Expression and localization of aqua-glyceroporins AQP3 and AQP9 in rat oral epithelia.
Poveda, Marlene; Hashimoto, Sadamitsu; Enokiya, Yasunobu; Matsuki-Fukushima, Miwako; Sasaki, Hodaka; Sakurai, Kaoru; Shimono, Masaki
2014-01-01
Aquaporins (AQPs) are a family of small integral membrane proteins made up of 6 hydrophobic, a-helical, membrane-spanning domains surrounding a highly selective aqueous pore. AQP3, AQP7, and AQP9, termed aqua-glyceroporins, are known to be involved in the transport of water, glycerol, and other small molecules. In this study, we investigated the expression and localization of aqua-glyceroporins in rat oral stratified squamous epithelia of the palate, the buccal mucosa, the inferior aspect of the tongue, and the oral floor by using RT-PCR, immunofluorescence, and immunogold electron microscopy. AQP3 and AQP9 mRNAs were expressed in whole oral epithelium. Immunostaining for AQP3 was recognized in each type of epithelium. The results suggest that AQP3 synthesis begins predominantly in the cytoplasm of the basal cells. During the process of epithelial cell differentiation, AQP3 protein appears to accumulate and be transported to the plasma membrane, from where it is incorporated into the cornified or surface layers. The intracellular localization of AQP3 appears to correlate with the differentiation of keratinocytes, suggesting that it acts as an enhancer of the physiological permeability barrier together with membrane coating granules. The distribution pattern of AQP9 was limited to the marginal areas of the basal and suprabasal layers, which was different from that of AQP3. This difference in distribution between AQP3 and AQP9 suggests that AQP9 in rat oral epithelia acts as a channel by facilitating glycerol uptake from the blood through the endothelial cells of the capillary vessels to the oral stratified squamous epithelium. AQP3 and AQP9 facilitate both transcellular osmotic water flow and glycerol transport as pore-like passive transporters in the keratinocytes of oral epithelia, and may play a key role in not only hydration and the permeability barrier, but also cell proliferation, differentiation, migration, development, and wound healing by generating ATP.
DEFF Research Database (Denmark)
Mylonakou, Maria N; Petersen, Petur H; Rinvik, Eric;
2009-01-01
AQP9 is an aquaglyceroporin that serves important functions in peripheral organs, including the liver. Reflecting the lack of AQP9 knockout mice, uncertainties still prevail regarding the localization and roles of AQP9 in the central nervous system. Here we present a comprehensive analysis of AQP9...... and mouse liver, the organ with the highest level of AQP9. By blue native gel analysis it could be demonstrated that the brain contains tetrameric AQP9, corresponding to the functional form of AQP9. The band corresponding to the AQP9 tetramer was absent in AQP9 knockout brain and liver. Immunocytochemistry...... and in situ hybridization analyses with AQP9 knockout controls show that subpopulations of nigral neurons express AQP9 both at the mRNA and at the protein levels and that populations of cortical cells (including hilar neurons in the hippocampus) contain AQP9 mRNA but no detectable AQP9 immunosignal...
Pentavalent methylated arsenicals are substrates of human AQP9.
McDermott, Joseph R; Jiang, Xuan; Beene, Lauren C; Rosen, Barry P; Liu, Zijuan
2010-02-01
Liver aquaglyceroporin AQP9 facilitates movement of trivalent inorganic arsenite (As(III)) and organic monomethylarsonous acid (MAs(III)). However, the transport pathway for the two major pentavalent arsenic cellular metabolites, MAs(V) and DMAs(V), remains unknown in mammals. These products of arsenic metabolism, in particular DMAs(V), are the major arsenicals excreted in the urine of mammals. In this study, we examined the uptake of the two pentavalent organic arsenicals by human AQP9 in Xenopus laevis oocytes. Xenopus laevis oocytes microinjected with AQP9 cRNA exhibited uptake of both MAs(V) and DMAs(V) in a pH-dependent manner. The rate of transport was much higher at acidic pH (pH5.5) than at neutral pH. Hg(II), an aquaporin inhibitor, inhibited transport of As(III), MAs(III), MAs(V) and DMAs(V) via AQP9. However, phloretin, which inhibits water and glycerol permeation via AQP9, can only inhibit transport of pentavalent MAs(V) and DMAs(V) but not trivalent As(III) and MAs(III), indicating the translocation mechanisms of these arsenic species are not exactly the same. Reagents such as FCCP, valinomycin and nigericin that dissipate transmembrane proton potential or change the transmemebrane pH gradient did not significantly inhibit all arsenic transport via AQP9, suggesting the transport of pentavalent arsenic is not proton coupled. The results suggest that in addition to the initial uptake of trivalent inorganic As(III) inside cells, AQP9 plays a dual role in the detoxification of arsenic metabolites by facilitating efflux from cells.
Arsenic transport by zebrafish aquaglyceroporins
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Landfear Scott M
2009-11-01
Full Text Available Abstract Background Arsenic is one of the most ubiquitous toxins and endangers the health of tens of millions of humans worldwide. It is a mainly a water-borne contaminant. Inorganic trivalent arsenic (AsIII is one of the major species that exists environmentally. The transport of AsIII has been studied in microbes, plants and mammals. Members of the aquaglyceroporin family have been shown to actively conduct AsIII and its organic metabolite, monomethylarsenite (MAsIII. However, the transport of AsIII and MAsIII in in any fish species has not been characterized. Results In this study, five members of the aquaglyceroporin family from zebrafish (Danio rerio were cloned, and their ability to transport water, glycerol, and trivalent arsenicals (AsIII and MAsIII and antimonite (SbIII was investigated. Genes for at least seven aquaglyceroporins have been annotated in the zebrafish genome project. Here, five genes which are close homologues to human AQP3, AQP9 and AQP10 were cloned from a zebrafish cDNA preparation. These genes were named aqp3, aqp3l, aqp9a, aqp9b and aqp10 according to their similarities to the corresponding human AQPs. Expression of aqp9a, aqp9b, aqp3, aqp3l and aqp10 in multiple zebrafish organs were examined by RT-PCR. Our results demonstrated that these aquaglyceroporins exhibited different tissue expression. They are all detected in more than one tissue. The ability of these five aquaglyceroporins to transport water, glycerol and the metalloids arsenic and antimony was examined following expression in oocytes from Xenopus leavis. Each of these channels showed substantial glycerol transport at equivalent rates. These aquaglyceroporins also facilitate uptake of inorganic AsIII, MAsIII and SbIII. Arsenic accumulation in fish larvae and in different tissues from adult zebrafish was studied following short-term arsenic exposure. The results showed that liver is the major organ of arsenic accumulation; other tissues such as gill, eye
Roles of vertebrate aquaglyceroporins in arsenic transport and detoxification.
Liu, Zijuan
2010-01-01
Aquaporins are important channel proteins that are responsible for the balance of cellular osmolarity and nutrient transport in vertebrates. Recently, new functions of these ancient channels have been found in the conduction of metalloid arsenic (As). Chronic As exposure through contaminated water and food sources is associated with multiple human diseases and endangers millions of people's health worldwide. Therefore, identification of the As transport pathways is necessary to elucidate the mechanisms of As carcinogenesis. Arsenic detoxification systems have been studied in multiple vertebrates such as mammalian mouse, rat, humans and nonmammalian vertebrates. Multiple transporters and enzymes have been shown to be involved in As translocation and cellular transformation. In these vertebrates, members ofaquaglyceroporins, which include AQP7 in kidney and AQP9 in liver, catalyze uptake of inorganic trivalent arsenite [As(III)]. AQP9, the major liver aquaglyceroporin, conducts both inorganic As(III) and organic monomethylarsonous acid [MMA(III)], an intermediate that is generated during the cellular methylation. As a channel that facilitates a downhill movement of substances dependent on the concentration gradient, AQP9 may play an important role in the simultaneous influx of inorganic As(III) from blood to liver and efflux of As metabolite MMA(III) from liver to blood. In this chapter, we will discuss the function ofaquaglyceroporins ofvertebrates in uptake and detoxification of the metalloid As.
Rodríguez, Amaia; Moreno, Natalia R; Balaguer, Inmaculada; Méndez-Giménez, Leire; Becerril, Sara; Catalán, Victoria; Gómez-Ambrosi, Javier; Portincasa, Piero; Calamita, Giuseppe; Soveral, Graça; Malagón, María M; Frühbeck, Gema
2015-07-10
Glycerol is an important metabolite for the control of lipid accumulation in white adipose tissue (WAT) and liver. We aimed to investigate whether exogenous administration of leptin improves features of non-alcoholic fatty liver disease (NAFLD) in leptin-deficient ob/ob mice via the regulation of AQP3 and AQP7 (glycerol channels mediating glycerol efflux in adipocytes) and AQP9 (aquaglyceroporin facilitating glycerol influx in hepatocytes). Twelve-week-old male wild type and ob/ob mice were divided in three groups as follows: control, leptin-treated (1 mg/kg/d) and pair-fed. Leptin deficiency was associated with obesity and NAFLD exhibiting an AQP3 and AQP7 increase in WAT, without changes in hepatic AQP9. Adipose Aqp3 and hepatic Aqp9 transcripts positively correlated with markers of adiposity and hepatic steatosis. Chronic leptin administration (4-weeks) was associated with improved body weight, whole-body adiposity, and hepatosteatosis of ob/ob mice and to a down-regulation of AQP3, AQP7 in WAT and an up-regulation of hepatic AQP9. Acute leptin stimulation in vitro (4-h) induced the mobilization of aquaglyceroporins towards lipid droplets (AQP3) and the plasma membrane (AQP7) in murine adipocytes. Our results show that leptin restores the coordinated regulation of fat-specific AQP7 and liver-specific AQP9, a step which might prevent lipid overaccumulation in WAT and liver in obesity.
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Néstor L. Uzcátegui
2013-09-01
Full Text Available Background: Trypanosoma brucei is a primitive parasitic protozoan that thrives in diverse environments such as the midgut of the tsetse fly and the blood of a mammalian host. For an adequate adaptation to these environments, the parasite´s aquaglyceroporins play an important role. Methods and Results: In order to test their ability to transport trivalent arsenic and antimony, we expressed the three known Trypanosoma brucei aquaglyceroporins (TbAQPs in the heterologous systems of yeast null aquaporin mutant and Xenopus laevis oocytes. For both expression systems, we found a pH dependent intracellular accumulation of As(III or Sb(III mediated by all of the three TbAQPs, with the exception of TbAQP1-As(III uptake. Additionally, we observed that Trypanosoma brucei aquaglyceroporins allow the passage of As(III in both directions. Conclusion: Taken together, these results demonstrated that T. brucei aquaglyceroporins can serve as entry routes for As(III and Sb(III into the parasitic cell, and that this uptake is pH sensitive. Therefore, aquaporins of protozoan parasites may be considered useful as a vehicle for drug delivery.
Glycerol inhibits water permeation through Plasmodium falciparum aquaglyceroporin.
Chen, Liao Y
2013-01-01
Plasmodium falciparum aquaglyceroporin (PfAQP) is a multifunctional membrane protein in the plasma membrane of P. falciparum, the parasite that causes the most severe form of malaria. The current literature has established the science of PfAQP's structure, functions, and hydrogen-bonding interactions but left unanswered the following fundamental question: does glycerol modulate water permeation through aquaglyceroporin that conducts both glycerol and water? This paper provides an affirmative answer to this question of essential importance to the protein's functions. On the basis of the chemical-potential profile of glycerol from the extracellular bulk region, throughout PfAQP's conducting channel, to the cytoplasmic bulk region, this study shows the existence of a bound state of glycerol inside aquaglyceroporin's permeation pore, from which the dissociation constant is approximately 14μM. A glycerol molecule occupying the bound state occludes the conducting pore through which permeating molecules line up in single file by hydrogen-bonding with one another and with the luminal residues of aquaglyceroporin. In this way, glycerol inhibits permeation of water and other permeants through aquaglyceroporin. The biological implications of this theory are discussed and shown to agree with the existent in vitro data. It turns out that the structure of aquaglyceroporin is perfect for the van der Waals interactions between the protein and glycerol to cause the existence of the bound state deep inside the conducting pore and, thus to play an unexpected but significant role in aquaglyceroporin's functions.
Institute of Scientific and Technical Information of China (English)
程春华; 曲书强; 吕莹
2010-01-01
目的 研究缺氧缺血性脑损伤(HIBD)后水通道蛋白9(AQP9)在脑组织中的表达变化规律,初步探讨AQP9与脑水肿的关系.方法 采用HIBD动物模型,实施定量PCR(基因水平)和Wester-Blot(免疫印迹)方法,检测AQP9表达的变化和AQP9 mRNA的变化.结果 HIBD组AQP9的表达随缺血时间延长而表达增加,对照组AQP9表达无明显变化,且AQP9表达在脑缺血2～3 d表达最强.结论 HIBD时,随着缺氧缺血时间的延长,AQP9表达增强,至72 h达高峰.
Aquaglyceroporins and metalloid transport: implications in human diseases.
Bhattacharjee, Hiranmoy; Rosen, Barry P; Mukhopadhyay, Rita
2009-01-01
Aquaglyceroporin (AQP) channels facilitate the diffusion of a wide range of neutral solutes, including water, glycerol, and other small uncharged solutes. More recently, AQPs have been shown to allow the passage of trivalent arsenic and antimony compounds. Arsenic and antimony are metalloid elements. At physiological pH, the trivalent metalloids behave as molecular mimics of glycerol, and are conducted through AQP channels. Arsenicals and antimonials are extremely toxic to cells. Despite their toxicity, both metalloids are used as chemotherapeutic agents for the treatment of cancer and protozoan parasitic diseases. The metalloid homeostasis property of AQPs can be a mixed blessing. In some cases, AQPs form part of the detoxification pathway, and extrude metalloids from cells. In other instances, AQPs allow the transport of metalloids into cells, thereby conferring sensitivity. Understanding the factors that modulate AQP expression will aid in a better understanding of metalloid toxicity and also provide newer approaches to metalloid based chemotherapy.
Metalloid transport by aquaglyceroporins: consequences in the treatment of human diseases.
Mukhopadhyay, Rita; Beitz, Eric
2010-01-01
Metalloids can severely harm human physiology in a toxicological sense if taken up from the environment in acute high doses or chronically. However, arsenic or antimony containing drugs are still being used as treatment and are often the sole regime for certain forms of cancer, mainly types of leukemia and diseases caused by parasites, such as sleeping sickness or leishmaniasis. In this chapter, we give an outline of the positive effects of arsenicals and antimonials against such diseases, we summarize data on uptake pathways through human and parasite aquaglyceroporins and we discuss the progress and options in the development of therapeutic aquaporin and aquaglyceroporin inhibitor compounds.
Null surfaces of null curves on 3-null cone
Sun, Jianguo; Pei, Donghe
2014-03-01
The null surfaces of null curves on 3-null cone have the applications in the studying of horizon types. Via the pseudo-scalar product and Frenet equations, the differential geometry of null curves on 3-null cone is obtained. In the local sense, the curvature describes the contact of submanifolds with pseudo-spheres. We introduce the geometric properties of the curvatures and show the singularities of null surfaces, which are constructed over the null curves.
The role of alanine 163 in solute permeability of Leishmania major aquaglyceroporin LmAQP1.
Mukhopadhyay, Rita; Mandal, Goutam; Atluri, Venkata Subba Rao; Figarella, Katherine; Uzcategui, Nestor L; Zhou, Yao; Beitz, Eric; Ajees, A Abdul; Bhattacharjee, Hiranmoy
2011-01-01
Leishmania major aquaglyceroporin LmAQP1 allows adventitious passage of antimonite, an activated form of the drug Pentostam, which is used as the first line treatment for leishmaniasis. The extracellular C-loop of an aquaglyceroporin confers substrate specificity. Alteration of Glu125 to serine in the Plasmodium falciparum aquaglyceroporin PfAQP has been shown to selectively affect water but not glycerol permeability. The C-loop of LmAQP1 is twelve residues longer than PfAQP, and Ala163 is at an equivalent position as Glu125 of PfAQP. The role of Ala163 in LmAQP1 solute permeability was investigated. Alteration of Ala163 to serine or threonine did not significantly affect conduction of solutes. However, alteration to aspartate, glutamate, and glutamine blocked passage of water, glycerol, and other organic solutes. While LmAQP1 is a mercurial insensitive water channel, mutation of the adjacent threonine (Thr164) to cysteine led to inhibition of water passage by Hg(2+). This inhibition could be reversed upon addition of β-mercaptoethanol. These data suggest that, unlike Glu125 (PfAQP), Ala163 is not involved in stabilization of the C-loop and selective solute permeability. Ala163 is located near the pore mouth of the channel, and replacement of Ala163 by bulkier residue sterically hinders the passage of solutes. Alteration of Ala163 to serine or threonine affected metalloid uptake in the order, wild-type>A163S>A163T. Metalloid conduction was near completely blocked when Ala163 was mutagenized to aspartate, glutamate, or glutamine. Mutations such as A163S and A163T that reduced the permeability to antimonite, without a significant loss in water or solute conductivity raises the possibility that, subtle changes in the side chain of the amino acid residue in position 163 of LmAQP1 may play a role in drug resistance.
Song, Jie; Baker, Nicola; Rothert, Monja; Henke, Björn; Jeacock, Laura; Horn, David; Beitz, Eric
2016-02-01
The chemotherapeutic arsenal against human African trypanosomiasis, sleeping sickness, is limited and can cause severe, often fatal, side effects. One of the classic and most widely used drugs is pentamidine, an aromatic diamidine compound introduced in the 1940s. Recently, a genome-wide loss-of-function screen and a subsequently generated trypanosome knockout strain revealed a specific aquaglyceroporin, TbAQP2, to be required for high-affinity uptake of pentamidine. Yet, the underlying mechanism remained unclear. Here, we show that TbAQP2 is not a direct transporter for the di-basic, positively charged pentamidine. Even though one of the two common cation filters of aquaglyceroporins, i.e. the aromatic/arginine selectivity filter, is unconventional in TbAQP2, positively charged compounds are still excluded from passing the channel. We found, instead, that the unique selectivity filter layout renders pentamidine a nanomolar inhibitor of TbAQP2 glycerol permeability. Full, non-covalent inhibition of an aqua(glycero)porin in the nanomolar range has not been achieved before. The remarkable affinity derives from an electrostatic interaction with Asp265 and shielding from water as shown by structure-function evaluation and point mutation of Asp265. Exchange of the preceding Leu264 to arginine abolished pentamidine-binding and parasites expressing this mutant were pentamidine-resistant. Our results indicate that TbAQP2 is a high-affinity receptor for pentamidine. Taken together with localization of TbAQP2 in the flagellar pocket of bloodstream trypanosomes, we propose that pentamidine uptake is by endocytosis.
Directory of Open Access Journals (Sweden)
Jie Song
2016-02-01
Full Text Available The chemotherapeutic arsenal against human African trypanosomiasis, sleeping sickness, is limited and can cause severe, often fatal, side effects. One of the classic and most widely used drugs is pentamidine, an aromatic diamidine compound introduced in the 1940s. Recently, a genome-wide loss-of-function screen and a subsequently generated trypanosome knockout strain revealed a specific aquaglyceroporin, TbAQP2, to be required for high-affinity uptake of pentamidine. Yet, the underlying mechanism remained unclear. Here, we show that TbAQP2 is not a direct transporter for the di-basic, positively charged pentamidine. Even though one of the two common cation filters of aquaglyceroporins, i.e. the aromatic/arginine selectivity filter, is unconventional in TbAQP2, positively charged compounds are still excluded from passing the channel. We found, instead, that the unique selectivity filter layout renders pentamidine a nanomolar inhibitor of TbAQP2 glycerol permeability. Full, non-covalent inhibition of an aqua(glyceroporin in the nanomolar range has not been achieved before. The remarkable affinity derives from an electrostatic interaction with Asp265 and shielding from water as shown by structure-function evaluation and point mutation of Asp265. Exchange of the preceding Leu264 to arginine abolished pentamidine-binding and parasites expressing this mutant were pentamidine-resistant. Our results indicate that TbAQP2 is a high-affinity receptor for pentamidine. Taken together with localization of TbAQP2 in the flagellar pocket of bloodstream trypanosomes, we propose that pentamidine uptake is by endocytosis.
Aquaglyceroporin 2 controls susceptibility to melarsoprol and pentamidine in African trypanosomes.
Baker, Nicola; Glover, Lucy; Munday, Jane C; Aguinaga Andrés, David; Barrett, Michael P; de Koning, Harry P; Horn, David
2012-07-03
African trypanosomes cause sleeping sickness in humans, a disease that is typically fatal without chemotherapy. Unfortunately, drug resistance is common and melarsoprol-resistant trypanosomes often display cross-resistance to pentamidine. Although melarsoprol/pentamidine cross-resistance (MPXR) has been an area of intense interest for several decades, our understanding of the underlying mechanisms remains incomplete. Recently, a locus encoding two closely related aquaglyceroporins, AQP2 and AQP3, was linked to MPXR in a high-throughput loss-of-function screen. Here, we show that AQP2 has an unconventional "selectivity filter." AQP2-specific gene knockout generated MPXR trypanosomes but did not affect resistance to a lipophilic arsenical, whereas recombinant AQP2 reversed MPXR in cells lacking native AQP2 and AQP3. AQP2 was also shown to be disrupted in a laboratory-selected MPXR strain. Both AQP2 and AQP3 gained access to the surface plasma membrane in insect life-cycle-stage trypanosomes but, remarkably, AQP2 was specifically restricted to the flagellar pocket in the bloodstream stage. We conclude that the unconventional aquaglyceroporin, AQP2, renders cells sensitive to both melarsoprol and pentamidine and that loss of AQP2 function could explain cases of innate and acquired MPXR.
Aquaglyceroporins are involved in uptake of arsenite into murine gastrointestinal tissues.
Wang, Chun; Chen, Gang; Jiang, Junkang; Qiu, Lianglin; Hosoi, Kazuo; Yao, Chenjuan
2009-01-01
Aquaglyceroporins (AQGPs) are members of aquaporin (AQP) family and belong to a subgroup of this water channel family; they are transmembrane proteins that transport water as well as glycerol and other solutes of small molecules. Recent studies have also identified that AQGPs are important transporters of trivalent metalloid in some mammalian cells. However, the uptake routes of arsenite in mammals are still less defined. In this study, to understand the routes of arsenite intake in mammals, mice were treated with Hg(II), glycerol, and As(III) and uptake of As(III) into the gastrointestinal tissues was measured. The level of inorganic arsenic (iAs) in gastrointestinal tissues after As(III) stimulation was much higher than Hg(II) +As(III) or glycerol+As(III) group. RT-PCR results showed that AQGPs were extensively expressed in gastrointestinal tissues of mice. We also treated Caco-2 cells with Hg(II) and As(III); the level of iAs in a group treated with Hg(II)+As(III) decreased compared with As(III)-treated group. Our results suggested that AQGPs could be important transporters in arsenite uptake into gastrointestinal tissues of mice, but more data are need to prove if AQGPs is the only pathway involved in As transport in mammals or just one of them.
Crystal structure of the aquaglyceroporin PfAQP from the malarial parasite Plasmodium falciparum
Newby, Zachary E R; O’Connell, Joseph; Robles-Colmenares, Yaneth; Khademi, Shahram; Miercke, Larry J; Stroud, Robert M
2008-01-01
The 2.05-Å resolution structure of the aquaglyceroporin from the malarial parasite Plasmodium falciparum (PfAQP), a protein important in the parasite’s life cycle, has been solved. The structure provides key evidence for the basis of water versus glycerol selectivity in aquaporin family members. Unlike its closest homolog of known structure, GlpF, the channel conducts both glycerol and water at high rates, framing the question of what determines high water conductance in aquaporin channels. The universally conserved arginine in the selectivity filter is constrained by only two hydrogen bonds in GlpF, whereas there are three in all water-selective aquaporins and in PfAQP. The decreased cost of dehydrating the triply-satisfied arginine cation may provide the basis for high water conductance. The two Asn-Pro-Ala (NPA) regions of PfAQP, which bear rare substitutions to Asn-Leu-Ala (NLA) and Asn-Pro-Ser (NPS), participate in preserving the orientation of the selectivity filter asparagines in the center of the channel. PMID:18500352
Geometry of null hypersurfaces
Jezierski, J
2004-01-01
We review some basic natural geometric objects on null hypersurfaces. Gauss-Codazzi constraints are given in terms of the analog of canonical ADM momentum which is a well defined tensor density on the null surface. Bondi cones are analyzed with the help of this object.
Identification of key residues involved in Si transport by the aquaglyceroporins.
Carpentier, Gabriel A; Garneau, Alexandre P; Marcoux, Andrée-Anne; Noël, Micheline; Frenette-Cotton, Rachelle; Isenring, Paul
2016-09-01
We recently demonstrated that the aquaglyceroporins (AQGPs) could act as potent transporters for orthosilicic acid (H4SiO4). Although interesting, this finding raised the question of whether water and H4SiO4, the transportable form of Si, permeate AQGPs by interacting with the same region of the pore, especially in view of the difference in molecular radius between the two substrates. Here, our goal was to identify residues that endow the AQGPs with the ability to facilitate Si diffusion by examining the transport characteristics of mutants in which residues were interchanged between a water-permeable but Si-impermeable channel (aquaporin 1 [AQP1]) and a Si-permeable but water-impermeable channel (AQP10). Our results indicate that the composition of the arginine filter (XX/R), known to include three residues that play an important role in water transport, may also be involved in Si selectivity. Interchanging the identities of the nonarginine residues within this filter causes Si transport to increase by approximately sevenfold in AQP1 and to decrease by approximately threefold in AQP10, whereas water transport and channel expression remain unaffected. Our results further indicate that two additional residues in the AQP arginine filter may be involved in substrate selectivity: replacing one of the residues has a profound effect on water permeability, and replacing the other has a profound effect on Si permeability. This study has thus led to the identification of residues that could play a key role in Si transport by the AQGPs and shown that substrate selectivity is likely ensured by more than one checkpoint within or near the pore.
Channel-mediated lactic acid transport: a novel function for aquaglyceroporins in bacteria.
Bienert, Gerd P; Desguin, Benoît; Chaumont, François; Hols, Pascal
2013-09-15
MIPs (major intrinsic proteins), also known as aquaporins, are membrane proteins that channel water and/or uncharged solutes across membranes in all kingdoms of life. Considering the enormous number of different bacteria on earth, functional information on bacterial MIPs is scarce. In the present study, six MIPs [glpF1 (glycerol facilitator 1)-glpF6] were identified in the genome of the Gram-positive lactic acid bacterium Lactobacillus plantarum. Heterologous expression in Xenopus laevis oocytes revealed that GlpF2, GlpF3 and GlpF4 each facilitated the transmembrane diffusion of water, dihydroxyacetone and glycerol. As several lactic acid bacteria have GlpFs in their lactate racemization operon (GlpF1/F4 phylogenetic group), their ability to transport this organic acid was tested. Both GlpF1 and GlpF4 facilitated the diffusion of D/L-lactic acid. Deletion of glpF1 and/or glpF4 in Lb. plantarum showed that both genes were involved in the racemization of lactic acid and, in addition, the double glpF1 glpF4 mutant showed a growth delay under conditions of mild lactic acid stress. This provides further evidence that GlpFs contribute to lactic acid metabolism in this species. This lactic acid transport capacity was shown to be conserved in the GlpF1/F4 group of Lactobacillales. In conclusion, we have functionally analysed the largest set of bacterial MIPs and demonstrated that the lactic acid membrane permeability of bacteria can be regulated by aquaglyceroporins.
David-Tabibi, Omid
2008-01-01
In this article we review standard null-move pruning and introduce our extended version of it, which we call verified null-move pruning. In verified null-move pruning, whenever the shallow null-move search indicates a fail-high, instead of cutting off the search from the current node, the search is continued with reduced depth. Our experiments with verified null-move pruning show that on average, it constructs a smaller search tree with greater tactical strength in comparison to standard null-move pruning. Moreover, unlike standard null-move pruning, which fails badly in zugzwang positions, verified null-move pruning manages to detect most zugzwangs and in such cases conducts a re-search to obtain the correct result. In addition, verified null-move pruning is very easy to implement, and any standard null-move pruning program can use verified null-move pruning by modifying only a few lines of code.
Speziale, Simone
2013-01-01
We define and investigate a quantisation of null hypersurfaces in the context of loop quantum gravity on a fixed graph. The main tool we use is the parametrisation of the theory in terms of twistors, which has already proved useful in discussing the interpretation of spin networks as the quantization of twisted geometries. The classical formalism can be extended in a natural way to null hypersurfaces, with the Euclidean polyhedra replaced by null polyhedra with space-like faces, and SU(2) by the little group ISO(2). The main difference is that the simplicity constraints present in the formalims are all first class, and the symplectic reduction selects only the helicity subgroup of the little group. As a consequence, information on the shapes of the polyhedra is lost, and the result is a much simpler, abelian geometric picture. It can be described by an Euclidean singular structure on the 2-dimensional space-like surface defined by a foliation of space-time by null hypersurfaces. This geometric structure is na...
Shao, M.; Samuel, R.; Wallace, K.; Levine, B.
2007-06-01
To date, nulling coronography has achieved the deepest level of starlight suppression than any other coronagraphic technique. The terms starlight suppression and contrast are often used interchangeably and incorrectly. At 3.5 lambda/D the airy function sidelobes has dropped to 0.001 of the stellar flux. Starlight suppression of 1e-7 will then produce a speckle pattern with a contrast of 1e-10. This paper describes three topics in nulling coronagraphs. The first is starlight suppression of 1.1e-7 in laser light, the level of star light suppression needed for 1e-10 contrast. A similar experiment in broadband (16%) white light has demonstrated ~1.2e-6 suppression. Both experiments were starlight suppression using a single mode optical fiber. Starlight suppression to 1e-6~1e-7 requires wavefront measurements with sub-angstrom level accuracy. This is most easily done with a wavefront sensor that works with light after the coronagraph rather than the bright starlight in front of the coronagraph. Our nulling coronagraph uses a post coronagraphic interferometer to perform two functions, 1) measure the wavefront and provide an correction/error signal for the deformable mirror, and 2) post coronagraph PSF subtraction. We show that the post coronagraph interferometer has very significant SNR advantages over other post coronagraph approaches such as speckle nulling. A secondary function of the post coronagraphic wavefront sensor is that since it measures the amplitude and phase of the wavefront of the starlight after exiting the coronagraph, that amp*exp(i*phi) can be used to estimate the residual speckle pattern for subsequent PSF subtraction. By measuring the PSF at the same time as we're measuring the science image, the stability requirements can be relaxed by many orders of magnitude. (over rotating the telescope around the line of sight for example). The post coronagraph interferometer is being used in three projects, the PICTURE project (coronagraph behind a 60 cm
Radiant Temperature Nulling Radiometer
2002-01-01
A nulling, self-calibrating infrared radiometer is being developed for use in noncontact measurement of temperature in any of a variety of industrial and scientific applications. This instrument is expected to be especially well-suited to measurement of ambient or near-ambient temperature and, even more specifically, for measuring the surface temperature of a natural body of water. Although this radiometer would utilize the long-wavelength infrared (LWIR) portion of the spectrum (wavelengths of 8 to 12 m), its basic principle of operation could also be applied to other spectral bands (corresponding to other temperature ranges) in which the atmosphere is transparent and in which design requirements for sensitivity and temperature-measurement accuracy could be satisfied. The underlying principle of nulling and self-calibration is the same as that of a typical microwave radiometer, but because of differences between the characteristics of signals in the infrared and microwave spectral regions, the principle must be implemented in a different way. A detailed description of the instrument including an infrared photodetector equipped with focusing input optics [e.g., lens(es) and/or mirrors] and an input LWIR band-pass filter is presented.
Gravitational action with null boundaries
Lehner, Luis; Poisson, Eric; Sorkin, Rafael D
2016-01-01
We present a complete discussion of the boundary term in the action functional of general relativity when the boundary includes null segments in addition to the more usual timelike and spacelike segments. We confirm that ambiguities appear in the contribution from a null segment, because it depends on an arbitrary choice of parametrization for the generators. We also show that similar ambiguities appear in the contribution from a codimension-two surface at which a null segment is joined to another (spacelike, timelike, or null) segment. The parametrization ambiguity can be tamed by insisting that the null generators be affinely parametrized; this forces each null contribution to the boundary action to vanish, but leaves intact the fredom to rescale the affine parameter by a constant factor on each generator. Once a choice of parametrization is made, the ambiguity in the joint contributions can be eliminated by formulating well-motivated rules that ensure the additivity of the gravitational action. Enforcing t...
Zhang, Jun-Guo; Liu, Xiu-Ying; He, Xiu-Ping; Guo, Xue-Na; Lu, Ying; Zhang, Bo-Run
2011-02-01
The FPS1 gene coding for the Fps1p aquaglyceroporin protein of an industrial strain of Saccharomyces cerevisiae was disrupted by inserting CUP1 gene. Wild-type strain, CE25, could only grow on YPD medium containing less than 0.45% (v/v) acetic acid, while recombinant strain T12 with FPS1 disruption could grow on YPD medium with 0.6% (v/v) acetic acid. Under 0.4% (v/v) acetic acid stress (pH 4.26), ethanol production and cell growth rates of T12 were 1.7 ± 0.1 and 0.061 ± 0.003 g/l h, while those of CE25 were 1.2 ± 0.1 and 0.048 ± 0.003 g/l h, respectively. FPS1 gene disruption in an industrial ethanologenic yeast thus increases cell growth and ethanol yield under acetic acid stress, which suggests the potential utility of FPS1 gene disruption for bioethanol production from renewable resources such as lignocelluloses.
On the randomness of pulsar nulls
Redman, Stephen L.; Rankin, Joanna M.
2009-05-01
Pulsar nulling is not always a random process; most pulsars, in fact, null non-randomly. The Wald-Wolfowitz statistical runs test is a simple diagnostic that pulsar astronomers can use to identify pulsars that have non-random nulls. It is not clear at this point how the dichotomy in pulsar nulling randomness is related to the underlying nulling phenomenon, but its nature suggests that there are at least two distinct reasons that pulsars null.
NULL Convention Floating Point Multiplier
Anitha Juliette Albert; Seshasayanan Ramachandran
2015-01-01
Floating point multiplication is a critical part in high dynamic range and computational intensive digital signal processing applications which require high precision and low power. This paper presents the design of an IEEE 754 single precision floating point multiplier using asynchronous NULL convention logic paradigm. Rounding has not been implemented to suit high precision applications. The novelty of the research is that it is the first ever NULL convention logic multiplier, designed to p...
Gravitational action with null boundaries
Lehner, Luis; Myers, Robert C.; Poisson, Eric; Sorkin, Rafael D.
2016-10-01
We present a complete discussion of the boundary term in the action functional of general relativity when the boundary includes null segments in addition to the more usual timelike and spacelike segments. We confirm that ambiguities appear in the contribution from a null segment, because it depends on an arbitrary choice of parametrization for the generators. We also show that similar ambiguities appear in the contribution from a codimension-two surface at which a null segment is joined to another (spacelike, timelike, or null) segment. The parametrization ambiguity can be tamed by insisting that the null generators be affinely parametrized; this forces each null contribution to the boundary action to vanish, but leaves intact the fredom to rescale the affine parameter by a constant factor on each generator. Once a choice of parametrization is made, the ambiguity in the joint contributions can be eliminated by formulating well-motivated rules that ensure the additivity of the gravitational action. Enforcing these rules, we calculate the time rate of change of the action when it is evaluated for a so-called "Wheeler-DeWitt patch" of a black hole in asymptotically anti de Sitter space. We recover a number of results cited in the literature, obtained with a less complete analysis.
Phase-Occultation Nulling Coronagraphy
Lyon, Richard G; Clampin, Mark; Petrone, Peter
2015-01-01
The search for life via characterization of earth-like planets in the habitable zone is one of the key scientific objectives in Astronomy. We describe a new phase-occulting (PO) interferometric nulling coronagraphy (NC) approach. The PO-NC approach employs beamwalk and freeform optical surfaces internal to the interferometer cavity to introduce a radially dependent plate scale difference between each interferometer arm (optical path) that nulls the central star at high contrast while transmitting the off-axis field. The design is readily implemented on segmented-mirror telescope architectures, utilizing a single nulling interferometer to achieve high throughput, a small inner working angle (IWA), sixth-order or higher starlight suppression, and full off-axis discovery space, a combination of features that other coronagraph designs generally must trade. Unlike previous NC approaches, the PO-NC approach does not require pupil shearing; this increases throughput and renders it less sensitive to on-axis common-mo...
NULL Convention Floating Point Multiplier
Directory of Open Access Journals (Sweden)
Anitha Juliette Albert
2015-01-01
Full Text Available Floating point multiplication is a critical part in high dynamic range and computational intensive digital signal processing applications which require high precision and low power. This paper presents the design of an IEEE 754 single precision floating point multiplier using asynchronous NULL convention logic paradigm. Rounding has not been implemented to suit high precision applications. The novelty of the research is that it is the first ever NULL convention logic multiplier, designed to perform floating point multiplication. The proposed multiplier offers substantial decrease in power consumption when compared with its synchronous version. Performance attributes of the NULL convention logic floating point multiplier, obtained from Xilinx simulation and Cadence, are compared with its equivalent synchronous implementation.
NULL convention floating point multiplier.
Albert, Anitha Juliette; Ramachandran, Seshasayanan
2015-01-01
Floating point multiplication is a critical part in high dynamic range and computational intensive digital signal processing applications which require high precision and low power. This paper presents the design of an IEEE 754 single precision floating point multiplier using asynchronous NULL convention logic paradigm. Rounding has not been implemented to suit high precision applications. The novelty of the research is that it is the first ever NULL convention logic multiplier, designed to perform floating point multiplication. The proposed multiplier offers substantial decrease in power consumption when compared with its synchronous version. Performance attributes of the NULL convention logic floating point multiplier, obtained from Xilinx simulation and Cadence, are compared with its equivalent synchronous implementation.
Fracture characterisation using geoelectric null-arrays
Falco, Pierik; Negro, François; Szalai, Sándor; Milnes, Ellen
2013-06-01
The term "geoelectric null-array" is used for direct current electrode configurations yielding a potential difference of zero above a homogeneous half-space. This paper presents a comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-γ null-array and Schlumberger null-array in response to a fracture, both in profiling and in azimuthal mode. The main objective is to determine which array(s) best localise fractures or best identify their orientation. Forward modelling of the three null-arrays revealed that the Wenner-γ and Schlumberger null-arrays localise vertical fractures the most accurately, whilst the midpoint null-array combined with the Schlumberger null-array allows accurate orientation of a fracture. Numerical analysis then served as a basis to interpret the field results. Field test measurements were carried out above a quarry in Les Breuleux (Switzerland) with the three null-arrays and classical arrays. The results were cross-validated with quarry-wall geological mapping. In real field circumstances, the Wenner-γ null-array proved to be the most efficient and accurate in localising fractures. The orientations of the fractures according to the numerical results were most efficiently determined with the midpoint null-array, whilst the Schlumberger null-array adds accuracy to the results. This study shows that geoelectrical null-arrays are more suitable than classical arrays for the characterisation of fracture geometry.
Null eikonal helices and Null eikonal slant helices in the 4-dimensional Lorentzian manifold
Zıplar, Evren
2014-01-01
In this paper, we define the notion of eikonal helix and eikonal slant helix for null curves in the 4-dimensional Lorentzian manifold M 1 4 and give a characterization for the null curve to be the null eikonal helix. Moreover, we indicate an important relation between the null eikonal helix and null eikonal slant helix and find the axis of the null eikonal helix. We obtain some relationships between the curvatures of these curves.
Shinkai, Yasuhiro; Sumi, Daigo; Toyama, Takashi; Kaji, Toshiyuki; Kumagai, Yoshito
2009-06-01
Aquaporin (AQP) 9 is a member of the aquaglyceroporin subfamily of AQPs in the transfer of water and small solutes such as glycerol and arsenite. It is well recognized that arsenic toxicity is associated with intracellular accumulation of this metalloid. In the present study, we examined the contribution of AQP9 to the uptake of inorganic arsenite, thereby increasing arsenic-induced cytotoxicity in primary mouse hepatocytes. Pretreatment with sorbitol as a competitive inhibitor of AQP9 and siRNA-mediated knockdown of AQP9 resulted in a significant decrease of arsenite uptake in the cell and its cytotoxicity. Furthermore, overexpression of AQP9 in HEK293 cells led to the enhancement of intracellular arsenic concentration, resulting in enhanced cytotoxicity after arsenite exposure. These results suggest that AQP9 is a channel to define arsenite sensitivity in primary mouse hepatocytes.
Parasitic interference in nulling interferometry
Matter, Alexis; Danchi, William C; Lopez, Bruno; Absil, Olivier
2013-01-01
Nulling interferometry aims to detect faint objects close to bright stars. Its principle is to produce a destructive interference along the line-of-sight so that the stellar flux is rejected, while the flux of the off-axis source can be transmitted. In practice, various instrumental perturbations can degrade the nulling performance. Any imperfection in phase, amplitude, or polarization produces a spurious flux that leaks to the interferometer output and corrupts the transmitted off-axis flux. One of these instrumental pertubations is the crosstalk phenomenon, which occurs because of multiple parasitic reflections inside transmitting optics, and/or diffraction effects related to beam propagation along finite size optics. It can include a crosstalk of a beam with itself, and a mutual crosstalk between different beams. This can create a parasitic interference pattern, which degrades the intrinsic transmission map - or intensity response - of the interferometer. In this context, we describe how this instrumental ...
Balloon Exoplanet Nulling Interferometer (BENI)
Lyon, Richard G.; Clampin, Mark; Woodruff, Robert A.; Vasudevan, Gopal; Ford, Holland; Petro, Larry; Herman, Jay; Rinehart, Stephen; Carpenter, Kenneth; Marzouk, Joe
2009-01-01
We evaluate the feasibility of using a balloon-borne nulling interferometer to detect and characterize exosolar planets and debris disks. The existing instrument consists of a 3-telescope Fizeau imaging interferometer with 3 fast steering mirrors and 3 delay lines operating at 800 Hz for closed-loop control of wavefront errors and fine pointing. A compact visible nulling interferometer is under development which when coupled to the imaging interferometer would in-principle allow deep suppression of starlight. We have conducted atmospheric simulations of the environment above 100,000 feet and believe balloons are a feasible path forward towards detection and characterization of a limited set of exoplanets and their debris disks. Herein we will discuss the BENI instrument, the balloon environment and the feasibility of such as mission.
Areas and volumes for null cones
Grant, James D E
2010-01-01
Motivated by recent work of Choquet-Bruhat, Chrusciel, and Martin-Garcia, we prove monotonicity properties and comparison results for the area of slices of the null cone of a point in a Lorentzian manifold. We also prove volume comparison results for subsets of the null cone analogous to the Bishop-Gromov relative volume monotonicity theorem and Guenther's volume comparison theorem. We briefly discuss how these estimates may be used to control the null second fundamental form of slices of the null cone in Ricci-flat Lorentzian four-manifolds with null curvature bounded above.
An analysis of radio pulsar nulling statistics
Biggs, James D.
1992-01-01
Survival analysis methods are used to seek correlations between the fraction of null pulsars and other pulsar characteristics for an ensemble of 72 radio pulsars. The strongest correlation is found between the null fraction and the pulse period, suggesting that nulling is a manifestation of a faltering emission mechanism. Correlations are also found between the fraction of null pulses and other parameters that have a strong dependence on the pulse period. The results presented here suggest that nulling is broad-band and may ultimately be explained in terms of polar cap models of pulsar emission.
Null Similar Curves with Variable Transformations in Minkowski 3-space
Önder, Mehmet
2012-01-01
In this study, we define a family of null curves in Minkowski 3-space and called null similar curves. We obtain some properties of these special curves. We show that two null curves are null similar curves if and only if these curves form a null Bertrand pair. Moreover, we obtain that the family of null geodesics and null helices form the families of null similar curves with variable transformation.
On the Penrose inequality along null hypersurfaces
Mars, Marc
2015-01-01
The null Penrose inequality, i.e. the Penrose inequality in terms of the Bondi energy, is studied by introducing a funtional on surfaces and studying its properties along a null hypersurface $\\Omega$ extending to past null infinity. We prove a general Penrose-type inequality which involves the limit at infinity of the Hawking energy along a specific class of geodesic foliations called Geodesic Asymptotic Bondi (GAB), which are shown to always exist. Whenever, this foliation approaches large spheres, this inequality becomes the null Penrose inequality and we recover the results of Ludvigsen-Vickers and Bergqvist. By exploiting further properties of the functional along general geodesic foliations, we introduce an approach to the null Penrose inequality called Renormalized Area Method and find a set of two conditions which implies the validity of the null Penrose inequality. One of the conditions involves a limit at infinity and the other a condition on the spacetime curvature along the flow. We investigate the...
The Importance of Proving the Null
Gallistel, C. R.
2009-01-01
Null hypotheses are simple, precise, and theoretically important. Conventional statistical analysis cannot support them; Bayesian analysis can. The challenge in a Bayesian analysis is to formulate a suitably vague alternative, because the vaguer the alternative is (the more it spreads out the unit mass of prior probability), the more the null is…
Collapsing spherical null shells in general relativity
Directory of Open Access Journals (Sweden)
S Khakshournia
2011-03-01
Full Text Available In this work, the gravitational collapse of a spherically symmetric null shell with the flat interior and a charged Vaidya exterior spacetimes is studied. There is no gravitational impulsive wave present on the null hypersurface which is shear-free and contracting. It follows that there is a critical radius at which the shell bounces and starts expanding.
Causal cells: spacetime polytopes with null hyperfaces
Neiman, Yasha
2012-01-01
We consider polyhedra and 4-polytopes in Minkowski spacetime - in particular, null polyhedra with zero volume, and 4-polytopes that have such polyhedra as their hyperfaces. We present the basic properties of several classes of null-faced 4-polytopes: 4-simplices, "tetrahedral diamonds" and 4-parallelotopes. We propose a "most regular" representative of each class. The most-regular parallelotope is of particular interest: its edges, faces and hyperfaces are all congruent, and it features both null hyperplanes and null segments. A tiling of spacetime with copies of this polytope can be viewed alternatively as a lattice with null edges, such that each point is at the intersection of four lightrays in a tetrahedral pattern. We speculate on the relevance of this construct for discretizations of curved spacetime and for quantum gravity.
Magnetic Nulls in the Earth's Magnetotail
Eriksson, Elin; Vaivads, Andris; Khotyaintsev, Yuri; Markidis, Stefano; André, Mats; Fu, Huishan; Karlsson, Tomas
2015-04-01
Regions with vanishing magnetic field, also referred to as magnetic nulls, are of high interest in plasma physics. Near magnetic nulls particles become unmagnetized and can by interacting with electric fields be accelerated up to high energies. Magnetic nulls have been observed and studied before using different methods for a few events. Here we present a statistical study of magnetic nulls in the Earth's magnetotail. In addition we study the role of magnetic field disturbances on the magnetic null identification. We study the magnetic nulls using full resolution data from all of the Cluster satellites when their maximum separation is less than one ion inertial length (approximately 1000 km). This is only fulfilled in 2003 when the maximum spacecraft separation is approximately 250 km. The magnetic nulls are not found using the more common method of Poincaré index. Instead we create a box surrounding the tetrahedron defined by the positions of the spacecrafts. If the positions of the magnetic nulls, using Taylor expansion, are within this box, they are saved for further analysis. All together 23 time intervals are found using this method and two error constraints. We find most of the nulls in the magnetotail current sheet, but a few of them are found at the magnetopause. We identify magnetic null types and currents associated with them. We present a detailed analysis of one example from August 6, 2003 00:45:40:00 UT - 00:45:41:05 UT when the satellites are in the magnetotail. Based on a linear magnetic field model created using parameters taken from the real data, we demonstrate the effect of magnetic field disturbance on the magnetic null identification. We show that magnetic disturbances of large enough amplitude can lead to a change in the magnetic null type, consistent with the data example. Therefore we suggest that for magnetic null type identification an additional constraint based on magnetic field disturbance amplitude have to be introduced. The obtained
IRAN: interferometric remapped array nulling
Aristidi, Eric; Vakili, Farrokh; Abe, Lyu; Belu, Adrian; Lopez, Bruno; Lanteri, Henri; Schutz, A.; Menut, Jean-Luc
2004-10-01
This paper describes a method of beam-combination in the so-called hypertelescope imaging technique recently introduced by Labeyrie in optical interferometry. The method we propose is an alternative to the Michelson pupil reconfiguration that suffers from the loss of the classical object-image convolution relation. From elementary theory of Fourier optics we demonstrate that this problem can be solved by observing in a combined pupil plane instead of an image plane. The point-source intensity distribution (PSID) of this interferometric "image" tends towards a psuedo Airy disc (similar to that of a giant monolithic telescope) for a sufficiently large number of telescopes. Our method is applicable to snap-shot imaging of extended sources with a field comparable to the Airy pattern of single telescopes operated in a co-phased multi-aperture interferometric array. It thus allows to apply conveniently pupil plane coronagraphy. Our technique called Interferometric Remapped Array Nulling (IRAN) is particularly suitable for high dynamic imaging of extra-solar planetary companions, circumstellar nebulosities or extra-galactic objects where long baseline interferometry would closely probe the central regions of AGNs for instance.
High-contrast Nulling Interferometry Techniques Project
National Aeronautics and Space Administration — "We are developing rotating-baseline nulling-interferometry techniques and algorithms on the single-aperture Hale and Keck telescopes at near-infrared wavelengths,...
Scientists Find a Magnetic Null in Nature
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
@@ An international team has found the first in situ evidence for the existance of a null point in the central area of magnetic reconnection. The discovery was reported in the July issue of Nature Physics.
Latex allergy and filaggrin null mutations
DEFF Research Database (Denmark)
Carlsen, Berit C; Meldgaard, Michael; Hamann, Dathan
2011-01-01
Objectives Natural rubber latex (NRL) contains over 200 proteins of which 13 have been identified as allergens and the cause of type I latex allergy. Health care workers share a high occupational risk for developing latex allergy. Filaggrin null mutations increase the risk of type I sensitizations...... to aeroallergens and it is possible that filaggrin null mutations also increase the risk of latex allergy. The aim of this paper was to examine the association between filaggrin null mutations and type I latex allergy. Methods Twenty latex allergic and 24 non-latex allergic dentists and dental assistants......, occupationally exposed to latex, were genotyped for filaggrin null mutations R501X and 2282del4. Latex allergy was determined by a positive reaction or a historical positive reaction to a skin prick test with NRL. Results 41 individuals were successfully genotyped. Three individuals were filaggrin mutation...
New null screen design for corneal topography
Campos-García, Manuel; Estrada-Molina, Amilcar; Díaz-Uribe, Rufino
2011-09-01
In this work we report the design of a null screen for corneal topography. Here we assume that the corneal surface is an ellipsoid with a diameter of 12 mm and a curvature radius of 7.8 mm. To avoid the difficulties in the alignment of the test system due to the face contour (eyebrows, nose, or eyelids), we design a conical null-screen with spots (similar to ellipses) drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact radial array of circular spots if the surface is perfect. Additionally, we performed a numerical simulation introducing Gaussian random errors in the coordinates of the centroids of the spots on the image plane, and in the coordinates of the sources (spots on the null-screen) in order to obtain the conical null-screen that reduces the error in the evaluation of the topography.
