the Sloan Digital Sky Survey, we report classifications of three systems: ...
Cataclysmic variables as probes of x-ray properties of interstellar grains
1983-01-01
Interstellar-grain properties have previously been probed at wavelengths ranging from the infrared to the ultraviolet. Recent work by other authors has shown that we may also observe the effects of scattering by such grains at x-ray wavelengths. In this paper we suggest that investigations of the x-ray properties of interstellar grains may profitably be conducted in sight lines to variable sources. Particular emphasis is given in this context to cataclysmic variables and related objects.
Can the activity of the secondary components explain the X-ray emission from cataclysmic variables
1984-12-01
The accretion-powered emission of the primary components of cataclysmic binaries seems to dominate the observed X-ray fluxes; but in some dwarf-nova systems with relatively large secondary components this emission is close to, or only marginally exceeds, that expected from the secondary components on the assumption that for them Lsub(X)/Lsub(bol) = 10/sup -2/, as is actually observed in rapidly rotating active M dwarfs.
Are the secondary stars in cataclysmic variables main sequence stars
1983-01-01
A spectral type-orbital period relation for cataclysmic variables with main sequence companions is presented. The spectral types of seventeen systems with known orbital periods are derived and compared with the observed ones. The analysis shows that they have in general later spectral types than main sequence stars of the same mass.
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