Characterization of Null Geodesics on Kerr Spacetimes
Paganini, Claudio F; Oancea, Marius A
2016-01-01
We consider null geodesics in the domain of outer communication of a sub-extremal Kerr spacetime. We show, that most fundamental properties of null geodesics can be represented in one plot. In particular one can see immediately that the ergoregion and trapping are separated in phase space. Furthermore we show that from the point of view of any timelike observer outside of a black hole, trapping can be understood as a smooth set of spacelike directions on the observers' celestial sphere.
Null-sissemakse - eraisikule riskantne / Tõnu Tramm
Tramm, Tõnu, 1968-
2005-01-01
Ilmunud ka: Delovõje Vedomosti 20. apr. lk. 26. Hansaliising ja Ühisliising käivitasid kampaania, mille käigus pakutakse uusi kuni 250 000 krooni maksvaid autosid null-sissemaksega. Kommenteerib ASi SEB Ühisliising arendusdirektor Ove Muuk. Tabel: Null-sissemaksega auto tuleb kallim. Lisad: Kuidas saavutada võimalikult väike kuumakse?; Kuidas maksta võimalikult vähe intressi? Vt. samas: Argo Rebane: Liisingufirmast saab parema hinna
Null vectors of the $WBC_2$ algebra
Bajnok, Z
1994-01-01
Using the fusion principle of Bauer et al. we give explicit expressions for some null vectors in the highest weight representations of the \\bc algebra in two different forms. These null vectors are the generalization of the Virasoro ones described by Benoit and Saint-Aubin and analogues of the $W_3$ ones constructed by Bowcock and Watts. We find connection between quantum Toda models and the fusion method.
Faddeev Null Plane Model of Proton
D'Araújo, W R B; Frederico, T
1998-01-01
The proton is formulated as a relativistic system of three constituent quarks interacting via a zero-range two-body force in the null-plane. The covariance of the null-plane Faddeev-like equation under kinematical front-form boosts is discussed. A simplified three-boson model of the nucleon wave-function is obtained numerically. The proton electric form-factor reproduces the experimental data for low momentum transfers and qualitatively describes the asymptotic region.
Phase-only nulling for transmit antenna
Hussain, Moayyed A.; Yu, Kai-Bor
1999-11-01
This paper describes a technique for transmit antenna nulling for low-cost large sparse phased array radar system. Radar system described includes an array of elemental antennas, each with a transmit/receive (T/R) module. The T/R modules are operated at or near maximum output to achieve maximum CD-to-RF efficiency. A phase controller controls the phase shift, which are imparted by each module to its signal, to form a mainbeam and its associated sidelobes. A perturbation phase generator adds phase shifts computed, to form wide nulls in the sidelobe structure. The nulls are achieved at very minimal loss of gain, in the order of fraction of a dB. The speed of obtaining these nulls in real time allows a rapid steering of these nulls in a hostile environment. The thinned aperture allow designing a light weigh mobile system. In radar context, these nulls may be placed on a source of ground clutter, a set of jammers or a set of undesirable radio sources.
The Emergence, Motion, and Disappearance of Magnetic Null Points
Murphy, Nicholas; Parnell, Clare; Haynes, Andrew; Pontin, David
2013-01-01
Magnetic reconnection frequently occurs at and around magnetic null points. We derive exact expressions for the motion of a magnetic null point in a smoothly varying magnetic field. We define xn as the position of a null, U = dxn/dt as the null's velocity, and M as the Jacobian matrix of the magnetic field at the null. By evaluating the derivative of the magnetic field following the motion of the null, we find the null velocity to be U = -M-1 ∂B/∂t with all quantities evaluated ...
Null structure groups in eleven dimensions
Cariglia, M; Conamhna, Oisin A. P. Mac
2004-01-01
We classify all the structure groups which arise as subgroups of the isotropy group, $(Spin(7)\\ltimes\\mathbb{R}^8)\\times\\mathbb{R}$, of a single null Killing spinor in eleven dimensions. We construct the spaces of spinors fixed by these groups. We determine the conditions under which structure subgroups of the maximal null strucuture group $(Spin(7)\\ltimes\\mathbb{R}^8)\\times\\mathbb{R}$ may also be embedded in SU(5), and hence the conditions under which supersymmetric spacetime admits only null, or both timelike and null, Killing spinors. This concludes, for spacetimes admitting at least one null Killing spinor, the first, purely algebraic, phase of the refined G-structure classification of supersymmetric spacetimes in eleven dimensions, the objective of which is the derivation of the general local bosonic solution of the Killing spinor equation of eleven dimensional supergravity. Finally, we discuss how the second phase of the classification, involving the direct analysis of the Killing spinor equation, may b...
Two Roads to the Null Energy Condition
Parikh, Maulik
2015-01-01
The null energy condition has sweeping consequences in general relativity. I argue here that it has been misunderstood as a property exclusively of matter, when in fact it arises only in a theory of both matter and gravity. I then derive an equivalent geometric formulation of the null energy condition from worldsheet string theory, where it arises beautifully as simply Einstein's equations in two dimensions. But further, I show that this condition also has a thermodynamic origin, following from a local version of the second law of thermodynamics, applied to gravitational entropy. Thus, far from being an incidental property of matter, the validity of the null energy condition hints at the deep dual origins of gravity.
Magnetized Emergent Universe with Null Radiation Flow
Singh, J. K.; Rani, Sarita
2016-01-01
In this paper, we study the Bianchi type-I cosmological model in a different basic form incorporating with null radiation flow with the perfect fluid in the presence as well as absence of a source free magnetic field. A set of new exact solutions of Einstein field equations are obtained in both the cases. We observe that the emergent universe model with null radiation flow approaches to de-sitter universe at late time obeying the same rate of expansion in presence and absence of the magnetic field.
Null Geodesics in Brane World Scenarios
Institute of Scientific and Technical Information of China (English)
ZHANG Li-Feng; ZHANG Yuan-Zhong
2004-01-01
We study the null bulk geodesic motion in the brane world in which the bulk metric has an un-stabilized extra spatial dimension. We find that the null bulk geodesic motion as observed on the 3-brane with Z2 symmetry would be a timelike geodesic motion even though there exists an extra non-gravitational force in contrast with the case of the stabilized extra spatial dimension. In other words the presence of the extra non-gravitational force would not violate thc Z2 symmetry.
The Emergence, Motion, and Disappearance of Magnetic Null Points
Murphy, Nicholas; Parnell, Clare; Haynes, Andrew; Pontin, David
2013-10-01
Magnetic reconnection frequently occurs at and around magnetic null points. We derive exact expressions for the motion of a magnetic null point in a smoothly varying magnetic field. We define xn as the position of a null, U = dxn/dt as the null's velocity, and M as the Jacobian matrix of the magnetic field at the null. By evaluating the derivative of the magnetic field following the motion of the null, we find the null velocity to be U = -M-1 ∂B/∂t with all quantities evaluated at the null point. For resistive MHD, this reduces to U =V (xn) - ηM-1∇2B. This expression indicates that any difference between the plasma flow velocity at the null and the velocity of the null itself is due to resistive diffusion of the magnetic field. Null points must diffuse in and out of existence. Null-null pairs first appear (or disappear) as a single degenerate null with singular M, and then instantaneously move apart (together) infinitely fast. An expression describing the motion of separators cannot depend solely on local parameters and must include information on connectivity changes due to reconnection along the entire field line.
The Null Hypothesis as the Research Hypothesis.
Myers, Barbara E.; Pohlmann, John T.
A procedure was developed within hypothesis-testing logic that allows researchers to support a hypothesis that has traditionally been the statistical or null hypothesis. Four activities involved in attainment of this goal were discussed: (1) development of statistical logic needed to define the sampling distribution associated with the hypothesis…
Polarization nulling interferometry for exoplanet detection
Spronck, J.; Pereira, S.F.; Braat, J.J.M.
2006-01-01
We introduce a new concept of nulling interferometer without any achromatic device, using polarization properties of light. This type of interferometer should enable a high rejection ratio in a theoretically unlimited spectral band. We analyze several consequences of the proposed design, notably, th
Infinite Blueshift of Charged Null Particles
Mann, R. B.; Sajko, W. N.
1994-01-01
We demonstrate that charged null particles can be infinitely blue\\-shifted in a Kerr-Newman spacetime. The surface of infinite blueshift can be outside of the ergosphere in a Kerr-Newman spacetime, and outside of the outer event horizon for a Reissner-Nordstrom spacetime. Implications for extensions of the standard model which incorporate charged neutrinos are discussed.
Gravitational collapse of a cylindrical null shell in vacuum
Directory of Open Access Journals (Sweden)
S. Khakshournia
2008-03-01
Full Text Available Barrabès-Israel null shell formalism is used to study the gravitational collapse of a thin cylindrical null shell in vacuum. In general the lightlike matter shell whose history coincides with a null hypersurface is characterized by a surface energy density. In addition, a gravitational impulsive wave is present on this null hypersurface whose generators admit both the shear and expansion. In the case of imposing the cylindrical flatness the surface energy-momentum tensor of the matter shell on the null hypersurface vanishes and the null hyper- surface is just the history of the gravitational wave .
Statistics and accuracy of magnetic null identification in multispacecraft data
Eriksson, E.; Vaivads, A.; Khotyaintsev, Yu. V.; Khotyayintsev, V. M.; André, M.
2015-09-01
Complex magnetic topologies are ubiquitous in astrophysical plasmas. Analyzing magnetic nulls, regions of vanishing magnetic field, is one way to characterize 3-D magnetic topologies. Magnetic nulls are believed to be important in 3-D reconnection and turbulence. In the vicinity of a null, plasma particles become unmagnetized and can be accelerated to high energies by electric fields. We present the first statistical study of the occurrence of magnetic nulls and their types in the Earth's nightside magnetosphere. We are able to identify the nulls both in the tail and in the magnetopause current sheets. On average, we find one null for every few current sheet crossings. We show that the type identification of magnetic nulls may be sensitive to local fluctuations in the magnetic field. We develop and demonstrate a method to estimate the reliability of the magnetic null type identification.
Statistics and accuracy of magnetic null identification in multispacecraft data
Eriksson, Elin; Vaivads, Andris; Khotyaintsev, Yuri V.; Khotyayintsev, V. M.; Andre, Mats
2015-01-01
Complex magnetic topologies are ubiquitous in astrophysical plasmas. Analyzing magnetic nulls, regions of vanishing magnetic field, is one way to characterize 3-D magnetic topologies. Magnetic nulls are believed to be important in 3-D reconnection and turbulence. In the vicinity of a null, plasma particles become unmagnetized and can be accelerated to high energies by electric fields. We present the first statistical study of the occurrence of magnetic nulls and their types in the Earth's nig...
A Conformal Extension Theorem based on Null Conformal Geodesics
Lübbe, Christian
2008-01-01
In this article we describe the formulation of null geodesics as null conformal geodesics and their description in the tractor formalism. A conformal extension theorem through an isotropic singularity is proven by requiring the boundedness of the tractor curvature and its derivatives to sufficient order along a congruence of null conformal geodesic. This article extends earlier work by Tod and Luebbe.
Null controllability and the algebraic Riccati equation in Banach Spaces
Van Neerven, J.M.A.M.
2005-01-01
By a recent result of Priola and Zabczyk, a null controllable linear system [y'(t) = Ay(t) + Bu(t)] in a Hilbert space E is null controllable with vanishing energy if and only if it is null controllable and the only positive self-adjoint solution of the associated algebraic Riccati equation [XA + A*
Morphological Uniformity and the Null Subject Parameter in Adult SLA.
Davies, William D.
1996-01-01
Focuses on the application of the Null Subject Parameter. Data reveals that some second-language learners exhibit knowledge that English is morphologically nonuniform yet still accept English null subject sentences. Findings disprove the Morphological Uniformity Hypothesis, indicating that any reformulation of the Null Subject Parameter must…
Blob dynamics in TORPEX poloidal null configurations
Shanahan, B. W.; Dudson, B. D.
2016-12-01
3D blob dynamics are simulated in X-point magnetic configurations in the TORPEX device via a non-field-aligned coordinate system, using an isothermal model which evolves density, vorticity, parallel velocity and parallel current density. By modifying the parallel gradient operator to include perpendicular perturbations from poloidal field coils, numerical singularities associated with field aligned coordinates are avoided. A comparison with a previously developed analytical model (Avino 2016 Phys. Rev. Lett. 116 105001) is performed and an agreement is found with minimal modification. Experimental comparison determines that the null region can cause an acceleration of filaments due to increasing connection length, but this acceleration is small relative to other effects, which we quantify. Experimental measurements (Avino 2016 Phys. Rev. Lett. 116 105001) are reproduced, and the dominant acceleration mechanism is identified as that of a developing dipole in a moving background. Contributions from increasing connection length close to the null point are a small correction.
Collapse and bounce of null fluids
Creelman, Bradley
2016-01-01
Exact solutions describing the spherical collapse of null fluids can contain regions which violate the energy conditions. Physically the violations occur when the infalling matter continues to move inwards even when non-gravitational repulsive forces become stronger than gravity. In 1991 Ori proposed a resolution for these violations: spacetime surgery should be used to replace the energy condition violating region with an outgoing solution. The matter bounces. We revisit and implement this proposal for the more general Husain null fluids. We find that: 1) generically there is a thin shell discontinuity along the junction surface between ingoing and outgoing solutions, 2) there are special cases where the shell vanishes and 3) these conclusions also apply to charged Vaidya (the original paper argued that there were no shells at the junctions). Along the way we note an apparent error in the standard classification of energy condition violations for Type II stress-energy tensors.
Compressional plasma flows near magnetic null points
Energy Technology Data Exchange (ETDEWEB)
Bulanov, S.V.; Ol' shanetskii, M.A.
1985-06-01
Self-similar solutions of the MHD equations describing time-varying plasma flows near magnetic null points are analyzed. Various classes of particular solutions are constructed. Special attention is paid to compressional flows which involve the development of sharp maxima. The stability of the self-similar solutions is studied. Solutions describing the motion of a vortex in MHD are constructed. The possibility of producing current sheets in nonuniform magnetic configurations is demonstrated.
Collapse and bounce of null fluids
Creelman, Bradley; Booth, Ivan
2016-01-01
Exact solutions describing the spherical collapse of null fluids can contain regions which violate the energy conditions. Physically the violations occur when the infalling matter continues to move inwards even when non-gravitational repulsive forces become stronger than gravity. In 1991 Ori proposed a resolution for these violations: spacetime surgery should be used to replace the energy condition violating region with an outgoing solution. The matter bounces. We revisit and implement this p...
PHASE CLOSURE NULLING: THEORY AND PRACTICE
Directory of Open Access Journals (Sweden)
A. Chelli
2009-01-01
Full Text Available We provide a complete theory of the phase closure of a binary system in which a small, feeble, and unresolved companion acts as a perturbing parameter on the spatial frequency spectrum of a dominant, bright, resolved source. We demonstrate that the in uence of the companion can be measured with precision by measuring the phase closure of the system near the nulls of the primary visibility function. In these regions of phase closure nulling, frequency intervals always exist where the phase closure signature of the companion is larger than any systematic error and can thus be measured. We show that this technique allows retrieval of many astrophysically relevant properties of faint and close companions such as ux, position, and in favorable cases, spectrum. As a proof of concept, using the AMBER/VLTI instrument with 3 auxiliary telescopes of 1.8 m and only 15 minutes of on-sky integration, we detected the ve magnitudes fainter companion of HD 59717 at only 3.5 stellar radii distance from the primary. This is one of the highest contrast detected by interferometry between a companion and its parent star. We conclude by a rapid study of the potentialities of phase closure nulling observations with current interferometers and explore the requirements for a new type of dedicated instrument.
Magnetic Null Points in Kinetic Simulations of Space Plasmas
Olshevsky, Vyacheslav; Deca, Jan; Divin, Andrey; Peng, Ivy Bo; Markidis, Stefano; Innocenti, Maria Elena; Cazzola, Emanuele; Lapenta, Giovanni
2016-03-01
We present a systematic attempt to study magnetic null points and the associated magnetic energy conversion in kinetic particle-in-cell simulations of various plasma configurations. We address three-dimensional simulations performed with the semi-implicit kinetic electromagnetic code iPic3D in different setups: variations of a Harris current sheet, dipolar and quadrupolar magnetospheres interacting with the solar wind, and a relaxing turbulent configuration with multiple null points. Spiral nulls are more likely created in space plasmas: in all our simulations except lunar magnetic anomaly (LMA) and quadrupolar mini-magnetosphere the number of spiral nulls prevails over the number of radial nulls by a factor of 3-9. We show that often magnetic nulls do not indicate the regions of intensive energy dissipation. Energy dissipation events caused by topological bifurcations at radial nulls are rather rare and short-lived. The so-called X-lines formed by the radial nulls in the Harris current sheet and LMA simulations are rather stable and do not exhibit any energy dissipation. Energy dissipation is more powerful in the vicinity of spiral nulls enclosed by magnetic flux ropes with strong currents at their axes (their cross sections resemble 2D magnetic islands). These null lines reminiscent of Z-pinches efficiently dissipate magnetic energy due to secondary instabilities such as the two-stream or kinking instability, accompanied by changes in magnetic topology. Current enhancements accompanied by spiral nulls may signal magnetic energy conversion sites in the observational data.
A note on inextensible flows of partially and pseudo null curves in E_1^4
Yuzbasi, Zuhal Kucukarslan; Bektas, Mehmet
2013-01-01
In this paper, we study inextensible flows of partially null and pseudo null curves in E_1^4. We give neccessary and sufficent conditions for inextensible flows of partially null and pseudo null curves in E_1^4
System and Method for Null-Lens Wavefront Sensing
Hill, Peter C. (Inventor); Thompson, Patrick L. (Inventor); Aronstein, David L. (Inventor); Bolcar, Matthew R. (Inventor); Smith, Jeffrey S. (Inventor)
2015-01-01
A method of measuring aberrations in a null-lens including assembly and alignment aberrations. The null-lens may be used for measuring aberrations in an aspheric optic with the null-lens. Light propagates from the aspheric optic location through the null-lens, while sweeping a detector through the null-lens focal plane. Image data being is collected at locations about said focal plane. Light is simulated propagating to the collection locations for each collected image. Null-lens aberrations may extracted, e.g., applying image-based wavefront-sensing to collected images and simulation results. The null-lens aberrations improve accuracy in measuring aspheric optic aberrations.
Null Object模式研究%Research on Null Object Pattern
Institute of Scientific and Technical Information of China (English)
吴清寿
2013-01-01
在许多面向对象的程序设计语言中,对象引用可能为空.在调用任何方法之前这些引用需要被检测以确保它们不为空.频繁的检测会引起代码的重复和系统的不稳定.Null Object模式能够用来解决这一问题.本文阐述了Null Object模式及其实现方式,针对空目标的单一实例化策略,给出了改进措施.Null Object模式对去除重复检测和减少空引用异常有较明显的效果.
Reconnection experiments with 3D magnetic nulls
Vrublevskis, A.; Egedal, J.; Le, A.; Montag, P.
2011-10-01
Three-dimensional effects have been crucial in explaining experiments at the Versatile Toroidal Facility (VTF) even in nominal axisymmetric plasmas with a non-vanishing toroidal field. In general, depending on the topological and geometric structure of the magnetic field, a rich collection of magnetic reconnection scenarios is possible in three dimensions. The new adjustable set of coils in VTF allows exploring reconnection in 2D and 3D geometries including configurations with magnetic null points. We present results of a numerical and experimental investigation of magnetic field topologies attainable in VTF. This work was supported by NSF CAREER Award 0844620.
Recent developments with the visible nulling coronagraph
Hicks, Brian A.; Lyon, Richard G.; Bolcar, Matthew R.; Clampin, Mark; Petrone, Peter; Helmbrecht, Michael A.; Howard, Joseph M.; Miller, Ian J.
2016-08-01
A wide array of general astrophysics studies including detecting and characterizing habitable exoplanets could be enabled by a future large segmented telescope with sensitivity in the UV, optical, and infrared bands. When paired with a starshade or coronagraph, such an observatory could enable direct imaging and detailed spectroscopic observations of nearby Earth-like habitable zone planets. Over the past several years, a laboratory-based Visible Nulling Coronagraph (VNC) has evolved to reach requisite contrasts over a 1 nm bandwidth at narrow source angle separation using a segmented deformable mirror in one arm of a Mach-Zehnder layout. More recent efforts targeted broadband performance following the addition of two sets of half-wave Fresnel rhomb achromatic phase shifters (APS) with the goal of reaching 10-9 contrast, at a separation of 2λ/D, using a 40 nm (6%) bandwidth single mode fiber source. Here we present updates on the VNC broadband nulling effort, including approaches to addressing system contrast limitations.
On the null origin of the ambitwistor string
Casali, Eduardo; Tourkine, Piotr
2016-11-01
In this paper we present the null string origin of the ambitwistor string. Classically, the null string is the tensionless limit of string theory, and so too is the ambitwistor string. Both have as constraint algebra the Galilean Conformal Algebra in two dimensions. But something interesting happens in the quantum theory since there is an ambiguity in quantizing the null string. We show that, given a particular choice of quantization scheme and a particular gauge, the null string coincides with the ambitwistor string both classically and quantum mechanically. We also show that the same holds for the spinning versions of the null string and ambitwistor string. With these results we clarify the relationship between the ambitwistor string, the null string, the usual string and the Hohm-Siegel-Zwiebach theory.
Particle acceleration near magnetic nulls using MMS data
Eriksson, Elin; Vaivads, Andris; Khotyaintsev, Yuri; Graham, Daniel; Markidis, Stefano; Peng, Ivy Bo; André, Mats; Burch, James; Lindqvist, Per-Arne; Ergun, Robert; Torbert, Roy; Magnes, Werner; Russell, Christopher; Giles, Barbara; Pollock, Craig
2016-04-01
Regions with vanishing magnetic field, also referred to as magnetic nulls, are of high interest in plasma physics. Near magnetic nulls particles become unmagnetized and can by interacting with electric fields be accelerated up to high energies. Magnetic nulls have been observed and studied before using using Cluster data with different methods. Magnetic nulls found by Cluster have been obtained with spacecraft separation comparable to ion scales and particle instrumentation is not sufficient to resolve in detail physical processes of particle acceleration around the null. Now we use the MMS (Magnetospheric Multiscale) data to study these processes in detail. The MMS separation is well below the ion scale and data from particle instruments has sufficient resolution during burst mode to resolve these processes for our events. We study nulls in detail during phase 1a of the MMS mission. Burst data during this phase are mainly from the magnetopause, but some intervals cover the magnetosheath, bowshock, and solar wind. We particularly focus on magnetic nulls associated with strong currents, which can potentially be associated with the electron diffusion region of magnetic reconnection. There we also expect particle acceleration to occur. A preliminary study has already identified several nulls of high interest in the burst data. We present a detailed study of these nulls.
Lelyakov, A. P.; Karpenko, A. S.
2017-01-01
We consider the dynamics of a probe null string in the gravitational field of a closed ( "thick") null string radially collapsing in a plane. Analysis of the obtained solutions suggests that there might exist several properties of a null-string gas interesting from the cosmological standpoint, such as acceleration of expansion or contraction, a granular structure of the gas, the emergence of stable polarized states, and a domain structure.
Averaged Null Energy Condition from Causality
Hartman, Thomas; Tajdini, Amirhossein
2016-01-01
Unitary, Lorentz-invariant quantum field theories in flat spacetime obey microcausality: commutators vanish at spacelike separation. For interacting theories in more than two dimensions, we show that this implies that the averaged null energy, $\\int du T_{uu}$, must be positive. This non-local operator appears in the operator product expansion of local operators in the lightcone limit, and therefore contributes to $n$-point functions. We derive a sum rule that isolates this contribution and is manifestly positive. The argument also applies to certain higher spin operators other than the stress tensor, generating an infinite family of new constraints of the form $\\int du X_{uuu\\cdots u} \\geq 0$. These lead to new inequalities for the coupling constants of spinning operators in conformal field theory, which include as special cases (but are generally stronger than) the existing constraints from the lightcone bootstrap, deep inelastic scattering, conformal collider methods, and relative entropy. We also comment ...
Null fluid collapse in brane world models
Harko, Tiberiu
2013-01-01
The brane world description of our universe entails a large extra dimension and a fundamental scale of gravity that may be lower than the Planck scale by several orders of magnitude. An interesting consequence of this scenario occurs in the nature of spherically-symmetric vacuum solutions to the brane gravitational field equations, which often have properties quite distinct from the standard black hole solutions of general relativity. In this paper, the spherically-symmetric collapse on the brane world of four types of null fluid, governed by the barotropic, polytropic, strange quark "bag" model and Hagedorn equations of state, is investigated. In each case, we solve the approximate gravitational field equations, obtained in the high density limit, determine the equation which governs the formation of apparent horizons and investigate the conditions for the formation of naked singularities. Though, naively, one would expect the increased effective energy density on the brane to favor the formation of black ho...
Wormholes minimally violating the null energy condition
Bouhmadi-Lopez, Mariam; Martin-Moruno, Prado
2014-01-01
We consider novel wormhole solutions supported by a matter content that minimally violates the null energy condition. More specifically, we consider an equation of state in which the sum of the energy density and radial pressure is proportional to a constant with a value smaller than that of the inverse area characterising the system, i.e., the area of the wormhole mouth. This approach is motivated by a recently proposed cosmological event, denoted "the little sibling of the big rip", where the Hubble rate and the scale factor blow up but the cosmic derivative of the Hubble rate does not [1]. By using the cut-and-paste approach, we match interior spherically symmetric wormhole solutions to an exterior Schwarzschild geometry, and analyze the stability of the thin-shell to linearized spherically symmetric perturbations around static solutions, by choosing suitable properties for the exotic material residing on the junction interface radius. Furthermore, we also consider an inhomogeneous generalisation of the eq...
Reconnection experiments including 3D magnetic nulls
Le, A.; Egedal, J.; Vrublevskis, A.
2010-11-01
A rich collection of magnetic reconnection scenarios is possible in three dimensions depending on the topological and geometric structure of the magnetic field [1]. In recent experiments at the Versatile Toroidal Facility (VTF) three-dimensional effects were essential even in nearly axisymmetric plasmas with a non-vanishing toroidal field [2]. To explore reconnection in 3D geometries including magnetic null points, a new adjustable set of coils will be installed in the vacuum chamber of VTF. The range of vacuum magnetic field topologies attainable in VTF will be explored numerically. Plasma reconnection experiments will be run in these configurations, and measurements will be presented if available. [4pt] [1] CE Parnell, et al., (2009) ``Three-Dimensional Magnetic Reconnection, in Magnetic Coupling between the Interior and the Atmosphere of the Sun,'' eds. S.S. Hasan and R.J. Rutten, Springer-Verlag, Heidelberg, Berlin. [0ex] [2] Katz, N. et al., (2010) Phys. Rev. Lett. 104, 255004.
MAGNETIC NULL POINTS IN KINETIC SIMULATIONS OF SPACE PLASMAS
Energy Technology Data Exchange (ETDEWEB)
Olshevsky, Vyacheslav; Innocenti, Maria Elena; Cazzola, Emanuele; Lapenta, Giovanni [Centre for Mathematical Plasma Astrophysics (CmPA), KU Leuven (Belgium); Deca, Jan [Laboratory for Atmospheric and Space Physics (LASP), University of Colorado Boulder, Boulder, CO (United States); Divin, Andrey [St. Petersburg State University, St. Petersburg (Russian Federation); Peng, Ivy Bo; Markidis, Stefano, E-mail: sya@mao.kiev.ua [High Performance Computing and Visualization (HPCViz), KTH Royal Institute of Technology, Stockholm (Sweden)
2016-03-01
We present a systematic attempt to study magnetic null points and the associated magnetic energy conversion in kinetic particle-in-cell simulations of various plasma configurations. We address three-dimensional simulations performed with the semi-implicit kinetic electromagnetic code iPic3D in different setups: variations of a Harris current sheet, dipolar and quadrupolar magnetospheres interacting with the solar wind, and a relaxing turbulent configuration with multiple null points. Spiral nulls are more likely created in space plasmas: in all our simulations except lunar magnetic anomaly (LMA) and quadrupolar mini-magnetosphere the number of spiral nulls prevails over the number of radial nulls by a factor of 3–9. We show that often magnetic nulls do not indicate the regions of intensive energy dissipation. Energy dissipation events caused by topological bifurcations at radial nulls are rather rare and short-lived. The so-called X-lines formed by the radial nulls in the Harris current sheet and LMA simulations are rather stable and do not exhibit any energy dissipation. Energy dissipation is more powerful in the vicinity of spiral nulls enclosed by magnetic flux ropes with strong currents at their axes (their cross sections resemble 2D magnetic islands). These null lines reminiscent of Z-pinches efficiently dissipate magnetic energy due to secondary instabilities such as the two-stream or kinking instability, accompanied by changes in magnetic topology. Current enhancements accompanied by spiral nulls may signal magnetic energy conversion sites in the observational data.
DARWIN nulling interferometer breadboard II: design and manufacturing
Vink, H.J.P.; Doelman, N.J.; Flatscher, R.; Sodnik, Z.
2003-01-01
Nulling interferometry is a direct method to detect earth-like planets. To determine whether a planet is earth-like spectrometry can be performed which requires a broadband optical input signal from the planet. Nulling interferometry should decrease the broadband (λ ≈ 6-18μm) star signal by about a
Visual and Plastic Arts in Teaching Literacy: Null Curricula?
Wakeland, Robin Gay
2010-01-01
Visual and plastic arts in contemporary literacy instruction equal null curricula. Studies show that painting and sculpture facilitate teaching reading and writing (literacy), yet such pedagogy has not been formally adopted into USA curriculum. An example of null curriculum can be found in late 19th - early 20th century education the USA…
Einstein equations in the null quasi-spherical gauge
Bartnik, R A
1997-01-01
The structure of the full Einstein equations in a coordinate gauge based on expanding null hypersurfaces foliated by metric 2-spheres is explored. The simple form of the resulting equations has many applications -- in the present paper we describe the structure of timelike boundary conditions; the matching problem across null hypersurfaces; and the propagation of gravitational shocks.
A new dynamic null model for phylogenetic community structure
Pigot, Alex L; Etienne, Rampal S
2015-01-01
Phylogenies are increasingly applied to identify the mechanisms structuring ecological communities but progress has been hindered by a reliance on statistical null models that ignore the historical process of community assembly. Here, we address this, and develop a dynamic null model of assembly by
Gravity Degrees of Freedom on a Null Surface
Hopfmüller, Florian
2016-01-01
A canonical analysis for general relativity is performed on a null surface without fixing the diffeomorphism gauge, and the canonical pairs of configuration and momentum variables are derived. Next to the well-known spin-2 pair, also spin-1 and spin-0 pairs are identified. The boundary action for a null boundary segment of spacetime is obtained, including terms on codimension two corners.
ENERGY DISSIPATION IN MAGNETIC NULL POINTS AT KINETIC SCALES
Energy Technology Data Exchange (ETDEWEB)
Olshevsky, Vyacheslav; Lapenta, Giovanni [Centre for Mathematical Plasma Astrophysics (CmPA), KU Leuven (Belgium); Divin, Andrey [Department of Physics, St. Petersburg State University (Russian Federation); Eriksson, Elin [Swedish Institute of Space Physics, Uppsala Division, Uppsala (Sweden); Markidis, Stefano, E-mail: sya@mao.kiev.ua [High Performance Computing and Visualization (HPCViz), KTH Royal Institute of Technology, Stockholm (Sweden)
2015-07-10
We use kinetic particle-in-cell and MHD simulations supported by an observational data set to investigate magnetic reconnection in clusters of null points in space plasma. The magnetic configuration under investigation is driven by fast adiabatic flux rope compression that dissipates almost half of the initial magnetic field energy. In this phase powerful currents are excited producing secondary instabilities, and the system is brought into a state of “intermittent turbulence” within a few ion gyro-periods. Reconnection events are distributed all over the simulation domain and energy dissipation is rather volume-filling. Numerous spiral null points interconnected via their spines form null lines embedded into magnetic flux ropes; null point pairs demonstrate the signatures of torsional spine reconnection. However, energy dissipation mainly happens in the shear layers formed by adjacent flux ropes with oppositely directed currents. In these regions radial null pairs are spontaneously emerging and vanishing, associated with electron streams and small-scale current sheets. The number of spiral nulls in the simulation outweighs the number of radial nulls by a factor of 5–10, in accordance with Cluster observations in the Earth's magnetosheath. Twisted magnetic fields with embedded spiral null points might indicate the regions of major energy dissipation for future space missions such as the Magnetospheric Multiscale Mission.
Energy Dissipation in Magnetic Null Points at Kinetic Scales
Olshevsky, Vyacheslav; Divin, Andrey; Eriksson, Elin; Markidis, Stefano; Lapenta, Giovanni
2015-07-01
We use kinetic particle-in-cell and MHD simulations supported by an observational data set to investigate magnetic reconnection in clusters of null points in space plasma. The magnetic configuration under investigation is driven by fast adiabatic flux rope compression that dissipates almost half of the initial magnetic field energy. In this phase powerful currents are excited producing secondary instabilities, and the system is brought into a state of “intermittent turbulence” within a few ion gyro-periods. Reconnection events are distributed all over the simulation domain and energy dissipation is rather volume-filling. Numerous spiral null points interconnected via their spines form null lines embedded into magnetic flux ropes; null point pairs demonstrate the signatures of torsional spine reconnection. However, energy dissipation mainly happens in the shear layers formed by adjacent flux ropes with oppositely directed currents. In these regions radial null pairs are spontaneously emerging and vanishing, associated with electron streams and small-scale current sheets. The number of spiral nulls in the simulation outweighs the number of radial nulls by a factor of 5-10, in accordance with Cluster observations in the Earth's magnetosheath. Twisted magnetic fields with embedded spiral null points might indicate the regions of major energy dissipation for future space missions such as the Magnetospheric Multiscale Mission.
Magnetic null points in kinetic simulations of space plasmas
Olshevsky, Vyacheslav; Divin, Andrey; Peng, Ivy Bo; Markidis, Stefano; Innocenti, Maria Elena; Cazzola, Emanuele; Lapenta, Giovanni
2015-01-01
We present a systematic attempt to study magnetic null points and the associated magnetic energy conversion in kinetic Particle-in-Cell simulations of various plasma configurations. We address three-dimensional simulations performed with the semi-implicit kinetic electromagnetic code iPic3D in different setups: variations of a Harris current sheet, dipolar and quadrupolar magnetospheres interacting with the solar wind; and a relaxing turbulent configuration with multiple null points. Spiral nulls are more likely created in space plasmas: in all our simulations except lunar magnetic anomaly and quadrupolar mini-magnetosphere the number of spiral nulls prevails over the number of radial nulls by a factor of 3-9. We show that often magnetic nulls do not indicate the regions of intensive energy dissipation. Energy dissipation events caused by topological bifurcations at radial nulls are rather rare and short-lived. The so-called X-lines formed by the radial nulls in the Harris current sheet and lunar magnetic ano...
Logarithmic corrections to gravitational entropy and the null energy condition
Parikh, Maulik; Svesko, Andrew
2016-10-01
Using a relation between the thermodynamics of local horizons and the null energy condition, we consider the effects of quantum corrections to the gravitational entropy. In particular, we find that the geometric form of the null energy condition is not affected by the inclusion of logarithmic corrections to the Bekenstein-Hawking entropy.
Logarithmic corrections to gravitational entropy and the null energy condition
Directory of Open Access Journals (Sweden)
Maulik Parikh
2016-10-01
Full Text Available Using a relation between the thermodynamics of local horizons and the null energy condition, we consider the effects of quantum corrections to the gravitational entropy. In particular, we find that the geometric form of the null energy condition is not affected by the inclusion of logarithmic corrections to the Bekenstein–Hawking entropy.
Exact null controllability of degenerate evolution equations with scalar control
Energy Technology Data Exchange (ETDEWEB)
Fedorov, Vladimir E; Shklyar, Benzion
2012-12-31
Necessary and sufficient conditions for the exact null controllability of a degenerate linear evolution equation with scalar control are obtained. These general results are used to examine the exact null controllability of the Dzektser equation in the theory of seepage. Bibliography: 13 titles.
Null hypersurfaces in generalized Robertson-Walker spacetimes
Navarro, Matias; Palmas, Oscar; Solis, Didier A.
2016-08-01
We study the geometry of null hypersurfaces M in generalized Robertson-Walker spacetimes. First we characterize such null hypersurfaces as graphs of generalized eikonal functions over the fiber and use this characterization to show that such hypersurfaces are parallel if and only if their fibers are also parallel. We further use this technique to construct several examples of null hypersurfaces in both de Sitter and anti de Sitter spaces. Then we characterize all the totally umbilical null hypersurfaces M in a Lorentzian space form (viewed as a quadric in a semi-Euclidean ambient space) as intersections of the space form with a hyperplane. Finally we study the totally umbilical spacelike hypersurfaces of null hypersurfaces in space forms and characterize them as planar sections of M.
Estimating Relatedness in the Presence of Null Alleles.
Huang, Kang; Ritland, Kermit; Dunn, Derek W; Qi, Xiaoguang; Guo, Songtao; Li, Baoguo
2016-01-01
Studies of genetics and ecology often require estimates of relatedness coefficients based on genetic marker data. However, with the presence of null alleles, an observed genotype can represent one of several possible true genotypes. This results in biased estimates of relatedness. As the numbers of marker loci are often limited, loci with null alleles cannot be abandoned without substantial loss of statistical power. Here, we show how loci with null alleles can be incorporated into six estimators of relatedness (two novel). We evaluate the performance of various estimators before and after correction for null alleles. If the frequency of a null allele is 0.5, the potency of estimation is too low and such a locus should be excluded. We make available a software package entitled PolyRelatedness v1.6, which enables researchers to optimize these estimators to best fit a particular data set.
Reconnection experiments with 3D magnetic nulls in different topologies
Vrublevskis, A.; Egedal, J.; Le, A.
2012-10-01
Magnetic reconnection has been predominantly investigated in two dimensions. However, depending on the topology and geometry of the magnetic field, a rich collection of magnetic reconnection scenarios is possible in 3D including reconnection at magnetic nulls. At the Versatile Toroidal Facility (VTF) we have implemented a new magnetic geometry with a pair of 3D null points in the background toroidal field. We form a flux rope along the background field and observe it to rapidly restructure and rewire as the nulls develop. We can adjust the topology of the configuration from one where a field line connects the nulls to one where the nulls are no longer linked. A suit of diagnostics will be deployed and results presented for how the topology affects the dynamics of the flux rope.
Energy dissipation in magnetic null points at kinetic scales
Olshevsky, Vyacheslav; Eriksson, Elin; Markidis, Stefano; Lapenta, Giovanni
2015-01-01
We use kinetic particle-in-cell and magnetohydrodynamic simulations supported by an observational dataset to investigate magnetic reconnection in clusters of null points in space plasma. The magnetic configuration under investigation is driven by fast adiabatic flux rope compression that dissipates almost half of the initial magnetic field energy. In this phase powerful currents are excited producing secondary instabilities, and the system is brought into a state of `intermittent turbulence' within a few ion gyro-periods. Reconnection events are distributed all over the simulation domain and energy dissipation is rather volume-filling. Numerous spiral null points interconnected via their spines form null lines embedded into magnetic flux ropes; null point pairs demonstrate the signatures of torsional spine reconnection. However, energy dissipation mainly happens in the shear layers formed by adjacent flux ropes with oppositely directed currents. In these regions radial null pairs are spontaneously emerging an...
Sidelobe Suppression with Null Steering by Independent Weight Control
Directory of Open Access Journals (Sweden)
Zafar-Ullah Khan
2015-01-01
Full Text Available A uniform linear array of n antenna elements can steer up to n-1 nulls. In situations where less than n-1 nulls are required to be steered, the existing algorithms have no criterion to utilize the remaining weights for sidelobe suppression. This work combines sidelobe suppression capability with null steering by independent weight control. For this purpose, the array factor is transformed as the product of two polynomials. One of the polynomials is used for null steering by independent weight control, while the second one is for sidelobe suppression whose coefficients or weights are determined by using convex optimization. Finally, a new structure is proposed to incorporate the product of two polynomials such that sidelobe suppression weights are decoupled from those of null steering weights. Simulation results validate the effectiveness of the proposed scheme.
McCabe, Declan J.; Knight, Evelyn J.
2016-01-01
Since being introduced by Connor and Simberloff in response to Diamond's assembly rules, null model analysis has been a controversial tool in community ecology. Despite being commonly used in the primary literature, null model analysis has not featured prominently in general textbooks. Complexity of approaches along with difficulty in interpreting…
A null model for Pearson coexpression networks.
Gobbi, Andrea; Jurman, Giuseppe
2015-01-01
Gene coexpression networks inferred by correlation from high-throughput profiling such as microarray data represent simple but effective structures for discovering and interpreting linear gene relationships. In recent years, several approaches have been proposed to tackle the problem of deciding when the resulting correlation values are statistically significant. This is most crucial when the number of samples is small, yielding a non-negligible chance that even high correlation values are due to random effects. Here we introduce a novel hard thresholding solution based on the assumption that a coexpression network inferred by randomly generated data is expected to be empty. The threshold is theoretically derived by means of an analytic approach and, as a deterministic independent null model, it depends only on the dimensions of the starting data matrix, with assumptions on the skewness of the data distribution compatible with the structure of gene expression levels data. We show, on synthetic and array datasets, that the proposed threshold is effective in eliminating all false positive links, with an offsetting cost in terms of false negative detected edges.
'Null method' determination of drug biophase concentration.
Tallarida, Ronald J; Lamarre, Neil; Raffa, Robert B
2012-03-01
PK/PD modeling is enhanced by improvements in the accuracy of its metrics. For PK/PD modeling of drugs and biologics that interact with enzymes or receptors, the equilibrium constant of the interaction can provide critical insight. Methodologies such as radioliogand binding and isolated tissue preparations can provide estimates of the equilibrium constants (as the dissociation constant, K value) for drugs and endogenous ligands that interact with specific enzymes and receptors. However, an impediment to further precision for PK/PD modeling is that it remains a problem to convert the concentration of drug in bulk solution (A) into an estimate of receptor occupation, since A is not necessarily the concentration (C) of drug in the biophase that yields fractional binding from the law of mass action, viz., C/(C + K). In most experimental studies A is much larger than K, so the use of administered instead of biophase concentration gives fractional occupancies very close to unity. We here provide a simple way to obtain an estimate of the factor that converts the total drug concentration into the biophase concentration in isolated tissue preparation. Our approach is an extension of the now classic 'null method' introduced and applied by Furchgott to determination of drug-receptor dissociation constants.
A null model for Pearson coexpression networks.
Directory of Open Access Journals (Sweden)
Andrea Gobbi
Full Text Available Gene coexpression networks inferred by correlation from high-throughput profiling such as microarray data represent simple but effective structures for discovering and interpreting linear gene relationships. In recent years, several approaches have been proposed to tackle the problem of deciding when the resulting correlation values are statistically significant. This is most crucial when the number of samples is small, yielding a non-negligible chance that even high correlation values are due to random effects. Here we introduce a novel hard thresholding solution based on the assumption that a coexpression network inferred by randomly generated data is expected to be empty. The threshold is theoretically derived by means of an analytic approach and, as a deterministic independent null model, it depends only on the dimensions of the starting data matrix, with assumptions on the skewness of the data distribution compatible with the structure of gene expression levels data. We show, on synthetic and array datasets, that the proposed threshold is effective in eliminating all false positive links, with an offsetting cost in terms of false negative detected edges.
The Curious Case of Null Warped Space
Anninos, Dionysios; de Buyl, Sophie; Detournay, Stéphane; Guica, Monica
2010-01-01
We initiate a comprehensive study of a set of solutions of topologically massive gravity known as null warped anti-de Sitter spacetimes. These are pp-wave extensions of three-dimensional anti-de Sitter space. We first perform a careful analysis of the linearized stability of black holes in these spacetimes. We find two qualitatively different types of solutions to the linearized equations of motion: the first set has an exponential time dependence, the second - a polynomial time dependence. The solutions polynomial in time induce severe pathologies and moreover survive at the non-linear level. In order to make sense of these geometries, it is thus crucial to impose appropriate boundary conditions. We argue that there exists a consistent set of boundary conditions that allows us to reject the above pathological modes from the physical spectrum. The asymptotic symmetry group associated to these boundary conditions consists of a centrally-extended Virasoro algebra. Using this central charge we can account for th...
Null fluid collapse in brane world models
Harko, Tiberiu; Lake, Matthew J.
2014-03-01
The brane world description of our Universe entails a large extra dimension and a fundamental scale of gravity that may be lower than the Planck scale by several orders of magnitude. An interesting consequence of this scenario occurs in the nature of spherically symmetric vacuum solutions to the brane gravitational field equations, which often have properties quite distinct from the standard black hole solutions of general relativity. In this paper, the spherically symmetric collapse on the brane world of four types of null fluid, governed by the barotropic, polytropic, strange quark "bag" model and Hagedorn equations of state, is investigated. In each case, we solve the approximate gravitational field equations, obtained in the high-density limit, determine the equation which governs the formation of apparent horizons and investigate the conditions for the formation of naked singularities. Though, naively, one would expect the increased effective energy density on the brane to favor the formation of black holes over naked singularities, we find that, for the types of fluid considered, this is not the case. However, the black hole solutions differ substantially from their general-relativistic counterparts and brane world corrections often play a role analogous to charge in general relativity. As an astrophysical application of this work, the possibility that energy emission from a Hagedorn fluid collapsing to form a naked singularity may be a source of GRBs in the brane world is also considered.
Null fields in the outer Jovian magnetosphere: Ulysses observations
Haynes, P. L.; Balogh, A.; Dougherty, M. K.; Southwood, D. J.; Fazakerley, A.; Smith, E. J.
1994-01-01
This paper reports on a magnetic field phenomenon, hereafter referred to as null fields, which were discovered during the inbound pass of the recent flyby of Jupiter by the Ulysses spacecraft. These null fields which were observed in the outer dayside magnetosphere are characterised by brief but sharp decreases of the field magnitude to values less than 1 nT. The nulls are distinguished from the current sheet signatures characteristic of the middle magnetosphere by the fact that the field does not reverse across the event. A field configuration is suggested that accounts for the observed features of the events.
The Density of Coronal Null Points from Hinode and MDI
Longcope, Dana; DeForest, Craig
2009-01-01
Magnetic null points can be located numerically in a potential field extrapolation or their average density can be estimated from the Fourier spectrum of a magnetogram. We use both methods to compute the null point density from a quiet Sun magnetogram made with Hinode's NFI and from magnetograms from SOHO's MDI in both its high-resolution and low-resolution modes. All estimates of the super-chromospheric column density (z>1.5 Mm) agree with one another and with the previous measurements: 0.003 null points per square Mm of solar surface.
A Null Space Approach for Solving Nonlinear Complementarity Problems
Institute of Scientific and Technical Information of China (English)
Pu-yan Nie
2006-01-01
In this work, null space techniques are employed to tackle nonlinear complementarity problems(NCPs). NCP conditions are transform into a nonlinear programming problem, which is handled by null space algorithms. The NCP conditions are divided into two groups. Some equalities and inequalities in an NCP are treated as constraints. While other equalities and inequalities in an NCP are to be regarded as objective function.Two groups are all updated in every step. Null space approaches are extended to nonlinear complementarity problems. Two different solvers are employed for an NCP in an algorithm.
Danchi, W. C.; Rajagopal, J.; Kuchner, M.; Richardson, J; Deming, D.
2006-01-01
We discuss the theory of the Bracewell nulling interferometer and explicitly demonstrate that the phase of the "white light" null fringe is the same as the phase of the bright output from an ordinary stellar interferometer. As a consequence a "closure phase" exists for a nulling interferometer with three or more telescopes. We calculate the phase offset as a function of baseline length for an Earth-like planet around the Sun at 10 pc, with a contrast ratio of $10^{-6}$ at 10 $\\mu$m. The magni...
Dynamics of a Spherical Null Shell within the Distributional Formalism
Khakshournia, Samad; Mansouri, Reza
2004-01-01
Dynamics of a null thin shell immersed in a generic spherically symmetric spacetime is obtained within the distributional formalism. It has been shown that the distributional formalism leads to the same result as in the conventional formalism.
Uniform Consistency for Nonparametric Estimators in Null Recurrent Time Series
DEFF Research Database (Denmark)
Gao, Jiti; Kanaya, Shin; Li, Degui;
2015-01-01
This paper establishes uniform consistency results for nonparametric kernel density and regression estimators when time series regressors concerned are nonstationary null recurrent Markov chains. Under suitable regularity conditions, we derive uniform convergence rates of the estimators. Our...
A new dynamic null model for phylogenetic community structure.
Pigot, Alex L; Etienne, Rampal S
2015-02-01
Phylogenies are increasingly applied to identify the mechanisms structuring ecological communities but progress has been hindered by a reliance on statistical null models that ignore the historical process of community assembly. Here, we address this, and develop a dynamic null model of assembly by allopatric speciation, colonisation and local extinction. Incorporating these processes fundamentally alters the structure of communities expected due to chance, with speciation leading to phylogenetic overdispersion compared to a classical statistical null model assuming equal probabilities of community membership. Applying this method to bird and primate communities in South America we show that patterns of phylogenetic overdispersion - often attributed to negative biotic interactions - are instead consistent with a species neutral model of allopatric speciation, colonisation and local extinction. Our findings provide a new null expectation for phylogenetic community patterns and highlight the importance of explicitly accounting for the dynamic history of assembly when testing the mechanisms governing community structure.
Waves and null congruences in a draining bathtub
Dempsey, David
2016-01-01
We study wave propagation in a draining bathtub: a fluid-mechanical black hole analogue in which perturbations are governed by a Klein-Gordon equation on an effective Lorentzian geometry. Like the Kerr spacetime, the draining bathtub geometry possesses an (effective) horizon, an ergosphere and null circular orbits. We propose that a `pulse' disturbance may be used to map out the light-cone of the effective geometry. First, we apply the eikonal approximation to elucidate the link between wavefronts, null geodesic congruences and the Raychaudhuri equation. Next, we solve the wave equation numerically in the time domain using the method of lines. Starting with Gaussian initial data, we demonstrate that a pulse will propagate along a null congruence and thus trace out the light-cone of the effective geometry. Our numerical results reveal features, such as wavefront intersections, frame-dragging, winding and interference effects, that are closely associated with the presence of null circular orbits and the ergosph...
Overt and Null Subject Pronouns in Jordanian Arabic
Directory of Open Access Journals (Sweden)
Islam M. Al-Momani
2015-08-01
Full Text Available The paper aims at examining the role that morphology plays in allowing and/or motivating sentences in Jordanian Arabic (hereafter JA to be formed with or without subject pronouns. It also aims at giving a comprehensive and descriptive presentation of the distribution of overt and null subject pronouns in JA, and tries to determine to what extent there is optionality in its system. Keywords: null subject pronouns, overt subjects, pro-drop languages, verbal inflectional morphology
Shear-free Null Quasi-Spherical Spacetimes
Bartnik, R A
1997-01-01
The residual gauge freedom within the null quasi-spherical coordinate condition is studied, for spacetimes admitting an {\\em expanding, shear-free} null foliation. The freedom consists of a boost and rotation at each coordinate sphere, corresponding to a specification of inertial frame at each sphere. Explicit formulae involving arbitrary functions of two variables are obtained for the accelerated Minkowski, Schwarzschild, and Robinson-Trautman spacetimes. These examples will be useful as test metrics in numerical relativity.
The geometry of D=11 null killing spinors
Energy Technology Data Exchange (ETDEWEB)
Gauntlett, Jerome P.; Gutowski, Jan B. E-mail: gutowski@maths.ox.ac.uk; Stathis Pakis
2003-12-01
We determine the necessary and sufficient conditions on the metric and the four-form for the most general bosonic supersymmetric configurations of D=11 supergravity which admit a null Killing spinor i.e. a Killing spinor which can be used to construct a null Killing vector. This class covers all supersymmetric time-dependent configurations and completes the classification of the most general supersymmetric configurations initiated in hep-th/0212008. (author)
The Geometry of D=11 Null Killing Spinors
Gauntlett, J P; Pakis, S
2003-01-01
We determine the necessary and sufficient conditions on the metric and the four-form for the most general bosonic supersymmetric configurations of D=11 supergravity which admit a null Killing spinor i.e. a Killing spinor which can be used to construct a null Killing vector. This class covers all supersymmetric time-dependent configurations and completes the classification of the most general supersymmetric configurations initiated in hep-th/0212008.
Magnetoacoustic shock formation near a magnetic null point
Gruszecki, M. (Marcin); Vasheghani Farahani, Soheil; Nakariakov, V. M.; Arber, T. D.
2011-01-01
We investigate the interaction of nonlinear fast magnetoacoustic waves with a magnetic null point in connection with the triggering of solar flares. \\ud \\ud Methods. We model the propagation of fast, initially axisymmetric waves towards a two-dimensional isothermal magnetic null point in terms of ideal magnetohydrodynamic equations. The numerical simulations are carried out with the Lagrangian remap code Lare2D. \\ud \\ud Results. Dynamics of initially axisymmetric fast pulses of small amplitud...
Development of New Sputter System by Magnetic Null Plasma
敦田, 悟; 楊, 鍾煥; 川尻, 晋平; 成, 烈[ブン; 本田, 親久; 大坪, 昌久
2004-01-01
Abstract ###A new type of plasma system based on the magnetic neutral loop discharge (NLD) concept ###has been developed for sputter application. This system is characterized by plasma production ###around the multi null magnetic field on the electrode surface, where a capacitive RF electric ###field is applied. From the experimental results and numerical analysis of electron behavior in ###this system, we found that electrons around the magnetic null region on the target surface ###moved in ...
Magnetic null points in kinetic simulations of space plasmas
Olshevsky, Vyacheslav; Deca, Jan; Divin, Andrey; Peng, Ivy Bo; Markidis, Stefano; Innocenti, Maria Elena; Cazzola, Emanuele; Lapenta, Giovanni
2015-01-01
We present a systematic attempt to study magnetic null points and the associated magnetic energy conversion in kinetic Particle-in-Cell simulations of various plasma configurations. We address three-dimensional simulations performed with the semi-implicit kinetic electromagnetic code iPic3D in different setups: variations of a Harris current sheet, dipolar and quadrupolar magnetospheres interacting with the solar wind; and a relaxing turbulent configuration with multiple null points. Spiral n...
Designing asynchronous circuits using NULL convention logic (NCL)
Smith, Scott
2009-01-01
Designing Asynchronous Circuits using NULL Convention Logic (NCL) begins with an introduction to asynchronous (clockless) logic in general, and then focuses on delay-insensitive asynchronous logic design using the NCL paradigm. The book details design of input-complete and observable dual-rail and quad-rail combinational circuits, and then discusses implementation of sequential circuits, which require datapath feedback. Next, throughput optimization techniques are presented, including pipelining, embedding registration, early completion, and NULL cycle reduction. Subsequently, low-power design
Using Multivalued Logic in Relational Database Containing Null Value
Institute of Scientific and Technical Information of China (English)
马宗民; YanLi
1996-01-01
In this paper,several kinds of multivalued logic for relational database and their developing process are presented on the basis of null value's semantics.A new 5 valued logic is led into relational database containing null value.The feasibility and necessity of using 5 valued logic are expounded.Comparative calculation and logical calculation under 5 valued logic are defined at the end of the paper.
Null controllability of a cascade system of Schrodinger equations
Directory of Open Access Journals (Sweden)
Marcos Lopez-Garcia
2016-03-01
Full Text Available This article presents a control problem for a cascade system of two linear N-dimensional Schrodinger equations. We address the problem of null controllability by means of a control supported in a region not satisfying the classical geometrical control condition. The proof is based on the application of a Carleman estimate with degenerate weights to each one of the equations and a careful analysis of the system in order to prove null controllability with only one control force.
Context-specific protection of TGFα null mice from osteoarthritis.
Usmani, Shirine E; Ulici, Veronica; Pest, Michael A; Hill, Tracy L; Welch, Ian D; Beier, Frank
2016-07-26
Transforming growth factor alpha (TGFα) is a growth factor involved in osteoarthritis (OA). TGFα induces an OA-like phenotype in articular chondrocytes, by inhibiting matrix synthesis and promoting catabolic factor expression. To better understand TGFα's potential as a therapeutic target, we employed two in vivo OA models: (1) post-traumatic and (2) aging related OA. Ten-week old and six-month old male Tgfa null mice and their heterozygous (control) littermates underwent destabilization of the medial meniscus (DMM) surgery. Disease progression was assessed histologically using the Osteoarthritis Research Society International (OARSI) scoring system. As well, spontaneous disease progression was analyzed in eighteen-month-old Tgfa null and heterozygous mice. Ten-week old Tgfa null mice were protected from OA progression at both seven and fourteen weeks post-surgery. No protection was seen however in six-month old null mice after DMM surgery, and no differences were observed between genotypes in the aging model. Thus, young Tgfa null mice are protected from OA progression in the DMM model, while older mice are not. In addition, Tgfa null mice are equally susceptible to spontaneous OA development during aging. Thus, TGFα might be a valuable therapeutic target in some post-traumatic forms of OA, however its role in idiopathic disease is less clear.
Reconnection Experiments with Flux Ropes near 3D Magnetic Nulls
Vrublevskis, A.; Egedal, J.; Le, A.
2012-12-01
Magnetic reconnection has been predominantly investigated in two dimensions. However, depending on the topology and geometry of the magnetic field, a rich collection of magnetic reconnection scenarios is possible in 3D including reconnection at magnetic nulls. Nulls have been reported in the solar corona [1] and in Earth's magnetosphere [2], yet there are a limited number of laboratory observations. At the Versatile Toroidal Facility (VTF) we have implemented a new magnetic geometry with a pair of 3D null points in the background toroidal field. We form a flux rope along the background field and observe it to rapidly restructure and rewire as the nulls develop. We can adjust the topology of the configuration from one where a field line connects the nulls to one where the nulls are no longer linked. A suit of diagnostics will be deployed and results presented for the dynamics of the flux rope. [1] Fletcher et al., Astrophys. J. 554, 451(2001) [2] Xiao et al., Nat. Phys. 2, 478 (2006)
The appearance, motion, and disappearance of three-dimensional magnetic null points
Murphy, Nicholas A; Haynes, Andrew L
2015-01-01
While theoretical models and simulations of magnetic reconnection often assume symmetry such that the magnetic null point when present is co-located with a flow stagnation point, the introduction of asymmetry typically leads to non-ideal flows across the null point. To understand this behavior, we present exact expressions for the motion of three-dimensional linear null points. The most general expression shows that linear null points move in the direction along which the vector field and its time derivative are antiparallel. Null point motion in resistive magnetohydrodynamics results from advection by the bulk plasma flow and resistive diffusion of the magnetic field, which allows non-ideal flows across topological boundaries. Null point motion is described intrinsically by parameters evaluated locally; however, global dynamics help set the local conditions at the null point. During a bifurcation of a degenerate null point into a null-null pair or the reverse, the instantaneous velocity of separation or conv...
Three-dimensional magnetic reconnection through a moving magnetic null
Directory of Open Access Journals (Sweden)
V. S. Lukin
2011-11-01
Full Text Available A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the spheromaks tilt, their magnetic fields begin to reconnect at the null, subsequently displacing both the null and the reconnection site. The motion of the reconnection region and the magnetic null are shown to be correlated, with stronger correlation and faster reconnection observed in plasmas with lower thermal to magnetic pressure ratio. It is also shown that ion inertial effects allow for yet faster reconnection, but do not qualitatively change the dynamics of the process. Implications of the coupling between moving magnetic nulls and reconnection sites, as well as of possible mechanisms for fast reconnection through a moving reconnection region, are discussed. The simulations are conducted using both single-fluid and Hall MHD plasma models within the HiFi multi-fluid modeling framework.
Three-dimensional magnetic reconnection through a moving magnetic null
Lukin, V. S.; Linton, M. G.
2011-11-01
A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the spheromaks tilt, their magnetic fields begin to reconnect at the null, subsequently displacing both the null and the reconnection site. The motion of the reconnection region and the magnetic null are shown to be correlated, with stronger correlation and faster reconnection observed in plasmas with lower thermal to magnetic pressure ratio. It is also shown that ion inertial effects allow for yet faster reconnection, but do not qualitatively change the dynamics of the process. Implications of the coupling between moving magnetic nulls and reconnection sites, as well as of possible mechanisms for fast reconnection through a moving reconnection region, are discussed. The simulations are conducted using both single-fluid and Hall MHD plasma models within the HiFi multi-fluid modeling framework.
Long-term Observations of Three Nulling Pulsars
Young, N J; Stappers, B W; Lyne, A G; Kramer, M
2015-01-01
We present an analysis of approximately 200 hours of observations of the pulsars J1634$-$5107, J1717$-$4054 and J1853$+$0505, taken over the course of 14.7 yr. We show that all of these objects exhibit long term nulls and radio-emitting phases (i.e. minutes to many hours), as well as considerable nulling fractions (NFs) in the range $\\sim67\\,\\% - 90\\,\\%$. PSR J1717$-$4054 is also found to exhibit short timescale nulls ($1 - 40~P$) and burst phases ($\\lesssim 200~P$) during its radio-emitting phases. This behaviour acts to modulate the NF, and therefore the detection rate of the source, over timescales of minutes. Furthermore, PSR J1853$+$0505 is shown to exhibit a weak emission state, in addition to its strong and null states, after sufficient pulse integration. This further indicates that nulls may often only represent transitions to weaker emission states which are below the sensitivity thresholds of particular observing systems. In addition, we detected a peak-to-peak variation of $33\\pm1\\,\\%$ in the spin-...
Visible Nulling Coronagraphy Testbed Development for Exoplanet Detection
Lyon, Richard G.; Clampin, Mark; Woodruff, Robert A.; Vasudevan, Gopal; Thompson, Patrick; Chen, Andrew; Petrone, Peter; Booth, Andrew; Madison, Timothy; Bolcar, Matthew; Noecker, M. Charley; Kendrick, Stephen; Melnick, Gary; Tolls, Volker
2010-01-01
Three of the recently completed NASA Astrophysics Strategic Mission Concept (ASMC) studies addressed the feasibility of using a Visible Nulling Coronagraph (VNC) as the prime instrument for exoplanet science. The VNC approach is one of the few approaches that works with filled, segmented and sparse or diluted aperture telescope systems and thus spans the space of potential ASMC exoplanet missions. NASA/Goddard Space Flight Center (GSFC) has a well-established effort to develop VNC technologies and has developed an incremental sequence of VNC testbeds to advance the this approach and the technologies associated with it. Herein we report on the continued development of the vacuum Visible Nulling Coronagraph testbed (VNT). The VNT is an ultra-stable vibration isolated testbed that operates under high bandwidth closed-loop control within a vacuum chamber. It will be used to achieve an incremental sequence of three visible light nulling milestones of sequentially higher contrasts of 10(exp 8) , 10(exp 9) and 10(exp 10) at an inner working angle of 2*lambda/D and ultimately culminate in spectrally broadband (>20%) high contrast imaging. Each of the milestones, one per year, is traceable to one or more of the ASMC studies. The VNT uses a modified Mach-Zehnder nulling interferometer, modified with a modified "W" configuration to accommodate a hex-packed MEMS based deformable mirror, a coherent fiber bundle and achromatic phase shifters. Discussed will be the optical configuration laboratory results, critical technologies and the null sensing and control approach.
The causal topology of neutral 4-manifolds with null boundary
Georgiou, Nikos
2016-01-01
This paper considers aspects of 4-manifold topology from the point of view of a neutral metric, a point of view we call neutral causal topology. In particular, we construct and investigate neutral 4-manifolds with null boundary that arise from canonical 3- and 4-dimensional settings. A null hypersurface is foliated by its normal and, in the neutral case, inherits a pair of totally null planes at each point. This paper focuses on this structure in a number of classical settings The first construction is the conformal compactification of flat neutral 4-space into the 4-ball. The null foliation on the boundary in this case is the Hopf fibration on the 3-sphere and the totally null planes in the boundary are integrable. The metric on the 4-ball is a conformally flat, scalar-flat, positive Ricci curvature neutral metric. The second constructions are subsets of the 4-dimensional space of oriented geodesics in a 3-dimensional space-form, equipped with its canonical neutral metric. We consider all oriented geodesics ...
Phase closure nulling: results from the 2009 campaign
Duvert, Gilles; Malbet, Fabien; Chelli, Alain; Millan-Gabet, Rafael; Monnier, John D.; Schaefer, Gail H.
2010-07-01
We present here a new observational technique, Phase Closure Nulling (PCN), which has the potential to obtain very high contrast detection and spectroscopy of faint companions to bright stars. PCN consists in measuring closure phases of fully resolved objects with a baseline triplet where one of the baselines crosses a null of the object visibility function. For scenes dominated by the presence of a stellar disk, the correlated flux of the star around nulls is essentially canceled out, and in these regions the signature of fainter, unresolved, scene object(s) dominates the imaginary part of the visibility in particular the closure phase. We present here the basics of the PCN method, the initial proof-of-concept observation, the envisioned science cases and report about the first observing campaign made on VLTI/AMBER and CHARA/MIRC using this technique.
Phase Closure Nulling: results from the 2009 campaign
Duvert, Gilles; Chelli, Alain; Millan-Gabet, Rafael; Monnier, John D; Schaefer, Gail H
2010-01-01
We present here a new observational technique, Phase Closure Nulling (PCN), which has the potential to obtain very high contrast detection and spectroscopy of faint companions to bright stars. PCN consists in measuring closure phases of fully resolved objects with a baseline triplet where one of the baselines crosses a null of the object visibility function. For scenes dominated by the presence of a stellar disk, the correlated flux of the star around nulls is essentially canceled out, and in these regions the signature of fainter, unresolved, scene object(s) dominates the imaginary part of the visibility in particular the closure phase. We present here the basics of the PCN method, the initial proof-of-concept observation, the envisioned science cases and report about the first observing campaign made on VLTI/AMBER and CHARA/MIRC using this technique.
Characterizing the Properties of Coronal Magnetic Null Points
Barnes, Graham; DeRosa, Marc; Wagner, Eric
2015-08-01
The topology of the coronal magnetic field plays a role in a wide range of phenomena, from Coronal Mass Ejections (CMEs) through heating of the corona. One fundamental topological feature is the null point, where the magnetic field vanishes. These points are natural sites of magnetic reconnection, and hence the release of energy stored in the magnetic field. We present preliminary results of a study using data from the Helioseismic and Magnetic Imager aboard NASA's Solar Dynamics Observatory to characterize the properties and evolution of null points in a Potential Field Source Surface model of the coronal field. The main properties considered are the lifetime of the null points, their distribution with height, and how they form and subsequently vanish.This work is supported by NASA/LWS Grant NNX14AD45G, and by NSF/SHINE grant 1357018.
Neutral evolution: A null model for language dynamics
Blythe, R A
2011-01-01
We review the task of aligning simple models for language dynamics with relevant empirical data, motivated by the fact that this is rarely attempted in practice despite an abundance of abstract models. We propose that one way to meet this challenge is through the careful construction of null models. We argue in particular that rejection of a null model must have important consequences for theories about language dynamics if modelling is truly to be worthwhile. Our main claim is that the stochastic process of neutral evolution (also known as genetic drift or random copying) is a viable null model for language dynamics. We survey empirical evidence in favour and against neutral evolution as a mechanism behind historical language changes, highlighting the theoretical implications in each case.
Thermodynamical interpretation of the geometrical variables associated with null surfaces
Chakraborty, Sumanta
2015-01-01
The emergent gravity paradigm interprets gravitational field equations as a describing the thermodynamic limit of the underlying statistical mechanics of microscopic degrees of freedom of the spacetime. The connection is established by attributing a heat density Ts to the null surfaces where T is the appropriate Davies-Unruh temperature and s is the entropy density. The field equations can be obtained from a thermodynamic variational principle which extremises the total heat density of all null surfaces. The explicit form of s determines the nature of the theory. We explore the consequences of this paradigm for an arbitrary null surface and highlight the thermodynamic significance of various geometrical quantities. In particular, we show that: (a) A conserved current, associated with the time development vector in a natural fashion, has direct thermodynamic interpretation in all Lanczos-Lovelock models of gravity. (b) One can generalize the notion of gravitational momentum, introduced in arXiv 1506.03814 to a...
Interpreting null findings from trials of alcohol brief interventions.
Heather, Nick
2014-01-01
The effectiveness of alcohol brief intervention (ABI) has been established by a succession of meta-analyses but, because the effects of ABI are small, null findings from randomized controlled trials are often reported and can sometimes lead to skepticism regarding the benefits of ABI in routine practice. This article first explains why null findings are likely to occur under null hypothesis significance testing (NHST) due to the phenomenon known as "the dance of the p-values." A number of misconceptions about null findings are then described, using as an example the way in which the results of the primary care arm of a recent cluster-randomized trial of ABI in England (the SIPS project) have been misunderstood. These misinterpretations include the fallacy of "proving the null hypothesis" that lack of a significant difference between the means of sample groups can be taken as evidence of no difference between their population means, and the possible effects of this and related misunderstandings of the SIPS findings are examined. The mistaken inference that reductions in alcohol consumption seen in control groups from baseline to follow-up are evidence of real effects of control group procedures is then discussed and other possible reasons for such reductions, including regression to the mean, research participation effects, historical trends, and assessment reactivity, are described. From the standpoint of scientific progress, the chief problem about null findings under the conventional NHST approach is that it is not possible to distinguish "evidence of absence" from "absence of evidence." By contrast, under a Bayesian approach, such a distinction is possible and it is explained how this approach could classify ABIs in particular settings or among particular populations as either truly ineffective or as of unknown effectiveness, thus accelerating progress in the field of ABI research.
Magnetoacoustic Waves in Stratified Atmospheres with a Magnetic Null Point
Tarr, Lucas A.; Linton, Mark; Leake, James E.
2016-05-01
Magnetic fields strongly modify the propagation of MHD waves from the photosphere to the low corona, as can be shown exactly for the most simple case of a uniform magnetic field and isothermally stratrified atmosphere. For slightly more realistic scenarios, where both the atmospheric parameters and the magnetic field vary spatially, the linear MHD equations typically cannot be solved analytically. We use the Lagrangian Remap code--a nonlinear, shock-capturing MHD code--to study the propagation of initially acoustic wavepackets through a model 2D atmosphere that includes a gravitationally stratified chromosphere, transition region, and low corona. The magnetic field is formed by three photospheric concentrations and includes a single magnetic null point, resulting in an inhomogeneous system with a magnetic dome topology. A portion of an introduced wavepacket will refract toward the null due to the varying Alfven speed. Waves incident on the equipartition contour surrounding the null, where the sound and Alfven speeds coincide, partially transmit, reflect, and mode convert between branches of the local dispersion relation. Outward propagating slow modes generated during conversion become strongly concentrated along the set of field lines passing near the null. Acoustic energy is beamed back downwards towards each photospheric foot point, and upwards along one separatrix that exits the top of the numerical domain. Changes in the dominant restoring force for the wavepacket, between the Lorentz and pressure gradient forces, lead to a buildup of current density along topologically important features of the system (the null point and its four separatrices) and can drive reconnection at the null point itself. Ohmic dissipation of the currents locally heats the plasma. We find that the amount of current accumulation depends on where the centroid of a wavepacket initial crosses the photosphere, but does not simply coincide with regions of open versus closed magnetic field or
Magnetic Reconnection at a Three-dimensional Solar Null Point
DEFF Research Database (Denmark)
Frederiksen, Jacob Trier; Baumann, Gisela; Galsgaard, Klaus
2012-01-01
-like). The MHD simulations start out from a potential magnetic field containing a null-point, obtained from a SOHO magnetogram extrapolation approximately 8 hours before a C-class flare was observed. The magnetic field is stressed with a boundary motion pattern similar to the horizontal motions observed by SOHO......Using a specific solar null point reconnection case studied by Masson et al (2009; ApJ 700, 559) we investigate the dependence of the reconnection rate on boundary driving speed, numerical resolution, type of resistivity (constant or numerical), and assumed stratification (constant density or solar...
On nulls of perturbed Fredholm operators and degenerate homoclinic bifurcations
Institute of Scientific and Technical Information of China (English)
无
2004-01-01
It is known that small perturbations of a Fredholm operator L have nulls of dimension not larger than dirnN(L). In this paper for any given positive integer κ≤ dimN(L)we prove that there is a perturbation of L which has an exactlyκ-dimensional null. Actually,our proof gives a construction of the perturbation. We further apply our result to concrete examples of differential equations with degenerate homoclinic orbits, showing how many independent homoclinic orbits can be bifurcated from a perturbation.
Cartan's Equivalence Method and Null coframes in General Relativity
Gallo, E; Kozameh, C; Gallo, Emanuel; Iriondo, Mirta; Kozameh, Carlos
2004-01-01
Using Cartan's equivalence method for point transformations we obtain from first principles the conformal geometry associated with third order ODEs and a special class of PDEs in two dimensions. We explicitly construct the null tetrads of a family of Lorentzian metrics, the conformal group in three and four dimensions and the so called normal metric connection. A special feature of this connection is that the non vanishing components of its torsion depend on one relative invariant, the (generalized) W\\"unschmann Invariant. We show that the above mentioned construction naturally contains the Null Surface Formulation of General Relativity.
Strength of the null singularity inside black holes
Burko, L M
1999-01-01
We study analytically the Cauchy horizon singularity inside spherically-symmetric charged black holes, coupled to a spherical self-gravitating, minimally-coupled, massless scalar field. We show that all causal geodesics terminate at the Cauchy horizon at a null singularity, which is weak according to the Tipler classification. The singularity is also deformationally-weak in the sense of Ori. Our results are valid at arbitrary points along the null singularity, in particular at late retarded times, when non-linear effects are crucial.
Null geodesics in a magnetically charged stringy black hole spacetime
Kuniyal, Ravi Shankar; Uniyal, Rashmi; Nandan, Hemwati; Purohit, K. D.
2016-04-01
We study the null geodesics of a four-dimensional magnetic charged black hole spacetime arising in string theory. The behaviour of effective potential in view of the different values of black hole parameters are analysed in the equatorial plane. The possible orbits for null geodesics are also discussed in view of the different values of the impact parameter. We have also calculated the frequency shift of photons in this spacetime. The results are compared to those obtained for the electrically charged stringy black hole spacetime and the Schwarzschild black hole spacetime in general relativity.
The appearance, motion, and disappearance of three-dimensional magnetic null points
Energy Technology Data Exchange (ETDEWEB)
Murphy, Nicholas A., E-mail: namurphy@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138 (United States); Parnell, Clare E.; Haynes, Andrew L. [School of Mathematics and Statistics, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS (United Kingdom)
2015-10-15
While theoretical models and simulations of magnetic reconnection often assume symmetry such that the magnetic null point when present is co-located with a flow stagnation point, the introduction of asymmetry typically leads to non-ideal flows across the null point. To understand this behavior, we present exact expressions for the motion of three-dimensional linear null points. The most general expression shows that linear null points move in the direction along which the magnetic field and its time derivative are antiparallel. Null point motion in resistive magnetohydrodynamics results from advection by the bulk plasma flow and resistive diffusion of the magnetic field, which allows non-ideal flows across topological boundaries. Null point motion is described intrinsically by parameters evaluated locally; however, global dynamics help set the local conditions at the null point. During a bifurcation of a degenerate null point into a null-null pair or the reverse, the instantaneous velocity of separation or convergence of the null-null pair will typically be infinite along the null space of the Jacobian matrix of the magnetic field, but with finite components in the directions orthogonal to the null space. Not all bifurcating null-null pairs are connected by a separator. Furthermore, except under special circumstances, there will not exist a straight line separator connecting a bifurcating null-null pair. The motion of separators cannot be described using solely local parameters because the identification of a particular field line as a separator may change as a result of non-ideal behavior elsewhere along the field line.
The appearance, motion, and disappearance of three-dimensional magnetic null points
Murphy, Nicholas A.; Parnell, Clare E.; Haynes, Andrew L.
2015-10-01
While theoretical models and simulations of magnetic reconnection often assume symmetry such that the magnetic null point when present is co-located with a flow stagnation point, the introduction of asymmetry typically leads to non-ideal flows across the null point. To understand this behavior, we present exact expressions for the motion of three-dimensional linear null points. The most general expression shows that linear null points move in the direction along which the magnetic field and its time derivative are antiparallel. Null point motion in resistive magnetohydrodynamics results from advection by the bulk plasma flow and resistive diffusion of the magnetic field, which allows non-ideal flows across topological boundaries. Null point motion is described intrinsically by parameters evaluated locally; however, global dynamics help set the local conditions at the null point. During a bifurcation of a degenerate null point into a null-null pair or the reverse, the instantaneous velocity of separation or convergence of the null-null pair will typically be infinite along the null space of the Jacobian matrix of the magnetic field, but with finite components in the directions orthogonal to the null space. Not all bifurcating null-null pairs are connected by a separator. Furthermore, except under special circumstances, there will not exist a straight line separator connecting a bifurcating null-null pair. The motion of separators cannot be described using solely local parameters because the identification of a particular field line as a separator may change as a result of non-ideal behavior elsewhere along the field line.
Averaged null energy condition and quantum inequalities in curved spacetime
Kontou, Eleni-Alexandra
2015-01-01
The Averaged Null Energy Condition (ANEC) states that the integral along a complete null geodesic of the projection of the stress-energy tensor onto the tangent vector to the geodesic cannot be negative. ANEC can be used to rule out spacetimes with exotic phenomena, such as closed timelike curves, superluminal travel and wormholes. We prove that ANEC is obeyed by a minimally-coupled, free quantum scalar field on any achronal null geodesic (not two points can be connected with a timelike curve) surrounded by a tubular neighborhood whose curvature is produced by a classical source. To prove ANEC we use a null-projected quantum inequality, which provides constraints on how negative the weighted average of the renormalized stress-energy tensor of a quantum field can be. Starting with a general result of Fewster and Smith, we first derive a timelike projected quantum inequality for a minimally-coupled scalar field on flat spacetime with a background potential. Using that result we proceed to find the bound of a qu...
Effectiveness of Null Signal Sky Localization in Pulsar Timing Arrays
Shafiq Hazboun, Jeffrey
2017-01-01
A null stream is constructed from the timing residuals of three pulsars by noting that the same source polarization amplitudes appear in the data stream from each pulsar. Linear combinations of a set of individual pulsar data streams can be shown to be a two-parameter family (the two sky position angles of the source) that can be minimized to determine the location of the source on the sky. Taking the product of a number of null streams allows for an even stronger localization of the gravitational wave's source; a large advantage in a PTA where there are more independent signals than other gravitational wave detectors. While a null stream contains the same information as any other data stream with the same number of pulsars, the statistics of a product of noisy signals is inherently different than for a sum of those same signals.A comparison of how null signal searches compare to other techniques for sky localization of PTA sources will be discussed, as well as an assessment of the types of searches for which the method may be useful.
Null Lens Assembly for X-Ray Mirror Segments
Robinson, David W.
2011-01-01
A document discusses a null lens assembly that allows laser interferometry of 60 deg. slumped glass mirror segments used in x-ray mirrors. The assembly consists of four lenses in precise alignment to each other, with incorporated piezoelectric nanometer stepping actuators to position the lenses in six degrees of freedom for positioning relative to each other.
Null Objects in Second Language Acquisition: Grammatical vs. Performance Models
Zyzik, Eve C.
2008-01-01
Null direct objects provide a favourable testing ground for grammatical and performance models of argument omission. This article examines both types of models in order to determine which gives a more plausible account of the second language data. The data were collected from second language (L2) learners of Spanish by means of four oral…
Overt and Null Subject Pronouns in Jordanian Arabic
Al-Momani, Islam M.
2015-01-01
The paper aims at examining the role that morphology plays in allowing and/or motivating sentences in Jordanian Arabic (hereafter JA) to be formed with or without subject pronouns. It also aims at giving a comprehensive and descriptive presentation of the distribution of overt and null subject pronouns in JA, and tries to determine to what extent…
Null controllability for a fourth order parabolic equation
Institute of Scientific and Technical Information of China (English)
YU Hang
2009-01-01
In the paper,the null interior controllability for a fourth order parabolic equation is obtained.The method Is based on Lebeau-Rabbiano inequality which is a quantitative unique continuation property for the sum of eigenfunctions of the Laplacian.
Do Null Subjects (Mis-)Trigger Pro-Drop Grammars?
Frazier, Lyn
2015-01-01
Native speakers of English regularly hear sentences without overt subjects. Nevertheless, they maintain a [[superscript -]pro] grammar that requires sentences to have an overt subject. It is proposed that listeners of English recognize that speakers reduce predictable material and thus attribute null subjects to this process, rather than changing…
Maxwell Fields and Shear-Free Null Geodesic Congruences
Newman, E
2004-01-01
We study and report on the class of vacuum Maxwell fields in Minkowski space that possess a non-degenerate, diverging, principle null vector field (null eigenvector field of the Maxwell tensor) that is tangent to a shear-free null geodesics congruence. These congruences can be either surface forming (the tangent vectors proportional to gradients) or not, i.e., the twisting congruences. In the non-twisting case, the associated Maxwell fields are precisely the Lienard-Wiechert fields, i.e., those Maxwell fields arising from an electric monopole moving on an arbitrary worldline. The null geodesic congruence is given by the generators of the light-cones with apex on the world-line. The twisting case is much richer, more interesting and far more complicated. In a twisting subcase, where our main interests lie, it can be given the following strange interpretation. If we allow the real Minkowski space to be complexified so that the real Minkowski coordinates x^a take complex values, i.e., x^a => z^a=x^a+iy^a with co...
Reassessing the Null-Subject Parameter in Second Language Acquisition.
Lantolf, James P.
A study is presented that examines the null-subject parameter (NSP) and that seeks to attain the following objectives: (1) to assess the validity of the implicational hierarchy for the NSP, especially as proposed by Liceras (1989); and (2) to determine if there is any evidence to support the theory of the Weaker Logical Problem of Acquisition…
Testing the null hypothesis: the forgotten legacy of Karl Popper?
Wilkinson, Mick
2013-01-01
Testing of the null hypothesis is a fundamental aspect of the scientific method and has its basis in the falsification theory of Karl Popper. Null hypothesis testing makes use of deductive reasoning to ensure that the truth of conclusions is irrefutable. In contrast, attempting to demonstrate the new facts on the basis of testing the experimental or research hypothesis makes use of inductive reasoning and is prone to the problem of the Uniformity of Nature assumption described by David Hume in the eighteenth century. Despite this issue and the well documented solution provided by Popper's falsification theory, the majority of publications are still written such that they suggest the research hypothesis is being tested. This is contrary to accepted scientific convention and possibly highlights a poor understanding of the application of conventional significance-based data analysis approaches. Our work should remain driven by conjecture and attempted falsification such that it is always the null hypothesis that is tested. The write up of our studies should make it clear that we are indeed testing the null hypothesis and conforming to the established and accepted philosophical conventions of the scientific method.
Dispersion in nulling interferometry for exoplanet detection: experimental validation
Spronck, J.F.P.; Los, J.W.N.; Pereira, S.F.
2009-01-01
It is well known that dispersion affects the performance of a wide-band nulling interferometer, since it induces wavelength-dependent phase differences between the arms of the interferometer. This property is used to create achromatic phase shift by combining several dielectric plates. In this paper
Progress in broadband infrared nulling technology for TPF
Wallace, J. Kent; Brown, Ken; Bartos, Randall; Gappinger, Robert; Loya, Frank; Macdonald, Dan; Moser, Steve; Negron, John
2005-01-01
TPF-I has set for itself a host of challenging technical milestones along its path to demonstrating the feasibility of infrared nulling for planet detection Progress in each of these areas of technical development will be reviewed as well as progress in meeting the overarching technical milestones.
MHD oscillations and waves near a magnetic null line
Energy Technology Data Exchange (ETDEWEB)
Bulanov, S.V.; Syrovatskii, S.I.
1980-11-01
An informative picture is drawn of the propagation of Alfven and magnetosonic waves in a two-dimensional magnetic field with a hyperbolic null point in the approximation of a cold plasma. The magnetosonic waves asymptotically transform into cylindrical waves. The wave amplitude increases toward the null point. A distortion of the plasma boundary produces excitation of noncylindrical magnetosonic waves. If the frequency of these waves is below the critical value, they will not penetrate into the plasma. Dissipation leads to a reflection of magnetosonic waves near the null line. Any arbitrarily slight dissipation leads to the appearance of a discrete spectrum of weakly damped Alfven oscillations. Oscillations of this type also occur in adiabatic confinement systems in which the magnetic field has null points. The nonlinear distortion of magnetosonic waves which leads to wave breaking and to the appearance of weak shock waves is studied. The amplitude of the magnetic field perturbations in a shock wave propagating toward the center asymptotically approaches a constant value.
Magnetoacoustic shock formation near a magnetic null point
Gruszecki, M.; Vasheghani Farahani, S.; Nakariakov, , V. M.; Arber, T. D.
2011-07-01
Aims: We investigate the interaction of nonlinear fast magnetoacoustic waves with a magnetic null point in connection with the triggering of solar flares. Methods: We model the propagation of fast, initially axisymmetric waves towards a two-dimensional isothermal magnetic null point in terms of ideal magnetohydrodynamic equations. The numerical simulations are carried out with the Lagrangian remap code Lare2D. Results: Dynamics of initially axisymmetric fast pulses of small amplitude is found to be consistent with a linear analytical solution proposed earlier. The increase in the amplitude leads to the nonlinear acceleration of the compression pulse and deceleration of the rarefaction pulse and hence the distortion of the wave front. The pulse experiences nonlinear steepening in the radial direction either on the leading or the back slopes for the compression and rarefaction pulses, respectively. This effect is most pronounced in the directions perpendicular to the field. Hence, the nonlinear evolution of the fast pulse depends on the polar angle. The nonlinear steepening generates the sharp spikes of the electric current density. As in the uniform medium, the position of the shock formation also depends on the initial width of the pulse. Only sufficiently smooth and low-amplitude initial pulses can reach the vicinity of the null point, create there current density spikes, and initiate magnetic reconnection by seeding anomalous electrical resistivity. Steeper and higher amplitude initial pulses overturn at larger distance from the null point, and cannot trigger reconnection.
Design of a polarization nulling interferometer for exoplanet detection
Spronck, J.; Vosteen, L.L.A.; Pereira, S.F.; Braat, J.J.M.
2007-01-01
We present the design of a new testbed experiment to demonstrate nulling interferometry using polarization properties. This three-beam set-up is perfectly symmetric with respect to the number of reflections and transmissions and should therefore allow a high rejection ratio in a wide spectral band.
Nulling interferometry for exoplanet detection using polarization properties
Spronck, J.; Pereira, S.F.; Braat, J.J.M.
2006-01-01
We present a new type of nulling interferometer that makes use of polarization properties to have on-axis destructive interference. The proposed design, which only involves commercial components and no achromatic device, is also suitable for internal modulation. This type of interferometer should en
Compensation and optimization of dispersion in nulling interferometry
Spronck, J.F.P.; Los, J.W.N.; Pereira, S.F.
2008-01-01
The optical properties of materials are wavelength-dependent. This property, called dispersion, affects the performance of a wide-band nulling interferometer by inducing wavelength-dependent phase differences between the arms of the interferometer. In this paper, we analyze the influence of dispersi
Waves and null congruences in a draining bathtub
Dempsey, David; Dolan, Sam R.
2016-04-01
We study wave propagation in a draining bathtub: a black hole analogue in fluid mechanics whose perturbations are governed by a Klein-Gordon equation on an effective Lorentzian geometry. Like the Kerr spacetime, the draining bathtub geometry possesses an (effective) horizon, an ergosphere and null circular orbits. We propose here that a ‘pulse’ disturbance may be used to map out the light-cone of the effective geometry. First, we apply the eikonal approximation to elucidate the link between wavefronts, null geodesic congruences and the Raychaudhuri equation. Next, we solve the wave equation numerically in the time domain using the method of lines. Starting with Gaussian initial data, we demonstrate that a pulse will propagate along a null congruence and thus trace out the light-cone of the effective geometry. Our new results reveal features, such as wavefront intersections, frame-dragging, winding and interference effects, that are closely associated with the presence of null circular orbits and the ergosphere.
Proof of a Null Penrose Conjecture using a new Quasi-local Mass
Roesch, Henri
2016-01-01
We define an explicit quasi-local mass functional which is non-decreasing along all foliations (satisfying a convexity assumption) of null cones. We use this new functional to prove the null Penrose conjecture under fairly generic conditions.
Defective intestinal amino acid absorption in Ace2 null mice.
Singer, Dustin; Camargo, Simone M R; Ramadan, Tamara; Schäfer, Matthias; Mariotta, Luca; Herzog, Brigitte; Huggel, Katja; Wolfer, David; Werner, Sabine; Penninger, Josef M; Verrey, François
2012-09-15
Mutations in the main intestinal and kidney luminal neutral amino acid transporter B(0)AT1 (Slc6a19) lead to Hartnup disorder, a condition that is characterized by neutral aminoaciduria and in some cases pellagra-like symptoms. These latter symptoms caused by low-niacin are thought to result from defective intestinal absorption of its precursor L-tryptophan. Since Ace2 is necessary for intestinal B(0)AT1 expression, we tested the impact of intestinal B(0)AT1 absence in ace2 null mice. Their weight gain following weaning was decreased, and Na(+)-dependent uptake of B(0)AT1 substrates measured in everted intestinal rings was defective. Additionally, high-affinity Na(+)-dependent transport of L-proline, presumably via SIT1 (Slc6a20), was absent, whereas glucose uptake via SGLT1 (Slc5a1) was not affected. Measurements of small intestine luminal amino acid content following gavage showed that more L-tryptophan than other B(0)AT1 substrates reach the ileum in wild-type mice, which is in line with its known lower apparent affinity. In ace2 null mice, the absorption defect was confirmed by a severalfold increase of L-tryptophan and of other neutral amino acids reaching the ileum lumen. Furthermore, plasma and muscle levels of glycine and L-tryptophan were significantly decreased in ace2 null mice, with other neutral amino acids displaying a similar trend. A low-protein/low-niacin diet challenge led to differential changes in plasma amino acid levels in both wild-type and ace2 null mice, but only in ace2 null mice to a stop in weight gain. Despite the combination of low-niacin with a low-protein diet, plasma niacin concentrations remained normal in ace2 null mice and no pellagra symptoms, such as photosensitive skin rash or ataxia, were observed. In summary, mice lacking Ace2-dependent intestinal amino acid transport display no total niacin deficiency nor clear pellagra symptoms, even under a low-protein and low-niacin diet, despite gross amino acid homeostasis alterations.
Axon and muscle spindle hyperplasia in the myostatin null mouse.
Elashry, Mohamed I; Otto, Anthony; Matsakas, Antonios; El-Morsy, Salah E; Jones, Lisa; Anderson, Bethan; Patel, Ketan
2011-02-01
Germline deletion of the myostatin gene results in hyperplasia and hypertrophy of the tension-generating (extrafusal) fibres in skeletal muscle. As this gene is expressed predominantly in myogenic tissues it offers an excellent model with which to investigate the quantitative relationship between muscle and axonal development. Here we show that skeletal muscle hyperplasia in myostatin null mouse is accompanied by an increase in nerve fibres in major nerves of both the fore- and hindlimbs. We show that axons within these nerves undergo hypertrophy. Furthermore, we provide evidence that the age-related neural atrophic process is delayed in the absence of myostatin. Finally, we show that skeletal muscle hyperplasia in the myostatin null mouse is accompanied by an increase in the number of muscle spindles (also called stretch receptors or proprioceptors). However, our work demonstrates that the mechanisms regulating intrafusal fibre hyperplasia and hypertrophy differ from those that control the aetiology of extrafusal fibres.
Quantization of black hole entropy from unstable circular null geodesics
Wei, Shao-Wen; Liu, Yu-Xiao; Fu, Chun-E.
2016-04-01
The quasinormal mode frequencies can be understood from the massless particles trapped at the unstable circular null geodesics and slowly leaking out to infinity. Based on this viewpoint, in this paper, we semiclassically construct the entropy spectrum of the static and stationary black holes from the null geodesics. The result shows that the spacing of the entropy spectrum only depends on the property of the black hole in the eikonal limit. Moreover, for a black hole far from the extremal case, the spacing is found to be smaller than 2πħ for any dimension, which is very different from the result of the previous work by using the usual quasinormal mode frequencies.
Null fluids: A new viewpoint of Galilean fluids
Banerjee, Nabamita; Dutta, Suvankar; Jain, Akash
2016-05-01
In this article, we study a Galilean fluid with a conserved U (1 ) current up to anomalies. We construct a relativistic system, which we call a null fluid and show that it is in one-to-one correspondence with a Galilean fluid living in one lower dimension. The correspondence is based on light cone reduction, which is known to reduce the Poincaré symmetry of a theory to Galilean in one lower dimension. We show that the proposed null fluid and the corresponding Galilean fluid have exactly same symmetries, thermodynamics, constitutive relations, and equilibrium partition to all orders in the derivative expansion. We also devise a mechanism to introduce U (1 ) anomaly in even dimensional Galilean theories using light cone reduction, and study its effect on the constitutive relations of a Galilean fluid.
Averaged null energy condition in Loop Quantum Cosmology
Li, Li-Fang
2008-01-01
Wormhole and time machine are very interesting objects in general relativity. However, they need exotic matters which are impossible in classical level to support them. But if we introduce the quantum effects of gravity into the stress-energy tensor, these peculiar objects can be constructed self-consistently. Fortunately, loop quantum cosmology (LQC) has the potential to serve as a bridge connecting the classical theory and quantum gravity. Therefore it provides a simple way for the study of quantum effect in the semiclassical case. As is well known, loop quantum cosmology is very successful to deal with the behavior of early universe. In the early stage, if taken the quantum effect into consideration, inflation is natural because of the violation of every kind of local energy conditions. Similar to the inflationary universe, the violation of the averaged null energy condition is the necessary condition for the traversable wormholes. In this paper, we investigate the averaged null energy condition in LQC in ...
Defocusing of null rays in infinite derivative gravity
Conroy, Aindriú; Koshelev, Alexey S.; Mazumdar, Anupam
2017-01-01
Einstein's General theory of relativity permits spacetime singularities, where null geodesic congruences focus in the presence of matter, which satisfies an appropriate energy condition. In this paper, we provide a minimal defocusing condition for null congruences without assuming any ansatz-dependent background solution. The two important criteria are: (1) an additional scalar degree of freedom, besides the massless graviton must be introduced into the spacetime; and (2) an infinite derivative theory of gravity is required in order to avoid tachyons or ghosts in the graviton propagator. In this regard, our analysis strengthens earlier arguments for constructing non-singular bouncing cosmologies within an infinite derivative theory of gravity, without assuming any ansatz to solve the full equations of motion.
Analysis of nulling phase functions suitable to image plane coronagraphy
Henault, Francois; Verinaud, Christophe
2016-01-01
Coronagraphy is a very efficient technique for identifying and characterizing extra-solar planets orbiting in the habitable zone of their parent star, especially when used in a space environment. An important family of coronagraphs is based on phase plates located at an intermediate image plane of the optical system, that spread the starlight outside the "Lyot" exit pupil plane of the instrument. In this communication we present a set of candidate phase functions generating a central null at the Lyot plane, and study how it propagates to the image plane of the coronagraph. These functions include linear azimuthal phase ramps (the well-known optical vortex), azimuthally cosine-modulated phase profiles, and circular phase gratings. Numerical simulations of the expected null depth, inner working angle, sensitivity to pointing errors, effect of central obscuration located at the pupil or image planes, and effective throughput including image mask and Lyot stop transmissions are presented and discussed. The prelim...
Null Fluids - A New Viewpoint of Galilean Fluids
Banerjee, Nabamita; Jain, Akash
2015-01-01
This article is a detailed version of our short letter `On equilibrium partition function for non-relativistic fluid' [arXiv:1505.05677] extended to include an anomalous $U(1)$ symmetry. We construct a relativistic system, which we call null fluid and show that it is in one-to-one correspondence with a Galilean fluid living in one lower dimension. The correspondence is based on light cone reduction, which is known to reduce the Poincare symmetry of a theory to Galilean in one lower dimension. We show that the proposed null fluid and the corresponding Galilean fluid have exactly same symmetries, thermodynamics, constitutive relations, and equilibrium partition to all orders in derivative expansion. We also devise a mechanism to introduce $U(1)$ anomaly in even dimensional Galilean theories using light cone reduction, and study its effect on the constitutive relations of a Galilean Fluid.
Averaged-null-energy condition for electromagnetism in Minkowski spacetime
Energy Technology Data Exchange (ETDEWEB)
Folacci, A. (Universite de Corse, Faculte des Sciences, Boite Postale 52, 20250 Corti (France))
1992-09-15
We show, on four-dimensional Minkowski spacetime, that {l angle}{psi}{vert bar}{ital T}{sub {mu}{nu}}{vert bar}{psi}{r angle}, the renormalized expectation value in a general quantum state {vert bar}{psi}{r angle} of the stress-energy tensor for electromagnetism, satisfies the averaged-null-energy condition, i.e., that {integral}{ital d}{lambda}{l angle}{psi}{vert bar}{ital T}{sub {mu}{nu}}{vert bar}{psi}{r angle}{ital t}{sup {mu}}{ital t{nu}}{ge}0 where this integral is along complete null geodesics with an affine parameter {lambda} and tangent vector {ital t}{sup {mu}}.
Magnetic Reconnection at a Three-dimensional Solar Null Point
Frederiksen, J. T.; Baumann, G.; Galsgaard, K.; Haugbølle, T.; Nordlund, Å.
2012-04-01
Using a specific solar null point reconnection case studied by Masson et al (2009; ApJ 700, 559) we investigate the dependence of the reconnection rate on boundary driving speed, numerical resolution, type of resistivity (constant or numerical), and assumed stratification (constant density or solar-like). The MHD simulations start out from a potential magnetic field containing a null-point, obtained from a SOHO magnetogram extrapolation approximately 8 hours before a C-class flare was observed. The magnetic field is stressed with a boundary motion pattern similar to the horizontal motions observed by SOHO during the period preceding the flare. The general behavior is nearly independent of driving speed and numerical resolution, and is also very similar in stratified and unstratified models, provided only that the boundary motions are slow enough.
MHD Mode Conversion around a 2D Magnetic Null Point
McDougall, A M D; 10.1063/1.3099224
2009-01-01
Mode conversion occurs when a wave passes through a region where the sound and Alfven speeds are equal. At this point there is a resonance, which allows some of the incident wave to be converted into a different mode. We study this phenomenon in the vicinity of a two-dimensional, coronal null point. As a wave approaches the null it passes from low- to high-beta plasma, allowing conversion to take place. We simulate this numerically by sending in a slow magnetoacoustic wave from the upper boundary; as this passes through the conversion layer a fast wave can clearly be seen propagating ahead. Numerical simulations combined with an analytical WKB investigation allow us to determine and track both the incident and converted waves throughout the domain.
Nonparametric Regression Estimation for Multivariate Null Recurrent Processes
Directory of Open Access Journals (Sweden)
Biqing Cai
2015-04-01
Full Text Available This paper discusses nonparametric kernel regression with the regressor being a \\(d\\-dimensional \\(\\beta\\-null recurrent process in presence of conditional heteroscedasticity. We show that the mean function estimator is consistent with convergence rate \\(\\sqrt{n(Th^{d}}\\, where \\(n(T\\ is the number of regenerations for a \\(\\beta\\-null recurrent process and the limiting distribution (with proper normalization is normal. Furthermore, we show that the two-step estimator for the volatility function is consistent. The finite sample performance of the estimate is quite reasonable when the leave-one-out cross validation method is used for bandwidth selection. We apply the proposed method to study the relationship of Federal funds rate with 3-month and 5-year T-bill rates and discover the existence of nonlinearity of the relationship. Furthermore, the in-sample and out-of-sample performance of the nonparametric model is far better than the linear model.
Advances in corneal topography measurements with conical null-screens
Campos-García, Manuel; Cossio-Guerrero, Cesar; Huerta-Carranza, Oliver; Moreno-Oliva, Víctor I.
2015-09-01
In this work we report the design of a null-screen for corneal topography. To avoid the difficulties in the alignment of the test system due to the face contour (eyebrows, nose, or eyelids), we design a conical null-screen with a novel radial points distribution drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact array of circular spots if the surface is perfect. Additionally, an algorithm to compute the sagittal and meridional radii of curvature for the corneal surface is presented. The sagittal radius is obtained from the surface normal, and the meridional radius is calculated from a function fitted to the derivative of the sagittal curvature by using the surfacenormals raw data. Experimental results for the testing a calibration spherical surface are shown. Also, we perform some corneal topography measurements.
Do electromagnetic waves always propagate along null geodesics?
Asenjo, Felipe A
2016-01-01
We find exact solutions to Maxwell equations written in terms of four-vector potentials in non--rotating, as well as in G\\"odel and Kerr spacetimes. Exact electromagnetic waves solutions are written on given gravitational field backgrounds where they evolve. We find that in non--rotating spherical symmetric spacetimes, electromagnetic plane waves travel along null geodesics. However, electromagnetic plane waves on G\\"odel and Kerr spacetimes do not exhibit that behavior.
Null controllability for a parabolic-elliptic coupled system
Fernández-Cara, E; de Menezes, S B
2012-01-01
In this paper, we prove the null controllability of some parabolic-elliptic systems. The control is distributed, locally supported in space and appears only in one PDE. The arguments rely on fixed-point reformulation and suitable Carleman estimates for the solutions to the adjoint system. Under appropriate assumptions, we also prove that the solution can be obtained as the asymptotic limit of some similar parabolic systems.
Null-Tetradic treatment of the Relativistic Dynamics (II)
Gottlieb, I.; Maftei, Gh.
The authors apply the Null-tetradic formalism as was given in the book by Kramer, Stephani, Herlt, Mac-Callum, Exact Solutions (1980) to some of the chapters of General Relativity which were not examined in the book above and such a way make a connection with another classic book in General Relativity: that of Landau and Lifchitz, Theorie des champs, Ed. Mir, Moscou (1989).
Three-dimensional magnetic reconnection through a moving magnetic null
Lukin, V. S.; Linton, M. G.
2011-01-01
A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the sphe...
Three-dimensional magnetic reconnection through a moving magnetic null
Lukin, V. S.; Linton, M. G.
2011-01-01
A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the spheromaks tilt, their magnetic fi...
(abstract) Ulysses Observations of Magnetic Nulls in the Solar Wind
Winterhalter, D.; Murphy, N.; Tsurutani, B. T.; Smith, E. J.; Balogh, A.; Erdos, G.
1993-01-01
High time resolution magnetic field measurements (1 vector/s) at radial distances out to 5.3 AU and heliographic latitudes from 0(deg) to > 35(deg) S reveal the presence of solitary pulses lasting tens of seconds in which the field magnitude approaches or reaches zero. The properties of these nulls, their spatial distribution and relation to solar wind structures and to similar-apppearing interplanetary and magnetospheric impulses will be discussed.
Energy dissipation in magnetic null points at kinetic scales
Olshevsky, Vyacheslav; Divin, Andrey; Eriksson, Elin; Markidis, Stefano; Lapenta, Giovanni
2015-01-01
We use kinetic particle-in-cell and MHD simulations supported by an observational data set to investigate magnetic reconnection in clusters of null points in space plasma. The magnetic configuration under investigation is driven by fast adiabatic flux rope compression that dissipates almost half of the initial magnetic field energy. In this phase powerful currents are excited producing secondary instabilities, and the system is brought into a state of "intermittent turbulence" within a few io...
Nulling interferometry for exoplanet detection using polarization properties
Spronck, J.; Pereira, S.F.; Braat, J.J.M.
2006-01-01
We present a new type of nulling interferometer that makes use of polarization properties to have on-axis destructive interference. The proposed design, which only involves commercial components and no achromatic device, is also suitable for internal modulation. This type of interferometer should enable a high rejection ratio in a theoretically unlimited spectral band. We implemented that concept on a two-beam white-light interferometer and we present here the first experimental results
Fresnel rhombs as achromatic phase shifters for infrared nulling interferometry
Mawet, D.; Hanot, Charles; Lenaers, C.; Riaud, Pierre; Defrere, Denis; Vandormael; Loicq, Jerôme; Fleury, K.; Plesseria, Jean-Yves; Surdej, Jean; Habraken, Serge
2007-01-01
We propose a new family of achromatic phase shifters for infrared nulling interferometry. These key optical components can be seen as optimized Fresnel rhombs, using the total internal reflection phenomenon, modulated or not. The total internal reflection indeed comes with a phase shift between the polarization components of the incident light. We propose a solution to implement this vectorial phase shift between interferometer arms to provide the destructive interference process needed to di...
The Steinhaus property and Haar-null sets
Dodos, Pandelis
2010-01-01
It is shown that if $G$ is an uncountable Polish group and $A\\subseteq G$ is a universally measurable set such that $A^{-1}A$ is meager, then the set $T_l(A)=\\{\\mu\\in P(G): \\mu(gA)=0 \\text{for all} g\\in G\\}$ is co-meager. In particular, if $A$ is analytic and not left Haar-null, then $1\\in\\mathrm{Int}(A^{-1}AA^{-1}A)$.
Null controllability for linear parabolic cascade systems with interior degeneracy
Directory of Open Access Journals (Sweden)
Idriss Boutaayamou
2016-11-01
Full Text Available We study the null controllability problem for linear degenerate parabolic systems with one control force through Carleman estimates for the associated adjoint problem. The novelty of this article is that for the first time it is considered a problem with an interior degeneracy and a control set that only requires to contain an interval lying on one side of the degeneracy points. The obtained result improves and complements a number of earlier works. As a consequence, observability inequalities are established.
4-dimensional spacetimes from 2-dimensional conformal null data
Goswami, Rituparno; Ellis, George F. R.
2017-03-01
In this paper we investigate whether the holographic principle proposed in string theory has a classical counterpart in general relativity theory. We show that there is a partial correspondence: at least in the case of vacuum Petrov type D spacetimes that admit a non-trivial Killing tensor, which encompass all the astrophysical black hole spacetimes, there exists a one-to-one correspondence between gravity in bulk and a 2-dimensional classical conformal scalar field on a null boundary.
Non-null annular subaperture stitching interferometry for aspheric test
Zhang, Lei; Liu, Dong; Shi, Tu; Yang, Yongying; Chong, Shiyao; Miao, Liang; Huang, Wei; Shen, Yibing; Bai, Jian
2015-10-01
A non-null annular subaperture stitching interferometry (NASSI), combining the subaperture stitching idea and non-null test method, is proposed for steep aspheric testing. Compared with standard annular subaperture stitching interferometry (ASSI), a partial null lens (PNL) is employed as an alternative to the transmission sphere, to generate different aspherical wavefronts as the references. The coverage subaperture number would thus be reduced greatly for the better performance of aspherical wavefronts in matching the local slope of aspheric surfaces. Instead of various mathematical stitching algorithms, a simultaneous reverse optimizing reconstruction (SROR) method based on system modeling and ray tracing is proposed for full aperture figure error reconstruction. All the subaperture measurements are simulated simultaneously with a multi-configuration model in a ray-tracing program, including the interferometric system modeling and subaperture misalignments modeling. With the multi-configuration model, full aperture figure error would be extracted in form of Zernike polynomials from subapertures wavefront data by the SROR method. This method concurrently accomplishes subaperture retrace error and misalignment correction, requiring neither complex mathematical algorithms nor subaperture overlaps. A numerical simulation exhibits the comparison of the performance of the NASSI and standard ASSI, which demonstrates the high accuracy of the NASSI in testing steep aspheric. Experimental results of NASSI are shown to be in good agreement with that of Zygo® VerifireTM Asphere interferometer.
Retarded Fields of Null Particles and the Memory Effect
Tolish, Alexander
2014-01-01
We consider the retarded solution to the scalar, electromagnetic, and linearized gravitational field equations in Minkowski spacetime, with source given by a particle moving on a null geodesic. In the scalar case and in the Lorenz gauge in the electromagnetic and gravitational cases, the retarded integral over the infinite past of the source does not converge as a distribution, so we cut off the null source suitably at a finite time $t_0$ and then consider two different limits: (i) the limit as the observation point goes to null infinity at fixed $t_0$, from which the ``$1/r$'' part of the fields can be extracted and (ii) the limit $t_0 \\to - \\infty$ at fixed ``observation point.'' The limit (i) gives rise to a ``velocity kick'' on distant test particles in the scalar and electromagnetic cases, and it gives rise to a ``memory effect'' (i.e., a permanent change in relative separation of two test particles) in the linearized gravitational case, in agreement with previous analyses. Although the second limit does...
Evaluating thermoregulation in reptiles: an appropriate null model.
Christian, Keith A; Tracy, Christopher R; Tracy, C Richard
2006-09-01
Established indexes of thermoregulation in ectotherms compare body temperatures of real animals with a null distribution of operative temperatures from a physical or mathematical model with the same size, shape, and color as the actual animal but without mass. These indexes, however, do not account for thermal inertia or the effects of inertia when animals move through thermally heterogeneous environments. Some recent models have incorporated body mass, to account for thermal inertia and the physiological control of warming and cooling rates seen in most reptiles, and other models have incorporated movement through the environment, but none includes all pertinent variables explaining body temperature. We present a new technique for calculating the distribution of body temperatures available to ectotherms that have thermal inertia, random movements, and different rates of warming and cooling. The approach uses a biophysical model of heat exchange in ectotherms and a model of random interaction with thermal environments over the course of a day to create a null distribution of body temperatures that can be used with conventional thermoregulation indexes. This new technique provides an unbiased method for evaluating thermoregulation in large ectotherms that store heat while moving through complex environments, but it can also generate null models for ectotherms of all sizes.
Zero emission city. Preliminary study; Null-Emissions-Stadt. Sondierungsstudie
Energy Technology Data Exchange (ETDEWEB)
Diefenbach, N.; Enseling, A.; Werner, P.; Flade, A.; Greiff, R.; Hennings, D.; Muehlich, E.; Wullkopf, U.; Sturm, P.; Kieslich, W.; Born, R.; Grossklos, M.; Hatteh, R.; Mueller, K.; Ratschow, A.; Valouch-Fornoff, C.
2002-10-01
The idea of a 'zero emission city' is investigated by the Institut Wohnen und Umwelt on behalf of the Federal Minister of Education and Research. After describing the current situation and defining the key parameters of a 'zero emission city', settlement structures, power supply, production processes and transportation are analyzed and linked with the communal action level to obtain a framework for research, activities and actions. The study ends with recommendations for a research programme 'zero emission city'. (orig.) [German] Die von den Staedten der Industrielaender ausgehenden Emissionen stellen im Hinblick auf die globalen Belastungen wie z.B. Treibhauseffekt, Ozonabbau und Versauerung das Hauptproblem dar. Aus diesem Grunde bietet es sich an, den Gedanken der 'Null-Emissions-Stadt', der Vision einer moeglichst emissionsfreien Stadt, aufzugreifen und auf seine Tragfaehigkeit fuer innovative Handlungsmodelle forschungsstrategisch zu ueberpruefen. Das Bundesministerium fuer Bildung und Forschung hat das Institut Wohnen und Umwelt beauftragt, in einer Sondierungsstudie dieser Fragestellung nachzugehen. Nach der Festlegung der Ausgangsbedingungen und Eckpunkte der Vision 'Null-Emissions-Stadt' und der Analyse der vier Handlungsfelder Siedlungsstrukturen, Energieversorgung, Produktionsprozesse (Kreislaufwirtschaft) und Verkehr werden diese aufgegriffen und mit der kommunalen Handlungsebene verknuepft und zu einem Forschungs-, Handlungs- und moeglichen Aktionsrahmen zusammengefuegt. Die Studie schliesst mit Hinweisen fuer die Gestaltung eines Forschungsprogramms 'Null-Emissions-Stadt'. (orig.)
Variational principle for gravity with null and non-null boundaries: a unified boundary counter-term
Energy Technology Data Exchange (ETDEWEB)
Parattu, Krishnamohan; Chakraborty, Sumanta; Padmanabhan, T. [IUCAA, Post Bag 4, Pune (India)
2016-03-15
It is common knowledge that the Einstein-Hilbert action does not furnish a well-posed variational principle. The usual solution to this problem is to add an extra boundary term to the action, called a counter-term, so that the variational principle becomes well-posed. When the boundary is spacelike or timelike, the Gibbons-Hawking-York counter-term is the most widely used. For null boundaries, we had proposed a counter-term in a previous paper. In this paper, we extend the previous analysis and propose a counter-term that can be used to eliminate variations of the ''off-the-surface'' derivatives of the metric on any boundary, regardless of its spacelike, timelike or null nature. (orig.)
Variational Principle for Gravity with Null and Non-null boundaries: A Unified Boundary Counter-term
Parattu, Krishnamohan; Padmanabhan, T
2016-01-01
It is common knowledge that the Einstein-Hilbert action does not furnish a well-posed variational principle. The usual solution to this problem is to add an extra boundary term to the action, called a counter-term, so that the variational principle becomes well-posed. When the boundary is spacelike or timelike, the Gibbons-Hawking-York counter-term is the most widely used. For null boundaries, we had proposed a counter-term in a previous paper. In this paper, we extend the previous analysis and propose a counter-term that can be used to eliminate variations of the "off-the-surface" derivatives of the metric on any boundary, regardless of its spacelike, timelike or null nature.
Vacuum Nuller Testbed Performance, Characterization and Null Control
Lyon, R. G.; Clampin, M.; Petrone, P.; Mallik, U.; Madison, T.; Bolcar, M.; Noecker, C.; Kendrick, S.; Helmbrecht, M. A.
2011-01-01
The Visible Nulling Coronagraph (VNC) can detect and characterize exoplanets with filled, segmented and sparse aperture telescopes, thereby spanning the choice of future internal coronagraph exoplanet missions. NASA/Goddard Space Flight Center (GSFC) has developed a Vacuum Nuller Testbed (VNT) to advance this approach, and assess and advance technologies needed to realize a VNC as a flight instrument. The VNT is an ultra-stable testbed operating at 15 Hz in vacuum. It consists of a MachZehnder nulling interferometer; modified with a "W" configuration to accommodate a hexpacked MEMS based deformable mirror (DM), coherent fiber bundle and achromatic phase shifters. The 2-output channels are imaged with a vacuum photon counting camera and conventional camera. Error-sensing and feedback to DM and delay line with control algorithms are implemented in a real-time architecture. The inherent advantage of the VNC is that it is its own interferometer and directly controls its errors by exploiting images from bright and dark channels simultaneously. Conservation of energy requires the sum total of the photon counts be conserved independent of the VNC state. Thus sensing and control bandwidth is limited by the target stars throughput, with the net effect that the higher bandwidth offloads stressing stability tolerances within the telescope. We report our recent progress with the VNT towards achieving an incremental sequence of contrast milestones of 10(exp 8) , 10(exp 9) and 10(exp 10) respectively at inner working angles approaching 2A/D. Discussed will be the optics, lab results, technologies, and null control. Shown will be evidence that the milestones have been achieved.
Why is the null HBT result at RHIC so interesting?
Gyulassy, M
2003-01-01
Pion interferometry (HBT of A+A) data have posed a thorn in the theoretical interpretation of AA collisions at RHIC (sq root s = 130 AGeV). How can R sub o sub u sub t approx R sub s sub i sub d sub e approx R sub l sub o sub n sub g and remain so between AGS and RHIC? Where is the QGP Stall? Can elephants hide along the x sub 0 sup + dimension? We rummage old hydrodynamic scenarios and uncover some previously ignored NULL solutions. (author)
Conformal symmetry wormholes and the null energy condition
Kuhfittig, Peter K F
2016-01-01
In this paper we seek a relationship between the assumption of conformal symmetry and the exotic matter needed to hold a wormhole open. By starting with a Morris-Thorne wormhole having a constant energy density, it is shown that the conformal factor provides the extra degree of freedom sufficient to account for the exotic matter. The same holds for Morris-Thorne wormholes in a noncommutative-geometry setting. Applied to thin shells, there would exist a radius that results in a wormhole with positive surface density and negative surface pressure and which violates the null energy condition on the thin shell.
An Efficient Null Model for Conformational Fluctuations in Proteins
DEFF Research Database (Denmark)
Harder, Tim Philipp; Borg, Mikael; Bottaro, Sandro
2012-01-01
limited to comparatively short timescales. TYPHON is a probabilistic method to explore the conformational space of proteins under the guidance of a sophisticated probabilistic model of local structure and a given set of restraints that represent nonlocal interactions, such as hydrogen bonds or disulfide...... bridges. The choice of the restraints themselves is heuristic, but the resulting probabilistic model is well-defined and rigorous. Conceptually, TYPHON constitutes a null model of conformational fluctuations under a given set of restraints. We demonstrate that TYPHON can provide information...
Midinfrared broadband achromatic astronomical beam combiner for nulling interferometry.
Hsiao, Hsien-kai; Winick, Kim A; Monnier, John D
2010-12-10
Integrated optic beam combiners offer many advantages over conventional bulk optic implementations for astronomical imaging. To our knowledge, integrated optic beam combiners have only been demonstrated at operating wavelengths below 4 μm. Operation in the midinfrared wavelength region, however, is highly desirable. In this paper, a theoretical design technique based on three coupled waveguides is developed to achieve fully achromatic, broadband, polarization-insensitive, lossless beam combining. This design may make it possible to achieve the very deep broadband nulls needed for exoplanet searching.
Scale anomalies imply violation of the averaged null energy condition
Visser, M
1994-01-01
Considerable interest has recently been expressed regarding the issue of whether or not quantum field theory on a fixed but curved background spacetime satisfies the averaged null energy condition (ANEC). A comment by Wald and Yurtsever [Phys. Rev. D43, 403 (1991)] indicates that in general the answer is no. In this note I explore this issue in more detail, and succeed in characterizing a broad class of spacetimes in which the ANEC is guaranteed to be violated. Finally, I add some comments regarding ANEC violation in Schwarzschild spacetime.
DBI Genesis: An Improved Violation of the Null Energy Condition
Hinterbichler, Kurt; Khoury, Justin; Miller, Godfrey E J
2013-01-01
We show that the DBI conformal galileons, derived from the world-volume theory of a 3-brane moving in an AdS bulk, admit a background, stable under quantum corrections, which violates the Null Energy Condition (NEC). The perturbations around this background are stable and propagate subluminally. Unlike other known examples of NEC violation, such as ghost condensation and conformal galileons, this theory also admits a stable, Poincare-invariant vacuum, with a Lorentz-invariant S-matrix satisfying standard analyticity conditions. Like conformal galileons, perturbations around deformations of the Poincare invariant vacuum propagate superluminally.
A Visualization of Null Geodesics for the Bonnor Massive Dipole
Oliva-Mercado, Guillermo Andree; Cordero-García, Iván; Frutos-Alfaro, Francisco
2015-01-01
In this work we simulate null geodesics for the Bonnor massive dipole metric by implementing a symbolic-numerical algorithm in Sage and Python. This program is also capable of visualizing in 3D, in principle, the geodesics for any given metric. Geodesics are launched from a common point, collectively forming a cone of light beams, simulating a solid-angle section of a point source in front of a massive object with a magnetic field. Parallel light beams also were considered, and their bending due to the curvature of the space-time was simulated.
Analysis of nulling phase functions suitable to image plane coronagraphy
Hénault, François; Carlotti, Alexis; Vérinaud, Christophe
2016-07-01
Coronagraphy is a very efficient technique for identifying and characterizing extra-solar planets orbiting in the habitable zone of their parent star, especially in a space environment. An important family of coronagraphs is actually based on phase plates located at an intermediate image plane of the optical system, and spreading the starlight outside the "Lyot" exit pupil plane of the instrument. In this commutation we present a set of candidate phase functions generating a central null at the Lyot plane, and study how it propagates to the image plane of the coronagraph. These functions include linear azimuthal phase ramps (the well-known optical vortex), azimuthally cosine-modulated phase profiles, and circular phase gratings. Nnumerical simulations of the expected null depth, inner working angle, sensitivity to pointing errors, effect of central obscuration located at the pupil or image planes, and effective throughput including image mask and Lyot stop transmissions are presented and discussed. The preliminary conclusion is that azimuthal cosine functions appear as an interesting alternative to the classical optical vortex of integer topological charge.
Holographic Description of Negative Null Energy in Squeezed Vacuum States
Lee, Da-Shin
2016-01-01
Using the AdS/CFT duality, we study the expectation value of stress tensor in squeezed vacuum states of $2+1$-dimensional quantum critical theories with a general dynamical scaling $z$. The holographic dual theory is the theory of gravity in 3+1-dimensional Lifshitz backgrounds. We then adopt a consistent approach to obtain the boundary stress tensor from bulk construction, which satisfies the trace Ward identity associated with Lifshitz scaling symmetry. The scheme for holographic dual of squeezed vacuum states is found to be the gravity theory in the geometry perturbed by gravitational wave. For small squeezing parameters, the expectation value of stress tensor in squeezed vacuum states is obtained for both strongly coupled quantum critical fields and free relativistic fields. We find that, in both cases with $z=1$, the stress tensor satisfies the averaged null energy condition and is consistent with the quantum interest conjecture. In particular, the negative lower bound on null-contracted stress tensor, w...
Null Zig-Zag Wilson Loops in N=4 SYM
Xie, Zhifeng
2009-01-01
In planar ${\\cal N}=4$ supersymmetric Yang-Mills theory we have studied supersymmetric Wilson loops composed of a large number of light-like segments, i.e., null zig-zags. These contours oscillate around smooth underlying spacelike paths. At one-loop in perturbation theory we have compared the finite part of the expectation value of null zig-zags to the finite part of the expectation value of non-scalar-coupled Wilson loops whose contours are the underlying smooth spacelike paths. In arXiv:0710.1060 [hep-th] it was argued that these quantities are equal for the case of a rectangular Wilson loop. Here we present a modest extension of this result to zig-zags of circular shape and zig-zags following non-parallel, disconnected line segments and show analytically that the one-loop finite part is indeed that given by the smooth spacelike Wilson loop without coupling to scalars which the zig-zag contour approximates. We make some comments regarding the generalization to arbitrary shapes.
Null Zig-Zag Wilson Loops in {N}=4 Sym
Xie, Zhifeng
In planar {N}=4 supersymmetric Yang-Mills theory we have studied one kind of (locally) BPS Wilson loops composed of a large number of light-like segments, i.e. null zig-zags. These contours oscillate around smooth underlying spacelike paths. At one-loop in perturbation theory, we have compared the finite part of the expectation value of null zig-zags to the finite part of the expectation value of non-scalar-coupled Wilson loops whose contours are the underlying smooth spacelike paths. In arXiv:0710.1060 [hep-th] it was argued that these quantities are equal for the case of a rectangular Wilson loop. Here we present a modest extension of this result to zig-zags of circular shape and zig-zags following non-parallel, disconnected line segments and show analytically that the one-loop finite part is indeed that given by the smooth spacelike Wilson loop without coupling to scalars which the zig-zag contour approximates. We make some comments regarding the generalization to arbitrary shapes.
Pituitary null cell adenoma in a domestic llama (Lama glama).
Chalkley, M D; Kiupel, M; Draper, A C E
2014-07-01
Pituitary gland neoplasia has been reported rarely in camelids. A 12-year-old neutered male llama (Lama glama) presented with lethargy, inappetence and neurological signs. On physical examination, the llama was mentally dull and exhibited compulsive pacing and circling to the left. Complete blood count and serum biochemistry revealed haemoconcentration, mild hypophosphataemia, hyperglycaemia, hypercreatininaemia and hyperalbuminaemia. Humane destruction was elected due to rapid clinical deterioration and poor prognosis. Post-mortem examination revealed a pituitary macroadenoma and bilateral internal hydrocephalus. Microscopically, the pituitary tumour was composed of neoplastic chromophobic pituitary cells. Ultrastructural studies revealed similar neoplastic cells to those previously described in human null cell adenomas. Immunohistochemically, the neoplastic cells were strongly immunoreactive for neuroendocrine markers (synaptophysin and chromogranin A), but did not exhibit immunoreactivity for epithelial, mesenchymal, neuronal and all major pituitary hormone markers (adrenocorticotropic hormone, follicle stimulating hormone, growth hormone, luteinizing hormone, melanocyte-stimulating hormone, prolactin and thyroid stimulating hormone), consistent with the diagnosis of a pituitary null cell adenoma. This is the first report of pituitary neoplasia in a llama.
Principal components null space analysis for image and video classification.
Vaswani, Namrata; Chellappa, Rama
2006-07-01
We present a new classification algorithm, principal component null space analysis (PCNSA), which is designed for classification problems like object recognition where different classes have unequal and nonwhite noise covariance matrices. PCNSA first obtains a principal components subspace (PCA space) for the entire data. In this PCA space, it finds for each class "i," an Mi-dimensional subspace along which the class' intraclass variance is the smallest. We call this subspace an approximate null space (ANS) since the lowest variance is usually "much smaller" than the highest. A query is classified into class "i" if its distance from the class' mean in the class' ANS is a minimum. We derive upper bounds on classification error probability of PCNSA and use these expressions to compare classification performance of PCNSA with that of subspace linear discriminant analysis (SLDA). We propose a practical modification of PCNSA called progressive-PCNSA that also detects "new" (untrained classes). Finally, we provide an experimental comparison of PCNSA and progressive PCNSA with SLDA and PCA and also with other classification algorithms-linear SVMs, kernel PCA, kernel discriminant analysis, and kernel SLDA, for object recognition and face recognition under large pose/expression variation. We also show applications of PCNSA to two classification problems in video--an action retrieval problem and abnormal activity detection.
Does horizon entropy satisfy a Quantum Null Energy Conjecture?
Fu, Zicao
2016-01-01
A modern version of the idea that the area of event horizons gives $4G$ times an entropy is the Hubeny-Rangamani Causal Holographic Information (CHI) proposal for holographic field theories. Given a region $R$ of a holographic QFTs, CHI computes $A/4G$ on a certain cut of an event horizon in the gravitational dual. The result is naturally interpreted as a coarse-grained entropy. CHI is known to be finitely greater than the fine-grained Hubeny-Rangamani-Takayanagi (HRT) entropy when $\\partial R$ lies on a Killing horizon of the QFT spacetime, and in this context satisfies other non-trivial properties expected of an entropy. Here we present evidence that it also satisfies the quantum null energy condition (QNEC), which bounds the second derivative of the entropy of a quantum field theory on one side of a non-expanding null surface by the flux of stress-energy across the surface. In particular, we show CHI to satisfy the QNEC in 1+1 holographic CFTs when evaluated in states dual to conical defects in AdS$_3$. Th...
Error analysis and system optimization of non-null aspheric testing system
Luo, Yongjie; Yang, Yongying; Liu, Dong; Tian, Chao; Zhuo, Yongmo
2010-10-01
A non-null aspheric testing system, which employs partial null lens (PNL for short) and reverse iterative optimization reconstruction (ROR for short) technique, is proposed in this paper. Based on system modeling in ray tracing software, the parameter of each optical element is optimized and this makes system modeling more precise. Systematic error of non-null aspheric testing system is analyzed and can be categorized into two types, the error due to surface parameters of PNL in the system modeling and the rest from non-null interferometer by the approach of error storage subtraction. Experimental results show that, after systematic error is removed from testing result of non-null aspheric testing system, the aspheric surface is precisely reconstructed by ROR technique and the consideration of systematic error greatly increase the test accuracy of non-null aspheric testing system.
Survival of glucose phosphate isomerase null somatic cells and germ cells in adult mouse chimaeras.
Keighren, Margaret A; Flockhart, Jean H; West, John D
2016-05-15
The mouse Gpi1 gene encodes the glycolytic enzyme glucose phosphate isomerase. Homozygous Gpi1(-/-) null mouse embryos die but a previous study showed that some homozygous Gpi1(-/-) null cells survived when combined with wild-type cells in fetal chimaeras. One adult female Gpi1(-/-)↔Gpi1(c/c) chimaera with functional Gpi1(-/-) null oocytes was also identified in a preliminary study. The aims were to characterise the survival of Gpi1(-/-) null cells in adult Gpi1(-/-)↔Gpi1(c/c) chimaeras and determine if Gpi1(-/-) null germ cells are functional. Analysis of adult Gpi1(-/-)↔Gpi1(c/c) chimaeras with pigment and a reiterated transgenic lineage marker showed that low numbers of homozygous Gpi1(-/-) null cells could survive in many tissues of adult chimaeras, including oocytes. Breeding experiments confirmed that Gpi1(-/-) null oocytes in one female Gpi1(-/-)↔Gpi1(c/c) chimaera were functional and provided preliminary evidence that one male putative Gpi1(-/-)↔Gpi1(c/c) chimaera produced functional spermatozoa from homozygous Gpi1(-/-) null germ cells. Although the male chimaera was almost certainly Gpi1(-/-)↔Gpi1(c/c), this part of the study is considered preliminary because only blood was typed for GPI. Gpi1(-/-) null germ cells should survive in a chimaeric testis if they are supported by wild-type Sertoli cells. It is also feasible that spermatozoa could bypass a block at GPI, but not blocks at some later steps in glycolysis, by using fructose, rather than glucose, as the substrate for glycolysis. Although chimaera analysis proved inefficient for studying the fate of Gpi1(-/-) null germ cells, it successfully identified functional Gpi1(-/-) null oocytes and revealed that some Gpi1(-/-) null cells could survive in many adult tissues.
Research on Null Verb Be in Chinese Based on Minimalist Program Theory
Institute of Scientific and Technical Information of China (English)
郭璐
2013-01-01
In this paper,based on the null categories and VP-shell light verb inthe Minimalist Program of Chomsky,the author proposed the concept of null verb be in Chinese and then studied the text of Moonlight over the Lotus Pondwritten by Zhuziqing to validate this assumption. The results indicate that null verb be could explain the classification of verbs and adjectives in Chinese as well as some other grammatical phenomena within the framework of Minimalist Program.
A TRUST REGION ALGORITHM WITH NULL SPACE TECHNIQUE FOR EQUALITY CONSTRAINED OPTIMIZATION
Institute of Scientific and Technical Information of China (English)
TONG Xiaojiao; LI Donghui
2004-01-01
This paper presents a trust region algorithm with null space technique fornonlinear equality constrained optimizationConsidering in the null space methods that,the convergent rate of range space step is faster than the null space step for the most cases,the proposed algorithm computes null steps more often than range space stepMoreover,the new algorithm is based on the reduced Hessian SQP methodGlobal convergence ofthe proposed algorithm is provedThe effectiveness of the method is demonstrated bysome numerical examples.
Null quadrature domains and a free boundary problem for the Laplacian
Karp, Lavi
2010-01-01
Null quadrature domains are unbounded domains in $\\R^n$ ($n \\geq 2$) with external gravitational force zero in some generalized sense. In this paper we prove a quadratic growth estimate of the Schwarz potential of a null quadrature domain and conclude by a theorem of Caffarelli, Karp and Shahgolian that any null quadrature domain is the complement of a convex set with analytic boundary. Using this result we prove that a null quadrature domain with a non-zero upper Lebesgue density at infinity is half-space.
Reduced infarct size in neuroglobin-null mice after experimental stroke in vivo
DEFF Research Database (Denmark)
Raida, Zindy; Hundahl, Christian Ansgar; Kelsen, Jesper;
2012-01-01
, then permanent cerebral ischemia would lead to larger infarct volumes in neuroglobin-null mice than in wild-type mice. METHODS: Using neuroglobin-null mice, we estimated the infarct volume 24 hours after permanent middle cerebral artery occlusion using Cavalieri's Principle, and compared the infarct volume...... in neuroglobin-null and wild-type mice. Neuroglobin antibody staining was used to examine neuroglobin expression in the infarct area of wild-type mice. RESULTS: Infarct volumes 24 hours after permanent middle cerebral artery occlusion were significantly smaller in neuroglobin-null mice than in wild-types (p
Alignment of optical system components using an ADM beam through a null assembly
Hayden, Joseph E. (Inventor); Olczak, Eugene G. (Inventor)
2010-01-01
A system for testing an optical surface includes a rangefinder configured to emit a light beam and a null assembly located between the rangefinder and the optical surface. The null assembly is configured to receive and to reflect the emitted light beam toward the optical surface. The light beam reflected from the null assembly is further reflected back from the optical surface toward the null assembly as a return light beam. The rangefinder is configured to measure a distance to the optical surface using the return light beam.
Evolution of clustered magnetic nulls in a turbulent-like reconnection region in the magnetotail
Guo, Ruilong; Pu, Zuyin; Fu, Suiyan; Xie, Lun; Dunlop, Malcolm; Bogdanova, Yulia V.; He, Jiansen; Wang, Xin; Yao, Zhonghua
2016-07-01
Magnetic null points and flux ropes play important roles in the three-dimensional process of magnetic reconnection. In this study, a cluster of null points are reconstructed in the reconnection region in the magnetotail by applying a fitting-reconstruction method to measurements from the Cluster mission. The number of reconstructed null points varies rapidly, presenting a turbulent-like evolution of the magnetic structure. The electron density and the flux of the accelerated electrons were enhanced in this turbulent-like region. During this unstable reconnection process, a B-As-B null structure was formed, showing flux rope features and resembling a secondary island in the observation.
How to Find Magnetic Nulls and Reconstruct Field Topology with MMS Data?
Fu, H.; Vaivads, A.; Khotyaintsev, Y. V.; Olshevsky, V.; Andre, M.; Cao, J.; Huang, S.; Retino, A.; Lapenta, G.
2015-12-01
In this study, we apply a new method—the first-order Taylor expansion (FOTE)—to find magnetic nulls and reconstruct magnetic field topology, in order to use it with the data from the forth-coming MMS mission. We compare this method with the previously used Poincare index (PI), and find that they are generally consistent, except that the PI method can only find a null inside the spacecraft (SC) tetrahedron, while the FOTE method can find a null both inside and outside the tetrahedron and also deduce its drift velocity. In addition, the FOTE method can (1) avoid limitations of the PI method such as data resolution, instrument uncertainty (Bz offset), and SC separation; (2) identify 3D null types (A, B, As, and Bs) and determine whether these types can degenerate into 2D (X and O); (3) reconstruct the magnetic field topology. We quantitively test the accuracy of FOTE in positioning magnetic nulls and reconstructing field topology, by using the data from 3D kinetic simulations. The influences of SC separation (0.05~1 di) and null-SC distance (0~1 di) on the accuracy are both considered. We find that: (1) for an isolated null, the method is accurate when the SC separation is smaller than 1 di, and the null-SC distance is smaller than 0.25~0.5 di; (2) for a null pair, the accuracy is same as in the isolated-null situation, except at the separator line, where the field is nonlinear. We define a parameter in terms of the eigenvalues of the null to quantify the quality of our method—the smaller this parameter the better the results. Comparing to the previously used one, this parameter is more relevant for null identification. Using the new method, we reconstruct the magnetic field topology around a radial-type null and a spiral-type null, and find that the topologies are well consistent with those predicted in theory. We therefore suggest using this method to find magnetic nulls and reconstruct field topology with four-point measurements, particularly from Cluster and
Lung mechanics in the TIMP3 null mouse and its response to mechanical ventilation.
Martin, Erica L; Truscott, Emily A; Bailey, Timothy C; Leco, Kevin J; McCaig, Lynda A; Lewis, James F; Veldhuizen, Ruud A W
2007-03-01
Tissue inhibitor of metalloproteinase-3 (TIMP3) null mice develop emphysema-like airspace enlargement due to an enzymatic imbalance. This study investigates how these abnormalities alter lung mechanics and the response to 2 different mechanical ventilation strategies. Phenotypically, TIMP3 null mice had increased compliance, and decreased resistance, tissue damping, and tissue elastance over wild-type controls. Decreased compliance and increased resistance were observed following the injurious ventilation strategy; however, the TIMP3 null response to both ventilation strategies was similar to wild-type mice. In conclusion, TIMP3 null mice have significant alterations in lung mechanics; however, this does not affect their response to ventilation.
Effects of osmolality on PLP-null myelin structure: Implications re axon damage
Rosenbluth, Jack; Schiff, Rolf; Lam, Pokman
2008-01-01
In order to test the adhesiveness of PLP-null compact myelin lamellae we soaked aldehyde-fixed CNS specimens from PLP-null and control mice overnight in distilled water, in Ringer’s solution or in Ringer’s solution with added 1M sucrose. Subsequent examination of the tissue by EM showed that both PLP-null and control white matter soaked in Ringer remained largely compact. After the distilled water soak, control myelin was virtually unchanged, but PLP-null myelin showed some decompaction, i.e....
Null-stream pointing with pulsar timing arrays
Hazboun, Jeffrey S
2016-01-01
Locating sources on the sky is one of the largest challenges in gravitational wave astronomy, owing to the omni-directional nature of gravitational wave detection techniques, and the often intrinsically weak signals being observed. Ground-based detectors can address the pointing problem by observing with a network of detectors, effectively triangulating signal locations by observing the arrival times across the network. Space-based detectors will observe long-lived sources that persist while the detector moves relative to their location on the sky, using Doppler shifts of the signal to locate the sky position. While these methods improve the pointing capability of a detector or network, the angular resolution is still coarse compared to the standards one expects from electromagnetic astronomy. Another technique that can be used for sky localization is null-stream pointing. In the case where multiple independent data streams exist, a single astrophysical source of gravitational waves will appear in each of the...
Linearized gravitational waves near space-like and null infinity
Beyer, Florian; Frauendiener, Jörg; Whale, Ben
2013-01-01
Linear perturbations on Minkowski space are used to probe numerically the remote region of an asymptotically flat space-time close to spatial infinity. The study is undertaken within the framework of Friedrich's conformal field equations and the corresponding conformal representation of spatial infinity as a cylinder. The system under consideration is the (linear) zero-rest-mass equation for a spin-2 field. The spherical symmetry of the underlying background is used to decompose the field into separate non-interacting multipoles. It is demonstrated that it is possible to reach null-infinity from initial data on an asymptotically Euclidean hyper-surface and that the physically important radiation field can be extracted accurately on $\\scri^+$.
From Satisfying to Violating the Null Energy Condition
Elder, Benjamin; Khoury, Justin
2013-01-01
We construct a theory which admits a time-dependent solution smoothly interpolating between a null energy condition (NEC)-satisfying phase at early times and a NEC-violating phase at late times. We first review earlier attempts to violate the NEC and an argument of Rubakov, presented in 1305.2614, which forbids the existence of such interpolating solutions in a single-field dilation-invariant theory. We then construct a theory which, in addition to possessing a Poincar\\'e-invariant vacuum, does admit such a solution. For a wide range of parameters, perturbations around this solution are at all times stable, comfortably subluminal and weakly-coupled. The theory requires us to explicitly break dilation-invariance, so it is unlikely that the theory is fully stable under quantum corrections, but we argue that the existence of a healthy interpolating solution is quantum-mechanically robust.
An Operator Product Expansion for Polygonal null Wilson Loops
Alday, Luis F; Maldacena, Juan; Sever, Amit; Vieira, Pedro
2010-01-01
We consider polygonal Wilson loops with null edges in conformal gauge theories. We derive an OPE-like expansion when several successive lines of the polygon are becoming aligned. The limit corresponds to a collinear, or multicollinear, limit and we explain the systematics of all the subleading corrections, going beyond the leading terms that were previously considered. These subleading corrections are governed by excitations of high spin operators, or excitations of a flux tube that goes between two Wilson lines. The discussion is valid for any conformal gauge theory, for any coupling and in any dimension. For N=4 super Yang Mills we check this expansion at strong coupling and at two loops at weak coupling . We also make predictions for the remainder function at higher loops. In the process, we also derived a new version for the TBA integral equations that determine the strong coupling answer and present the area as the associated Yang-Yang functional.
A new interferometer architecture combining nulling with phase closure measurements
Lacour, S; Monnier, J D; Kotani, T; Gauchet, L; Labeye, P
2013-01-01
Imaging the direct light signal from a faint exoplanet against the overwhelming glare of its host star presents one of the fundamental challenges to modern astronomical instrumentation. Achieving sufficient signal-to-noise for detection by direct imaging is limited by three basic physical processes: aberration of the wavefronts (both instrumental and atmospheric), photon noise, and detector noise. In this paper, we advance a novel optical setup which synthesizes the advantages of two different techniques: nulling interferometry to mitigate photon noise, and closure phase to combat optical aberrations. Our design, which employs technology from integrated optics and photonics, is intended to combine the advantageous aspects of both a coronagraph and a non-redundant interferometer. We show that such an instrument would allow readout noise limited detection of exoplanets, even in the presence of residual co-phasing errors. As a result, this concept would be ideal for space interferometry and for ground based obse...
On the Null Trajectories in Conformal Weyl Gravity
Villanueva, J R
2013-01-01
In this work we find analytical solutions to the null geodesics around a black hole in the conformal Weyl gravity. Exact expressions for the horizons are found, and they depend on the cosmological constant and the coupling constants of the conformal Weyl gravity. Then, we study the radial motion from the point of view of the proper and coordinate frames, and compare it with that found in spacetimes of general relativity. The angular motion is also examined qualitatively by means of an effective potential; quantitatively, the equation of motion is solved in terms of $\\wp$-Weierstrass elliptic function. Thus, we find the deflection angle for photons without using any approximation, which is a novel result for this kind of gravity.
Power spectrum nulls due to non-standard inflationary evolution
Goswami, Gaurav
2010-01-01
The simplest models of inflation based on slow roll produce nearly scale invariant primordial power spectra (PPS). But there are also numerous models that predict radically broken scale invariant PPS. In particular, markedly cuspy dips in the PPS correspond to nulls where the perturbation amplitude, hence PPS, goes through a zero at a specific wavenumber. Near this wavenumber, the true quantum nature of the generation mechanism of the primordial fluctuations may be revealed. Naively these features may appear to arise from fine tuned initial conditions. However, we show that this behavior arises under fairly generic set of conditions involving super-Hubble scale evolution of perturbation modes during inflation. We illustrate this with the well-studied examples of punctuated inflation and the Starobinsky-break model.
Null polarimetry near shot noise limit at 1 Hz.
He, Dechao; Xie, Boya; Feng, Sheng
2016-04-01
We describe the principle and report on the realization of a null polarimeter with two demonstrated features: (1) the sensitivity of the system is near shot noise limit and (2) quasi-stationary signals at 1 Hz can be measured without signal modulation. The achieved single-pass sensitivity is 7 × 10(-9) rad/Hz with a pair of Glan-Taylor polarizers, which should be of great interest for experiments such as observation of vacuum magnetic birefringence and search for new particles. The system is brought near its shot noise limit by appropriate polarization control and coherent heterodyne detection of light, resulting in a sensitivity improvement by two orders of magnitude in comparison with the case of no control on light polarization.
Jet phenomena above null points of the coronal magnetic field
Filippov, B.; Koutchmy, S.; Golub, L.
2009-12-01
Short-lived plasma jets of various scales, from giant X-ray jets more than 300 Mm in extent to numerous small jets with sizes typical of macrospicules, are the phenomena observed in the solar corona in extreme ultraviolet and X-ray emission. Small jets are particularly prominent in polar coronal holes. They are close neighbors of tiny bright loops and coincide in time with their sudden brightening and increase in size. The geometric shape of the jets and their location suggest that they arise near singular null points of the coronal magnetic field. These points appear in coronal holes due to the emergence of small bipolar or unipolar magnetic structures within large-scale unipolar cells. Polar jets show a distinct vertical plasma motion in a coronal hole that introduces significant momentum and mass into the solar wind flow. Investigating the dynamics of polar jets can elucidate certain details in the problem of fast solar wind acceleration.
Null Geodesics in a Magnetically Charged Stringy Black Hole Spacetime
Kuniyal, Ravi Shankar; Nandan, Hemwati; Purohit, K D
2015-01-01
We study the geodesic motion of massless test particles in the background of a magnetic charged black hole spacetime in four dimensions in dilaton-Maxwell gravity. The behaviour of effective potential in view of the different values of black hole parameters is analysed in the equatorial plane. The possible orbits for null geodesics are also discussed in detail in view of the different values of the impact parameter. We have also calculated the frequency shift of photons in this spacetime. The results obtained are then compared with those for the electrically charged stringy black hole spacetime and the Schwarzschild black hole spacetime. It is observed that there exists no stable circular orbit outside the event horizon for massless test particles.
Fresnel rhombs as achromatic phase shifters for infrared nulling interferometry
Mawet, D.; Hanot, C.; Lenaers, C.; Riaud, P.; Defrère, D.; Vandormael, D.; Loicq, J.; Fleury, K.; Plesseria, J. Y.; Surdej, J.; Habraken, S.
2007-09-01
We propose a new family of achromatic phase shifters for infrared nulling interferometry. These key optical components can be seen as optimized Fresnel rhombs, using the total internal reflection phenomenon, modulated or not. The total internal reflection indeed comes with a phase shift between the polarization components of the incident light. We propose a solution to implement this vectorial phase shift between interferometer arms to provide the destructive interference process needed to disentangle highly contrasted objects from one another. We also show that, modulating the index transition at the total internal reflection interface allows compensating for the intrinsic material dispersion in order to make the subsequent phase shift achromatic over especially broad bands. The modulation can be induced by a thin film of a well-chosen material or a subwavelength grating whose structural parameters are thoroughly optimized. We present results from theoretical simulations! together with preliminary fabrication outcomes and measurements for a prototype in Zinc Selenide.
Solar Particle Acceleration at Reconnecting 3D Null Points
Stanier, Adam J; Dalla, Silvia
2012-01-01
Context: The strong electric fields associated with magnetic reconnection in solar flares are a plausible mechanism to accelerate populations of high energy, non-thermal particles. One such reconnection scenario occurs at a 3D magnetic null point, where global plasma flows give rise to strong currents in the spine axis or fan plane. Aims: To understand the mechanism of charged particle energy gain in both the external drift region and the diffusion region associated with 3D magnetic reconnection. In doing so we evaluate the efficiency of resistive spine and fan models for particle acceleration, and find possible observables for each. Method: We use a full orbit test particle approach to study proton trajectories within electromagnetic fields that are exact solutions to the steady and incompressible magnetohydrodynamic equations. We study single particle trajectories and find energy spectra from many particle simulations. The scaling properties of the accelerated particles with respect to field and plasma para...
Causal Space-Times on a Null Lattice
Schaden, Martin
2015-01-01
I investigate a model of quantum gravity based on the first order Hilbert Palatini action with cosmological constant, discretized on a causal null-lattice with SL(2,C) structure group. The description is coordinate invariant and foliates in a causal and physically transparent manner. Lattice variables and observables are constructed. Conditions for a lattice configuration to describe a triangulated causal manifold are derived and encoded by a topological lattice theory. An equivariant BRST-construction is used to partially localize the SL(2,C) structure group of this model to the compact SU(2) of local spatial rotations. The latter in turn is completely localized using the spinors of this formulation. The integration measure of this completely localized model is derived from the SL(2,C)-invariant integration measure and is expressed in terms of SL(2,C)-invariant variables. An invariant regularization of the lattice integration measure that suppresses configurations with small local four-volumes is proposed. N...
Dinucleotide controlled null models for comparative RNA gene prediction
Directory of Open Access Journals (Sweden)
Gesell Tanja
2008-05-01
Full Text Available Abstract Background Comparative prediction of RNA structures can be used to identify functional noncoding RNAs in genomic screens. It was shown recently by Babak et al. [BMC Bioinformatics. 8:33] that RNA gene prediction programs can be biased by the genomic dinucleotide content, in particular those programs using a thermodynamic folding model including stacking energies. As a consequence, there is need for dinucleotide-preserving control strategies to assess the significance of such predictions. While there have been randomization algorithms for single sequences for many years, the problem has remained challenging for multiple alignments and there is currently no algorithm available. Results We present a program called SISSIz that simulates multiple alignments of a given average dinucleotide content. Meeting additional requirements of an accurate null model, the randomized alignments are on average of the same sequence diversity and preserve local conservation and gap patterns. We make use of a phylogenetic substitution model that includes overlapping dependencies and site-specific rates. Using fast heuristics and a distance based approach, a tree is estimated under this model which is used to guide the simulations. The new algorithm is tested on vertebrate genomic alignments and the effect on RNA structure predictions is studied. In addition, we directly combined the new null model with the RNAalifold consensus folding algorithm giving a new variant of a thermodynamic structure based RNA gene finding program that is not biased by the dinucleotide content. Conclusion SISSIz implements an efficient algorithm to randomize multiple alignments preserving dinucleotide content. It can be used to get more accurate estimates of false positive rates of existing programs, to produce negative controls for the training of machine learning based programs, or as standalone RNA gene finding program. Other applications in comparative genomics that require
Does horizon entropy satisfy a quantum null energy conjecture?
Fu, Zicao; Marolf, Donald
2016-12-01
A modern version of the idea that the area of event horizons gives 4G times an entropy is the Hubeny-Rangamani causal holographic information (CHI) proposal for holographic field theories. Given a region R of a holographic QFTs, CHI computes A/4G on a certain cut of an event horizon in the gravitational dual. The result is naturally interpreted as a coarse-grained entropy for the QFT. CHI is known to be finitely greater than the fine-grained Hubeny-Rangamani-Takayanagi (HRT) entropy when \\partial R lies on a Killing horizon of the QFT spacetime, and in this context satisfies other non-trivial properties expected of an entropy. Here we present evidence that it also satisfies the quantum null energy condition (QNEC), which bounds the second derivative of the entropy of a quantum field theory on one side of a non-expanding null surface by the flux of stress-energy across the surface. In particular, we show CHI to satisfy the QNEC in 1 + 1 holographic CFTs when evaluated in states dual to conical defects in AdS3. This surprising result further supports the idea that CHI defines a useful notion of coarse-grained holographic entropy, and suggests unprecedented bounds on the rate at which bulk horizon generators emerge from a caustic. To supplement our motivation, we include an appendix deriving a corresponding coarse-grained generalized second law for 1 + 1 holographic CFTs perturbatively coupled to dilaton gravity.
Cadmium modulates adipocyte functions in metallothionein-null mice
Energy Technology Data Exchange (ETDEWEB)
Kawakami, Takashige; Nishiyama, Kaori; Kadota, Yoshito; Sato, Masao; Inoue, Masahisa; Suzuki, Shinya, E-mail: suzukis@ph.bunri-u.ac.jp
2013-11-01
Our previous study has demonstrated that exposure to cadmium (Cd), a toxic heavy metal, causes a reduction of adipocyte size and the modulation of adipokine expression. To further investigate the significance of the Cd action, we studied the effect of Cd on the white adipose tissue (WAT) of metallothionein null (MT{sup −/−}) mice, which cannot form atoxic Cd–MT complexes and are used for evaluating Cd as free ions, and wild type (MT{sup +/+}) mice. Cd administration more significantly reduced the adipocyte size of MT{sup −/−} mice than that of MT{sup +/+} mice. Cd exposure also induced macrophage recruitment to WAT with an increase in the expression level of Ccl2 (MCP-1) in the MT{sup −/−} mice. The in vitro exposure of Cd to adipocytes induce triglyceride release into culture medium, decrease in the expression levels of genes involved in fatty acid synthesis and lipid hydrolysis at 24 h, and at 48 h increase in phosphorylation of the lipid-droplet-associated protein perilipin, which facilitates the degradation of stored lipids in adipocytes. Therefore, the reduction in adipocyte size by Cd may arise from an imbalance between lipid synthesis and lipolysis. In addition, the expression levels of leptin, adiponectin and resistin decreased in adipocytes. Taken together, exposure to Cd may induce unusually small adipocytes and modulate the expression of adipokines differently from the case of physiologically small adipocytes, and may accelerate the risk of developing insulin resistance and type 2 diabetes. - Highlights: • Cd causes a marked reduction in adipocyte size in MT-null mice. • Cd enhances macrophage migration into adipose tissue and disrupt adipokine secretion. • MT gene alleviates Cd-induced adipocyte dysfunctions. • Cd enhances the degradation of stored lipids in adipocytes, mediated by perilipin. • Cd induces unusually small adipocytes and the abnormal expression of adipokines.
Background: Simulation studies have previously demonstrated that time-series analyses using smoothing splines correctly model null health-air pollution associations. Methods: We repeatedly simulated season, meteorology and air quality for the metropolitan area of Atlanta from cyc...
How to find magnetic null and construct field topology with MMS data?
Fu, Huishan; Vaivads, Andris; Khotyaintsev, Yuri; Olshevsky, Vyacheslav; Andre, Mats; Cao, Jinbin; Huang, Shiyong; Retino, Alessandro; Eastwood, Jonathan
2015-04-01
In this study, we apply a new method'Taylor expansion'to find magnetic null and construct magnetic field topology, in order to use it with the data from the forth-coming MMS mission. We compare this method with the previously used Poincare index (PI), and find that they are generally consistent, except that the PI method can only find a null inside the spacecraft (SC) tetrahedron, while the Taylor expansion can find a null both inside and outside the tetrahedron and also deduce its drift velocity. Taylor expansion can also: (1) avoid the limitations of PI method such as data resolution, instrument uncertainty (Bz offset), and SC separation; (2) identify 3D null types (A, B, As, and Bs) and determine whether these types can degenerate into 2D (X and O); (3) construct the magnetic field topology. We quantitively test the accurateness of Taylor expansion in positioning magnetic null and constructing field topology, by using the data from 3D kinetic simulations. The influences of SC separation (from 0.05 to 1 di) and null-SC distance (from 0 to 1 di) on the accurateness are both considered. We find that: (1) for single null, the method is accurate when the SC separation is smaller than 1 di, and the null-SC distance is smaller than 0.5 di (weakly chaotic reconnection) or 0.25 di (strongly chaotic reconnection); (2) for null pair, the accurateness is same as the single-null situation, except at the null-null line, where the field is nonlinear. We invent a parameter ξ ≡|(λ1 + λ2 + λ3)|/ |λ|max to quantify the quality of the method'the smaller this parameter the better the results. Comparing to the previously used one (η ≡|downtriangle -B|/ |downtriangle × B |), this parameter is more relevant. Using the new method, we construct the magnetic field topology around a radial-type null and a spiral-type null, and find that the topologies are well consistent with those predicted in theory. This means that our method is reliable. We therefore suggest using this
Renal NHE expression and activity in neonatal NHE3- and NHE8-null mice.
Pirojsakul, Kwanchai; Gattineni, Jyothsna; Dwarakanath, Vangipuram; Baum, Michel
2015-01-01
Na(+)/H(+) exchanger (NHE)3 is the predominant NHE on the brush-border membrane of the proximal tubule in adult animals. NHE8 has been localized to the brush-border membrane of proximal tubules and is more highly expressed in neonates than in adult animals. However, the relative role of NHE8 in neonatal renal acidification is unclear. The present study examined if there was a compensatory increase in NHE3 in NHE8-null neonatal mice and whether there was a compensatory increase in NHE8 in NHE3-null neonatal mice. In addition, we examined whether wild-type, NHE3-null, and NHE8-null mice had an increase in NHE activity in response to metabolic acidosis. We found that at baseline, there was comparable renal NHE3 mRNA, total protein, and brush-border membrane protein abundance as in neonatal control and NHE8-null mice. There was comparable renal NHE8 mRNA, total protein, and brush-border membrane protein abundance in NHE3-null neonatal and control mice. Both NHE3- and NHE8-null mice had a comparable but lower rate of NHE activity than control mice. We next imposed metabolic acidosis in wild-type, NHE3-null, and NHE8-null mice. Acidemic NHE8-null mice had an increase in brush-border membrane vesicle NHE3 protein abundance and NHE activity compared with vehicle-treated mice. Likewise, NHE3-null mice had an increase in NHE8 brush-border membrane protein abundance and NHE activity in response to metabolic acidosis. In conclusion, both NHE3 and NHE8 likely play a role in neonatal acidification.
Agreement and Null Subjects in German L2 Development: New Evidence from Reaction-Time Experiments.
Clahsen, Harald; Hong, Upyong
1995-01-01
Reports on reaction time experiments investigating subject-verb agreement and null subjects in 33 Korean learners of German and a control group of 20 German native speakers. Results found that the two phenomena do not covary in the Korean learners, indicating that properties of agreement and null subjects are acquired separately from one another.…
Qualification of a Null Lens Using Image-Based Phase Retrieval
Bolcar, Matthew R.; Aronstein, David L.; Hill, Peter C.; Smith, J. Scott; Zielinski, Thomas P.
2012-01-01
In measuring the figure error of an aspheric optic using a null lens, the wavefront contribution from the null lens must be independently and accurately characterized in order to isolate the optical performance of the aspheric optic alone. Various techniques can be used to characterize such a null lens, including interferometry, profilometry and image-based methods. Only image-based methods, such as phase retrieval, can measure the null-lens wavefront in situ - in single-pass, and at the same conjugates and in the same alignment state in which the null lens will ultimately be used - with no additional optical components. Due to the intended purpose of a Dull lens (e.g., to null a large aspheric wavefront with a near-equal-but-opposite spherical wavefront), characterizing a null-lens wavefront presents several challenges to image-based phase retrieval: Large wavefront slopes and high-dynamic-range data decrease the capture range of phase-retrieval algorithms, increase the requirements on the fidelity of the forward model of the optical system, and make it difficult to extract diagnostic information (e.g., the system F/#) from the image data. In this paper, we present a study of these effects on phase-retrieval algorithms in the context of a null lens used in component development for the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission. Approaches for mitigation are also discussed.
Ghosh, Soma; Sur, Surojit; Yerram, Sashidhar R; Rago, Carlo; Bhunia, Anil K; Hossain, M Zulfiquer; Paun, Bogdan C; Ren, Yunzhao R; Iacobuzio-Donahue, Christine A; Azad, Nilofer A; Kern, Scott E
2014-01-01
Large-magnitude numerical distinctions (>10-fold) among drug responses of genetically contrasting cancers were crucial for guiding the development of some targeted therapies. Similar strategies brought epidemiological clues and prevention goals for genetic diseases. Such numerical guides, however, were incomplete or low magnitude for Fanconi anemia pathway (FANC) gene mutations relevant to cancer in FANC-mutation carriers (heterozygotes). We generated a four-gene FANC-null cancer panel, including the engineering of new PALB2/FANCN-null cancer cells by homologous recombination. A characteristic matching of FANCC-null, FANCG-null, BRCA2/FANCD1-null, and PALB2/FANCN-null phenotypes was confirmed by uniform tumor regression on single-dose cross-linker therapy in mice and by shared chemical hypersensitivities to various inter-strand cross-linking agents and γ-radiation in vitro. Some compounds, however, had contrasting magnitudes of sensitivity; a strikingly high (19- to 22-fold) hypersensitivity was seen among PALB2-null and BRCA2-null cells for the ethanol metabolite, acetaldehyde, associated with widespread chromosomal breakage at a concentration not producing breaks in parental cells. Because FANC-defective cancer cells can share or differ in their chemical sensitivities, patterns of selective hypersensitivity hold implications for the evolutionary understanding of this pathway. Clinical decisions for cancer-relevant prevention and management of FANC-mutation carriers could be modified by expanded studies of high-magnitude sensitivities.
Toward quantifying uncertainty in travel time tomography using the null-space shuttle
Wit, R.W.L. de; Trampert, J.; van der Hilst, R.D.
2012-01-01
The solution of large linear tomographic inverse problems is fundamentally non-unique. We suggest to explore the non-uniqueness explicitly by examining the null-space of the forward operator. We show that with the null-space shuttle it is possible to assess robustness in tomographic models, and we i
Null controllability of the viscous Camassa–Holm equation with moving control
Indian Academy of Sciences (India)
Peng Gao
2016-02-01
In this paper, we study the null controllability of the viscous Camassa–Holm equation on the one-dimensional torus. By using a moving distributed control, we obtain that the system is null controllable for a given data with certain regularity.
The role of amplitude, phase, polarization and their interconnection in nulling interferometry
Spronck, J.F.P.
2008-01-01
Nulling interferometry is a promising technique to directly detect Earth-like exoplanets. Unfortunately, it is extremely challenging to build a nulling interferometer and to meet the requirements needed for Earth-like planet detection. In this, thesis, we analyze the role of amplitude, phase and pol
Chromatism compensation in wide-band nulling interferometry for exoplanet detection
Spronck, J.; Pereira, S.F.; Braat, J.J.M.
2006-01-01
We introduce the concept of chromatism compensation in nulling interferometry that enables a high rejection ratio in a wide spectral band. Therefore the achromaticity condition considered in most nulling interferometers can be relaxed. We show that this chromatism compensation cannot be applied to a
Spronck, J.F.P.; Pereira, S.F.
2009-01-01
We show a fundamental limitation of multi-axial beam combiners in nulling interferometry. The longitudinal electric field induced by the focusing optics can drastically limit the performance of such a nulling interferometer. We further analyze the filtering capabilities of a single-mode optical fibe
Learning How to License Null Noun-Class Prefixes in Sesotho
Demuth, Katherine; Machobane, Malillo; Moloi, Francina
2009-01-01
Noun-class prefixes are obligatory in most Bantu languages. However, the Sotho languages (Sesotho, Setswana, Sepedi) permit a subset of prefixes to be realized as null at the intersection of "unmarked" phonological, syntactic, and discourse conditions. This raises the question of how and when the licensing of null prefixes is learned. Using…
Fibrosis and inflammation are greater in muscles of beta-sarcoglycan-null mouse than mdx mouse.
Gibertini, Sara; Zanotti, Simona; Savadori, Paolo; Curcio, Maurizio; Saredi, Simona; Salerno, Franco; Andreetta, Francesca; Bernasconi, Pia; Mantegazza, Renato; Mora, Marina
2014-05-01
The Sgcb-null mouse, with knocked-down β-sarcoglycan, develops severe muscular dystrophy as in type 2E human limb girdle muscular dystrophy. The mdx mouse, lacking dystrophin, is the most used model for Duchenne muscular dystrophy (DMD). Unlike DMD, the mdx mouse has mild clinical features and shows little fibrosis in limb muscles. To characterize ECM protein deposition and the progression of muscle fibrosis, we evaluated protein and transcript levels of collagens I, III and VI, decorin, and TGF-β1, in quadriceps and diaphragm, at 2, 4, 8, 12, 26, and 52 weeks in Sgcb-null mice, and protein levels at 12, 26, and 52 weeks in mdx mice. In Sgcb-null mice, severe morphological disruption was present from 4 weeks in both quadriceps and diaphragm, and included conspicuous deposition of extracellular matrix components. Histopathological features of Sgcb-null mouse muscles were similar to those of age-matched mdx muscles at all ages examined, but, in the Sgcb-null mouse, the extent of connective tissue deposition was generally greater than mdx. Furthermore, in the Sgcb-null mouse, the amount of all three collagen isoforms increased steadily, while, in the mdx, they remained stable. We also found that, at 12 weeks, macrophages were significantly more numerous in mildly inflamed areas of Sgcb-null quadriceps compared to mdx quadriceps (but not in highly inflamed regions), while, in the diaphragm, macrophages did not differ significantly between the two models, in either region. Osteopontin mRNA was also significantly greater at 12 weeks in laser-dissected highly inflamed areas of the Sgcb-null quadriceps compared to the mdx quadriceps. TGF-β1 was present in areas of degeneration-regeneration, but levels were highly variable and in general did not differ significantly between the two models and controls. The roles of the various subtypes of macrophages in muscle repair and fibrosis in the two models require further study. The Sgcb-null mouse, which develops early fibrosis
National Oceanic and Atmospheric Administration, Department of Commerce — Through the study of faults and their effects, much can be learned about the size and recurrence intervals of earthquakes. Faults also teach us about crustal...
A 3+1 perspective on null hypersurfaces and isolated horizons
Gourgoulhon, E
2006-01-01
The isolated horizon formalism recently introduced by Ashtekar et al. aims at providing a quasi-local concept of a black hole in equilibrium in an otherwise possibly dynamical spacetime. In this formalism, a hierarchy of geometrical structures is constructed on a null hypersurface. On the other side, the 3+1 formulation of general relativity provides a powerful setting for studying the spacetime dynamics, in particular gravitational radiation from black hole systems. We revisit the kinematics and dynamics of null hypersurfaces by making use of the 3+1 slicing. In particular, the additional structures induced on null hypersurfaces by the 3+1 slicing of spacetime permit a natural extension to the full spacetime of geometrical quantities defined on the null hypersurface. This 4-dimensional point of view facilitates the link between the null and spatial geometries. We proceed by reformulating the isolated horizon structure in this framework. We also reformulate previous works, such as Damour's black hole mechanic...
PSF and field of view characteristics of imaging and nulling interferometers
Hénault, François
2010-07-01
In this communication are presented some complements to a recent paper entitled "Simple Fourier optics formalism for high angular resolution systems and nulling interferometry" [1], dealing with imaging and nulling capacities of a few types of multi-aperture optical systems. Herein the characteristics of such systems in terms of Point Spread Function (PSF) and Field of View (FoV) are derived from simple analytical expressions that are further evaluated numerically for various configurations. We consider successively the general cases of Fizeau and Michelson interferometers, and those of a monolithic pupil, nulling telescope, of a nulling, Sheared-Pupil Telescope (SPT), and of a sparse aperture, Axially Combined Interferometer (ACI). The analytical formalism also allows establishing the exact Object-Image relationships applicable to nulling PSTs or ACIs that are planned for future space missions searching for habitable extra-solar planets.
PSF and field of view characteristics of imaging and nulling interferometers
Hénault, François
2010-01-01
In this communication are presented some complements to a recent paper entitled "Simple Fourier optics formalism for high angular resolution systems and nulling interferometry", dealing with imaging and nulling capacities of a few types of multi-aperture optical systems. Herein the characteristics of such systems in terms of Point Spread Function (PSF) and Field of View (FoV) are derived from simple analytical expressions that are further evaluated numerically for various configurations. We consider successively the general cases of Fizeau and Michelson interferometers, and those of a monolithic pupil, nulling telescope, of a nulling, Sheared-Pupil Telescope (SPT), and of a sparse aperture, Axially Combined Interferometer (ACI). The analytical formalism also allows establishing the exact Object-Image relationships applicable to nulling PSTs or ACIs that are planned for future space missions searching for habitable extra-solar planets.
Current Structure and Non-Ideal Behavior at Magnetic Null Points in the Turbulent Magnetosheath
Wendel, D. E.; Adrian, M. L.
2012-12-01
The Poincaré index indicates the Cluster spacecraft tetrahedron entraps a number of magnetic nulls during an encounter with the turbulent magnetosheath. Previous researchers have found evidence for reconnection at one of the many filamentary current layers observed by Cluster in this region. We find that many of the entrained nulls are also associated with strong currents. We dissect the current structure of a pair of spiral nulls that may be topologically connected. At both nulls, we find a strong current along the spine, accompanied by a modest current perpendicular to the spine that tilts the axis of the spine toward the fan plane. At least one of the nulls manifests a non-ideal rotational flow pattern in the fan plane that is consistent with torsional spine reconnection as predicted by theory. These results emphasize the importance of examining the magnetic topology in interpreting the nature of currents and reconnection in three-dimensional turbulence.
Current sheet formation and non-ideal behaviour at three-dimensional magnetic null points
Pontin, D I; Galsgaard, K
2007-01-01
The nature of the evolution of the magnetic field, and of current sheet formation, at three-dimensional (3D) magnetic null points is investigated. A kinematic example is presented which demonstrates that there is no possible choice of boundary conditions which renders the evolution of the field ideal at the null, when the ratios of the null eigenvalues are time-dependent. Resistive MHD simulations are described which demonstrate that this evolution is generic. A 3D null is subjected to boundary driving by shearing motions, and it is shown that a current sheet localised at the null is formed. The qualitative and quantitative properties of the current sheet are discussed. Accompanying the sheet development is the growth of a localised parallel electric field, one of the signatures of magnetic reconnection. Finally, the relevance of the results to a recent theory of turbulent reconnection are discussed.
Continuous development of current sheets near and away from magnetic nulls
Kumar, Sanjay; Bhattacharyya, R.
2016-04-01
The presented computations compare the strength of current sheets which develop near and away from the magnetic nulls. To ensure the spontaneous generation of current sheets, the computations are performed congruently with Parker's magnetostatic theorem. The simulations evince current sheets near two dimensional and three dimensional magnetic nulls as well as away from them. An important finding of this work is in the demonstration of comparative scaling of peak current density with numerical resolution, for these different types of current sheets. The results document current sheets near two dimensional magnetic nulls to have larger strength while exhibiting a stronger scaling than the current sheets close to three dimensional magnetic nulls or away from any magnetic null. The comparative scaling points to a scenario where the magnetic topology near a developing current sheet is important for energetics of the subsequent reconnection.
Blind Null-space Tracking for MIMO Underlay Cognitive Radio Networks
Manolakos, Alexandros; Goldsmith, Andrea J
2012-01-01
Blind Null Space Learning (BNSL) has recently been proposed for fast and accurate learning of the null-space associated with the channel matrix between a secondary transmitter and a primary receiver. In this paper we propose a channel tracking enhancement of the algorithm, namely the Blind Null Space Tracking (BNST) algorithm that allows transmission of information to the Secondary Receiver (SR) while simultaneously learning the null-space of the time-varying target channel. Specifically, the enhanced algorithm initially performs a BNSL sweep in order to acquire the null space. Then, it performs modified Jacobi rotations such that the induced interference to the primary receiver is kept lower than a given threshold $P_{Th}$ with probability $p$ while information is transmitted to the SR simultaneously. We present simulation results indicating that the proposed approach has strictly better performance over the BNSL algorithm for channels with independent Rayleigh fading with a small Doppler frequency.
Computer generated hologram null test of a freeform optical surface with rectangular aperture
Su, Ping; Ma, Jianshe; Tan, Qiaofeng; Kang, Guoguo; Liu, Yi; Jin, Guofan
2012-02-01
In null computed generated hologram (CGH) test of optical elements, fitting method is needed in null CGH design to generate continuous phase function from the ray-traced discrete phase data. The null CGH for freeform testing usually has a deformed aperture and a high order phase function, because of the aberrations introduced by freeform wavefront propagation. With traditional Zernike polynomial fitting method, selection of an orthogonal basis set and choosing number of terms are needed before fitting. Zernike polynomial fitting method is not suitable in null CGH design for freeform testing; a novel CGH design method with cubic B-spline interpolation is developed. For a freeform surface with 18×18 mm2 rectangular aperture and 630 μm peak-to-valley undulation, the null CGH with a curved rectangular aperture is designed by using the method proposed. Simulation and experimental results proved the feasibility of the novel CGH design method.
Gibberellins are involved in effect of near-null magnetic field on Arabidopsis flowering.
Xu, Chunxiao; Yu, Yang; Zhang, Yuxia; Li, Yue; Wei, Shufeng
2017-01-01
We previously found that flowering of Arabidopsis was suppressed by near-null magnetic field, which was related to the modification of cryptochrome. To disclose the physiological mechanism of this effect, we detected gibberellin (GA) levels and expressions of GA biosynthetic and signaling genes in wild type Arabidopsis plants and cryptochrome double mutant, cry1/cry2, grown in near-null magnetic field. We found that levels of GA4 , GA9 , GA34 , and GA51 in wild type plants in near-null magnetic field were significantly decreased compared with local geomagnetic field controls. However, GA levels in cry1/cry2 mutants in near-null magnetic field were similar to controls. Expressions of three GA20-oxidase (GA20ox) genes (GA20ox1, GA20ox2, and GA20ox3) and four GA3-oxidase (GA3ox) genes (GA3ox1, GA3ox2, GA3ox3, and GA3ox4) in wild type plants in near-null magnetic field were significantly reduced compared with controls, while expressions of GA20ox4, GA20ox5, GA2-oxidase (GA2ox) genes, and GA signaling-related genes in wild type plants in near-null magnetic field were not significantly different from controls. In contrast, expressions of all the detected GA biosynthetic and signaling genes in cry1/cry2 mutants were not affected by near-null magnetic field. Moreover, transcriptions of flowering-related genes, LFY and SOC1, in wild type plants were downregulated by near-null magnetic field, while they were not affected by near-null magnetic field in cry1/cry2 mutants. Our results suggest that the effect of near-null magnetic field on Arabidopsis flowering is GA-related, which is caused by cryptochrome-involved suppression of GA biosynthesis. Bioelectromagnetics. 38:1-10, 2017. © 2016 Wiley Periodicals, Inc.
Role of Plasmodium vivax Duffy-binding protein 1 in invasion of Duffy-null Africans.
Gunalan, Karthigayan; Lo, Eugenia; Hostetler, Jessica B; Yewhalaw, Delenasaw; Mu, Jianbing; Neafsey, Daniel E; Yan, Guiyun; Miller, Louis H
2016-05-31
The ability of the malaria parasite Plasmodium vivax to invade erythrocytes is dependent on the expression of the Duffy blood group antigen on erythrocytes. Consequently, Africans who are null for the Duffy antigen are not susceptible to P. vivax infections. Recently, P. vivax infections in Duffy-null Africans have been documented, raising the possibility that P. vivax, a virulent pathogen in other parts of the world, may expand malarial disease in Africa. P. vivax binds the Duffy blood group antigen through its Duffy-binding protein 1 (DBP1). To determine if mutations in DBP1 resulted in the ability of P. vivax to bind Duffy-null erythrocytes, we analyzed P. vivax parasites obtained from two Duffy-null individuals living in Ethiopia where Duffy-null and -positive Africans live side-by-side. We determined that, although the DBP1s from these parasites contained unique sequences, they failed to bind Duffy-null erythrocytes, indicating that mutations in DBP1 did not account for the ability of P. vivax to infect Duffy-null Africans. However, an unusual DNA expansion of DBP1 (three and eight copies) in the two Duffy-null P. vivax infections suggests that an expansion of DBP1 may have been selected to allow low-affinity binding to another receptor on Duffy-null erythrocytes. Indeed, we show that Salvador (Sal) I P. vivax infects Squirrel monkeys independently of DBP1 binding to Squirrel monkey erythrocytes. We conclude that P. vivax Sal I and perhaps P. vivax in Duffy-null patients may have adapted to use new ligand-receptor pairs for invasion.
Abnormal Mammary Development in 129:STAT1-Null Mice is Stroma-Dependent.
Chen, Jane Q; Mori, Hidetoshi; Cardiff, Robert D; Trott, Josephine F; Hovey, Russell C; Hubbard, Neil E; Engelberg, Jesse A; Tepper, Clifford G; Willis, Brandon J; Khan, Imran H; Ravindran, Resmi K; Chan, Szeman R; Schreiber, Robert D; Borowsky, Alexander D
2015-01-01
Female 129:Stat1-null mice (129S6/SvEvTac-Stat1(tm1Rds) homozygous) uniquely develop estrogen-receptor (ER)-positive mammary tumors. Herein we report that the mammary glands (MG) of these mice have altered growth and development with abnormal terminal end buds alongside defective branching morphogenesis and ductal elongation. We also find that the 129:Stat1-null mammary fat pad (MFP) fails to sustain the growth of 129S6/SvEv wild-type and Stat1-null epithelium. These abnormalities are partially reversed by elevated serum progesterone and prolactin whereas transplantation of wild-type bone marrow into 129:Stat1-null mice does not reverse the MG developmental defects. Medium conditioned by 129:Stat1-null epithelium-cleared MFP does not stimulate epithelial proliferation, whereas it is stimulated by medium conditioned by epithelium-cleared MFP from either wild-type or 129:Stat1-null females having elevated progesterone and prolactin. Microarrays and multiplexed cytokine assays reveal that the MG of 129:Stat1-null mice has lower levels of growth factors that have been implicated in normal MG growth and development. Transplanted 129:Stat1-null tumors and their isolated cells also grow slower in 129:Stat1-null MG compared to wild-type recipient MG. These studies demonstrate that growth of normal and neoplastic 129:Stat1-null epithelium is dependent on the hormonal milieu and on factors from the mammary stroma such as cytokines. While the individual or combined effects of these factors remains to be resolved, our data supports the role of STAT1 in maintaining a tumor-suppressive MG microenvironment.
Why Are Flare Ribbons Associated with the Spines of Magnetic Null Points Generically Elongated?
Pontin, David; Galsgaard, Klaus; Démoulin, Pascal
2016-08-01
Coronal magnetic null points exist in abundance, as demonstrated by extrapolations of the coronal field, and have been inferred to be important for a broad range of energetic events. These null points and their associated separatrix and spine field lines represent discontinuities of the field line mapping, making them preferential locations for reconnection. This field line mapping also exhibits strong gradients adjacent to the separatrix (fan) and spine field lines, which can be analysed using the "squashing factor", Q. In this article we analyse in detail the distribution of Q in the presence of magnetic nulls. While Q is formally infinite on both the spine and fan of the null, the decay of Q away from these structures is shown in general to depend strongly on the null-point structure. For the generic case of a non-radially-symmetric null, Q decays most slowly away from the spine or fan in the direction in which |{B}| increases most slowly. In particular, this demonstrates that the extended elliptical high-Q halo around the spine footpoints observed by Masson et al. ( Astrophys. J. 700, 559, 2009) is a generic feature. This extension of the Q halos around the spine or fan footpoints is important for diagnosing the regions of the photosphere that are magnetically connected to any current layer that forms at the null. In light of this, we discuss how our results can be used to interpret the geometry of observed flare ribbons in circular ribbon flares, in which typically a coronal null is implicated. We conclude that both the physics in the vicinity of the null and how this is related to the extension of Q away from the spine or fan can be used in tandem to understand observational signatures of reconnection at coronal null points.
Electric currents in the solar atmosphere in the presence of magnetic null points
Carlo Santos, Jean; Büchner, Jörg; Otto, Antonius
So far the role of magnetic null points in 3D reconnection was investigated mainly for the close vicinity of the null, with perturbations being applied at the nearby boundaries. In the solar atmosphere, however, electric currents are generated due to perturbations originating at the photosphere, far a way from coronal 3D nulls. We investigate the consequences of photospheric motion for the development of electric cur-rents in a coronal magnetic field configuration containing a null, located far away from the boundaries, and the influence of topological structures on their spatial distribution. We use a 3D resistive MHD code to investigate the consequences of photospheric plasma motion for the generation of currents in a coronal magnetic field containing a null. The plasma is consid-ered fully compressible and is initially in hydrostatic equilibrium. The initial magnetic field is current free (potential). Initially the photospheric plasma motion creates a magnetic field perturbation that propagates to the corona along the field lines at the local Alfvén speed. The shear Alfvenic wave pertur-e bation corresponds to a propagating current. The currents are mainly parallel to the magnetic field. The perturbations starting close to the foot points of the field lines that connect to the null eventually reach the vicinity of the null. Since the local Alfvén speed decreases as we approach the magnetic null point, the perturbations of the magnetic field never reach the null. Meanwhile, strong currents develop around the null point where the perturbations reach the intersection of two separatrices. On those regions, when there is an appropriate perturbation, a shear of the magnetic field is created in a length scale much smaller than the characteristic length scale of the system, generating a strong current channel.
Strong subadditivity, null energy condition and charged black holes
Energy Technology Data Exchange (ETDEWEB)
Caceres, Elena [Facultad de Ciencias, Universidad de Colima,Bernal Diaz del Castillo 340, Colima (Mexico); Theory Group, Department of Physics, The University of Texas,Austin, TX 78712 (United States); Kundu, Arnab [Theory Group, Department of Physics, The University of Texas,Austin, TX 78712 (United States); Pedraza, Juan F.; Tangarife, Walter [Theory Group, Department of Physics, The University of Texas,Austin, TX 78712 (United States); Texas Cosmology Center, The University of Texas,Austin, TX 78712 (United States)
2014-01-16
Using the Hubeny-Rangamani-Takayanagi (HRT) conjectured formula for entanglement entropy in the context of the AdS/CFT correspondence with time-dependent backgrounds, we investigate the relation between the bulk null energy condition (NEC) of the stress-energy tensor with the strong sub-additivity (SSA) property of entanglement entropy in the boundary theory. In a background that interpolates between an AdS to an AdS-Reissner-Nordstrom-type geometry, we find that generically there always exists a critical surface beyond which the violation of NEC would naively occur. However, the extremal area surfaces that determine the entanglement entropy for the boundary theory, can penetrate into this forbidden region only for certain choices for the mass and the charge functions in the background. This penetration is then perceived as the violation of SSA in the boundary theory. We also find that this happens only when the critical surface lies above the apparent horizon, but not otherwise. We conjecture that SSA, which is thus non-trivially related to NEC, also characterizes the entire time-evolution process along which the dual field theory may thermalize.
Strong Subadditivity, Null Energy Condition and Charged Black Holes
Caceres, Elena; Pedraza, Juan F; Tangarife, Walter
2014-01-01
Using the Hubeny-Rangamani-Takayanagi (HRT) conjectured formula for entanglement entropy in the context of the AdS/CFT correspondence with time-dependent backgrounds, we investigate the relation between the bulk null energy condition (NEC) of the stress-energy tensor with the strong sub-additivity (SSA) property of entanglement entropy in the boundary theory. In a background that interpolates between an AdS to an AdS-Reissner-Nordstrom-type geometry, we find that generically there always exists a critical surface beyond which the violation of NEC would naively occur. However, the extremal area surfaces that determine the entanglement entropy for the boundary theory, can penetrate into this forbidden region only for certain choices for the mass and the charge functions in the background. This penetration is then perceived as the violation of SSA in the boundary theory. We also find that this happens only when the critical surface lies above the apparent horizon, but not otherwise. We conjecture that SSA, which...
Muscular dystrophy in PTFR/cavin-1 null mice
Ding, Shi-Ying; Pilch, Paul F.
2017-01-01
ice and humans lacking the caveolae component polymerase I transcription release factor (PTRF, also known as cavin-1) exhibit lipo- and muscular dystrophy. Here we describe the molecular features underlying the muscle phenotype for PTRF/cavin-1 null mice. These animals had a decreased ability to exercise, and exhibited muscle hypertrophy with increased muscle fiber size and muscle mass due, in part, to constitutive activation of the Akt pathway. Their muscles were fibrotic and exhibited impaired membrane integrity accompanied by an apparent compensatory activation of the dystrophin-glycoprotein complex along with elevated expression of proteins involved in muscle repair function. Ptrf deletion also caused decreased mitochondrial function, oxygen consumption, and altered myofiber composition. Thus, in addition to compromised adipocyte-related physiology, the absence of PTRF/cavin-1 in mice caused a unique form of muscular dystrophy with a phenotype similar or identical to that seen in humans lacking this protein. Further understanding of this muscular dystrophy model will provide information relevant to the human situation and guidance for potential therapies.
A null relationship between media multitasking and well-being.
Directory of Open Access Journals (Sweden)
Shui-I Shih
Full Text Available There is a rapidly increasing trend in media-media multitasking or MMM (using two or more media concurrently. In a recent conference, scholars from diverse disciplines expressed concerns that indulgence in MMM may compromise well-being and/or cognitive abilities. However, research on MMM's impacts is too sparse to inform the general public and policy makers whether MMM should be encouraged, managed, or minimized. The primary purpose of the present study was to develop an innovative computerized instrument--the Survey of the Previous Day (SPD--to quantify MMM as well as media-nonmedia and nonmedia-nonmedia multitasking and sole-tasking. The secondary purpose was to examine whether these indices could predict a sample of well-being related, psychosocial measures. In the SPD, participants first recalled (typed what they did during each hour of the previous day. In later parts of the SPD, participants analysed activities and their timing and duration for each hour of the previous day, while relevant recall was on display. Participants also completed the Media Use Questionnaire. The results showed non-significant relationship between tasking measures and well-being related measures. Given how little is known about the associations between MMM and well-being, the null results may offer some general reassurance to those who are apprehensive about negative impacts of MMM.
‘Null Method’ Determination of Drug Biophase Concentration
Tallarida, Ronald J.; Lamarre, Neil
2014-01-01
PK/PD modeling is enhanced by improvements in the accuracy of its metrics. For PK/PD modeling of drugs and biologics that interact with enzymes or receptors, the equilibrium constant of the interaction can provide critical insight. Methodologies such as radioliogand binding and isolated tissue preparations can provide estimates of the equilibrium constants (as the dissociation constant, K value) for drugs and endogenous ligands that interact with specific enzymes and receptors. However, an impediment to further precision for PK/PD modeling is that it remains a problem to convert the concentration of drug in bulk solution (A) into an estimate of receptor occupation, since A is not necessarily the concentration (C) of drug in the biophase that yields fractional binding from the law of mass action, viz., C/(C + K). In most experimental studies A is much larger than K, so the use of administered instead of biophase concentration gives fractional occupancies very close to unity. We here provide a simple way to obtain an estimate of the factor that converts the total drug concentration into the biophase concentration in isolated tissue preparation. Our approach is an extension of the now classic ‘null method’ introduced and applied by Furchgott to determination of drug-receptor dissociation constants. PMID:22037914
Charged particle motion near a linear magnetic null
Energy Technology Data Exchange (ETDEWEB)
Kim, J.; Cary, J.R.
1983-08-01
Charged particle motion near the null of a two-dimensional magnetic field is studied. Specifically, the magnetic field is given by the vector potential A = zpsi/sub 0/((y/a)/sup 2/+(epsilonx/a)/sup 2/), in which psi/sub 0/,a, and epsilon are constants with epsilon parameterizing the ellipticity of the flux surfaces. Conservation of canonical z momentum p/sub z/ reduces the number of nontrivial degrees of freedom to two. Scaling reduces the number of parameters in the system to two, epsilon and sigma (the sign of p/sub z/ ). Analytical and numerical methods are used to study the nature of orbits. The results are expressed conveniently in terms of epsilon and Qequivalent(2mE)/sup 1/2//p/sub z/. When epsilon is unity, the additional symmetry implies integrability. When epsilon is less than unity (the case epsilon>1 is trivially related) three regimes are found: (1) For Vertical BarQVertical Bar>>1 particle orbits are regular, (2) for epsilon/sup 3/2/< or approx. =Vertical BarQVertical Bar< or approx. =1 most particle orbits are stochastic, and (3) for Vertical BarQVertical Bar<
Magnetic flipping - Reconnection in three dimensions without null points
Priest, E. R.; Forbes, T. G.
1992-01-01
In three dimensions, magnetic reconnection may take place in a sheared magnetic field at any singular field line, where the nearby field has X-type topology in planes perpendicular to the field line and where an electric field is present parallel to the field line. In the ideal region around the singular line there will, in general, be singularities in the plasma flow and electric field, both at the singular line and at 'magnetic flipping layers', which are remnants of local magnetic separatrices. In the absence of a three-dimensional magnetic neutral point or null point, reconnection of field lines can still occur by a process of magnetic flipping, in which the plasma crosses the flipping layers but the field lines rapidly flip along them by magnetic diffusion. Depending on the boundary conditions, there may be two or four flipping layers which converge on the singular line. A boundary layer analysis of a flipping layer is given, in which the magnetic field parallel to the layer decreases as one crosses it while the plasma pressure (or magnetic pressure associated with the field along the singular line) increases. The width of the flipping layer decreases with distance from the singular line.
Magnetic flipping: Reconnection in three-dimensions without null points
Energy Technology Data Exchange (ETDEWEB)
Priest, E.R.; Forbes, T.G. (Univ. of New Hampshire, Durham (United States))
1992-02-01
In three dimensions, magnetic reconnection may take place in a sheared magnetic field at any singular field line, where the nearby field has X-type topology in planes perpendicular to the field line and where an electric field is present parallel to the field line. In the ideal region around the singular line there will, in general, be singularities in the plasma flow and electric field, both at the singular line and at magnetic flipping layers, which are remnants of local magnetic separatrices. In the absence of a three-dimensional magnetic point or null point, reconnection of field lines can still occur by a process of magnetic flipping, in which the plasma crosses the flipping layers but the field lines rapidly flip along them by magnetic diffusion. Depending on the boundary conditions, there may be two or four flipping layers which converge on the singular line. A boundary layer analysis of a flipping layer is given, in which the magnetic field parallel to the layer decreases as one crosses it while the plasma pressure (or magnetic pressure associated with the field along the singular line) increases. The width of the flipping layer decreases with distance from the singular line.
Metric-based Hamiltonians, null boundaries, and isolated horizons
Booth, I S
2001-01-01
We extend the quasilocal (metric-based) Hamiltonian formulation of general relativity so that it may be used to study regions of spacetime with null boundaries. In particular we use this generalized Brown-York formalism to study the physics of isolated horizons. We show that the first law of isolated horizon mechanics follows directly from the first variation of the Hamiltonian. This variation is not restricted to the phase space of solutions to the equations of motion but is instead through the space of all (off-shell) spacetimes that contain isolated horizons. We find two-surface integrals evaluated on the horizons that are consistent with the Hamiltonian and which define the energy and angular momentum of these objects. These are closely related to the corresponding Komar integrals and for Kerr-Newman spacetime are equal to the corresponding ADM/Bondi quantities. Thus, the energy of an isolated horizon calculated by this method is in agreement with that recently calculated by Ashtekar and collaborators but...
Aspects of QCD current algebra on a null plane
Beane, S. R.; Hobbs, T. J.
2016-09-01
Consequences of QCD current algebra formulated on a light-like hyperplane are derived for the forward scattering of vector and axial-vector currents on an arbitrary hadronic target. It is shown that current algebra gives rise to a special class of sum rules that are direct consequences of the independent chiral symmetry that exists at every point on the two-dimensional transverse plane orthogonal to the lightlike direction. These sum rules are obtained by exploiting the closed, infinite-dimensional algebra satisfied by the transverse moments of null-plane axial-vector and vector charge distributions. In the special case of a nucleon target, this procedure leads to the Adler-Weisberger, Gerasimov-Drell-Hearn, Cabibbo-Radicati and Fubini-Furlan-Rossetti sum rules. Matching to the dispersion-theoretic language which is usually invoked in deriving these sum rules, the moment sum rules are shown to be equivalent to algebraic constraints on forward S-matrix elements in the Regge limit.
Rac-null leukocytes are associated with increased inflammation-mediated alveolar bone loss.
Sima, Corneliu; Gastfreund, Shoshi; Sun, Chunxiang; Glogauer, Michael
2014-02-01
Periodontitis is characterized by altered host-biofilm interactions that result in irreversible inflammation-mediated alveolar bone loss. Genetic and epigenetic factors that predispose to ineffective control of biofilm composition and maintenance of tissue homeostasis are not fully understood. We elucidated how leukocytes affect the course of periodontitis in Rac-null mice. Mouse models of acute gingivitis and periodontitis were used to assess the early inflammatory response and patterns of chronicity leading to loss of alveolar bone due to inflammation in Rac-null mice. Leukocyte margination was differentially impaired in these mice during attachment in conditional Rac1-null (granulocyte/monocyte lineage) mice and during rolling and attachment in Rac2-null (all blood cells) mice. Inflammatory responses to subgingival ligatures, assessed by changes in peripheral blood differential leukocyte numbers, were altered in Rac-null compared with wild-type mice. In response to persistent subgingival ligature-mediated challenge, Rac-null mice had increased loss of alveolar bone with patterns of resorption characteristic of aggressive forms of periodontitis. These findings were partially explained by higher osteoclastic coverage of the bone-periodontal ligament interface in Rac-null compared with wild-type mice. In conclusion, this study demonstrates that leukocyte defects, such as decreased endothelial margination and tissue recruitment, are rate-limiting steps in the periodontal inflammatory process that lead to more aggressive forms of periodontitis.
Suppression of Arabidopsis flowering by near-null magnetic field is affected by light.
Xu, Chunxiao; Li, Yue; Yu, Yang; Zhang, Yuxia; Wei, Shufeng
2015-09-01
We previously reported that a near-null magnetic field suppressed Arabidopsis flowering in white light, which might be related to the function modification of cryptochrome (CRY). To further demonstrate that the effect of near-null magnetic field on Arabidopsis flowering is associated with CRY, Arabidopsis wild type and CRY mutant plants were grown in the near-null magnetic field under blue or red light with different light cycle and photosynthetic photon flux density. We found that Arabidopsis flowering was significantly suppressed by near-null magnetic field in blue light with lower intensity (10 µmol/m(2) /s) and shorter cycle (12 h period: 6 h light/6 h dark). However, flowering time of CRY1/CRY2 mutants did not show any difference between plants grown in near-null magnetic field and in local geomagnetic field under detected light conditions. In red light, no significant difference was shown in Arabidopsis flowering between plants in near-null magnetic field and local geomagnetic field under detected light cycles and intensities. These results suggest that changes of blue light cycle and intensity alter the effect of near-null magnetic field on Arabidopsis flowering, which is mediated by CRY.
Why are flare ribbons generically elongated in configurations with magnetic null points?
Pontin, David Iain; Galsgaard, Klaus; Demoulin, Pascal
2016-05-01
Coronal magnetic null points exist in abundance as demonstrated by extrapolations of the coronal field, and have been inferred to be important for a broad range of energetic events. These null points and their associated separatrix and spine field lines represent discontinuities of the field line mapping, making them preferential locations for reconnection in the corona. In addition, the field line mapping in the vicinity of these null points exhibits strong gradients as measured by the “squashing factor”, Q. We demonstrate that the extension of the Q halos around the spine/fan footpoints is in general important for diagnosing the regions of the photosphere that are magnetically connected to any current layer that forms at the null. In light of this, we discuss the extent to which our results can be used to interpret the geometry of observed flare ribbons in events in which a coronal null is implicated. We conclude that together the physics in the vicinity of the null and how this is related to the extension of Q away from the spine/fan can be used in tandem to understand observational signatures of reconnection at coronal null points.
Assessment of the association between GSTM1 null genotype and risk of type 2 diabetes.
Yi, Ran; Liu, Bin; Dong, Qi
2013-06-01
Many studies have investigated the association between Glutathione S-Transferase M1 (GSTM1) null genotype and risk of diabetes mellitus, but the impact of GSTM1 null genotype on diabetes mellitus is unclear owing to the obvious inconsistence among those studies. This study aimed to quantify the strength of association between GSTM1 null genotype and risk of diabetes mellitus. We searched the PubMed, Embase and Wangfang databases for studies relating the association between GSTM1 null genotype and risk of diabetes mellitus. We estimated summary odds ratio (OR) with their 95 % confidence interval (95 % CI) to assess the association. Subgroup analyses were performed by type of diabetes and ethnicity. 10 case-control studies with 7, 054 subjects were included into this meta-analysis. Meta-analysis of total 10 studies showed GSTM1 null genotype was associated increased risk of diabetes mellitus (OR = 1.59, 95 % CI 1.14-2.22, P = 0.007). Subgroup analyses by type of diabetes mellitus suggested GSTM1 null genotype was associated increased risk of type 2 diabetes (OR = 1.90, 95 % CI 1.37-2.64, P null genotype and increased risk of type 2 diabetes. The cumulative meta-analyses showed a trend of obvious association between GSTM1 null genotype and risk of type 2 diabetes as information accumulated. No evidence of publication bias was observed. Thus, evidence from current meta-analysis suggests an association between GSTM1 null genotype and risk of type 2 diabetes.
Dąbrowski, M J; Pilot, M; Kruczyk, M; Żmihorski, M; Umer, H M; Gliwicz, J
2014-03-01
Microsatellite loci are widely used in population genetic studies, but the presence of null alleles may lead to biased results. Here, we assessed five methods that indirectly detect null alleles and found large inconsistencies among them. Our analysis was based on 20 microsatellite loci genotyped in a natural population of Microtus oeconomus sampled during 8 years, together with 1200 simulated populations without null alleles, but experiencing bottlenecks of varying duration and intensity, and 120 simulated populations with known null alleles. In the natural population, 29% of positive results were consistent between the methods in pairwise comparisons, and in the simulated data set, this proportion was 14%. The positive results were also inconsistent between different years in the natural population. In the null-allele-free simulated data set, the number of false positives increased with increased bottleneck intensity and duration. We also found a low concordance in null allele detection between the original simulated populations and their 20% random subsets. In the populations simulated to include null alleles, between 22% and 42% of true null alleles remained undetected, which highlighted that detection errors are not restricted to false positives. None of the evaluated methods clearly outperformed the others when both false-positive and false-negative rates were considered. Accepting only the positive results consistent between at least two methods should considerably reduce the false-positive rate, but this approach may increase the false-negative rate. Our study demonstrates the need for novel null allele detection methods that could be reliably applied to natural populations.
Low frequency of filaggrin null mutations in Croatia and their relation with allergic diseases.
Sabolić Pipinić, I; Varnai, V M; Turk, R; Breljak, D; Kezić, S; Macan, J
2013-06-01
Filaggrin gene (FLG) null mutations are considered associated with atopic dermatitis. This study was conducted to determine the prevalence of FLG null mutations R501X, 2282del4, R2447X and S3247X in the Croatian population and their role in the occurrence of allergic diseases including atopic dermatitis, allergic rhinitis, asthma and allergic contact dermatitis (ACD). Study enrolled 440 freshmen with defined allergic diseases by means of both present symptoms in International Study of Asthma and Allergies in Childhood questionnaire (relevant respiratory and/or skin symptoms) and markers of allergic sensitization (positive skin prick and/or patch test). FLG null mutations were successfully genotyped in 423 students of which 11 (2.6%) were carriers of FLG null mutation: 1/423 (0.2%) was heterozygous for R501X and 10/423 (2.4%) were heterozygous for 2282del4. No carriers of R2447X and S3247X mutations were identified. In wild-type FLG carriers (412 subjects), atopic dermatitis was present in 45 (11%), allergic rhinitis in 70 (17%) and allergic asthma in 29 (7%) students. Twenty-five of 393 (7%) patch-tested wild-type FLG carriers had ACD. Among 11 FLG null mutation carriers, four had one or more allergic diseases, and five had reported skin symptoms without defined allergic sensitization (positive skin prick test and/or patch test). FLG null mutations were not confirmed as a predictor of analysed allergic diseases, but were confirmed as an independent predictor of skin symptoms (OR 17.19, 95% CI 3.41-86.6, P null mutations in the studied Croatian population supporting a theory of a latitude-dependent distribution of FGL null mutations in Europe, with a decreasing north-south gradient of R501X and 2282del4 mutation frequency. The relation between FLG null mutations and skin disorders was confirmed.
Resistance to acetaminophen-induced hepatotoxicity in glutathione S-transferase Mu 1-null mice.
Arakawa, Shingo; Maejima, Takanori; Fujimoto, Kazunori; Yamaguchi, Takashi; Yagi, Masae; Sugiura, Tomomi; Atsumi, Ryo; Yamazoe, Yasushi
2012-01-01
We investigated the role of glutathione S-transferases Mu 1 (GSTM1) in acetaminophen (APAP)-induced hepatotoxicity using Gstm1-null mice. A single oral administration of APAP resulted in a marked increase in plasma alanine aminotransferase accompanied by hepatocyte necrosis 24 hr after administration in wild-type mice, but its magnitude was unexpectedly attenuated in Gstm1-null mice. Therefore, it is suggested that Gstm1-null mice are resistant to APAP-induced hepatotoxicity. To examine the mechanism of this resistance in Gstm1-null mice, we measured phosphorylation of c-jun N-terminal kinase (JNK), which mediates the signal of APAP-induced hepatocyte necrosis, by Western blot analysis 2 and 6 hr after APAP administration. A marked increase in phosphorylated JNK was observed in wild-type mice, but the increase was markedly suppressed in Gstm1-null mice. Therefore, it is suggested that suppressed phosphorylation of JNK may be a main mechanism of the resistance to APAP-induced hepatotoxicity in Gstm1-null mice, although other possibilities of the mechanism cannot be eliminated. Additionally, phosphorylation of glycogen synthase kinase-3β and mitogen-activated protein kinase kinase 4, which are upstream kinases of JNK in APAP-induced hepatotoxicity, were also suppressed in Gstm1-null mice. A decrease in liver total glutathione 2 hr after APAP administration, which is an indicator for exposure to N-acetyl-p-benzoquinoneimine, the reactive metabolite of APAP, were similar in wild-type and Gstm1-null mice. In conclusion, Gstm1-null mice are considered to be resistant to APAP-induced hepatotoxicity perhaps by the suppression of JNK phosphorylation. This study indicates the novel role of GSTM1 as a factor mediating the cellular signal for APAP-induced hepatotoxicity.
Magnetoacoustic Waves in a Stratified Atmosphere with a Magnetic Null Point
Tarr, Lucas A.; Linton, Mark; Leake, James
2017-03-01
We perform nonlinear MHD simulations to study the propagation of magnetoacoustic waves from the photosphere to the low corona. We focus on a 2D system with a gravitationally stratified atmosphere and three photospheric concentrations of magnetic flux that produce a magnetic null point with a magnetic dome topology. We find that a single wavepacket introduced at the lower boundary splits into multiple secondary wavepackets. A portion of the packet refracts toward the null owing to the varying Alfvén speed. Waves incident on the equipartition contour surrounding the null, where the sound and Alfvén speeds coincide, partially transmit, reflect, and mode-convert between branches of the local dispersion relation. Approximately 15.5% of the wavepacket’s initial energy (E input) converges on the null, mostly as a fast magnetoacoustic wave. Conversion is very efficient: 70% of the energy incident on the null is converted to slow modes propagating away from the null, 7% leaves as a fast wave, and the remaining 23% (0.036E input) is locally dissipated. The acoustic energy leaving the null is strongly concentrated along field lines near each of the null’s four separatrices. The portion of the wavepacket that refracts toward the null, and the amount of current accumulation, depends on the vertical and horizontal wavenumbers and the centroid position of the wavepacket as it crosses the photosphere. Regions that refract toward or away from the null do not simply coincide with regions of open versus closed magnetic field or regions of particular field orientation. We also model wavepacket propagation using a WKB method and find that it agrees qualitatively, though not quantitatively, with the results of the numerical simulation.
Observation of Magnetic Reconnection at a 3D Null Point Associated with a Solar Eruption
Sun, J. Q.; Zhang, J.; Yang, K.; Cheng, X.; Ding, M. D.
2016-10-01
Magnetic null has long been recognized as a special structure serving as a preferential site for magnetic reconnection (MR). However, the direct observational study of MR at null-points is largely lacking. Here, we show the observations of MR around a magnetic null associated with an eruption that resulted in an M1.7 flare and a coronal mass ejection. The Geostationary Operational Environmental Satellites X-ray profile of the flare exhibited two peaks at ∼02:23 UT and ∼02:40 UT on 2012 November 8, respectively. Based on the imaging observations, we find that the first and also primary X-ray peak was originated from MR in the current sheet (CS) underneath the erupting magnetic flux rope (MFR). On the other hand, the second and also weaker X-ray peak was caused by MR around a null point located above the pre-eruption MFR. The interaction of the null point and the erupting MFR can be described as a two-step process. During the first step, the erupting and fast expanding MFR passed through the null point, resulting in a significant displacement of the magnetic field surrounding the null. During the second step, the displaced magnetic field started to move back, resulting in a converging inflow and subsequently the MR around the null. The null-point reconnection is a different process from the current sheet reconnection in this flare; the latter is the cause of the main peak of the flare, while the former is the cause of the secondary peak of the flare and the conspicuous high-lying cusp structure.
Dąbrowski, M J; Bornelöv, S; Kruczyk, M; Baltzer, N; Komorowski, J
2015-05-01
Null alleles are alleles that for various reasons fail to amplify in a PCR assay. The presence of null alleles in microsatellite data is known to bias the genetic parameter estimates. Thus, efficient detection of null alleles is crucial, but the methods available for indirect null allele detection return inconsistent results. Here, our aim was to compare different methods for null allele detection, to explain their respective performance and to provide improvements. We applied several approaches to identify the 'true' null alleles based on the predictions made by five different methods, used either individually or in combination. First, we introduced simulated 'true' null alleles into 240 population data sets and applied the methods to measure their success in detecting the simulated null alleles. The single best-performing method was ML-NullFreq_frequency. Furthermore, we applied different noise reduction approaches to improve the results. For instance, by combining the results of several methods, we obtained more reliable results than using a single one. Rule-based classification was applied to identify population properties linked to the false discovery rate. Rules obtained from the classifier described which population genetic estimates and loci characteristics were linked to the success of each method. We have shown that by simulating 'true' null alleles into a population data set, we may define a null allele frequency threshold, related to a desired true or false discovery rate. Moreover, using such simulated data sets, the expected null allele homozygote frequency may be estimated independently of the equilibrium state of the population.
Simple computation of null-geodesics, with applications to vortex boundary detection
Serra, Mattia; Haller, George
2016-11-01
Recent results show that boundaries of coherent vortices (elliptic coherent structures) can be computed as closed null-geodesics of appropriate Lorentzian metrics defined on the physical domain of the underlying fluid. Here we derive a new method for computing null-geodesics of general Lorentzian metrics, founded on the geometry of geodesic flows. We also derive the correct set of initial conditions for the computation of closed null-geodesics, based on simple topological properties of planar closed curves. This makes the computation of coherent vortex boundaries fully automated, simpler and more accurate compared to the existing procedure. As an illustration, we compute objective coherent vortex boundaries in Oceanic and Atmospheric Flows.
Chen, Yu-Che; Walker, Ian D.; Cheatham, John B., Jr.
1992-01-01
We present a unified formulation for the inverse kinematics of redundant arms, based on a special formulation of the null space of the Jacobian. By extending (appropriately re-scaling) previously used null space parameterizations, we obtain, in a unified fashion, the manipulability measure, the null space projector, and particular solutions for the joint velocities. We obtain the minimum norm pseudo-inverse solution as a projection from any particular solution, and the method provides an intuitive visualization of the self-motion. The result is a computationally efficient, consistent approach to computing redundant robot inverse kinematics.
Direction finding of GPS receiver interference based on the nulling weights
Wang, Jing; Amin, Moeness
2007-04-01
Most military applications of GPS require performing both jammer nulling and localization. While nulling can be achieved using adaptive gradient techniques applied to the input sampled data, high resolution direction of arrival estimation can precede using subspace and eigenstructure methods applied to the estimate of the covariance matrix. In this paper, we extract the jammer direction of arrival (DOA) information directly from the adaptive weights, in which case we assume interference nulling precedes interference localization. This high resolution DOA estimation approach based on available beamforming weight values leads to simplified receiver structure and allows a choice of IF or baseband processing as well as flexibility for analog, digital or mixed mode implementations.
Estrada-Molina, Amilcar; Díaz-Uribe, Rufino
2011-08-01
A new method for computing the tangential and sagittal curvatures from the normals to a cornea is proposed. The normals are obtained through a Null Screen method from the coordinates of the drops shaped spots at the null screen, the coordinates on a reference approximating surface and the centroids on the image plane. This method assumes that the cornea has rotational symmetry and our derivations will be carried out in the meridional plane that contains the symmetry axis. Experimental results are shown for a calibration spherical surface, using cylindrical null screens with radial point arrays.
Lukashenko, A. T.; Veselovsky, I. S.
2015-12-01
General principles of describing secondand higher-order null points of a potential magnetic field are formulated. The potential near a second-order null of the general form can be specified by a linear combination of four basic functions, the list of which is presented. Near secondand higher-order null points, field line equations often cannot be integrated analytically; however, in some cases, it is possible to present a qualitative description of the geometry of null vicinities with consideration of the behavior of field lines near rays outgoing from null, at which the field is radial or equals zero.
Vlasov Fluid stability of a 2-D plasma with a linear magnetic field null
Energy Technology Data Exchange (ETDEWEB)
Kim, J.S.
1984-01-01
Vlasov Fluid stability of a 2-dimensional plasma near an O type magnetic null is investigated. Specifically, an elongated Z-pinch is considered, and applied to Field Reversed Configurations at Los Alamos National Laboratory by making a cylindrical approximation of the compact torus. The orbits near an elliptical O type null are found to be very complicated; the orbits are large and some are stochastic. The kinetic corrections to magnetohydrodynamics (MHD) are investigated by evaluating the expectation values of the growth rates of a Vlasov Fluid dispersion functional by using a set of trial functions based on ideal MHD. The dispersion functional involves fluid parts and orbit dependent parts. The latter involves phase integral of two time correlations. The phase integral is replaced by the time integral both for the regular and for the stochastic orbits. Two trial functions are used; one has a large displacement near the null and the other away from the null.
Entropy of a generic null surface from its associated Virasoro algebra
Chakraborty, Sumanta; Bhattacharya, Sourav; Padmanabhan, T.
2016-12-01
Null surfaces act as one-way membranes, blocking information from those observers who do not cross them (e.g., in the black hole and the Rindler spacetimes) and these observers associate an entropy (and temperature) with the null surface. The black hole entropy can be computed from the central charge of an appropriately defined, local, Virasoro algebra on the horizon. We show that one can extend these ideas to a general class of null surfaces, all of which possess a Virasoro algebra and a central charge, leading to an entropy density (i.e., per unit area) which is just (1 / 4). All the previously known results of associating entropy with horizons arise as special cases of this very general property of null surfaces demonstrated here and we believe this work represents the derivation of the entropy-area law in the most general context. The implications are discussed.
Institute of Scientific and Technical Information of China (English)
刘惟一
1989-01-01
In this paper the conflict between the null constraints and the set of functional dependencies is defined.Some rules for determining the conflicts and a method for processing the conflicts are obtained.
Proper Accelerations of Time-Like Curves near a Null Geodesic
Institute of Scientific and Technical Information of China (English)
田贵花; 赵峥
2003-01-01
It is well known that when given a null geodesic γ0(λ) with a point r in (p, q) conjugate to p along γ0(λ), there will be a variation of γ0(λ) which can give a time-like curve from p to q. Here we prove that the time-like curves coming from the above-mentioned variation (with the second derivative β2 ≠ 0) have a proper acceleration A = √AaAa which approaches infinity as the time-like curve approaches the null geodesic. Because the curve obtained from variation of the null geodesic must be everywhere time-like, we also discuss the constraint of the vector field Za on the null geodesic γ0(λ) cannot be zero.
Divertor with a third-order null of the poloidal field
Energy Technology Data Exchange (ETDEWEB)
Ryutov, D. D.; Umansky, M. V. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)
2013-09-15
A concept and preliminary feasibility analysis of a divertor with the third-order poloidal field null is presented. The third-order null is the point where not only the field itself but also its first and second spatial derivatives are zero. In this case, the separatrix near the null-point has eight branches, and the number of strike-points increases from 2 (as in the standard divertor) to six. It is shown that this magnetic configuration can be created by a proper adjustment of the currents in a set of three divertor coils. If the currents are somewhat different from the required values, the configuration becomes that of three closely spaced first-order nulls. Analytic approach, suitable for a quick orientation in the problem, is used. Potential advantages and disadvantages of this configuration are briefly discussed.
Current Singularities at Quasi-Separatrix Layers and Three-Dimensional Magnetic Nulls
Craig, I J D
2014-01-01
The open problem of how singular current structures form in line-tied, three-dimensional magnetic fields is addressed. A Lagrangian magneto-frictional relaxation method is employed to model the field evolution towards the final near-singular state. Our starting point is an exact force-free solution of the governing magnetohydrodynamic (MHD) equations which is sufficiently general to allow for topological features like magnetic nulls to be inside or outside the computational domain, depending on a simple set of parameters. Quasi-separatrix layers (QSLs) are present in these structures and together with the magnetic nulls, they significantly influence the accumulation of current. It is shown that perturbations affecting the lateral boundaries of the configuration lead not only to collapse around the magnetic null, but also to significant QSL currents. Our results show that once a magnetic null is present, the developing currents are always attracted to that specific location and show a much stronger scaling wit...
Magnetic reconnection at 3D null points: effect of magnetic field asymmetry
Al-Hachami, A K
2009-01-01
The aim of this paper is to investigate the properties of magnetic reconnection at a 3D null point, with respect to their dependence on the symmetry of the magnetic field around the null. In particular we examine the rate of flux transport across the null point with symmetric/asymmetric diffusion regions, as well as how the current sheet forms in time, and its properties. Mathematical modelling and finite difference resistive MHD simulations are used. It is found that the basic structure of the mode of magnetic reconnection considered is unaffected by varying the magnetic field symmetry, that is, the plasma flow is found cross both the spine and fan of the null. However, the peak intensity and dimensions of the current sheet are dependent on the symmetry/ asymmetry of the field lines. As a result, the reconnection rate is also found to be strongly dependent on the field asymmetry.
Octet Magnetic Moments with Null Instantons and Semibosonized Nambu-Jona-Lasinio Model
Bukina, E N
1999-01-01
It is shown that the difference between the magnetic moment results in the quark model with null instantons and semibosonized Nambu-Jona-Lasinio model lies in the description of the magnetic moment of the $ \\Lambda$-hyperon.
Vlasov fluid stability of a 2-D plasma with a linear magnetic field null
Energy Technology Data Exchange (ETDEWEB)
Kim, J.S.
1984-01-01
Vlasov fluid stability of a 2-dimensional plasma near an O type magnetic null is investigated. Specifically, an elongated Z-pinch is considered, and applied to Field Reversed Configurations at Los Alamos National Laboratory by making a cylindrical approximation of the compact torus. The orbits near an elliptical O type null are found to be very complicated; the orbits are large and some are stochastic. The kinetic corrections to magnetohydrodynamics (MHD) are investigated by evaluating the expectation values of the growth rates of a Vlasov fluid dispersion functional by using set of trial functions based on ideal MHD. The dispersion functional involves fluid parts and orbit dependent parts. The latter involves phase integral of two time correlations. The phase integral is replaced by the time integral both for the regular and for the stochastic orbits. Two trial functions are used; one has a large displacement near the null and the other away from the null.
Spronck, J.; Pereira, S.F.; Braat, J.J.M.
2007-01-01
We show the theoretical limitations of a multi-axial nulling interferometer with respect to longitudinal polarization. We furthermore analyze the filtering capabilities of a single-mode fiber in this case.
Konijn, Elly A.; van de Schoot, Rens; Winter, Sonja D.; Ferguson, Christopher J.
2015-01-01
The present paper argues that an important cause of publication bias resides in traditional frequentist statistics forcing binary decisions. An alternative approach through Bayesian statistics provides various degrees of support for any hypothesis allowing balanced decisions and proper null hypothes
Current sheets at three-dimensional magnetic nulls: Effect of compressibility
Pontin, D. I.; Bhattacharjee, A.; Galsgaard, K.
2007-05-01
The nature of current sheet formation in the vicinity of three-dimensional (3D) magnetic null points is investigated. The particular focus is upon the effect of the compressibility of the plasma on the qualitative and quantitative properties of the current sheet. An initially potential 3D null is subjected to shearing perturbations, as in a previous paper [Pontin et al., Phys. Plasmas 14, 052106 (2007)]. It is found that as the incompressible limit is approached, the collapse of the null point is suppressed and an approximately planar current sheet aligned to the fan plane is present instead. This is the case regardless of whether the spine or fan of the null is sheared. Both the peak current and peak reconnection rate are reduced. The results have a bearing on previous analytical solutions for steady-state reconnection in incompressible plasmas, implying that fan current sheet solutions are dynamically accessible, while spine current sheet solutions are not.
Null test of the cosmic curvature using $H(z)$ and supernovae data
Cai, Rong-Gen; Yang, Tao
2015-01-01
We introduce a model-independent approach to the null test of the cosmic curvature which is geometrically related to the Hubble parameter $H(z)$ and luminosity distance $d_L(z)$. Combining the independent observations of $H(z)$ and $d_L(z)$, we use the model-independent smoothing technique, Gaussian processes, to reconstruct them and determine the cosmic curvature $\\Omega_K^{(0)}$ in the null test relation. The null test is totally geometrical and without assuming any cosmological model. We show that the cosmic curvature $\\Omega_K^{(0)}=0$ is consistent with current observational data sets, falling within the $1\\sigma$ limit. To demonstrate the effect on the precision of the null test, we produce a series of simulated data of the models with different $\\Omega_K^{(0)}$. Future observations in better quality can provide a greater improvement to constrain or refute the flat universe with $\\Omega_K^{(0)}=0$.
Structures of magnetic null points in reconnection diffusion region: Cluster observations
Institute of Scientific and Technical Information of China (English)
HU YunHui; R.NAKAMURA; W.BAUMJOHANN; H.R'EME; C.M.CARR; DENG XiaoHua; ZHOU Meng; TANG RongXin; ZHAO Hui; FU Song; SU ZhiWen; WANG JingFang; YUAN ZhiGang
2008-01-01
Magnetic reconnection is a very important and fundamental plasma process in transferring energy from magnetic field into plasma. Previous theory, numerical simulations and observations mostly concen-trate on 2-dimensional (2D) model; however, magnetic reconnection is a 3-dimensional (3D) nonlinear process in nature. The properties of reconnection in 3D and its associated singular structure have not been resolved completely. Here we investigate the structures and characteristics of null points inside the reconnection diffusion region by introducing the discretized Poincaré index through Gauss integral and using magnetic field data with high resolution from the four satellites of Cluster mission. We esti-mate the velocity and trajectory of null points by calculating its position in different times, and compare and discuss the observations with different reconnection models with null points based on character-istics of electric current around null points.
Institute of Scientific and Technical Information of China (English)
Hongheng LI; Qi L(U)
2012-01-01
The authors establish the null controllability for some systems coupled by two backward stochastic heat equations.The desired controllability result is obtained by means of proving a suitable observability estimate for the dual system of the controlled system.
Magnetohydrodynamics dynamical relaxation of coronal magnetic fields. IV. 3D tilted nulls
Fuentes-Fernández, J.; Parnell, C. E.
2013-06-01
Context. There are various types of reconnection that may take place at 3D magnetic null points. Each different reconnection scenario must be associated with a particular type of current layer. Aims: A range of current layers may form because the topology of 3D nulls permits currents to form by either twisting the field about the spine of the null or by folding the fan and spine into each other. Additionally, the initial geometry of the field can lead to variations in the currents that are accumulated. Here, we study current accumulations in so-called 3D "tilted" nulls formed by a folding of the spine and fan. A non-zero component of current parallel to the fan is required such that the null's fan plane and spine are not perpendicular. Our aims are to provide valid magnetohydrostatic equilibria and to describe the current accumulations in various cases involving finite plasma pressure. Methods: To create our equilibrium current structures we use a full, non-resistive, magnetohydrodynamic (MHD) code so that no reconnection is allowed. A series of experiments are performed in which a perturbed 3D tilted null relaxes towards an equilibrium via real, viscous damping forces. Changes to the initial plasma pressure and to magnetic parameters are investigated systematically. Results: An initially tilted fan is associated with a non-zero Lorentz force that drives the fan and spine to collapse towards each other, in a similar manner to the collapse of a 2D X-point. In the final equilibrium state for an initially radial null with only the current perpendicular to the spine, the current concentrates along the tilt axis of the fan and in a layer about the null point with a sharp peak at the null itself. The continued growth of this peak indicates that the system is in an asymptotic regime involving an infinite time singularity at the null. When the initial tilt disturbance (current perpendicular to the spine) is combined with a spiral-type disturbance (current parallel to the
On the Domain of the Triangle on the Spaces of Null, Convergent, and Bounded Sequences
Directory of Open Access Journals (Sweden)
Naim L. Braha
2013-01-01
Full Text Available We introduce the spaces of -null, -convergent, and -bounded sequences. We examine some topological properties of the spaces and give some inclusion relations concerning these sequence spaces. Furthermore, we compute -, -, and -duals of these spaces. Finally, we characterize some classes of matrix transformations from the spaces of -bounded and -convergent sequences to the spaces of bounded, almost convergent, almost null, and convergent sequences and present a Steinhaus type theorem.
Bodegas, Elena; Martínez, Alfredo; Ozbun, Laurent L; Garayoa, Mercedes; Letterio, John J; Montuenga, Luis M; Jakowlew, Sonia B
2004-02-01
Transforming growth factor-beta (TGF-beta) and adrenomedullin are multifunctional regulatory proteins which are expressed in developing embryonic and adult tissues. Because of their colocalization, TGF-beta1 and adrenomedullin may be able to coordinately act to influence development and differentiation. In order to learn more about the biology of adrenomedullin in the absence of the effects of TGF-beta1 in vivo, we examined adrenomedullin in the TGF-beta1 null mouse. A generally lower amount of adrenomedullin was detected by immunohistochemical staining analysis in multiple tissues from embryonic TGF-beta1 null mice compared to wildtype animals, including the heart, lung, brain, liver, and kidney, among others. In contrast, immunohistochemical staining for adrenomedullin was more intense in tissues of the postnatal TGF-beta1 null mouse compared to the wildtype mouse. These observations were confirmed by quantitative real time RT-PCR for adrenomedullin in both embryos and postnatal animals, as well as in cultured mouse embryo fibroblasts from TGF-beta1 null and wildtype mice. In addition, when cultured mouse embryo fibroblasts were treated with a neutralizing monoclonal antibody against TGF-beta1, the levels of adrenomedullin expression were statistically reduced compared to untreated cells. Our data show that expression of adrenomedullin is reduced in tissues of the developing embryonic TGF-beta1 null mouse compared to the wildtype mouse, but increases during postnatal development in TGF-beta1 null mice. The elevated expression of adrenomedullin which occurs postnatally in the TGF-beta1 null mouse may be a cause or a consequence of the multifocal wasting syndrome which is characteristic of postnatal TGF-beta1 null mice.
Cardiac Characterization of sgca-Null Mice Using High Resolution Echocardiography.
Fayssoil, Abdallah; Renault, Gilles; Guerchet, Nicolas; Marchiol-Fournigault, Carmen; Fougerousse, Françoise; Richard, Isabelle
2013-01-01
Limb-girdle muscular dystrophy 2D (LGMD2D) is an inherited myogenic disorder belonging to the group of muscular dystrophies. Sgca-null mouse is a knock-out model of LGMD2D. Little is known about cardiac phenotype characterization in this model at different ages. We conducted a prospective study to characterize cardiac sgca-null mice phenotype using high resolution Doppler echocardiography at different ages. Conventional echocardiography was performed on anesthetised mice using a Vevo 770 (Visualsonics) with 30 MHz cardiac probe. Wild Type (WT) and sgca-null mice were scanned at 13, 15 and 17 months. From M-mode, we measured interventricular septal (IVS) wall thickness, posterior wall (PW) thickness, and end-left ventricular diameter in systolic and diastolic. From the above parameters, we calculated left ventricular (LV) shortening fraction (SF), LV ejection fraction (EF) and LV mass. At age 13 months, PW diastolic thickness was increased in sgca-null mice (0.89±0.14 mm vs 0.73±0.2 mm; P=0.020) and LV mass was higher in sgca-null mice (LV mass 205.2 mg vs 143 mg; P=0.001). We found also dilation of the LV (LVEDD: 4.84 mm vs 4.29 mm; P=0.019) in sgca-null mice. At age 15 months, dilation of the LV (LVEDD: 4.86 mm vs 4 mm; P=0.05) with an increase of the LV mass (165.7 mg vs 127.12; P=0.03) are found in sgca-null mice. At age 17 months, we found a decrease of the PW thickening (17% vs 30%; P=0.036). This work provides echocardiographic insights for the assessment of pharmaceutical therapies in sgca-null mice.
A NOVEL NULLING ALGORITHM IN THE SUBARRAY OF A LARGE ARRAY
Institute of Scientific and Technical Information of China (English)
Liu Hui; Zhou Yinqing; Xu Huaping
2006-01-01
Forming nulls in the radiation pattern of an antenna is to suppress the interference from certain directions or to cancel desired signals. This letter presents an effective method based on the Gram-Schmidt orthogonal algorithm for forming nulls in the subarray of a large array. The theory and realizing methods are discussed, and the corresponding formulas are derived in details. The simulation results are given to demonstrate the feasibility, the availability and the quick-convergence of the presented method.
Some magnetic null lines of astrophysical interest. II. [in magnetic Ap stars
Adelman, S. J.
1974-01-01
A list of magnetic null lines from selected spectroscopic analyses is presented for possible use in detailed studies of magnetic Ap stars. The presented data represent an extension of the magnetic null lines whose usefulness Shore and Adelman (1974) have recently demonstrated for the study of the overall physical conditions prevailing in the atmospheres of peculiar A stars and for testing the consequences of the mechanism of selective elemental diffusion.
Kahel korral järjest null häält / Maarius Suviste
Suviste, Maarius, 1966-
2005-01-01
Kohalike omavalitsuste volikogude valimistel ei saanud ühtegi häält 233 kandidaati. Oma kandideerimise põhjusi selgitavad juba teist korda valimistel null häält saanud Viljandi tisler Kaljo Jürman, Põlvamaa mahetalunik Liisi Kutkina ja Ida-Virumaa pensionär Vaike Zaitseva. Lisatud statistilised andmed null häält saanud kandidaatide kohta maakondade ja erakondade kaupa
Gender- and region-specific alterations in bone metabolism in Scarb1-null female mice.
Martineau, Corine; Martin-Falstrault, Louise; Brissette, Louise; Moreau, Robert
2014-08-01
A positive correlation between plasma levels of HDL and bone mass has been reported by epidemiological studies. As scavenger receptor class B, type I (SR-BI), the gene product of Scarb1, is known to regulate HDL metabolism, we recently characterized bone metabolism in Scarb1-null mice. These mice display high femoral bone mass associated with enhanced bone formation. As gender differences have been reported in HDL metabolism and SR-BI function, we investigated gender-specific bone alterations in Scarb1-null mice by microtomography and histology. We found 16% greater relative bone volume and 39% higher bone formation rate in the vertebrae from 2-month-old Scarb1-null females. No such alteration was seen in males, indicating gender- and region-specific differences in skeletal phenotype. Total and HDL-associated cholesterol levels, as well as ACTH plasma levels, were increased in both Scarb1-null genders, the latter being concurrent to impaired corticosterone response to fasting. Plasma levels of estradiol did not differ between null and WT females, suggesting that the estrogen metabolism alteration is not relevant to the higher vertebral bone mass in female Scarb1-null mice. Constitutively, high plasma levels of leptin along with 2.5-fold increase in its expression in white adipose tissue were measured in female Scarb1-null mice only. In vitro exposure of bone marrow stromal cells to ACTH and leptin promoted osteoblast differentiation as evidenced by increased gene expression of osterix and collagen type I alpha. Our results suggest that hyperleptinemia may account for the gender-specific high bone mass seen in the vertebrae of female Scarb1-null mice.
Glutathione S-transferase M1 null genotype related to poor prognosis of colorectal cancer.
Yan, Shushan; Wang, Zengfang; Wang, Zengyan; Duan, Quanhong; Wang, Xiaochen; Li, Jun; Sun, Beicheng
2016-08-01
Published studies showed controversial findings about the relationship between glutathione S-transferase M1 (GSTM1) null genotype and clinical outcomes of patients with colorectal cancer. We performed a meta-analysis to quantitatively assess the association between GSTM1 null genotype and prognosis of patients with colorectal cancer. We systematically searched Pubmed, Embase, and Web of Science to identify prospective or retrospective cohort studies assessing the association of GSTM1 null genotype with overall survival (OS) or disease-free survival (DFS) in colorectal cancer. The hazard ratios (HRs) and 95 % confidence intervals (95 % CIs) were used to assess the association of GSTM1 null genotype with OS or DFS. Finally, 15 studies from 14 publications with 4326 colorectal cancer patients were included into the meta-analysis. There was no heterogeneity in the meta-analysis relating OS (I (2) = 0 %) and DFS (I (2) = 0 %). Overall, GSTM1 null genotype was significantly associated with poor OS in patients with colorectal cancer (HR = 1.18, 95 % CI 1.07-1.30, P = 0.001). In addition, GSTM1 null genotype was also significantly associated with poor DFS in patients with colorectal cancer (HR = 1.15, 95 % CI 1.03-1.28, P = 0.015). No obvious risk of publication bias was observed. GSTM1 null genotype is significantly associated with poor OS and DFS in patients with colorectal cancer, which suggests that GSTM1 null genotype confers poor effect on the prognosis of colorectal cancer.
PSF and field of view characteristics of imaging and nulling interferometers
Hénault, François
2010-01-01
In this communication are presented some complements to a recent paper entitled "Simple Fourier optics formalism for high angular resolution systems and nulling interferometry", dealing with imaging and nulling capacities of a few types of multi-aperture optical systems. Herein the characteristics of such systems in terms of Point Spread Function (PSF) and Field of View (FoV) are derived from simple analytical expressions that are further evaluated numerically for various configurations. We c...
Hamiltonian analysis of the double null 2+2 decomposition of Ashtekar variables
d'Inverno, R A; Vickers, J A
2006-01-01
We derive a canonical analysis of a double null 2+2 Hamiltonian description of General Relativity in terms of complex self-dual 2-forms and the associated SO(3) connection variables. The algebra of first class constraints is obtained and forms a Lie algebra that consists of two constraints that generate diffeomorphisms in the two surface, a constraint that generates diffeomorphisms along the null generators and a constraint that generates self-dual spin and boost transformations.
Computer model simulation of null-flux magnetic suspension and guidance
Energy Technology Data Exchange (ETDEWEB)
He, Jianliang; Rote, D.M.
1992-06-01
This paper discusses the magnetic force computations in a null-flux suspension system using dynamic circuit theory. A computer simulation model that can be used to compute magnetic forces and predict the system performance is developed on the basis of dynamic circuit theory. Numerical examples are presented to demonstrate the application of the model. The performance of the null-flux suspension system is simulated and discussed. 8 refs.
Computer model simulation of null-flux magnetic suspension and guidance
Energy Technology Data Exchange (ETDEWEB)
He, Jianliang; Rote, D.M.
1992-01-01
This paper discusses the magnetic force computations in a null-flux suspension system using dynamic circuit theory. A computer simulation model that can be used to compute magnetic forces and predict the system performance is developed on the basis of dynamic circuit theory. Numerical examples are presented to demonstrate the application of the model. The performance of the null-flux suspension system is simulated and discussed. 8 refs.
Current accumulation at an asymmetric 3D null point caused by generic shearing motions
Galsgaard, K.; Pontin, D. I.
2011-10-01
Context. Here we investigate the dynamical evolution of the reconnection process at an initially linear 3D null point that is stressed by a localised shear motion across the spine axis. The difference to previous investigations is that the fan plane is not rotationally symmetric and this allows for different behaviours depending on the alignment of the fan plane relative to the imposed driver direction. Aims: The aim is to show how the current accumulation and the associated reconnection process at the non-axisymmetric null depends on the relative orientation between the driver imposed stress across the spine axis of the null and the main eigenvector direction in the fan plane. Methods: The time evolution of the 3D null point is investigated solving the 3D non-ideal MHD equations numerically in a Cartesian box. The magnetic field is frozen to the boundaries and the boundary velocity is only non-zero where the imposed driving for stressing the system is applied. Results: The current accumulation is found to be along the direction of the fan eigenvector associated with the smallest eigenvalue until the direction of the driver is almost parallel to this eigenvector. When the driving velocity is parallel to the weak eigenvector and has an impulsive temporal profile the null only has a weak collapse forming only a weak current layer. However, when the null point is stressed continuously boundary effects dominates the current accumulation. Conclusions: There is a clear relation between the orientation of the current concentration and the direction of the fan eigenvector corresponding to the small eigenvalue. This shows that the structure of the magnetic field is the most important in determining where current is going to accumulate when a single 3D null point is perturbed by a simple shear motion across the spine axis. As the angle between the driving direction and the strong eigenvector direction increases, the current that accumulates at the null becomes progressively
Increased susceptibility of Nrf2-null mice to 1-bromopropane-induced hepatotoxicity.
Liu, Fang; Ichihara, Sahoko; Valentine, William M; Itoh, Ken; Yamamoto, Masayuki; Sheik Mohideen, Sahabudeen; Kitoh, Junzoh; Ichihara, Gaku
2010-06-01
1-Bromopropane (1-BP) was introduced as an alternative to ozone-depleting solvents. However, it was found to exhibit neurotoxicity, reproductive toxicity, and hepatotoxicity in rodents and neurotoxicity in human. However, the mechanisms underlying the toxicities of 1-BP remain elusive. The present study investigated the role of oxidative stress in 1-BP-induced hepatotoxicity using nuclear factor erythroid 2-related factor 2 (Nrf2)-null mice. Groups of 24 male Nrf2-null mice and 24 male wild-type (WT) C57BL/6J mice were each divided into three groups of eight and exposed to 1-BP at 0, 100, or 300 ppm for 8 h/day for 28 days by inhalation. Liver histopathology showed significantly larger area of necrosis in Nrf2-null mice relative to WT mice at the same exposure level. Nrf2-null mice also had greater malondialdehyde (MDA) levels, higher ratio of oxidized glutathione/reduced form of glutathione, and lower total glutathione content. The constitutive level and the increase in ratio per exposure level of glutathione S-transferase (GST) activity were lower in the liver of Nrf2-null mice than WT mice. Exposure to 1-BP at 300 ppm increased the messenger RNA levels of heme oxygenase-1 (HO-1), glutamate-cysteine ligase modifier subunit (GcLm), glutamate-cysteine synthetase (GcLc), glutathione reductase, and NAD(P)H: quinone oxidoreductase 1 (NQO1) in WT mice but not in Nrf2-null mice except for GST Yc2. Nrf2-null mice were more susceptible to 1-BP-induced hepatotoxicity. That oxidative stress plays a role in 1-BP hepatotoxicity is deduced from the low expression levels and activities of antioxidant enzymes and high MDA levels in Nrf2-null mice.
Power Analysis and Experimental Study of the Fiber Null Coupler with an Acousto-optic Device
Institute of Scientific and Technical Information of China (English)
WU Lei; ZHENG Yuan; QI Jiang; PU Hongtu; CHEN Shuqiang
2002-01-01
A single-mode fiber acousto-optic (AO) switch based on a null coupler at wavelength of 1.55 μm is reported.According to the coupled mode theory,power distribution of the null coupler with the acoustic-wave is formulated for general case.Excess loss of 0.1 dB and the schematic graph of throughput and coupled power are obtained experimentally.
pyNSMC: A Python Module for Null-Space Monte Carlo Uncertainty Analysis
White, J.; Brakefield, L. K.
2015-12-01
The null-space monte carlo technique is a non-linear uncertainty analyses technique that is well-suited to high-dimensional inverse problems. While the technique is powerful, the existing workflow for completing null-space monte carlo is cumbersome, requiring the use of multiple commandline utilities, several sets of intermediate files and even a text editor. pyNSMC is an open-source python module that automates the workflow of null-space monte carlo uncertainty analyses. The module is fully compatible with the PEST and PEST++ software suites and leverages existing functionality of pyEMU, a python framework for linear-based uncertainty analyses. pyNSMC greatly simplifies the existing workflow for null-space monte carlo by taking advantage of object oriented design facilities in python. The core of pyNSMC is the ensemble class, which draws and stores realized random vectors and also provides functionality for exporting and visualizing results. By relieving users of the tedium associated with file handling and command line utility execution, pyNSMC instead focuses the user on the important steps and assumptions of null-space monte carlo analysis. Furthermore, pyNSMC facilitates learning through flow charts and results visualization, which are available at many points in the algorithm. The ease-of-use of the pyNSMC workflow is compared to the existing workflow for null-space monte carlo for a synthetic groundwater model with hundreds of estimable parameters.
Observation of Magnetic reconnection at a 3D null point associated with a solar eruption
Sun, J Q; Yang, K; Cheng, X; Ding, M D
2016-01-01
Magnetic null has long been recognized as a special structure serving as a preferential site for magnetic reconnection (MR). However, the direct observational study of MR at null-points is largely lacking. Here, we show the observations of MR around a magnetic null associated with an eruption that resulted in an M1.7 flare and a coronal mass ejection. The GOES X- ray profile of the flare exhibited two peaks at 02:23 UT and 02:40 UT on 2012 November 8, respectively. Based on the imaging observations, we find that the first and also primary X- ray peak was originated from MR in the current sheet underneath the erupting magnetic flux rope (MFR). On the other hand, the second and also weaker X-ray peak was caused by MR around a null-point located above the pre-eruption MFR. The interaction of the null-point and the erupting MFR can be described as a two-step process. During the first step, the erupting and fast expanding MFR passed through the null-point, resulting in a significant displacement of the magnetic fi...
Dynamical Relaxation of Coronal Magnetic Fields. III. 3D Spiral Nulls
Fuentes-Fernandez, Jorge
2012-01-01
Context: The majority of studies on stressed 3D magnetic null points consider magnetic reconnection driven by an external perturbation, but the formation of a genuine current sheet equilibrium remains poorly understood. This problem has been considered more extensively in two-dimensions, but lacks a generalization into 3D fields. Aims: 3D magnetic nulls are more complex than 2D nulls and the field can take a greater range of magnetic geometries local to the null. Here, we focus on one type and consider the dynamical non-resistive relaxation of 3D spiral nulls with initial spine-aligned current. We aim to provide a valid magnetohydrostatic equilibrium, and describe the electric current accumulations in various cases, involving a finite plasma pressure. Methods: A full MHD code is used, with the resistivity set to zero so that reconnection is not allowed, to run a series of experiments in which a perturbed spiral 3D null point is allowed to relax towards an equilibrium, via real, viscous damping forces. Changes...
Review article: MHD wave propagation near coronal null points of magnetic fields
McLaughlin, J A; De Moortel, I; 10.1007/s11214-010-9654-y
2010-01-01
We present a comprehensive review of MHD wave behaviour in the neighbourhood of coronal null points: locations where the magnetic field, and hence the local Alfven speed, is zero. The behaviour of all three MHD wave modes, i.e. the Alfven wave and the fast and slow magnetoacoustic waves, has been investigated in the neighbourhood of 2D, 2.5D and (to a certain extent) 3D magnetic null points, for a variety of assumptions, configurations and geometries. In general, it is found that the fast magnetoacoustic wave behaviour is dictated by the Alfven-speed profile. In a $\\beta=0$ plasma, the fast wave is focused towards the null point by a refraction effect and all the wave energy, and thus current density, accumulates close to the null point. Thus, null points will be locations for preferential heating by fast waves. Independently, the Alfven wave is found to propagate along magnetic fieldlines and is confined to the fieldlines it is generated on. As the wave approaches the null point, it spreads out due to the di...
Null Points in Three-Dimensional Kinetic Simulations of Magnetic Reconnection
Deca, J.; Olshevsky, V.; Divin, A. V.; Innocenti, M. E.; Cazzola, E.; Peng, B.; Markidis, S.; Ormvråk, M.; Lapenta, G.
2015-12-01
Kinetic particle-in-cell simulations are the primary tool for studying magnetic reconnection in space plasmas. Magnetic null points are believed to be the preferred locations in space where magnetic reconnection is luckily to happen, and are in the focus of interest of space missions such as Cluster and MMS. Simulations of magnetic reconnection in various configurations performed with the implicit particle-in-cell code iPic3D revealed that nulls are ubiquitious in these models. We apply the Poincare index technique to locate and identify the topological characteristics of the magnetic null points in different three-dimensional simulations. We investigate the relevance of magnetic nulls to energy dissipation, turbulence and plasma instabilities. In particular, we found out that magnetic nulls of spiral type associated with magnetic islands and flux ropes play more important role in the energy release than the radial nulls. This finding is in accordance with some recent MHD simulations and in situ observations of Cluster spacecraft.
Proton acceleration in three-dimensional non-null magnetic reconnection
Akbari, Z.; Hosseinpour, M.; Mohammadi, M. A.
2016-10-01
In a three-dimensional non-null magnetic reconnection, the process of magnetic reconnection takes place in the absence of a null point where the magnetic field vanishes. By randomly injecting a population of 10 000 protons, the trajectory and energy distribution of accelerated protons are investigated in the presence of magnetic and electric fields of a particular model of non-null magnetic reconnection with the typical parameters for the solar corona. The results show that protons are accelerated along the magnetic field lines away from the non-null point only at azimuthal angles where the magnitude of the electric field is strongest and therefore particles obtain kinetic energies of the order of thousands of MeV and even higher. Moreover, the energy distribution of the population depends strongly on the amplitude of the electric and magnetic fields. Comparison shows that a non-null magnetic reconnection is more efficient in accelerating protons to very high GeV energies than a null-point reconnection.
Why are flare ribbons associated with the spines of magnetic null points generically elongated?
Pontin, D I; Demoulin, P
2016-01-01
Coronal magnetic null points exist in abundance as demonstrated by extrapolations of the coronal field, and have been inferred to be important for a broad range of energetic events. These null points and their associated separatrix and spine field lines represent discontinuities of the field line mapping, making them preferential locations for reconnection. This field line mapping also exhibits strong gradients adjacent to the separatrix (fan) and spine field lines, that can be analysed using the `squashing factor', $Q$. In this paper we make a detailed analysis of the distribution of $Q$ in the presence of magnetic nulls. While $Q$ is formally infinite on both the spine and fan of the null, the decay of $Q$ away from these structures is shown in general to depend strongly on the null-point structure. For the generic case of a non-radially-symmetric null, $Q$ decays most slowly away from the spine/fan in the direction in which $|{\\bf B}|$ increases most slowly. In particular, this demonstrates that the extend...
Electron acceleration by whistler-mode waves around the magnetic null during 3D reconnection
Energy Technology Data Exchange (ETDEWEB)
Xiao Fuliang [School of Physics and Electronic Sciences, Changsha University of Science and Technology, Changsha, 410004 (China); Zong Qiugang; Pu Zuyin; He Jiansen; Wang Yongfu [School of Earth and Space Sciences, Peking University, Beijing 100871 (China); Su Zhenpeng; Zheng Huinan [CAS Key Laboratory for Basic Plasma Physics, School of Earth and Space Sciences, University of Science and Technology of China, Hefei (China); Cao Jinbin, E-mail: qgzong@pku.edu.c [State Key Laboratory of Space Weather, PO Box 8701, Beijing 100080 (China)
2010-05-15
The magnetic field configuration around a magnetic null pair and its associated electron behavior during 3D magnetic reconnection have recently been reported from in situ observations. Electrons are suggested to be temporarily trapped in the central reconnection region as indicated by an electron density peak observed near the magnetic null (He J-S et al 2008 Geophys. Res. Lett. 35 L14104). It is highly interesting that energetic electron beams of a few kiloelectronvolts are found to be related to the magnetic null structure. However, the acceleration mechanism is still not fully understood. In this paper, we show that strong whistler-mode electromagnetic waves are indeed found around the magnetic null. Further we propose a new electron acceleration scenario of trapped electrons near the magnetic null points driven by the whistler-mode waves, which is confirmed by numerical results. It is demonstrated that whistler waves can enhance the phase space density (PSD) of electrons for energies of approx2 keV by a factor of 100 at lower pitch angles very rapidly, typically within 2 s. The accelerated electrons may escape from the loss cone of the magnetic cusp mirrors around the magnetic null, leading to the observed energetic beams. (brief communication)
Magnetoacoustic Waves in a Stratified Atmosphere with a Magnetic Null Point
Tarr, Lucas A; Leake, James
2016-01-01
We perform nonlinear MHD simulations to study the propagation of magnetoacoustic waves from the photosphere to the low corona. We focus on a 2D system with a gravitationally stratified atmosphere and three photospheric concentrations of magnetic flux that give rise to a magnetic null point with a magnetic dome topology. We find that a single wavepacket introduced at the lower boundary splits into multiple secondary wavepackets. A portion of the packet refracts towards the null due to the varying Alfv\\'en speed. Waves incident on the equipartition contour surrounding the null, where the sound and Alfv\\'en speeds coincide, partially transmit, reflect, and mode convert between branches of the local dispersion relation. Approximately $15.5\\%$ of the wavepacket's initial energy ($E_{input}$) converges on the null, mostly as a fast magnetoacoustic wave. Conversion is very efficient: $70\\%$ of the energy incident on the null is converted to slow modes propagating away from the null, $7\\%$ leaves as a fast wave, and ...
Lang, Julie; Weiss, Nicholas; Freed, Brian M; Torres, Raul M; Pelanda, Roberta
2011-07-01
Hematopoietic humanized mice generated via transplantation of human hematopoietic stem cells (hHSCs) into immunodeficient mice are a valuable tool for studying development and function of the human immune system. This study was performed to generate a protocol that improves development and quality of humanized mice in the BALB/c-Rag2(null)Il2rγ(null) strain, testing route of injection, in vitro culture and freezing of hHSCs, types of cytokines in the culture, and co-injection of lineage-depleted CD34(-) cells. Specific hHSC culturing conditions and the addition of support cells were found to increase the frequency, and human hematopoietic chimerism, of humanized mice. The optimized protocol resulted in BALB/c-Rag2(null)Il2rγ(null) humanized mice displaying more consistent human hematopoietic and lymphoid engraftment. Thus, hematopoietic humanized mice generated on a BALB/c immunodeficient background represent a useful model to study the human immune system.
Abnormal Activation of BMP Signaling Causes Myopathy in Fbn2 Null Mice.
Directory of Open Access Journals (Sweden)
Gerhard Sengle
2015-06-01
Full Text Available Fibrillins are large extracellular macromolecules that polymerize to form the backbone structure of connective tissue microfibrils. Mutations in the gene for fibrillin-1 cause the Marfan syndrome, while mutations in the gene for fibrillin-2 cause Congenital Contractural Arachnodactyly. Both are autosomal dominant disorders, and both disorders affect musculoskeletal tissues. Here we show that Fbn2 null mice (on a 129/Sv background are born with reduced muscle mass, abnormal muscle histology, and signs of activated BMP signaling in skeletal muscle. A delay in Myosin Heavy Chain 8, a perinatal myosin, was found in Fbn2 null forelimb muscle tissue, consistent with the notion that muscle defects underlie forelimb contractures in these mice. In addition, white fat accumulated in the forelimbs during the early postnatal period. Adult Fbn2 null mice are already known to demonstrate persistent muscle weakness. Here we measured elevated creatine kinase levels in adult Fbn2 null mice, indicating ongoing cycles of muscle injury. On a C57Bl/6 background, Fbn2 null mice showed severe defects in musculature, leading to neonatal death from respiratory failure. These new findings demonstrate that loss of fibrillin-2 results in phenotypes similar to those found in congenital muscular dystrophies and that FBN2 should be considered as a candidate gene for recessive congenital muscular dystrophy. Both in vivo and in vitro evidence associated muscle abnormalities and accumulation of white fat in Fbn2 null mice with abnormally activated BMP signaling. Genetic rescue of reduced muscle mass and accumulation of white fat in Fbn2 null mice was accomplished by deleting a single allele of Bmp7. In contrast to other reports that activated BMP signaling leads to muscle hypertrophy, our findings demonstrate the exquisite sensitivity of BMP signaling to the fibrillin-2 extracellular environment during early postnatal muscle development. New evidence presented here suggests that
Attainment of brown adipocyte features in white adipocytes of hormone-sensitive lipase null mice.
Directory of Open Access Journals (Sweden)
Kristoffer Ström
Full Text Available BACKGROUND: Hormone-sensitive lipase (HSL is expressed predominantly in adipose tissue, where it plays an important role in catecholamine-stimulated hydrolysis of stored tri- and diglycerides, thus mobilizing fatty acids. HSL exhibits broad substrate specificity and besides acylglycerides it hydrolyzes cholesteryl esters, retinyl esters and lipoidal esters. Despite its role in fatty acid mobilization, HSL null mice have been shown to be resistant to diet-induced obesity. METHODOLOGY/PRINCIPAL FINDINGS: Following a high-fat diet (HFD regimen, energy expenditure, measured using indirect calorimetry, was increased in HSL null mice. White adipose tissue of HSL null mice was characterized by reduced mass and reduced protein expression of PPARgamma, a key transcription factor in adipogenesis, and stearoyl-CoA desaturase 1, the expression of which is known to be positively correlated to the differentiation state of the adipocyte. The protein expression of uncoupling protein-1 (UCP-1, the highly specific marker of brown adipocytes, was increased 7-fold in white adipose tissue of HSL null mice compared to wildtype littermates. Transmission electron microscopy revealed an increase in the size of mitochondria of white adipocytes of HSL null mice. The mRNA expression of pRb and RIP140 was decreased in isolated white adipocytes, while the expression of UCP-1 and CPT1 was increased in HSL null mice compared to wildtype littermates. Basal oxygen consumption was increased almost 3-fold in white adipose tissue of HSL null mice and was accompanied by increased uncoupling activity. CONCLUSIONS: These data suggest that HSL is involved in the determination of white versus brown adipocytes during adipocyte differentiation The exact mechanism(s underlying this novel role of HSL remains to be elucidated, but it seems clear that HSL is required to sustain normal expression levels of pRb and RIP140, which both promote differentiation into the white, rather than the brown
Effects of Local Heart Irradiation in a Glutathione S-Transferase Alpha 4-Null Mouse Model.
Boerma, Marjan; Singh, Preeti; Sridharan, Vijayalakshmi; Tripathi, Preeti; Sharma, Sunil; Singh, Sharda P
2015-06-01
Glutathione S-transferase alpha 4 (GSTA4-4) is one of the enzymes responsible for the removal of 4-hydroxynonenal (4-HNE), an electrophilic product of lipid peroxidation in cellular membranes during oxidative stress. 4-HNE is a direct activator of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), a transcription factor with many target genes encoding antioxidant and anti-electrophile enzymes. We have previously shown that Gsta4-null mice on a 129/Sv background exhibited increased activity of Nrf2 in the heart. Here we examined the sensitivity of this Gsta4-null mouse model towards cardiac function and structure loss due to local heart irradiation. Male Gsta4-null and wild-type mice were exposed to a single X-ray dose of 18 Gy to the heart. Six months after irradiation, immunohistochemical staining for respiratory complexes 2 and 5 indicated that radiation exposure had caused most pronounced alterations in mitochondrial morphology in Gsta4-null mice. On the other hand, wild-type mice showed a decline in cardiac function and an increase in plasma levels of troponin-I, while no such changes were observed in Gsta4-null mice. Radiation-induced Nrf2-target gene expression only in Gsta4-null mice. In conclusion, although loss of GSTA4-4 led to enhanced susceptibility of cardiac mitochondria to radiation-induced loss of morphology, cardiac function was preserved in Gsta4-null mice. We propose that this protection against cardiac function loss may occur, at least in part, by upregulation of the Nrf2 pathway.
The atherogenic Scarb1 null mouse model shows a high bone mass phenotype.
Martineau, Corine; Martin-Falstrault, Louise; Brissette, Louise; Moreau, Robert
2014-01-01
Scavenger receptor class B, type I (SR-BI), the Scarb1 gene product, is a receptor associated with cholesteryl ester uptake from high-density lipoproteins (HDL), which drives cholesterol movement from peripheral tissues toward the liver for excretion, and, consequently, Scarb1 null mice are prone to atherosclerosis. Because studies have linked atherosclerosis incidence with osteoporosis, we characterized the bone metabolism in these mice. Bone morphometry was assessed through microcomputed tomography and histology. Marrow stromal cells (MSCs) were used to characterize influence of endogenous SR-BI in cell functions. Total and HDL-associated cholesterol in null mice were increased by 32-60%, correlating with its role in lipoprotein metabolism. Distal metaphyses from 2- and 4-mo-old null mice showed correspondingly 46 and 37% higher bone volume fraction associated with a higher number of trabeculae. Histomorphometric analyses in 2-mo-old null male mice revealed 1.42-fold greater osteoblast surface, 1.37-fold higher percent mineralizing surface, and 1.69-fold enhanced bone formation rate. In vitro assays for MSCs from null mice revealed 37% higher proliferation rate, 48% more alkaline phosphatase activity, 70% greater mineralization potential and a 2-fold osterix (Sp7) expression, yet a 0.5-fold decrease in caveolin-1 (Cav1) expression. Selective uptake levels of HDL-associated cholesteryl oleate and estradiol were similar between MSC from wild-type and Scarb1 null mice, suggesting that its contribution to this process is not its main role in these cells. However, Scarb1 knockout stunted the HDL-dependent regulation of Cav1 genic expression. Scarb1 null mice are not prone to osteoporosis but show higher bone mass associated with enhanced bone formation.
Abnormal Activation of BMP Signaling Causes Myopathy in Fbn2 Null Mice.
Sengle, Gerhard; Carlberg, Valerie; Tufa, Sara F; Charbonneau, Noe L; Smaldone, Silvia; Carlson, Eric J; Ramirez, Francesco; Keene, Douglas R; Sakai, Lynn Y
2015-06-01
Fibrillins are large extracellular macromolecules that polymerize to form the backbone structure of connective tissue microfibrils. Mutations in the gene for fibrillin-1 cause the Marfan syndrome, while mutations in the gene for fibrillin-2 cause Congenital Contractural Arachnodactyly. Both are autosomal dominant disorders, and both disorders affect musculoskeletal tissues. Here we show that Fbn2 null mice (on a 129/Sv background) are born with reduced muscle mass, abnormal muscle histology, and signs of activated BMP signaling in skeletal muscle. A delay in Myosin Heavy Chain 8, a perinatal myosin, was found in Fbn2 null forelimb muscle tissue, consistent with the notion that muscle defects underlie forelimb contractures in these mice. In addition, white fat accumulated in the forelimbs during the early postnatal period. Adult Fbn2 null mice are already known to demonstrate persistent muscle weakness. Here we measured elevated creatine kinase levels in adult Fbn2 null mice, indicating ongoing cycles of muscle injury. On a C57Bl/6 background, Fbn2 null mice showed severe defects in musculature, leading to neonatal death from respiratory failure. These new findings demonstrate that loss of fibrillin-2 results in phenotypes similar to those found in congenital muscular dystrophies and that FBN2 should be considered as a candidate gene for recessive congenital muscular dystrophy. Both in vivo and in vitro evidence associated muscle abnormalities and accumulation of white fat in Fbn2 null mice with abnormally activated BMP signaling. Genetic rescue of reduced muscle mass and accumulation of white fat in Fbn2 null mice was accomplished by deleting a single allele of Bmp7. In contrast to other reports that activated BMP signaling leads to muscle hypertrophy, our findings demonstrate the exquisite sensitivity of BMP signaling to the fibrillin-2 extracellular environment during early postnatal muscle development. New evidence presented here suggests that fibrillin-2 can
Influence of choice of null network on small-world parameters of structural correlation networks.
Hosseini, S M Hadi; Kesler, Shelli R
2013-01-01
In recent years, coordinated variations in brain morphology (e.g., volume, thickness) have been employed as a measure of structural association between brain regions to infer large-scale structural correlation networks. Recent evidence suggests that brain networks constructed in this manner are inherently more clustered than random networks of the same size and degree. Thus, null networks constructed by randomizing topology are not a good choice for benchmarking small-world parameters of these networks. In the present report, we investigated the influence of choice of null networks on small-world parameters of gray matter correlation networks in healthy individuals and survivors of acute lymphoblastic leukemia. Three types of null networks were studied: 1) networks constructed by topology randomization (TOP), 2) networks matched to the distributional properties of the observed covariance matrix (HQS), and 3) networks generated from correlation of randomized input data (COR). The results revealed that the choice of null network not only influences the estimated small-world parameters, it also influences the results of between-group differences in small-world parameters. In addition, at higher network densities, the choice of null network influences the direction of group differences in network measures. Our data suggest that the choice of null network is quite crucial for interpretation of group differences in small-world parameters of structural correlation networks. We argue that none of the available null models is perfect for estimation of small-world parameters for correlation networks and the relative strengths and weaknesses of the selected model should be carefully considered with respect to obtained network measures.
Nonlinear Alfvén wave dynamics at a 2D magnetic null point: ponderomotive force
Thurgood, J. O.; McLaughlin, J. A.
2013-07-01
Context. In the linear, β = 0 MHD regime, the transient properties of magnetohydrodynamic (MHD) waves in the vicinity of 2D null points are well known. The waves are decoupled and accumulate at predictable parts of the magnetic topology: fast waves accumulate at the null point; whereas Alfvén waves cannot cross the separatricies. However, in nonlinear MHD mode conversion can occur at regions of inhomogeneous Alfvén speed, suggesting that the decoupled nature of waves may not extend to the nonlinear regime. Aims: We investigate the behaviour of low-amplitude Alfvén waves about a 2D magnetic null point in nonlinear, β = 0 MHD. Methods: We numerically simulate the introduction of low-amplitude Alfvén waves into the vicinity of a magnetic null point using the nonlinear LARE2D code. Results: Unlike in the linear regime, we find that the Alfvén wave sustains cospatial daughter disturbances, manifest in the transverse and longitudinal fluid velocity, owing to the action of nonlinear magnetic pressure gradients (viz. the ponderomotive force). These disturbances are dependent on the Alfvén wave and do not interact with the medium to excite magnetoacoustic waves, although the transverse daughter becomes focused at the null point. Additionally, an independently propagating fast magnetoacoustic wave is generated during the early stages, which transports some of the initial Alfvén wave energy towards the null point. Subsequently, despite undergoing dispersion and phase-mixing due to gradients in the Alfvén-speed profile (∇cA ≠ 0) there is no further nonlinear generation of fast waves. Conclusions: We find that Alfvén waves at 2D cold null points behave largely as in the linear regime, however they sustain transverse and longitudinal disturbances - effects absent in the linear regime - due to nonlinear magnetic pressure gradients.
Particle Transport along Magnetic Null Lines as Sputter or Antihydrogen Source
Lane, R. A.; Ordonez, C. A.
Particle transport along null magnetic lines is investigated using classical trajectory Monte Carlo simulations and described as a traveling wave and through diffusion equations. A magnetic null line is defined as a one-dimensional region where the magnetic field magnitude is zero. This region may take any shape in three-dimensional space. The field used in the simulations is generated by two infinite wires of negligible thickness carrying identical current and separated by a small distance. Thus, an infinite magnetic null line exists directly between the wires. The particle trajectories are simulated by solving the equations of motion for each simulated particle of a mono- energetic set. Each is considered individually, with all trajectories starting from the same position along the null line. Each trajectory is simulated until it reaches a specified distance from the initial point or a maximum time elapses. The simulation is repeated using a full set for multiple endpoints and maximum times for ten different amounts of current in the wires. Each current value is selected so that no particles can travel more than seven times the distance between the wires from the null line. The fraction of particles that reach the endpoint in a given time is calculated and used to describe particle transport parallel to the null line. The results are given in normalized, dimensionless units and their possible applications as an antihydrogen source and use in ultra-high purity sputter are discussed. The results are used to find the conditions necessary to obtain a steady and uniform particle flux suitable for ultra-high purity sputter, assuming that plasma is generated near the null line.
3D Alfvén wave behaviour about proper and improper magnetic null points
Thurgood, J. O.; McLaughlin, J. A.
2013-10-01
Context. Magnetohydrodynamic (MHD) waves and magnetic null points are both prevalent in many astrophysical plasmas, including the solar atmosphere. Interaction between waves and null points has been implicated as a possible mechanism for localised heating events. Aims: Here we investigate the transient behaviour of the Alfvén wave about fully 3D proper and improper magnetic null points. Methods: We introduce an Alfvén wave into the vicinity of both proper and improper null points by numerically solving the ideal, β = 0 MHD equations using the LARE3D code. A magnetic fieldline and flux-based coordinate system permits the isolation of resulting wave modes and the analysis of their interaction. Results: We find that the Alfvén wave propagates throughout the region and accumulates near the fan-plane, causing current build up. For different values of null point eccentricity, the qualitative behaviour changes only by the imposition of anisotropic pulse dilation, owing to the differing rates at which fieldlines diverge from the spine. For all eccentricities, we find that the fast and Alfvén waves are linearly decoupled. During the driving phase, an independently propagating fast wave is nonlinearly generated owing to the ponderomotive force. Subsequently, no further excitation of fast waves occurs. Conclusions: We find that the key aspects of the theory of Alfvén waves about 2D null points extends intuitively to the fully 3D case; i.e. the wave propagates along fieldlines and thus accumulates at predictable parts of the topology. We also highlight that unlike in the 2D case, in 3D Alfvén-wave pulses are always toroidal, and thus any aspects of 2D Alfvén-wave-null models that are pulse-geometry specific must be reconsidered in 3D.
Review Article: MHD Wave Propagation Near Coronal Null Points of Magnetic Fields
McLaughlin, J. A.; Hood, A. W.; de Moortel, I.
2011-07-01
We present a comprehensive review of MHD wave behaviour in the neighbourhood of coronal null points: locations where the magnetic field, and hence the local Alfvén speed, is zero. The behaviour of all three MHD wave modes, i.e. the Alfvén wave and the fast and slow magnetoacoustic waves, has been investigated in the neighbourhood of 2D, 2.5D and (to a certain extent) 3D magnetic null points, for a variety of assumptions, configurations and geometries. In general, it is found that the fast magnetoacoustic wave behaviour is dictated by the Alfvén-speed profile. In a β=0 plasma, the fast wave is focused towards the null point by a refraction effect and all the wave energy, and thus current density, accumulates close to the null point. Thus, null points will be locations for preferential heating by fast waves. Independently, the Alfvén wave is found to propagate along magnetic fieldlines and is confined to the fieldlines it is generated on. As the wave approaches the null point, it spreads out due to the diverging fieldlines. Eventually, the Alfvén wave accumulates along the separatrices (in 2D) or along the spine or fan-plane (in 3D). Hence, Alfvén wave energy will be preferentially dissipated at these locations. It is clear that the magnetic field plays a fundamental role in the propagation and properties of MHD waves in the neighbourhood of coronal null points. This topic is a fundamental plasma process and results so far have also lead to critical insights into reconnection, mode-coupling, quasi-periodic pulsations and phase-mixing.
Magnetohydrodynamics dynamical relaxation of coronal magnetic fields. III. 3D spiral nulls
Fuentes-Fernández, J.; Parnell, C. E.
2012-08-01
Context. The majority of studies on stressed 3D magnetic null points consider magnetic reconnection driven by an external perturbation, but the formation of a genuine current sheet equilibrium remains poorly understood. This problem has been considered more extensively in two dimensions, but lacks a generalization into 3D fields. Aims: 3D magnetic nulls are more complex than 2D nulls and the field can take a greater range of magnetic geometries local to the null. Here, we focus on one type and consider the dynamical non-resistive relaxation of 3D spiral nulls with initial spine-aligned current. We aim to provide a valid magnetohydrostatic equilibrium, and describe the electric current accumulations in various cases, involving a finite plasma pressure. Methods: A full MHD code was used, with the resistivity set to zero so that reconnection is not allowed, to run a series of experiments in which a perturbed spiral 3D null point was allowed to relax towards an equilibrium via real, viscous damping forces. Changes to the initial plasma pressure and other magnetic parameters were systematically investigated. Results: For the axisymmetric case, the evolution of the field and the plasma is such that it concentrates the current density into two cone-shaped regions along the spine, thus concentrating the twist of the magnetic field around the spine, leaving a radial configuration in the fan plane. The plasma pressure redistributes to maintain the current density accumulations. However, it is found that changes in the initial plasma pressure do not significantly modify the final state. In the cases where the initial magnetic field is not axisymmetric, an infinite-time singularity of current perpendicular to the fan is found at the location of the null.
Current Structure and Nonideal Behavior at Magnetic Null Points in the Turbulent Magnetosheath
Wendel, D. E.; Adrian, M. L.
2013-01-01
The Poincaré index indicates that the Cluster spacecraft tetrahedron entraps a number of 3-D magnetic nulls during an encounter with the turbulent magnetosheath. Previous researchers have found evidence for reconnection at one of the many filamentary current layers observed by Cluster in this region. We find that many of the entrained nulls are also associated with strong currents. We dissect the current structure of a pair of spiral nulls that may be topologically connected. At both nulls, we find a strong current along the spine, accompanied by a somewhat more modest current perpendicular to the spine that tilts the fan toward the axis of the spine. The current along the fan is comparable to the that along the spine. At least one of the nulls manifests a rotational flow pattern in the fan plane that is consistent with torsional spine reconnection as predicted by theory. These results emphasize the importance of examining the magnetic topology in interpreting the nature of currents and reconnection in 3-D turbulence.
Susceptibility to hepatocellular carcinoma associated with null genotypes of GSTM1 and GSTT1
Institute of Scientific and Technical Information of China (English)
Jian Chao Bian; Fu Min Shen; Li Shen; Tian Ru Wang; Xiao Hong Wang; Gong Chao Chen; Jin Bing Wang
2000-01-01
ALM In order to study the association between the null genotypes of GSTM1 and GSTT1 and the genetic susceptibility to hepatocellular carcinoma (HCC). METHODS The genotypes of GSTM1 and GSTT1 of 63 cases of HCC and 88 controls were detected with the multiple PCR technique. RESULTS The frequency of GSTM1 null genotype was 57.1% among the cases, and 42.0% among the controls, the difference being statistically significant (x2 = 3.35, P = 0.067),but X2 value approaching the significance level.The odds ratio was 1.84 (95% Cl=0.91 - 3.37).The frequency of GSTT1 non-null genotype was 87.3% among the cases and 62.5% among the controls, the difference being statistically significant (X2=11.42, P=0.0007274). The odds ratio was 4.13 (95% Cl = 1.64 - 10.70).According to the cross analysis, the GSTT1 nonnull genotype was more closely associated with HCC than GSTM1 null genotype, and these two factors play an approximate addlitive interaction in the occurrence of HCC. CONCLUSION The persons with GSTM1 nullgenotype and GSTT1 non-null genotype have the increased risk to HCC.
Vacuum Nuller Testbed (VNT) Performance, Characterization and Null Control: Progress Report
Lyon, Richard G.; Clampin, Mark; Petrone, Peter; Mallik, Udayan; Madison, Timothy; Bolcar, Matthew R.; Noecker, M. Charley; Kendrick, Stephen; Helmbrecht, Michael
2011-01-01
Herein we report on the development. sensing and control and our first results with the Vacuum Nuller Testbed to realize a Visible Nulling Coronagraph (VNC) for exoplanet coronagraphy. The VNC is one of the few approaches that works with filled. segmented and sparse or diluted-aperture telescope systems. It thus spans a range of potential future NASA telescopes and could be Hown as a separate instrument on such a future mission. NASA/Goddard Space Flight Center (GSFC) has a well-established effort to develop VNC technologies. and has developed an incremental sequence of VNC testbeds to advance this approach and the enabling technologies associated with it. We discuss the continued development of the vacuum Visible Nulling Coronagraph testbed (VNT). Tbe VNT is an ultra-stable vibration isolated testbed that operates under closed-loop control within a vacuum chamber. It will be used to achieve an incremental sequence of three visible-light nulling milestones with sequentially higher contrasts of 10(sup 8), 10(sup 9) and ideally 10(sup 10) at an inner working angle of 2*lambda/D. The VNT is based on a modified Mach-Zehnder nulling interferometer, with a "W" configuration to accommodate a hex-packed MEMS based deformable mirror, a coherent fiber bundle and achromatic phase shifters. We discuss the initial laboratory results, the optical configuration, critical technologies and the null sensing and control approach.
Valiente Kroon, Juan Antonio
2004-12-01
The conformal Einstein equations and the representation of spatial infinity as a cylinder introduced by Friedrich are used to analyse the behaviour of the gravitational field near null and spatial infinity for the development of data which are asymptotically Euclidean, conformally flat and time asymmetric. Our analysis allows for initial data whose second fundamental form is more general than the one given by the standard Bowen York ansatz. The conformal Einstein equations imply, upon evaluation on the cylinder at spatial infinity, a hierarchy of transport equations which can be used to calculate asymptotic expansions for the gravitational field in a recursive way. It is found that the solutions to these transport equations develop logarithmic divergences at the critical sets where null infinity meets spatial infinity. Associated with these, there is a series of quantities expressible in terms of the initial data (obstructions), which if zero, preclude the appearance of some of the logarithmic divergences. The obstructions are, in general, time asymmetric. That is, the obstructions at the intersection of future null infinity with spatial infinity are in general different from those obtained at the intersection of past null infinity with spatial infinity. The latter allows for the possibility of having spacetimes where future and past null infinity have different degrees of smoothness. Finally, it is shown that if both sets of obstructions vanish up to a certain order, then the initial data have to be asymptotically Schwarzschildean in a certain sense.
Spacetime characterizations of Λ-vacuum metrics with a null Killing 2-form
Mars, Marc; Senovilla, José M. M.
2016-10-01
An exhaustive list of four-dimensional Λ-vacuum spacetimes admitting a Killing vector ξ whose self-dual Killing two-form {{ F }}μ ν is null is obtained assuming that the self-dual Weyl tensor is proportional to the tensor product of {{ F }}μ ν by itself. Our analysis complements previous results (Mars 1999 Class Quantum Grav. 16 2507-23 Mars and Senovilla 2015 Ann. H. Poincaré 16 1509-50) concerning the case with non-null {{ F }}μ ν . We analyze both cases with Λ vanishing or not. In the latter case we prove that {{Λ }}\\lt 0 must hold necessarily, and we find a characterization of the Einstein spacetimes conformal to pp-waves. In the former case we obtain spacetime characterizations of vacuum plane waves and of the stationary vacuum Brinkmann spacetimes. At the light of the full set of results, old and new, we reformulate the case with non-null {{ F }}μ ν and {{Λ }}=0. We finally present a table collecting the results for both null, and non-null, {{ F }}μ ν .
A Null Space Control of Two Wheels Driven Mobile Manipulator Using Passivity Theory
Shibata, Tsuyoshi; Murakami, Toshiyuki
This paper describes a control strategy of null space motion of a two wheels driven mobile manipulator. Recently, robot is utilized in various industrial fields and it is preferable for the robot manipulator to have multiple degrees of freedom motion. Several studies of kinematics for null space motion have been proposed. However stability analysis of null space motion is not enough. Furthermore, these approaches apply to stable systems, but they do not apply unstable systems. Then, in this research, base of manipulator equips with two wheels driven mobile robot. This robot is called two wheels driven mobile manipulator, which becomes unstable system. In the proposed approach, a control design of null space uses passivity based stabilizing. A proposed controller is decided so that closed-loop system of robot dynamics satisfies passivity. This is passivity based control. Then, control strategy is that stabilizing of the robot system applies to work space observer based approach and null space control while keeping end-effector position. The validity of the proposed approach is verified by simulations and experiments of two wheels driven mobile manipulator.
Mid-infrared laser light nulling experiment using single-mode conductive waveguides
Labadie, L; Maurand, R; Labeye, P; Kern, P; Arezki, B; Broquin, J -E
2007-01-01
Aims: In the context of space interferometry missions devoted to the search of exo-Earths, this paper investigates the capabilities of new single mode conductive waveguides at providing modal filtering in an infrared and monochromatic nulling experiment; Methods: A Michelson laser interferometer with a co-axial beam combination scheme at 10.6 microns is used. After introducing a Pi phase shift using a translating mirror, dynamic and static measurements of the nulling ratio are performed in the two cases where modal filtering is implemented and suppressed. No additional active control of the wavefront errors is involved. Results: We achieve on average a statistical nulling ratio of 2.5e-4 with a 1-sigma upper limit of 6e-4, while a best null of 5.6e-5 is obtained in static mode. At the moment, the impact of external vibrations limits our ability to maintain the null to 10 to 20 seconds.; Conclusions: A positive effect of SM conductive waveguide on modal filtering has been observed in this study. Further improv...
Current structure and nonideal behavior at magnetic null points in the turbulent magnetosheath
Wendel, D. E.; Adrian, M. L.
2013-04-01
The Poincaré index indicates that the Cluster spacecraft tetrahedron entraps a number of 3-D magnetic nulls during an encounter with the turbulent magnetosheath. Previous researchers have found evidence for reconnection at one of the many filamentary current layers observed by Cluster in this region. We find that many of the entrained nulls are also associated with strong currents. We dissect the current structure of a pair of spiral nulls that may be topologically connected. At both nulls, we find a strong current along the spine, accompanied by a somewhat more modest current perpendicular to the spine that tilts the fan toward the axis of the spine. The current along the fan is comparable to the that along the spine. At least one of the nulls manifests a rotational flow pattern in the fan plane that is consistent with torsional spine reconnection as predicted by theory. These results emphasize the importance of examining the magnetic topology in interpreting the nature of currents and reconnection in 3-D turbulence.
Steady state reconnection at a single 3D magnetic null point
Galsgaard, K.; Pontin, D. I.
2011-05-01
Aims: We systematically stress a rotationally symmetric 3D magnetic null point by advecting the opposite footpoints of the spine axis in opposite directions. This stress eventually concentrates in the vicinity of the null point, thereby forming a local current sheet through which magnetic reconnection takes place. The aim is to look for a steady state evolution of the current sheet dynamics, which may provide scaling relations for various characteristic parameters of the system. Methods: The evolution is followed by solving numerically the non-ideal MHD equations in a Cartesian domain. The null point is embedded in an initially constant density and temperature plasma. Results: It is shown that a quasi-steady reconnection process can be set up at a 3D null by continuous shear driving. It appears that a true steady state is unlikely to be realised because the current layer tends to grow until it is restricted by the geometry of the computational domain and the imposed driving profile. However, ratios between characteristic quantities clearly settle after some time to stable values, so that the evolution is quasi-steady. The experiments show a number of scaling relations, but they do not provide a clear consensus for extending to lower magnetic resistivity or faster driving velocities. More investigations are needed to fully clarify the properties of current sheets at magnetic null points.
Current amplification and magnetic reconnection at a 3D null point. I - Physical characteristics
Pontin, D I
2007-01-01
The behaviour of magnetic perturbations of an initially potential three-dimensional equilibrium magnetic null point are investigated. The basic components which constitute a typical disturbance are taken to be rotations and shears, in line with previous work. The spine and fan of the null point (the field lines which asymptotically approach or recede from the null) are subjected to such rotational and shear perturbations, using three-dimensional magnetohydrodynamic simulations. It is found that rotations of the fan plane and about the spine lead to current sheets which are spatially diffuse in at least one direction, and form in the locations of the spine and fan. However, shearing perturbations lead to 3D-localised current sheets focused at the null point itself. In addition, rotations are associated with a growth of current parallel to the spine, driving rotational flows and a type of rotational reconnection. Shears, on the other hand, cause a current through the null which is parallel to the fan plane, and...
Magnetic nulls in three-dimensional kinetic simulations of space plasmas
Olshevsky, Vyacheslav; Deca, Jan; Divin, Andrey; Peng, Ivy Bo; Markidis, Stefano; Innocenti, Maria Elena; Cazzola, Emanuele; Lapenta, Giovanni
2016-04-01
We present a survey of magnetic nulls and associated energy dissipation in different three-dimensional kinetic particle-in-cell simulations of space plasmas. The configurations under study include: a traditional Harris current sheet and current sheets with asymmetric density distribution, dipolar and quadrupolar planetary magnetospheres, lunar magnetic anomalies, and decaying turbulence. Nulls are detected in the simulation snapshots by the topological degree method. In all runs except the quadrupolar magnetospere the dominating majority of nulls are of spiral topological type. When supported by strong currents, these nulls indicate the regions of strong energy dissipation. Dissipation, often accompanied by the changes in magnetic topology, is caused by plasma instabilities in the current channels or on their interfaces. Radial nulls show less activity, they can be created or destroyed in pairs, via topological bifurcations. Although such events demonstrate energy release, they are rather rare and short-living. An important implication of our study to observations is that magnetic topology should not be considered independently of other plasma properties such as currents.
Influence of frame-dragging on magnetic null points near rotating black holes
Karas, V.; Kopáček, O.; Kunneriath, D.
2012-02-01
Understanding the mechanisms of particle acceleration from the vicinity of black holes poses a challenge. Electromagnetic effects are thought to be a prime suspect, but details still need an explanation. To this end, we study a three-dimensional structure of oblique magnetic fields near a rotating black hole in vacuum. It has been proposed that such a setup can lead to efficient acceleration when plasma is injected near a magnetic null point. We focus our attention especially on the magnetic field in the immediate neighborhood of the magnetic null point, which was previously shown to occur in the equatorial plane. By employing the line integral convolution method, we visualize the magnetic field lines and explore the electric lines rising out of the equatorial plane. We show the magnetic field structure near the boundary of ergosphere, depending on the spin of the black hole. Electric field develops a non-vanishing component passing through the magnetic null point and ensuring efficient acceleration of charged particles from this particular location near the horizon. We also examine the effect of translatory boost on the field lines. Similarly to the frame-dragging by rotation, the linear motion carries field lines along with the black hole. The position of the magnetic null point recedes from the black hole horizon as the spin parameter increases. For the extreme value of a = 1, the null point can occur outside the ergosphere.
Current Singularities at Quasi-separatrix Layers and Three-dimensional Magnetic Nulls
Craig, I. J. D.; Effenberger, Frederic
2014-11-01
The open problem of how singular current structures form in line-tied, three-dimensional magnetic fields is addressed. A Lagrangian magneto-frictional relaxation method is employed to model the field evolution toward the final near-singular state. Our starting point is an exact force-free solution of the governing magnetohydrodynamic equations that is sufficiently general to allow for topological features like magnetic nulls to be inside or outside the computational domain, depending on a simple set of parameters. Quasi-separatrix layers (QSLs) are present in these structures and, together with the magnetic nulls, they significantly influence the accumulation of current. It is shown that perturbations affecting the lateral boundaries of the configuration lead not only to collapse around the magnetic null but also to significant QSL currents. Our results show that once a magnetic null is present, the developing currents are always attracted to that specific location and show a much stronger scaling with resolution than the currents that form along the QSL. In particular, the null-point scalings can be consistent with models of "fast" reconnection. The QSL currents also appear to be unbounded but give rise to weaker singularities, independent of the perturbation amplitude.
3D Alfven wave behaviour around proper and improper magnetic null points
Thurgood, J O
2013-01-01
Context: MHD waves and magnetic null points are both prevalent in many astrophysical plasmas, including the solar atmosphere. Interaction between waves and null points has been implicated as a possible mechanism for localised heating events. Aims: Here we investigate the transient behaviour of the Alfven wave about fully 3D proper and improper 3D magnetic null points. Previously, the behaviour of fast magnetoacoustic waves at null points in 3D, cold MHD was considered by Thurgood & McLaughlin (Astronomy & Astrophysics, 2012, 545, A9). Methods: We introduce an Alfven wave into the vicinity of both proper and improper null points by numerically solving the ideal, $\\beta=0$ MHD equations using the LARE3D code. A magnetic fieldline and flux-based coordinate system permits the isolation of resulting wave-modes and the analysis of their interaction. Results: We find that the Alfven wave propagates throughout the region and accumulates near the fan-plane, causing current build up. For different values of nul...
Barnes, Daniel; Braxton-Gravin, Asiha; Jenkins, Jade; Ali, Halima; Punjabi, Alkesh
2013-10-01
The double-null map is the simplest symplectic map that has the generic magnetic topology of double-null divertor tokamaks. The generating function of the double-null map is given by S (x , y) = x2 /2 +y2 /2-y4/4. The equilibrium magnetic surfaces of the double-null map are calculated from the generating function. 0 1/4 gives open surfaces. The scaling of safety factor on the magnetic axis, q0, with map parameter k is calculated. The scaling of root mean square deviation of energy on the q95 surface with map parameter k is calculated and taken as the estimate of magnetic asymmetry to represent the magnetic perturbation. The results of this work will be reported. These results are used to calculate heteroclinic tangles of the separatrix of double-null map. This work is supported by grants DE-FG02-01ER54624, DE-FG02-04ER54793, and DE-FG02-07ER54937.
Feasibility of a self-nulling beam combiner using no external phase inverter
Bloemhof, E. E.
2005-08-01
Space-based nulling interferometers will play a major role in the search for exoplanets, as both NASA and ESA plan missions for the near future. Current architectures produce the requisite broadband π phase shift in one arm of each nulling telescope pair by means of a system of "field flip" optics that may involve one of a number of sophisticated technologies (periscope, phase plates, through-focus, or other). The two beams, of equal intensity but conjugate phase, are then combined, perhaps in a modified Mach-Zehnder (MMZ) or similar beam combiner of high configurational symmetry. A novel approach has recently been proposed, however, in which the achromatic π phase shift is supplied by two applications of the innate π/2 phase shift between transmitted and reflected beams in a beam splitter. This simply requires using the traditionally bright output port of the MMZ as a nulled port; adaptive nulling can be used to ease the tolerances on matching the moduli of reflection and transmission coefficients. The rather substantial systems benefit that accrues is that the external phase shifting ("field flipping") optics may be entirely eliminated. Here, I discuss the feasibility of this "self-nulling" beam combiner scheme.
On Bäcklund transformation and vortex filament equation for pseudo null curves in Minkowski 3-space
Grbović, Milica; Nešović, Emilija
2016-04-01
In this paper, we introduce Bäcklund transformation of a pseudo null curve in Minkowski 3-space as a transformation mapping a pseudo null helix to another pseudo null helix congruent to the given one. We also give the sufficient conditions for a transformation between two pseudo null curves in the Minkowski 3-space such that these curves have equal constant torsions. By using the Da Rios vortex filament equation, based on localized induction approximation (LIA), we derive the vortex filament equation for a pseudo null curve and prove that the evolution equation for the torsion is the viscous Burger’s equation. As an application, we show that pseudo null curves and their Frenet frames generate solutions of the Da Rios vortex filament equation.
Chudecki, Adam
2016-01-01
4-dimensional spaces equipped with 2-dimensional (complex holomorphic or real smooth) completely integrable distributions are considered. The integral manifolds of such distributions are totally null and totally geodesics 2-dimensional surfaces which are called the null strings. Properties of congruences (foliations) of such 2-surfaces are studied. Relation between properties of congruences of null strings and Petrov-Penrose type of SD Weyl spinor and algebraic types of traceless Ricci tensor is analyzed.
Üheksa nulli : null null null null null null null... / Anthony de Kowalsky
Kowalsky, Anthony de
2008-01-01
Lühiarvustus 18.- 20. 07. Põlvamaal Intsikurmu laululaval etendunud vabaõhulavastusele "Üheksa nulliga Eesti". Stsenaariumi on kirjutanud Kadri Pettai, Aapo Ilves, Olavi Ruitlane ja Veiko Märka. Lavastanud Reeda Toots
Sun, Fei; Liu, Yichao; He, Sailing
2016-07-01
A so-called anti-optic-null medium (anti-ONM), which can be utilized to cancel the optic-null medium (ONM) and create many novel optical illusions, is introduced and designed by transformation optics (TO). Optical separation illusions can be achieved with an anti-ONM. With the help of the anti-ONM, we can achieve the same optical illusions where ONM is required via a shelled structure filled with low anisotropic medium, which is easier to realize for some novel optical devices designed by TO and optical surface transformation. The special function of the anti-ONM will lead to a new way to design optical devices or simplify the material requirements. Overlapping illusions, and wave-front reshapers are designed to demonstrate the function of the proposed method.
Herbonnet, Ricardo; Kuijken, Konrad
2016-01-01
Current optical imaging surveys for cosmology are covering large areas of sky. To exploit the statistical power of these surveys for weak lensing measurements requires shape measurement methods with subpercent systematic errors. We introduce a new weak lensing shear measurement algorithm, Shear Nulling after PSF Gaussianisation (SNAPG), designed to avoid the noise biases that affect most other methods. SNAPG operates on images that have been convolved with a kernel that renders the Point Spread Function (PSF) a circular Gaussian, and uses weighted second moments of the sources. The response of such second moments to a shear of the pre-seeing galaxy image can be predicted analytically, allowing us to construct a shear nulling scheme that finds the shear parameters for which the observed galaxies are consistent with an unsheared, isotropically oriented population of sources. The inverse of this nulling shear is then an estimate of the gravitational lensing shear. We identify the uncertainty of the estimated cen...
Maxwell, Yang-Mills, Weyl and eikonal fields defined by any null shear-free congruence
Kassandrov, Vladimir V.; Rizcallah, Joseph A.
We show that (specifically scaled) equations of shear-free null geodesic congruences on the Minkowski space-time possess intrinsic self-dual, restricted gauge and algebraic structures. The complex eikonal, Weyl 2-spinor, SL(2, ℂ) Yang-Mills and complex Maxwell fields, the latter produced by integer-valued electric charges (“elementary” for the Kerr-like congruences), can all be explicitly associated with any shear-free null geodesic congruence. Using twistor variables, we derive the general solution of the equations of the shear-free null geodesic congruence (as a modification of the Kerr theorem) and analyze the corresponding “particle-like” field distributions, with bounded singularities of the associated physical fields. These can be obtained in a straightforward algebraic way and exhibit nontrivial collective dynamics simulating physical interactions.
A New Method of Identifying 3D Null Points in Solar Vector Magnetic Fields
Institute of Scientific and Technical Information of China (English)
Hui Zhao; Jing-Xiu Wang; Jun Zhang; Chi-Jie Xiao
2005-01-01
Employing the Poincaré index of isolated null-points in a vector field,we worked out a mathematical method of searching for 3D null-points in coronal magnetic fields. After introducing the relevant differential topology, we test the method by using the analytical model of Brown & Priest. The location of nullpoint identified by our method coincides precisely with the analytical solution.Finally we apply the method to the 3D coronal magnetic fields reconstructed from an observed MDI magnetogram of a super-active region (NOAA 10488). We find that the 3D null-point seems to be a key element in the magnetic topology associated with flare occurrence.
Null reconstruction of orthogonal circular polarization hologram with large recording angle.
Wu, An'an; Kang, Guoguo; Zang, Jinliang; Liu, Ying; Tan, Xiaodi; Shimura, Tsutomu; Kuroda, Kazuo
2015-04-01
We report on the null reconstruction of polarization volume hologram recorded by orthogonal circularly polarized waves with a large cross angle. Based on the recently developed tensor theory for polarization holography, the disappearance of the reconstruction was analytically verified, where a nice agreement was found between the experimental and theoretical results. When the polarization and intensity hologram attain a balance, not only the null reconstruction but also the faithful reconstruction can be realized by the illumination of the orthogonal reference wave and original reference wave. As a consequence of the hologram recorded without paraxial approximation, the null reconstruction may lead to important applications, such as a potential enhancement in optical storage capacity for volume holograms.
Investigation of the extraordinary null reconstruction phenomenon in polarization volume hologram.
Wang, J; Kang, G; Wu, A; Liu, Y; Zang, J; Li, P; Tan, X; Shimura, T; Kuroda, K
2016-01-25
Polarization holography is the superposition of differently polarized beams. Due to its ability to record the polarization states, some extraordinary optical phenomena were found in the polarization holography. For example, the recently reported null-reconstruction phenomenon in polarization volume hologram is odd for the conventional holography which only records the amplitude and phase. In this paper, we perform a thorough investigation of the null reconstruction of polarization hologram recorded by orthogonal circularly polarized waves. To explore the mechanism behind this phenomenon, an interferometry was built to measure the phase difference between the same polarized components within the reconstructed wave. The phase difference of π was secured in our experiment, indicating a destructive interfering effect, which nicely explains the extraordinary null reconstruction observed in the polarization hologram.
Phase Retrieval with One or Two Diffraction Patterns by Alternating Projections of the Null Vector
Chen, Pengwen; Liu, Gi-Ren
2015-01-01
Two versions of alternating projection (AP), the parallel alternating projection (PAP) and the serial alternating projection (SAP), are proposed to solve phase retrieval with at most two coded diffraction patterns. The proofs of geometric convergence are given with sharp bounds on the rates of convergence in terms of a spectral gap condition. To compensate for the local nature of convergence, the null vector method is proposed for initialization and proved to produce asymptotically accurate initialization for the Gaussian case. Extensive numerical experiments are performed to show that the null vector method produces more accurate initialization than the spectral vector method and that PAP/SAP converge faster to more accurate solutions than other iterative schemes for non-convex optimization such as the Wirtinger flow. Moreover, SAP converges still faster than PAP. In practice AP and the null vector method together produce globally convergent iterates to the true object.
Quasi-local mass at the null infinity of the Vaidya spacetime
Chen, Po-Ning; Yau, Shing-Tung
2016-01-01
There are two important statements regarding the Trautman-Bondi mass [1,8,5] at null infinity: one is the positivity [7,6], and the other is the Bondi mass loss formula [1], which are both global in nature. The positivity of the quasi-local mass can potentially lead to a local description at null infinity. This is confirmed for the Vaidya spacetime in this note. We study the Wang-Yau quasi-local mass on surfaces of fixed size at the null infinity of the Vaidya spacetime. The optimal embedding equation is solved explicitly and the quasi-local mass is evaluated in terms of the mass aspect function of the Vaidya spacetime.
Probing the X-ray emission of old nulling pulsars with high magnetic fields
Posselt, Bettina
2013-10-01
We propose XMM-Newton observations of two nulling radio pulsars with magnetic fields B>10^(13)G. These long-period pulsars have spin-down properties, including characteristic ages, similar to those of the Magnificent Seven which are bright thermal X-ray emitters. Nulling pulsars have been suggested as evolutionary stage where the magnetospheric emission of a pulsar ceases. In contrast, no magnetospheric emission was detected at all at X-ray or radio wavelengths for the Magnificent Seven. The proposed XMM-Newton observations will probe the magneto-thermal NS evolution model as a potential link between the radio pulsar population and the Magnificent Seven. They will also provide for the first time an X-ray characterization of nulling pulsars with large magnetic fields.
Development of electric currents in a magnetic field configuration containing a magnetic null point
Santos, J. C.; Büchner, J.; Otto, A.
2011-01-01
Context. In the past the role of magnetic null points in the generation of electric currents was investigated mainly in the close vicinity of the null, with perturbations being applied at nearby boundaries, or for a magnetic null configuration with a dome-shaped fan. In the solar atmosphere, however, electric currents are generated by perturbations originating at the photosphere, far away from coronal 3D nulls, and the occurence of magnetic nulls with a dome-shaped fan is apparently not common. Aims: We investigate the consequences of photospheric motion for the development of electric currents in a coronal magnetic field configuration containing a null, located far away from the boundaries, and the influence of topological structures on the spatial distribution of the currents. Methods: We use a 3D resistive MHD code to investigate the consequences of photospheric plasma motion for the generation of currents in a coronal magnetic field containing a null. The plasma is considered fully compressible and is initially in hydrostatic equilibrium. The initial magnetic field is potential (current free). Results: The photospheric plasma motion causes magnetic field perturbations that propagate to the corona along the field lines at the local Alfvén speed. The Alfvénic wave perturbations correspond to a propagating current directed mainly parallel to the magnetic field. Perpendicular currents connect to return currents to close the current system. The magnetic perturbations eventually reach the vicinity of the null. However, the currents forming in and around the null, near the fan surface or near the spine field lines, are not always the strongest currents developing in the simulation box. In our simulation, the strongest currents develop close to the bottom boundary, where the plasma is moved, and below the null point, in a region where field line connectivity considerably changes. Conclusions: Our simulation shows that the presence of a magnetic null point does not
Magnetic reconnection and tearing in a 3D current sheet about a solar coronal null
Pontin, David; Wyper, Peter
2014-06-01
Three-dimensional magnetic null points are ubiquitous in the solar corona and in any generic mixed-polarity magnetic field. We discuss the nature of flux transfer during reconnection an isolated coronal null point, that occurs across the fan plane when a current sheet forms about the null. We then go on to discuss the breakup of the current sheet via a non-linear tearing-type instability and show that the instability threshold corresponds to a Lundquist number comparable to the 2D case. We also discuss the resulting topology of the magnetic field, which involves a layer in which open and closed magnetic fields are effectively mixed, with implications for particle transport.
Observation of the lower hybrid waves near the three-dimensional null pair
Institute of Scientific and Technical Information of China (English)
ZHOU Meng; DENG XiaoHua; FU Song; TANG RongXin; HU YunHui; LI ShiYou; A. VAIVADS; M. ANDRE; LIN Xi; LIN MingHui; ZHOU XiaoMin
2009-01-01
Magnetic reconnection is a fundamental process in plasma, which is thought to play important roles both in laboratory and natural plasmas through affecting magnetic topology, heating and accelerating particles. During an event on Oct. 1st, 2001, the Cluster tetrahedron circled around the magnetic re-connection region several times, and Xiao et al. First identified the null pair and found that the spectrum of the null-point oscillation shows the maximum power near the lower-hybrid frequency. In this paper we report the observation of electromagnetic and electrostatic wave enhancements near lower hybrid frequency associated with the reconnection process near the null pair. The lower hybrid waves (LHWs) with quasi-perpendicular propagation were identified and also confirmed by the power law of the spectrum of electric and magnetic fields.
Kinetic simulations of magnetic reconnection in three-dimensional null-points.
Olshevsky, Vyacheslav; Lapenta, Giovanni; Divin, Andrey; Markidis, Stefano
2015-04-01
We report kinetic particle-in-cell simulations of an essentially three-dimensional magnetized plasma configuration. Initially the evolution is governed by large-scale fluid modes excited by the pressure imbalance. At this phase current channels (pinches) are created along the sequences of spiral null-points. After ten ion gyroperiods the relaxation is over, and about half of magnetic energy is converted to ion currents, particle heating, and generation of suprathermal particles. At the next phase the evolution is dominated by volumetric magnetic reconnection, mainly associated with spiral null-points (pinches); non-spiral nulls don't play important role in the energy release. Such reconection is a possible mechanism of magnetic energy dissipation in turbulent space plasmas where currents and twisted field lines are ubiquitous.
Dichotomies of the set of test measures of a Haar-null set
Dodos, Pandelis
2010-01-01
We prove that if $X$ is a Polish space and $F$ is a face of $P(X)$ with the Baire property, then $F$ is either a meager or a co-meager subset of $P(X)$. As a consequence we show that for every abelian Polish group $X$ and every analytic Haar-null set $A\\subseteq X$, the set of test measures $T(A)$ of $A$ is either meager or co-meager. We characterize the non-locally-compact groups as the ones for which there exists a closed Haar-null set $F\\subseteq X$ with $T(F)$ is meager. Moreover, we answer negatively a question of J. Mycielski by showing that for every non-locally-compact abelian Polish group and every $\\sigma$-compact subgroup $G$ of $X$ there exists a $G$-invariant $F_\\sigma$ subset of $X$ which is neither prevalent nor Haar-null.
Kinematic reconnection at a magnetic null point: spine-aligned current
Pontin, D. I.; Hornig, G.; Priest, E. R.
2004-05-01
Magnetic reconnection at a three-dimensional null point is the natural extension of the familiar two-dimensional X-point reconnection. A model is set up here for reconnection at a spiral null point, by solving the kinematic, steady, resistive magnetohydrodynamic equations in its vicinity. A steady magnetic field is assumed, as well as the existence of a localised diffusion region surrounding the null point. Outside the diffusion region the plasma and magnetic field move ideally. Particular attention is focussed on the way that the magnetic flux changes its connections as a result of the reconnection. The resultant plasma flows are found to be rotational in nature, as is the change in connections of the magnetic field lines.
Directory of Open Access Journals (Sweden)
Wendy C. Wong
2010-01-01
Full Text Available We propose a transmit scheme for WiMAX systems, where multiple base stations (BSs employ downlink transmit beamforming and nulling for interference mitigation, with minimal coordination amongst BSs. This scheme improves system throughput and robustness, by increasing cell edge and overall cell throughputs by 68% and 19%, respectively, and by delivering improvement for mobile speed up to 60 km/h. First, cell edge users suffering from severe interferences are identified. Next, the RRM unit allocates resource to serving cell edge users only. BSs will schedule to serve their cell edge users independently using the allocated resources by the RRM. A special uplink sounding region is designed for BSs to learn the interference environment and form proper beams and nulls. The nulls formed towards users served by other BSs reduced interference from a BS towards these users and is the basic building block of our algorithm.
Energetics of kinetic reconnection in a three-dimensional null points cluster
Olshevsky, Vyacheslav; Markidis, Stefano
2015-01-01
We performed three-dimensional Particle-in-Cell simulations of magnetic reconnection with multiple magnetic null points. Magnetic field energy conversion into kinetic energy was about five times higher than in traditional Harris sheet configuration. More than 85% of initial magnetic field energy was transferred to particle energy during 25 reversed ion cyclofrequencies. Magnetic reconnection in the cluster of null points evolved in three phases. During the first phase, ion beams were excited, that then gave part of their energy back to magnetic field in the second phase. In the third phase, magnetic reconnection occurs in many small patches around the current channels formed along the stripes of low magnetic field. Magnetic reconnection in null points presents essentially three-dimensional features, with no two dimensional symmetries or current sheets.
Observation of the lower hybrid waves near the three-dimensional null pair
Institute of Scientific and Technical Information of China (English)
A.; VAIVADS; M.; ANDRE
2009-01-01
Magnetic reconnection is a fundamental process in plasma,which is thought to play important roles both in laboratory and natural plasmas through affecting magnetic topology,heating and accelerating particles. During an event on Oct. 1st,2001,the Cluster tetrahedron circled around the magnetic reconnection region several times,and Xiao et al. first identified the null pair and found that the spectrum of the null-point oscillation shows the maximum power near the lower-hybrid frequency. In this paper we report the observation of electromagnetic and electrostatic wave enhancements near lower hybrid frequency associated with the reconnection process near the null pair. The lower hybrid waves(LHWs) with quasi-perpendicular propagation were identified and also confirmed by the power law of the spectrum of electric and magnetic fields.
Energetics of kinetic reconnection in a three-dimensional null-point cluster.
Olshevsky, V; Lapenta, G; Markidis, S
2013-07-26
We perform three-dimensional particle-in-cell simulations of magnetic reconnection with multiple magnetic null points. Magnetic field energy conversion into kinetic energy is about five times higher than in traditional Harris sheet configuration. More than 85% of initial magnetic field energy is transferred to particle energy during 25 reversed ion cyclofrequencies. Magnetic reconnection in the cluster of null points evolves in three phases. During the first phase, ion beams are excited, then give part of their energy back to the magnetic field in the second phase. In the third phase, magnetic reconnection occurs in many small patches around the current channels formed along the stripes of a low magnetic field. Magnetic reconnection in null points essentially presents three-dimensional features, with no two-dimensional symmetries or current sheets.
High performance testbed for four-beam infrared interferometric nulling and exoplanet detection.
Martin, Stefan; Booth, Andrew; Liewer, Kurt; Raouf, Nasrat; Loya, Frank; Tang, Hong
2012-06-10
Technology development for a space-based infrared nulling interferometer capable of earthlike exoplanet detection and characterization started in earnest in the last 10 years. At the Jet Propulsion Laboratory, the planet detection testbed was developed to demonstrate the principal components of the beam combiner train for a high performance four-beam nulling interferometer. Early in the development of the testbed, the importance of "instability noise" for nulling interferometer sensitivity was recognized, and the four-beam testbed would produce this noise, allowing investigation of methods for mitigating this noise source. The testbed contains the required features of a four-beam combiner for a space interferometer and performs at a level matching that needed for the space mission. This paper describes in detail the design, functions, and controls of the testbed.
Null subjects: a problem for parameter-setting models of language acquisition.
Valian, V
1990-05-01
Some languages, like English, require overt surface subjects, while others, like Italian and Spanish, allow "null" subjects. How does the young child determine whether or not her language allows null subjects? Modern parameter-setting theory has proposed a solution, in which the child begins acquisition with the null subject parameter set for either the English-like value or the Italian-like value. Incoming data, or the absence thereof, force a resetting of the parameter if the original value was incorrect. This paper argues that the single-value solution cannot work, no matter which value is chosen as the initial one, because of inherent limitations in the child's parser, and because of the presence of misleading input. An alternative dual-value solution is proposed, in which the child begins acquisition with both values available, and uses theory-confirmation procedures to decide which value is best supported by the available data.
Rizzi, Anthony
2001-01-01
I show that the definition of angular momentum at null infinity given by A. Rizzi, Phys. Rev. Lett. 81, 1150 (1998), reduces to the Arnowitt-Deser-Misner definition at spatial infinity in the appropriate limit. This identification reinforces the gauge condition of the null definition as well as the null definition itself. Insight into the place of the null and spatial definitions is also gained. The methods used in this paper are very useful for understanding far-field problems in general rel...
Stimulation of Sigma-1 Receptor Ameliorates Depressive-like Behaviors in CaMKIV Null Mice.
Moriguchi, Shigeki; Sakagami, Hiroyuki; Yabuki, Yasushi; Sasaki, Yuzuru; Izumi, Hisanao; Zhang, Chen; Han, Feng; Fukunaga, Kohji
2015-12-01
Sigma-1 receptor (Sig-1R) is a molecular chaperone regulating calcium efflux from the neuronal endoplasmic reticulum to the mitochondria. Calcium/calmodulin-dependent protein kinase IV (CaMKIV) null mice exhibit depressive-like behaviors and impaired neurogenesis as assessed by bromodeoxyuridine (BrdU) incorporation into newborn cells of the hippocampal dentate gyrus (DG). Here, we demonstrate that chronic stimulation of Sig-1R by treatment with the agonist SA4503 or the SSRI fluvoxamine for 14 days improves depressive-like behaviors in CaMKIV null mice. By contrast, treatment with paroxetine, which lacks affinity for Sig-1R, did not alter these behaviors. Reduced numbers of BrdU-positive cells and decreased brain-derived neurotrophic factor (BDNF) mRNA expression and protein kinase B (Akt; Ser-473) phosphorylation seen in the DG of CaMKIV null mice were significantly rescued by chronic Sig-1R stimulation. Interestingly, reduced ATP production observed in the DG of CaMKIV null mice was improved by chronic Sig-1R stimulation. Such stimulation also improved hippocampal long-term potentiation (LTP) induction and maintenance, which are impaired in the DG of CaMKIV null mice. LTP rescue was closely associated with both increases in calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation and GluA1 (Ser-831) phosphorylation. Taken together, Sig-1R stimulation by SA4503 or fluvoxamine treatment increased hippocampal neurogenesis, which is closely associated with amelioration of depressive-like behaviors in CaMKIV null mice.
Otx1 null mutant mice show partial segregation of sensory epithelia comparable to lamprey ears
Fritzsch, B.; Signore, M.; Simeone, A.
2001-01-01
We investigated the development of inner ear innervation in Otx1 null mutants, which lack a horizontal canal, between embryonic day 12 (E12) and postnatal day 7 (P7) with DiI and immunostaining for acetylated tubulin. Comparable to control animals, horizontal crista-like fibers were found to cross over the utricle in Otx1 null mice. In mutants these fibers extend toward an area near the endolymphatic duct, not to a horizontal crista. Most Otx1 null mutants had a small patch of sensory hair cells at this position. Measurement of the area of the utricular macula suggested it to be enlarged in Otx1 null mutants. We suggest that parts of the horizontal canal crista remain incorporated in the utricular sensory epithelium in Otx1 null mutants. Other parts of the horizontal crista appear to be variably segregated to form the isolated patch of hair cells identifiable by the unique fiber trajectory as representing the horizontal canal crista. Comparison with lamprey ear innervation reveals similarities in the pattern of innervation with the dorsal macula, a sensory patch of unknown function. SEM data confirm that all foramina are less constricted in Otx1 null mutants. We propose that Otx1 is not directly involved in sensory hair cell formation of the horizontal canal but affects the segregation of the horizontal canal crista from the utricle. It also affects constriction of the two main foramina in the ear, but not their initial formation. Otx1 is thus causally related to horizontal canal morphogenesis as well as morphogenesis of these foramina.
Collins, Carol M; Ellis, Joseph; Holaska, James M
2017-02-10
Mutations in the gene encoding emerin cause Emery-Dreifuss muscular dystrophy (EDMD). Emerin is an integral inner nuclear membrane protein and a component of the nuclear lamina. EDMD is characterized by skeletal muscle wasting, cardiac conduction defects and tendon contractures. The failure to regenerate skeletal muscle is predicted to contribute to the skeletal muscle pathology of EDMD. We hypothesize muscle regeneration defects are caused by impaired muscle stem cell differentiation. Myogenic progenitors derived from emerin-null mice were used to confirm their impaired differentiation and analyze selected myogenic molecular pathways. Emerin-null progenitors were delayed in their cell cycle exit, had decreased myosin heavy chain (MyHC) expression and formed fewer myotubes. Emerin binds to and activates histone deacetylase 3 (HDAC3). Here we show theophylline, an HDAC3-specific activator, improved myotube formation in emerin-null cells. Addition of the HDAC3-specific inhibitor RGFP966 blocked myotube formation and MyHC expression in wildtype and emerin-null myogenic progenitors, but did not affect cell cycle exit. Downregulation of emerin was previously shown to affect the p38 and ERK MAPK pathways in C2C12 myoblast differentiation. Using a pure population of myogenic progenitors completely lacking emerin expression we show these pathways are also disrupted. ERK inhibition improved MyHC expression in emerin-null cells, but failed to rescue myotube formation or cell cycle exit. p38 MAPK inhibition prevented differentiation in both wildtype and emerin-null progenitors. These results show each of these molecular pathways specifically regulate particular stages of myogenic differentiation in an emerin-dependent manner. Thus, pharmacological targeting of multiple pathways acting at specific differentiation stages may be a better therapeutic approach in the future to rescue muscle regeneration in vivo.
Improving accuracy in the MPM method using a null space filter
Gritton, Chris; Berzins, Martin
2017-01-01
The material point method (MPM) has been very successful in providing solutions to many challenging problems involving large deformations. Nevertheless there are some important issues that remain to be resolved with regard to its analysis. One key challenge applies to both MPM and particle-in-cell (PIC) methods and arises from the difference between the number of particles and the number of the nodal grid points to which the particles are mapped. This difference between the number of particles and the number of grid points gives rise to a non-trivial null space of the linear operator that maps particle values onto nodal grid point values. In other words, there are non-zero particle values that when mapped to the grid point nodes result in a zero value there. Moreover, when the nodal values at the grid points are mapped back to particles, part of those particle values may be in that same null space. Given positive mapping weights from particles to nodes such null space values are oscillatory in nature. While this problem has been observed almost since the beginning of PIC methods there are still elements of it that are problematical today as well as methods that transcend it. The null space may be viewed as being connected to the ringing instability identified by Brackbill for PIC methods. It will be shown that it is possible to remove these null space values from the solution using a null space filter. This filter improves the accuracy of the MPM methods using an approach that is based upon a local singular value decomposition (SVD) calculation. This local SVD approach is compared against the global SVD approach previously considered by the authors and to a recent MPM method by Zhang and colleagues.
Magnetic reconnection at 3D null points: effect of magnetic field asymmetry
Al-Hachami, A. K.; Pontin, D. I.
2010-03-01
Context. The magnetic field in many astrophysical plasmas, for example in the solar corona, is known to have a highly complex - and clearly three-dimensional - structure. Turbulent plasma motions in high-β regions where field lines are anchored, such as the solar interior, can store large amounts of energy in the magnetic field. This energy can only be released when magnetic reconnection occurs. Reconnection may only occur in locations where huge gradients of the magnetic field develop, and one candidate for such locations are magnetic null points, known to be abundant for example in the solar atmosphere. Reconnection leads to changes in the topology of the magnetic field, and energy being released as heat, kinetic energy and acceleration of particles. Thus reconnection is responsible for many dynamic processes, for instance flares and jets. Aims: The aim of this paper is to investigate the properties of magnetic reconnection at a 3D null point, with respect to their dependence on the symmetry of the magnetic field around the null. In particular we examine the rate of reconnection of magnetic flux at the null point, as well as how the current sheet forms and its properties. Methods: We use mathematical modelling and finite difference resistive MHD simulations. Results: It is found that the basic structure of the mode of magnetic reconnection considered is unaffected by varying the magnetic field symmetry, that is, the plasma flow is found to cross both the spine and fan of the null. However, the peak intensity and dimensions of the current sheet are dependent on the symmetry/asymmetry of the field lines. As a result, the reconnection rate is also found to be strongly dependent on the field asymmetry. Conclusions: The symmetry/asymmetry of the magnetic field in the vicinity of a magnetic null can have a profound effect on the geometry of any associated reconnection region, and the rate at which the reconnection process proceeds.
Einstein equations in the null quasi-spherical gauge; 3, numerical algorithms
Bartnik, R A; Bartnik, Robert A.; Norton, Andrew H.
1999-01-01
We describe numerical techniques used in the construction of our 4th order evolution for the full Einstein equations, and assess the accuracy of representative solutions. The code is based on a null gauge with a quasi-spherical radial coordinate, and simulates the interaction of a single black hole with gravitational radiation. Techniques used include spherical harmonic representations, convolution spline interpolation and filtering, and an RK4 "method of lines" evolution. For sample initial data of "intermediate" size (gravitational field with 19% of the black hole mass), the code is accurate to 1 part in 10^5, until null time z=55 when the coordinate condition breaks down.
Organic anion transporting polypeptide 1a1 null mice are sensitive to cholestatic liver injury.
Zhang, Youcai; Csanaky, Iván L; Cheng, Xingguo; Lehman-McKeeman, Lois D; Klaassen, Curtis D
2012-06-01
Organic anion transporting polypeptide 1a1 (Oatp1a1) is predominantly expressed in livers of mice and is thought to transport bile acids (BAs) from blood into liver. Because Oatp1a1 expression is markedly decreased in mice after bile duct ligation (BDL). We hypothesized that Oatp1a1-null mice would be protected against liver injury during BDL-induced cholestasis due largely to reduced hepatic uptake of BAs. To evaluate this hypothesis, BDL surgeries were performed in both male wild-type (WT) and Oatp1a1-null mice. At 24 h after BDL, Oatp1a1-null mice showed higher serum alanine aminotransferase levels and more severe liver injury than WT mice, and all Oatp1a1-null mice died within 4 days after BDL, whereas all WT mice survived. At 24 h after BDL, surprisingly Oatp1a1-null mice had higher total BA concentrations in livers than WT mice, suggesting that loss of Oatp1a1 did not prevent BA accumulation in the liver. In addition, secondary BAs dramatically increased in serum of Oatp1a1-null BDL mice but not in WT BDL mice. Oatp1a1-null BDL mice had similar basolateral BA uptake (Na(+)-taurocholate cotransporting polypeptide and Oatp1b2) and BA-efflux (multidrug resistance-associated protein [Mrp]-3, Mrp4, and organic solute transporter α/β) transporters, as well as BA-synthetic enzyme (Cyp7a1) in livers as WT BDL mice. Hepatic expression of small heterodimer partner Cyp3a11, Cyp4a14, and Nqo1, which are target genes of farnesoid X receptor, pregnane X receptor, peroxisome proliferator-activated receptor alpha, and NF-E2-related factor 2, respectively, were increased in WT BDL mice but not in Oatp1a1-null BDL mice. These results demonstrate that loss of Oatp1a1 function exacerbates cholestatic liver injury in mice and suggest that Oatp1a1 plays a unique role in liver adaptive responses to obstructive cholestasis.
Null tests for oblate spheroids. [aspheric surfaces in reflecting optical system designs
Rodgers, J. M.; Parks, R. E.
1984-01-01
In most real cases requiring simple null optics, the optical path difference cannot be reduced to zero but can be kept at a fractional wavelength level so that interferometric data reduction can be used to account for the residual error. In other cases, computer-generated holograms may be used to obtain apparently straight fringes when the desired surface is obtained. Two examples, one involving an f/2.5 concave oblate spheroid and the other a Paul-Baker secondary, are examined. It is shown that although the null tests are not generally perfect, the residual error is small and the tests are simple.
Noncolocated Time-Reversal MUSIC: High-SNR Distribution of Null Spectrum
Ciuonzo, Domenico; Rossi, Pierluigi Salvo
2017-04-01
We derive the asymptotic distribution of the null spectrum of the well-known Multiple Signal Classification (MUSIC) in its computational Time-Reversal (TR) form. The result pertains to a single-frequency non-colocated multistatic scenario and several TR-MUSIC variants are here investigated. The analysis builds upon the 1st-order perturbation of the singular value decomposition and allows a simple characterization of null-spectrum moments (up to the 2nd order). This enables a comparison in terms of spectrums stability. Finally, a numerical analysis is provided to confirm the theoretical findings.
An efficient algorithm for antenna synthesis updating following null-constraint changes
Magdy, M. A.; Paoloni, F. J.; Cheah, J. Y. C.
1985-08-01
The procedure to maximize the array signal to noise ratio with null constraints involves an optimization problem that can be solved efficiently using a modified Cholesky decomposition (UD) technique. Following changes in the main lobe and/or null positions, the optimal element weight vector can be updated without the need for a new complete matrix inversion. Some properties of the UD technique can be utilized such that the updating algorithm reprocesses only a part of the unit triangular matrix U. Proper ordering of matrix entries can minimize the dimension of the updated part.
Balance recovery control for biped robot based on reaction null space method
Institute of Scientific and Technical Information of China (English)
Baoping WANG; Renxi HU; Jinming ZHANG; Chuangfeng HUAI
2009-01-01
A biped walking robot should be able to keep balance even in the presence of disturbing forces.This paper presents a step strategy concept of biped walking robot that is stabilized by using reaction null space method.The called "step strategy" can be modeled by means of the reaction null space method that introduced earlier to tackle dynamic interaction problems of free-floating robots,or moving base robots in general.6-DOF biped robot model simulations are used to confirm the validity.
A Fortran Code for Null Geodesic Solutions in the Lemaitre-Tolman-Bondi Spacetime
Ribeiro, Marcelo B.
2002-01-01
This paper describes the Fortran 77 code SIMU, version 1.1, designed for numerical simulations of observational relations along the past null geodesic in the Lemaitre-Tolman-Bondi (LTB) spacetime. SIMU aims at finding scale invariant solutions of the average density, but due to its full modularity it can be easily adapted to any application which requires LTB's null geodesic solutions. In version 1.1 the numerical output can be read by the GNUPLOT plotting package to produce a fully graphical...
A Fortran Code for Null Geodesic Solutions in the Lemaitre-Tolman-Bondi Spacetime
Ribeiro, M B
2002-01-01
This paper describes the Fortran 77 code SIMU, version 1.1, designed for numerical simulations of observational relations along the past null geodesic in the Lemaitre-Tolman-Bondi (LTB) spacetime. SIMU aims at finding scale invariant solutions of the average density, but due to its full modularity it can be easily adapted to any application which requires LTB's null geodesic solutions. In version 1.1 the numerical output can be read by the GNUPLOT plotting package to produce a fully graphical output, although other plotting routines can be easily adapted. Details of the code's subroutines are discussed, and an example of its output is shown.
A Fortran code for null geodesic solutions in the Lemaître-Tolman-Bondi spacetime
Ribeiro, Marcelo B.
2002-10-01
This paper describes the Fortran 77 code SIMU, version 1.1, designed for numerical simulations of observational relations along the past null geodesic in the Lemaître-Tolman-Bondi (LTB) spacetime. SIMU aims at finding scale invariant solutions of the average density, but due to its full modularity it can be easily adapted to any application which requires LTB's null geodesic solutions. In version 1.1 the numerical output can be read by the GNUPLOT plotting package to produce a fully graphical output, although other plotting routines can be easily adapted. Details of the code's subroutines are discussed, and an example of its output is shown.
Current sheets at three-dimensional magnetic nulls: Effect of compressibility
Pontin, D I; Galsgaard, K
2007-01-01
The nature of current sheet formation in the vicinity of three-dimensional magnetic null points is investigated. The particular focus is upon the effect of the compressibility of the plasma on the qualitative and quantitative properties of the current sheet. It is found that as the incompressible limit is approached, the collapse of the null point is suppressed, and instead an approximately planar current sheet aligned to the fan plane is present. Both the peak current and peak reconnection rate are reduced. The results imply that previous analytical solutions for steady-state reconnection at fan current sheets are dynamically accessible, while spine current sheet solutions are not.
Magnetic reconnection in turbulent space plasmas: null-points or pinches?
Olshevsky, Vyacheslav; Lapenta, Giovanni; Markidis, Stefano; Divin, Andrey
2014-05-01
We report particle-in-cell simulations of magnetic reconnection in the configuration containing both null-points and pinches. All indicators suggest that secondary magnetic reconnection driven by kinking of the pinches plays a dominant role in the energetics of the system. While there is no substantial energy dissipation in the vicinity of X-type null-points. Such reconnection results in tremendous release of magnetic energy, generation of suprathermal particles and waves. Similar scenario may take place in turbulent space plasmas, where current channels and twisted magnetic fields are detected.
Numata, Ryusuke; Yoshida, Zensho
2003-07-01
Magnetic null points act as scattering centers where particles describe chaotic orbits, and the mixing effect brings about increase of the kinetic entropy. The resultant "chaos-induced resistivity" may explain anomalous diffusion of current in magnetic null regions [Phys. Rev. Lett. 88, 045003 (2002)], which can be much larger than the conventional collisionless resistivity in a high temperature plasma. To study the statistical properties of the system (such as Lyapunov exponents and distribution functions), strong spatial inhomogeneity of the system has been studied to specify the responsible "chaos region."
The effects of near null magnetic field upon the leucocyte response in rats.
Dorofteiu, M; Morariu, V V; Marina, C; Zirbo, M
1995-01-01
Wistar rats were kept for 2 and 4 weeks in conditions of near null magnetic field. The total serum proteins, lipids and glucides, as well as the leucocyte and neutrophil counts showed no significant changes against controls kept in natural magnetic field conditions. A significant monocytosis, a decrease in the circulating phagocyte count and in the phagocytic activity was noticed in null magnetic field. These results suggest that the natural magnetic field significantly influences health both on the ground and possibly in cosmic conditions.
On-sky speckle nulling demonstration at small angular separation with SCExAO
Martinache, Frantz; Jovanovic, Nemanja; Clergeon, Christophe; Singh, Garima; Kudo, Tomoyuki; Currie, Thayne; Thalmann, Christian; McElwain, Michael; Tamura, Motohide
2014-01-01
This paper presents the first on-sky demonstration of speckle nulling, which was achieved at the Subaru Telescope in the context of the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) Project. Despite the absence of a high-order high-bandwidth closed-loop AO system, observations conducted with SCExAO show that even in poor-to-moderate observing conditions, speckle nulling can be used to suppress static and slow speckles even in the presence of a brighter dynamic speckle halo, suggesting that more advanced high-contrast imaging algorithms developed in the laboratory can be applied to ground-based systems.
Influence of C4 null alleles on C4 activation in systemic lupus erythematosus.
Briggs, D C; Senaldi, G; Isenberg, D A; Welsh, K I; Vergani, D.
1991-01-01
Deficiencies of early components of the classical complement pathway are known to be associated with systemic lupus erythematosus (SLE). C4 null alleles, C4A Q0 and C4B Q0, are prime candidates for the major histocompatibility complex associated factor which determines susceptibility to SLE. There is poor correlation, however, between the presence of low concentrations of C4 and possession of C4 null alleles, and thus the basis of the association between C4A Q0, C4B Q0 and SLE remains obscure...
Corneal topography with conical null-screen for non-symmetric aspheric corneas
Armengol-Cruz, Victor de Emanuel; Osorio-Infante, Arturo I.; Campos-García, Manuel; Cossio-Guerrero, Cesar; Díaz-Uribe, José Rufino
2016-09-01
In this work, we will present some improvements to the conical null-screen based corneal topographer, for testing aspheric surfaces without rotational symmetry. We present the formulae to design the conical null-screen in such a way that the image on the CCD is a perfect array of spots; departures from this geometry are due to deformation or misalignment of the surface. Additionally, we will explain how to improve the algorithms to find the normals of corneal surface. Finally, we will evaluate the topography of a spherical surface.
A Review of Phase-Only Sidelobe Nulling Investigations at RADC (Rome Air Development Center).
1985-08-01
IC.ntno ,1 reon nir-. ’I0P0ITAd Ident~y by blocknonbI FIEL GRUP SB G Linear Arrays-, Pattern Synthesis, 093 10 Phase-Only Weight Control,. Adaptive Nulling...Obtaining the phase perturbations that satisfy the null equations (1) subject 4. to minimizing the objective function F, given by Eq. (2), is a nonlinear...dnum) 0 m 1, 2. M , N even n=l (N-)/2 an cos(on ++ + d )+ a m 1, 2, M nflI N odd and the objective function , Eq. (2), as N/2 c 8 sin2 n , N evenF = 8
Causality and entropic arguments pointing to a null Big Bag hypersurface
Energy Technology Data Exchange (ETDEWEB)
Minguzzi, E, E-mail: ettore.minguzzi@unifi.it [Dipartimento di Matematica Applicata, Universita degli Studi di Firenze, Via S. Marta 3, I-50139 Firenze (Italy)
2011-09-22
I propose a causality argument in order to solve the homogeneity (horizon) problem and the entropy problem of cosmology. The solution is based on the replacement of the spacelike Big Bang boundary with a null boundary behind which stays a chronology violating region. This solution requires a tilting of the light cones near the null boundary and thus it is based more on the behavior of the light cones and hence on causality than on the behavior of the scale factor (expansion). The connection of this picture with Augustine of Hippo famous philosophical discussion on time and creation is mentioned.
A combined nulling and imaging pupil-plane beam-combiner for DARWIN
Haaksman, R.P.H.; Vries, C.P. de; Herder, J.-W. den; Vosteen, L.L.A.; Bokhove, H.; Mieremet, A.L.
2006-01-01
The primary goal of DARWIN is to detect earth-like extrasolar planets and to search for biomarkers. This is achieved by means of nulling interferometry, using three free-flying telescopes and a Beam-Combiner (BC) hub. DARWIN will be able to perform astrophysical imaging with high spectral and spatia
Reduced infarct size in neuroglobin-null mice after experimental stroke in vivo
Directory of Open Access Journals (Sweden)
Raida Zindy
2012-08-01
Full Text Available Abstract Background Neuroglobin is considered to be a novel important pharmacological target in combating stroke and neurodegenerative disorders, although the mechanism by which this protection is accomplished remains an enigma. We hypothesized that if neuroglobin is directly involved in neuroprotection, then permanent cerebral ischemia would lead to larger infarct volumes in neuroglobin-null mice than in wild-type mice. Methods Using neuroglobin-null mice, we estimated the infarct volume 24 hours after permanent middle cerebral artery occlusion using Cavalieri’s Principle, and compared the infarct volume in neuroglobin-null and wild-type mice. Neuroglobin antibody staining was used to examine neuroglobin expression in the infarct area of wild-type mice. Results Infarct volumes 24 hours after permanent middle cerebral artery occlusion were significantly smaller in neuroglobin-null mice than in wild-types (p Conclusions Neuroglobin-deficiency resulted in reduced tissue infarction, suggesting that, at least at endogenous expression levels, neuroglobin in itself is non-protective against ischemic injury.
Interpretation of Chinese Overt and Null Embedded Arguments by English-Speaking Learners
Zhao, Lucy Xia
2012-01-01
It has been proposed that external interfaces are vulnerable to residue optionality, whereas pure syntax and internal interfaces are acquirable in second language (L2) acquisition (Sorace, 2005, 2011; Sorace and Filiaci, 2006). The proposal was tested in this article through the interpretation of overt and null embedded arguments in L2 Chinese…
High Contrast Vacuum Nuller Testbed (VNT) Contrast, Performance and Null Control
Lyon, Richard G.; Clampin, Mark; Petrone, Peter; Mallik, Udayan; Madison, Timothy; Bolcar, Matthew R.
2012-01-01
Herein we report on our Visible Nulling Coronagraph high-contrast result of 109 contrast averaged over a focal planeregion extending from 14 D with the Vacuum Nuller Testbed (VNT) in a vibration isolated vacuum chamber. TheVNC is a hybrid interferometriccoronagraphic approach for exoplanet science. It operates with high Lyot stopefficiency for filled, segmented and sparse or diluted-aperture telescopes, thereby spanning the range of potential futureNASA flight telescopes. NASAGoddard Space Flight Center (GSFC) has a well-established effort to develop the VNCand its technologies, and has developed an incremental sequence of VNC testbeds to advance this approach and itsenabling technologies. These testbeds have enabled advancement of high-contrast, visible light, nulling interferometry tounprecedented levels. The VNC is based on a modified Mach-Zehnder nulling interferometer, with a W configurationto accommodate a hex-packed MEMS based deformable mirror, a coherent fiber bundle and achromatic phase shifters.We give an overview of the VNT and discuss the high-contrast laboratory results, the optical configuration, criticaltechnologies and null sensing and control.
A Range-Null Hypothesis Approach for Testing DIF under the Rasch Model
Wells, Craig S.; Cohen, Allan S.; Patton, Jeffrey
2009-01-01
A primary concern with testing differential item functioning (DIF) using a traditional point-null hypothesis is that a statistically significant result does not imply that the magnitude of DIF is of practical interest. Similarly, for a given sample size, a non-significant result does not allow the researcher to conclude the item is free of DIF. To…
Application of a Null-Beamformer to Source Localisation in MEG Data of Deep Brain Stimulation
DEFF Research Database (Denmark)
Mohseni, Hamid R.; Kringelbach, Morten L.; Smith, Penny Probert;
2010-01-01
to reconstruct the neural activity of interest is challenging because of interference to the signal from the DBS device. We demonstrate that a null-beamformer can be used to localise neural activity despite artefacts caused by the presence of DBS electrodes and stimulus pulses. We subsequently verified...
A Critical Assessment of Null Hypothesis Significance Testing in Quantitative Communication Research
Levine, Timothy R.; Weber, Rene; Hullett, Craig; Park, Hee Sun; Lindsey, Lisa L. Massi
2008-01-01
Null hypothesis significance testing (NHST) is the most widely accepted and frequently used approach to statistical inference in quantitative communication research. NHST, however, is highly controversial, and several serious problems with the approach have been identified. This paper reviews NHST and the controversy surrounding it. Commonly…
LeMire, Steven D.
2010-01-01
This paper proposes an argument framework for the teaching of null hypothesis statistical testing and its application in support of research. Elements of the Toulmin (1958) model of argument are used to illustrate the use of p values and Type I and Type II error rates in support of claims about statistical parameters and subject matter research…
Impaired insulin secretion and glucose intolerance in synaptotagmin-7 null mutant mice
DEFF Research Database (Denmark)
Gustavsson, Natalia; Lao, Ye; Maximov, Anton;
2008-01-01
secretion in pancreatic beta-cells. Of these other synaptotagmins, synaptotagmin-7 is one of the most abundant and is present in pancreatic beta-cells. To determine whether synaptotagmin-7 regulates Ca(2+)-dependent insulin secretion, we analyzed synaptotagmin-7 null mutant mice for glucose tolerance...
Stable deep nulling in polychromatic unpolarized light with multiaxial beam combination.
Buisset, Christophe; Rejeaunier, Xavier; Rabbia, Yves; Barillot, Marc
2007-11-10
In the context of the space-based nulling mission ESA-Darwin, Thales Alenia Space has developed a nulling breadboard for the European Space Agency (ESA): the multiaperture imaging interferometer (MAII) to demonstrate deep and stable nulling and to investigate various subsystems of the ESA-Darwin interferometer. Recently, we have extended our investigations to the multiaxial beam combination. This combination scheme presents many advantages: simplicity, compactness, and a high coupling efficiency for a three-beam combination. The near-infrared (lambda approximately 1.55 microm) MAII breadboard has been upgraded to the multiaxial beam combination. Polarization and stability issues have been thoroughly investigated. We report on the recent results we have obtained with the multiaxial configuration of MAII in unpolarized light with a relative spectral bandwidth of 5%: nulling ratios of mean value N=1.7 x 10(-5), stable over 1 h with a standard deviation sigma( N )=5.7 x 10(-7). These results indicate that the multiaxial beam combination has the potential to meet Darwin requirements.
Determination of the true null electrode spacing of an extrapolation chamber for X-ray dosimetry
Energy Technology Data Exchange (ETDEWEB)
Figueiredo, M.T.T.; Bastos, F.M.; Silva, T.A. da, E-mail: mttf@cdtn.br, E-mail: fmb@cdtn.br, E-mail: silvata@cdtn.br [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil). Pos-Graduacao em Ciencia e Tecnologia da Radiacao, Minerais e Materiais
2015-07-01
An accurate determination of the actual null distance is critical for the establishment of primary measurement method for absorbed dose in tissue, since the concept of the true null electrode spacing is used to define the sensitive volume of an extrapolation chamber. In this paper, a critical analysis of two methodologies for determining the true null electrode spacing of an extrapolation chamber was done. Firstly, the ionization current as a function of electrode spacing was measured in ISO 4037 low energy X-ray beams. In the second procedure, a LC Bridge was used to measure the capacitance between the electrodes of a 23392 Böhm model PTW ionization chamber and a reliable relationship between capacitance and relative distance was established. Results showed that the true null spacing values varied from 0.0015 to 0.38 mm. Since capacitance meters with high resolution are not always available in calibration laboratories, the second method showed values with large uncertainties. The first method proved to be highly sensitive to the quality of the X-ray beams used. (author)
Null geodesics in the Reissner-Nordstr\\"om Anti-de Sitter black holes
Cruz, Norman; Saavedra, Joel; Villanueva, J R
2011-01-01
In this work we address the study of null geodesics in the background of Reissner-Nordstr\\"om Anti de Sitter black holes. We compute the exact trajectories in terms of elliptic functions of Weierstrass, obtaining a detailed description of the orbits in terms of charge, mass and the cosmological constant. The trajectories of the photon are classified using the impact parameter.
Global Null Controllability of the 1-Dimensional Nonlinear Slow Diffusion Equation
Institute of Scientific and Technical Information of China (English)
Jean-Michel CORON; Jesús Ildefonso D（I）AZ; Abdelmalek DRICI; Tommaso MINGAZZINI
2013-01-01
The authors prove the global null controllability for the 1-dimensional nonlinear slow diffusion equation by using both a boundary and an internal control.They assume that the internal control is only time dependent.The proof relies on the return method in combination with some local controllability results for nondegenerate equations and rescaling techniques.
Incisional wound healing in transforming growth factor-beta1 null mice.
Koch, R M; Roche, N S; Parks, W T; Ashcroft, G S; Letterio, J J; Roberts, A B
2000-01-01
Expression of endogenous transforming growth factor-beta1 is reduced in many animal models of impaired wound healing, and addition of exogenous transforming growth factor-beta has been shown to improve healing. To test the hypothesis that endogenous transforming growth factor-beta1 is essential for normal wound repair, we have studied wound healing in mice in which the transforming growth factor-beta1 gene has been deleted by homologous recombination. No perceptible differences were observed in wounds made in 3-10-day-old neonatal transforming growth factor-beta1 null mice compared to wild-type littermates. To preclude interference from maternally transferred transforming growth factor-beta1, cutaneous wounds were also made on the backs of 30-day-old transforming growth factor-beta1 null and littermate control mice treated with rapamycin, which extends their lifetime and suppresses the inflammatory response characteristic of the transforming growth factor-beta1 null mice. Again, no impairment in healing was seen in transforming growth factor-beta1 null mice. Instead these wounds showed an overall reduction in the amount of granulation tissue and an increased rate of epithelialization compared to littermate controls. Our data suggest that release of transforming growth factor-beta1 from degranulating platelets or secretion by infiltrating macrophages and fibroblasts is not critical to initiation or progression of tissue repair and that endogenous transforming growth factor-beta1 may actually function to increase inflammation and retard wound closure.
Experimental progress in deep and broadband infrared nulling for TPF-I
Wallace, J. Kent; Bartos, Randall; Gappinger, Robert; Loya, Frank; Moser, Steve; Negron, John
2005-01-01
Our activities are focused upon the experimental demonstration of deep nulling in the mid-IR over a wide bandpass. Specifically, our near-term goal is demonstrating a contrast of 10^-6 at 10 um with a 25% spectral bandwidth.
Charged null fluid collapse in anti-de Sitter spacetimes and naked singularities
Ghosh, S G
2000-01-01
We investigate the occurrence of naked singularities in the spherically symmetric, plane symmetric and cylindrically symmetric collapse of charged null fluid in an anti-de Sitter background. The naked singularities are found to be strong in Tipler's sense and thus violate the cosmic censorship conjecture, but not hoop conjecture.
Rao, Shanti R.; Wallacea, J. Kent; Samuele, Rocco; Chakrabarti, Supriya; Cook, Timothy; Hicks, Brian; Jung, Paul; Lane, Benjamin; Levine, B. Martin; Mendillo, Chris; Schmidtlin, Edouard; Shao, Mike; Stewart, Jason B.
2008-01-01
We report progress on a nulling coronagraph intended for direct imaging of extrasolar planets. White light is suppressed in an interferometer, and phase errors are measured by a second interferometer. A 1020-pixel MEMS deformable mirror in the first interferometer adjusts the path length across the pupil. A feedback control system reduces deflections of the deformable mirror to order of 1 nm rms.
Magnetohydrodynamics dynamical relaxation of coronal magnetic fields. IV. 3D tilted nulls
Fuentes-Fernandez, Jorge
2013-01-01
In this paper we study current accumulations in 3D "tilted" nulls formed by a folding of the spine and fan. A non-zero component of current parallel to the fan is required such that the null's fan plane and spine are not perpendicular. Our aims are to provide valid magnetohydrostatic equilibria and to describe the current accumulations in various cases involving finite plasma pressure.To create our equilibrium current structures we use a full, non-resistive, magnetohydrodynamic (MHD) code so that no reconnection is allowed. A series of experiments are performed in which a perturbed 3D tilted null relaxes towards an equilibrium via real, viscous damping forces. Changes to the initial plasma pressure and to magnetic parameters are investigated systematically.An initially tilted fan is associated with a non-zero Lorentz force that drives the fan and spine to collapse towards each other, in a similar manner to the collapse of a 2D X-point. In the final equilibrium state for an initially radial null with only the ...
3D MHD Coronal Oscillations About a Magnetic Null Point: Application of WKB Theory
McLaughlin, J A; Hood, A W
2007-01-01
This paper is a demonstration of how the WKB approximation can be used to help solve the linearised 3D MHD equations. Using Charpit's Method and a Runge-Kutta numerical scheme, we have demonstrated this technique for a potential 3D magnetic null point, ${\\bf{B}}=(x,\\epsilon y -(\\epsilon +1)z)$. Under our cold plasma assumption, we have considered two types of wave propagation: fast magnetoacoustic and Alfv\\'en waves. We find that the fast magnetoacoustic wave experiences refraction towards the magnetic null point, and that the effect of this refraction depends upon the Alfv\\'en speed profile. The wave, and thus the wave energy, accumulates at the null point. We have found that current build up is exponential and the exponent is dependent upon $\\epsilon$. Thus, for the fast wave there is preferential heating at the null point. For the Alfv\\'en wave, we find that the wave propagates along the fieldlines. For an Alfv\\'en wave generated along the fan-plane, the wave accumulates along the spine. For an Alfv\\'en wa...
Electric Current Filamentation at a Non-potential Magnetic Null-point Due to Pressure Perturbation
Jelínek, P.; Karlický, M.; Murawski, K.
2015-10-01
An increase of electric current densities due to filamentation is an important process in any flare. We show that the pressure perturbation, followed by an entropy wave, triggers such a filamentation in the non-potential magnetic null-point. In the two-dimensional (2D), non-potential magnetic null-point, we generate the entropy wave by a negative or positive pressure pulse that is launched initially. Then, we study its evolution under the influence of the gravity field. We solve the full set of 2D time dependent, ideal magnetohydrodynamic equations numerically, making use of the FLASH code. The negative pulse leads to an entropy wave with a plasma density greater than in the ambient atmosphere and thus this wave falls down in the solar atmosphere, attracted by the gravity force. In the case of the positive pressure pulse, the plasma becomes evacuated and the entropy wave propagates upward. However, in both cases, owing to the Rayleigh-Taylor instability, the electric current in a non-potential magnetic null-point is rapidly filamented and at some locations the electric current density is strongly enhanced in comparison to its initial value. Using numerical simulations, we find that entropy waves initiated either by positive or negative pulses result in an increase of electric current densities close to the magnetic null-point and thus the energy accumulated here can be released as nanoflares or even flares.
The Number Of Magnetic Null Points In The Quiet Sun Corona
Longcope, D W
2008-01-01
The coronal magnetic field above a particular photospheric region will vanish at a certain number of points, called null points. These points can be found directly in a potential field extrapolation or their density can be estimated from Fourier spectrum of the magnetogram. The spectral estimate, which assumes that the extrapolated field is random, homogeneous and has Gaussian statistics, is found here to be relatively accurate for quiet Sun magnetograms from SOHO's MDI. The majority of null points occur at low altitudes, and their distribution is dictated by high wavenumbers in the Fourier spectrum. This portion of the spectrum is affected by Poisson noise, and as many as five-sixths of null points identified from a direct extrapolation can be attributed to noise. The null distribution above 1500 km is found to depend on wavelengths that are reliably measured by MDI in either its low-resolution or high-resolution mode. After correcting the spectrum to remove white noise and compensate for the modulation tran...
Reconnection at three dimensional magnetic null points: Effect of current sheet asymmetry
Wyper, P. F.; Jain, Rekha
2013-05-01
Asymmetric current sheets are likely to be prevalent in both astrophysical and laboratory plasmas with complex three dimensional (3D) magnetic topologies. This work presents kinematic analytical models for spine and fan reconnection at a radially symmetric 3D null (i.e., a null where the eigenvalues associated with the fan plane are equal) with asymmetric current sheets. Asymmetric fan reconnection is characterized by an asymmetric reconnection of flux past each spine line and a bulk flow of plasma across the null point. In contrast, asymmetric spine reconnection is characterized by the reconnection of an equal quantity of flux across the fan plane in both directions. The higher modes of spine reconnection also include localized wedges of vortical flux transport in each half of the fan. In this situation, two definitions for reconnection rate become appropriate: a local reconnection rate quantifying how much flux is genuinely reconnected across the fan plane and a global rate associated with the net flux driven across each semi-plane. Through a scaling analysis, it is shown that when the ohmic dissipation in the layer is assumed to be constant, the increase in the local rate bleeds from the global rate as the sheet deformation is increased. Both models suggest that asymmetry in the current sheet dimensions will have a profound effect on the reconnection rate and manner of flux transport in reconnection involving 3D nulls.
Magnetic moments of baryons with null instanton in relation to SU[sub 6] model
Energy Technology Data Exchange (ETDEWEB)
Iwao, Syurei (Kanazawa Univ. (Japan). Faculty of Science)
1993-10-01
A dynamical symmetry breaking effect on the SU[sub 6] model for the magnetic moments of baryons is considered, based on the null instanton picture for them. A certain improvement of the fit to the available data is obtained. (author).
Steady state reconnection at a single 3D magnetic null point
Galsgaard, K
2011-01-01
To systematically stress a rotationally symmetric 3D magnetic null point by advecting the opposite footpoints of the spine axis in opposite directions. This stress eventually concentrates in the vicinity of the null point forming a local current sheet through which magnetic reconnection takes place. The aim is to look for a steady state evolution of the current sheet dynamics which may provide scaling relations for various characteristic parameters of the system. The evolution is followed by solving numerically the non-ideal MHD equations in a Cartesian domain. The null point is embedded in an initially constant density and temperature plasma. It is shown that a quasi-steady reconnection process can be set up at a 3D null by continuous shear driving. It appears that a true steady state in unlikely to be realised as the current layer tends to grow until restricted by the geometry of the computational domain and imposed driving profile. However, ratios between characteristic quantities clearly settle after some...
Nonlinear Alfv\\'en wave dynamics at a 2D magnetic null point: ponderomotive force
Thurgood, J O
2013-01-01
Context : In the linear, {\\beta}=0 MHD regime, the transient properties of MHD waves in the vicinity of 2D null points are well known. The waves are decoupled and accumulate at predictable parts of the magnetic topology: fast waves accumulate at the null point; whereas Alfv\\'en waves cannot cross the separatricies. However, in nonlinear MHD mode conversion can occur at regions of inhomogeneous Alfv\\'en speed, suggesting that the decoupled nature of waves may not extend to the nonlinear regime. Aims: We investigate the behaviour of low-amplitude Alfv\\'en waves about a 2D magnetic null point in nonlinear, {\\beta}= 0 MHD. Methods: We numerically simulate the introduction of low-amplitude Alfv\\'en waves into the vicinity of a magnetic null point using the nonlinear LARE2D code. Results: Unlike in the linear regime, we find that the Alfv\\'en wave sustains cospatial daughter disturbances, manifest in the transverse and longitudinal fluid velocity, owing to the action of nonlinear magnetic pressure gradients (viz. t...
ELECTRIC CURRENT FILAMENTATION AT A NON-POTENTIAL MAGNETIC NULL-POINT DUE TO PRESSURE PERTURBATION
Energy Technology Data Exchange (ETDEWEB)
Jelínek, P. [University of South Bohemia, Faculty of Science, Institute of Physics and Biophysics, Branišovská 10, CZ-37005 České Budějovice (Czech Republic); Karlický, M. [Academy of Sciences of the Czech Republic, v. v. i., Astronomical Institute, Fričova 258, CZ-25165 Ondřejov (Czech Republic); Murawski, K., E-mail: pjelinek@prf.jcu.cz [Maria Curie-Skłodowska University, Institute of Physics, Group of Astrophysics, Radziszewskiego 10, PL-20031 Lublin (Poland)
2015-10-20
An increase of electric current densities due to filamentation is an important process in any flare. We show that the pressure perturbation, followed by an entropy wave, triggers such a filamentation in the non-potential magnetic null-point. In the two-dimensional (2D), non-potential magnetic null-point, we generate the entropy wave by a negative or positive pressure pulse that is launched initially. Then, we study its evolution under the influence of the gravity field. We solve the full set of 2D time dependent, ideal magnetohydrodynamic equations numerically, making use of the FLASH code. The negative pulse leads to an entropy wave with a plasma density greater than in the ambient atmosphere and thus this wave falls down in the solar atmosphere, attracted by the gravity force. In the case of the positive pressure pulse, the plasma becomes evacuated and the entropy wave propagates upward. However, in both cases, owing to the Rayleigh–Taylor instability, the electric current in a non-potential magnetic null-point is rapidly filamented and at some locations the electric current density is strongly enhanced in comparison to its initial value. Using numerical simulations, we find that entropy waves initiated either by positive or negative pulses result in an increase of electric current densities close to the magnetic null-point and thus the energy accumulated here can be released as nanoflares or even flares.
Reconnection at three dimensional magnetic null points: Effect of current sheet asymmetry
Energy Technology Data Exchange (ETDEWEB)
Wyper, P. F.; Jain, Rekha [School of Mathematics and Statistics, University of Sheffield, Sheffield, South Yorkshire S3 7RH (United Kingdom)
2013-05-15
Asymmetric current sheets are likely to be prevalent in both astrophysical and laboratory plasmas with complex three dimensional (3D) magnetic topologies. This work presents kinematic analytical models for spine and fan reconnection at a radially symmetric 3D null (i.e., a null where the eigenvalues associated with the fan plane are equal) with asymmetric current sheets. Asymmetric fan reconnection is characterized by an asymmetric reconnection of flux past each spine line and a bulk flow of plasma across the null point. In contrast, asymmetric spine reconnection is characterized by the reconnection of an equal quantity of flux across the fan plane in both directions. The higher modes of spine reconnection also include localized wedges of vortical flux transport in each half of the fan. In this situation, two definitions for reconnection rate become appropriate: a local reconnection rate quantifying how much flux is genuinely reconnected across the fan plane and a global rate associated with the net flux driven across each semi-plane. Through a scaling analysis, it is shown that when the ohmic dissipation in the layer is assumed to be constant, the increase in the local rate bleeds from the global rate as the sheet deformation is increased. Both models suggest that asymmetry in the current sheet dimensions will have a profound effect on the reconnection rate and manner of flux transport in reconnection involving 3D nulls.
A null coframe formulation of quadratic curvature gravity and gravitational wave solutions
Baykal, Ahmet
2014-01-01
Quadratic curvature gravity equations are projected to a complex null coframe by using the algebra of exterior forms and expressed in terms of the spinor quantities defined originally by Newman and Penrose. As an application, a new family of impulsive gravitational wave solutions propagating in various type D backgrounds are introduced.
Moving non-null curves according to Bishop frame in Minkowski 3-space
Gürbüz, Nevin
2015-04-01
In this paper, we introduce three new transformations and establish connections between moving non-null curves and soliton equations according to Bishop frame in Minkowski 3-space. Later we find formulas for differentials of these three new transformations associated with the nonlinear heat system and repulsive type nonlinear Schrödinger equation.
Null exact controllability of the parabolic equations with equivalued surface boundary condition
Directory of Open Access Journals (Sweden)
2006-01-01
Full Text Available This paper is devoted to showing the null exact controllability for a class of parabolic equations with equivalued surface boundary condition. Our method is based on the duality argument and global Carleman-type estimate for a parabolic operator.
Directory of Open Access Journals (Sweden)
Amar Debbouche
2012-01-01
Full Text Available We introduce a new concept called implicit evolution system to establish the existence results of mild and strong solutions of a class of fractional nonlocal nonlinear integrodifferential system, then we prove the exact null controllability result of a class of fractional evolution nonlocal integrodifferential control system in Banach space. As an application that illustrates the abstract results, two examples are provided.
The Acquisition of Null and Overt Pronominals in Japanese by English Speakers.
Kanno, Kazue
1997-01-01
Examines the role of Universal Grammar in the second-language acquisition of Japanese by English speakers. The study focuses on the acquisition of the principle that prevents overt pronouns from having quantified noun phrases as antecedents in languages (such as Japanese) that have null pronouns. (16 references) (Author/CK)
Intimal hyperplasia in loop-injured carotid arteries is attenuated in transglutaminase 2-null mice.
Min, Seung-Kee; Min, Sang-Il; Jeong, Eui Man; Cho, Sung-Yup; Ha, Jongwon; Kim, Sang Joon; Kim, In-Gyu
2014-03-01
Arterial restenosis frequently develops after open or endovascular surgery due to intimal hyperplasia. Since tissue transglutaminase (TG2) is known to involve in fibrosis, wound healing, and extracellular matrix remodeling, we examined the role of TG2 in the process of intimal hyperplasia using TG2-null mice. The neointimal formation was compared between TG2-null and wild-type (C57BL/6) mice by two different injury models; carotid ligation and carotid loop injury. In ligation model, there was no difference in intimal thickness between two groups. In loop injury model, intimal hyperplasia developed in both groups and the intimal/medial area ratio was significantly reduced in TG2-null mice (P = 0.007). TG2 was intensely stained in neointimal cells in 2 weeks. In situ activity of TG2 in the injured arteries steadily increased until 4 weeks compared to uninjured arteries. Taken together, intimal hyperplasia was significantly reduced in TG2-null mice, indicating that TG2 has an important role in the development of intimal hyperplasia. This suggests that TG2 may be a novel target to prevent the arterial restenosis after vascular surgery.
Generation and characterization of UL21-null herpes simplex virus type 1
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Yoshifumi eMuto
2012-11-01
Full Text Available UL21 of herpes simplex virus type 1 (HSV-1 is an accessory gene that encodes a component of the tegument. Homologs of this protein have been identified in the alpha, beta, and gamma herpesvirus subfamilies, although their functions are unclear. To clarify the functions of UL21, we generated a UL21-null HSV-1 mutant. Growth analysis showed that the synthesis of infectious UL21-null HSV-1 in glial cells was delayed and that the overall yield was low. The plaque sizes of the UL21-null mutant were smaller than those of wild-type HSV-1. We identified several candidate UL21-interacting proteins, including intermediate filaments, by yeast two-hybrid screening. The distribution of glial fibrillary acidic protein (GFAP, which is the main component of intermediate filaments, was altered in UL21-null mutant-infected glial cells compared to wild-type virus-infected cells. These results will help clarify the function of UL21 and broaden our understanding of the life cycle of HSV.
Directory of Open Access Journals (Sweden)
Hongshan Liu
Full Text Available BACKGROUND: Keratoplasty is the most effective treatment for corneal blindness, but suboptimal medical conditions and lack of qualified medical personnel and donated cornea often prevent the performance of corneal transplantation in developing countries. Our study aims to develop alternative treatment regimens for congenital corneal diseases of genetic mutation. METHODOLOGY/PRINCIPAL FINDINGS: Human mesenchymal stem cells isolated from neonatal umbilical cords were transplanted to treat thin and cloudy corneas of lumican null mice. Transplantation of umbilical mesenchymal stem cells significantly improved corneal transparency and increased stromal thickness of lumican null mice, but human umbilical hematopoietic stem cells failed to do the same. Further studies revealed that collagen lamellae were re-organized in corneal stroma of lumican null mice after mesenchymal stem cell transplantation. Transplanted umbilical mesenchymal stem cells survived in the mouse corneal stroma for more than 3 months with little or no graft rejection. In addition, these cells assumed a keratocyte phenotype, e.g., dendritic morphology, quiescence, expression of keratocyte unique keratan sulfated keratocan and lumican, and CD34. Moreover, umbilical mesenchymal stem cell transplantation improved host keratocyte functions, which was verified by enhanced expression of keratocan and aldehyde dehydrogenase class 3A1 in lumican null mice. CONCLUSIONS/SIGNIFICANCE: Umbilical mesenchymal stem cell transplantation is a promising treatment for congenital corneal diseases involving keratocyte dysfunction. Unlike donated corneas, umbilical mesenchymal stem cells are easily isolated, expanded, stored, and can be quickly recovered from liquid nitrogen when a patient is in urgent need.
The frequency of GSTT1 null genotype in Turkish population and lung cancer risk
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Demir A
2005-01-01
Full Text Available BACKGROUND : Previous studies have suggested that Glutathione S -transferase (GST genotypes may play a role in determining susceptibility to lung cancer, though the data are often conflicting. In different ethnic groups variations in null allele frequency has been observed. AIMS: We aimed to evaluate whether genetic polymorphisms of Glutathione S -transferase theta (GSTT1 influence individual susceptibility to lung cancer in Turkish population. We tried to clarify the frequencies of GSTM1 gene polymorphisms in a Turkish population. METHODS: DNA samples, extracted from the whole blood were amplified using polymerase chain reaction (PCR method in all of the 68 cases, composed of 31 previously diagnosed lung cancer and 37 healthy controls. RESULTS: The prevalence of GSTT1 null genotype in the lung cancer patients was 29%, compared to 11% in control group. GSTT1 null genotype was found to be higher in cancer group compared to the control group, although it was not statistically significant (OR = 3.37, 95% CI = 0.92-12.32, P = 0.06. There was also no significant relation in GSTT1 genotypes among histopathology types of lung cancers. The frequency of GSTT1 was found to be 25.4% ( n = 952 when the studies of Turkish population were reviewed. CONCLUSION: It can be concluded that carrying the GSTT1 null genotype may be accepted as a weak risk factor for the susceptibility to lung cancer.
Differential protein expression in heart in UT-B null mice with cardiac conduction defects.
Yu, Hao; Meng, Yan; Wang, Li-Shun; Jin, Xian; Gao, Li-Fang; Zhou, Lei; Ji, Kun; Li, Yang; Zhao, Li-Juan; Chen, Guo-Qiang; Zhao, Xue-Jian; Yang, Baoxue
2009-02-01
Cardiac conduction defects were found in transgenic mice deficient in urea transporter UT-B. To investigate the molecular mechanisms of the conduction defects caused by UT-B deletion, we studied the protein expression profiles of heart tissue (comprising most conduction system) in wild-type versus UT-B null mice at different ages. By two-dimensional electrophoresis-based comparative analysis, we found that more than dozen proteins were modulated (>two-fold) in the myocardium of UT-B null mice. Out of these modulated proteins, troponin T (TNNT2) presented significant changes in UT-B null mice at early stage prior to the development of P-R interval elongation, while the change of atrial natriuretic peptide (ANP) occurred only at late stage in UT-B null mice that had the AV block. These data indicate that UT-B deletion caused the dynamic expression regulation of TNNT2 and ANP, and these proteins may provide new clues to investigate the molecular events involved in cardiac conduction.
Sanabria, Federico; Killeen, Peter R.
2007-01-01
Despite being under challenge for the past 50 years, null hypothesis significance testing (NHST) remains dominant in the scientific field for want of viable alternatives. NHST, along with its significance level "p," is inadequate for most of the uses to which it is put, a flaw that is of particular interest to educational practitioners…
Topology optimization of piezo modal transducers with null-polarity phases
DEFF Research Database (Denmark)
Donoso, A.; Sigmund, O.
2016-01-01
Piezo modal transducers in 2d can be designed theoretically by tailoring polarity of the surface electrodes. However, it is also necessary to include null-polarity phases of known width separating areas of opposite polarity in the manufacturing process in order to avoid short-circuiting. Otherwise...
Dmp1 Null Mice Develop a Unique Osteoarthritis-like Phenotype.
Zhang, Qi; Lin, Shuxian; Liu, Ying; Yuan, Baozhi; Harris, Steph E; Feng, Jian Q
2016-01-01
Patients with hypophosphatemia rickets (including DMP1 mutations) develop severe osteoarthritis (OA), although the mechanism is largely unknown. In this study, we first identified the expression of DMP1 in hypertrophic chondrocytes using immunohistochemistry (IHC) and X-gal analysis of Dmp1-knockout-lacZ-knockin heterozygous mice. Next, we characterized the OA-like phenotype in Dmp1 null mice from 7-week-old to one-year-old using multiple techniques, including X-ray, micro-CT, H&E staining, Goldner staining, scanning electronic microscopy, IHC assays, etc. We found a classical OA-like phenotype in Dmp1 null mice such as articular cartilage degradation, osteophyte formation, and subchondral osteosclerosis. These Dmp1 null mice also developed unique pathological changes, including a biphasic change in their articular cartilage from the initial expansion of hypertrophic chondrocytes at the age of 1-month to a quick diminished articular cartilage layer at the age of 3-months. Further, these null mice displayed severe enlarged knees and poorly formed bone with an expanded osteoid area. To address whether DMP1 plays a direct role in the articular cartilage, we deleted Dmp1 specifically in hypertrophic chondrocytes by crossing the Dmp1-loxP mice with Col X Cre mice. Interestingly, these conditional knockout mice didn't display notable defects in either the articular cartilage or the growth plate. Because of the hypophosphatemia remained in the entire life span of the Dmp1 null mice, we also investigated whether a high phosphate diet would improve the OA-like phenotype. A 8-week treatment of a high phosphate diet significantly rescued the OA-like defect in Dmp1 null mice, supporting the critical role of phosphate homeostasis in maintaining the healthy joint morphology and function. Taken together, this study demonstrates a unique OA-like phenotype in Dmp1 null mice, but a lack of the direct impact of DMP1 on chondrogenesis. Instead, the regulation of phosphate homeostasis
A dynamical system's approach to Schwarzschild null geodesics
Energy Technology Data Exchange (ETDEWEB)
Belbruno, Edward [Courant Institute of Mathematical Sciences, New York University, NY (United States); Pretorius, Frans, E-mail: belbruno@Princeton.edu, E-mail: fpretori@Princeton.edu [Department of Physics, Princeton University, Princeton, NJ (United States)
2011-10-07
The null geodesics of a Schwarzschild black hole are studied from a dynamical system's perspective. Written in terms of Kerr-Schild coordinates, the null geodesic equation takes on the simple form of a particle moving under the influence of a Newtonian central force with an inverse-cubic potential. We apply a McGehee transformation to these equations, which clearly elucidates the full phase space of solutions. All the null geodesics belong to one of the four families of invariant manifolds and their limiting cases, further characterized by the angular momentum L of the orbit: for |L| > |L{sub c}|, (1) the set that flow outward from the white hole, turn around, and then fall into the black hole, (2) the set that fall inward from past null infinity, turn around outside the black hole to continue to future null infinity, and for |L| < |L{sub c}|, (3) the set that flow outward from the white hole and continue to future null infinity and (4) the set that flow inward from past null infinity and into the black hole. The critical angular momentum L{sub c} corresponds to the unstable circular orbit at r = 3M, and the homoclinic orbits associated with it. There are two additional critical points of the flow at the singularity at r = 0. Though the solutions of geodesic motion and Hamiltonian flow we describe here are well known, what we believe is that a novel aspect of this work is the mapping between the two equivalent descriptions, and the different insights each approach can give to the problem. For example, the McGehee picture points to a particularly interesting limiting case of the class (1) that move from the white to black hole: in the L {yields} {infinity} limit, as described in Schwarzschild coordinates, these geodesics begin at r = 0, flow along t = constant lines, turn around at r = 2M, and then continue to r = 0. During this motion they circle in azimuth exactly once, and complete the journey in zero affine time.
Dmp1 Null Mice Develop a Unique Osteoarthritis-like Phenotype
Zhang, Qi; Lin, Shuxian; Liu, Ying; Yuan, Baozhi; Harris, Steph E; Feng, Jian Q.
2016-01-01
Patients with hypophosphatemia rickets (including DMP1 mutations) develop severe osteoarthritis (OA), although the mechanism is largely unknown. In this study, we first identified the expression of DMP1 in hypertrophic chondrocytes using immunohistochemistry (IHC) and X-gal analysis of Dmp1-knockout-lacZ-knockin heterozygous mice. Next, we characterized the OA-like phenotype in Dmp1 null mice from 7-week-old to one-year-old using multiple techniques, including X-ray, micro-CT, H&E staining, Goldner staining, scanning electronic microscopy, IHC assays, etc. We found a classical OA-like phenotype in Dmp1 null mice such as articular cartilage degradation, osteophyte formation, and subchondral osteosclerosis. These Dmp1 null mice also developed unique pathological changes, including a biphasic change in their articular cartilage from the initial expansion of hypertrophic chondrocytes at the age of 1-month to a quick diminished articular cartilage layer at the age of 3-months. Further, these null mice displayed severe enlarged knees and poorly formed bone with an expanded osteoid area. To address whether DMP1 plays a direct role in the articular cartilage, we deleted Dmp1 specifically in hypertrophic chondrocytes by crossing the Dmp1-loxP mice with Col X Cre mice. Interestingly, these conditional knockout mice didn't display notable defects in either the articular cartilage or the growth plate. Because of the hypophosphatemia remained in the entire life span of the Dmp1 null mice, we also investigated whether a high phosphate diet would improve the OA-like phenotype. A 8-week treatment of a high phosphate diet significantly rescued the OA-like defect in Dmp1 null mice, supporting the critical role of phosphate homeostasis in maintaining the healthy joint morphology and function. Taken together, this study demonstrates a unique OA-like phenotype in Dmp1 null mice, but a lack of the direct impact of DMP1 on chondrogenesis. Instead, the regulation of phosphate homeostasis
DEFF Research Database (Denmark)
Carlsen, Berit Christina; Johansen, Jeanne Duus; Menné, Torkil;
2010-01-01
Filaggrin null (FLG) mutations lead to skin barrier disruption with a reduced resistance towards exogenous agents and also influence the course of disease in atopic dermatitis.......Filaggrin null (FLG) mutations lead to skin barrier disruption with a reduced resistance towards exogenous agents and also influence the course of disease in atopic dermatitis....
Oddou-Muratorio, S.; Vendramin, G.G.; Buiteveld, J.; Fady, B.
2009-01-01
Nuclear SSRs are notorious for having relatively high frequencies of null alleles, i.e. alleles that fail to amplify and are thus recessive and undetected in heterozygotes. In this paper, we compare two kinds of approaches for estimating null allele frequencies at seven nuclear microsatellite marker
Aquaporins Mediate Silicon Transport in Humans.
Garneau, Alexandre P; Carpentier, Gabriel A; Marcoux, Andrée-Anne; Frenette-Cotton, Rachelle; Simard, Charles F; Rémus-Borel, Wilfried; Caron, Luc; Jacob-Wagner, Mariève; Noël, Micheline; Powell, Jonathan J; Bélanger, Richard; Côté, François; Isenring, Paul
2015-01-01
In animals, silicon is an abundant and differentially distributed trace element that is believed to play important biological functions. One would thus expect silicon concentrations in body fluids to be regulated by silicon transporters at the surface of many cell types. Curiously, however, and even though they exist in plants and algae, no such transporters have been identified to date in vertebrates. Here, we show for the first time that the human aquaglyceroporins, i.e., AQP3, AQP7, AQP9 and AQP10 can act as silicon transporters in both Xenopus laevis oocytes and HEK-293 cells. In particular, heterologously expressed AQP7, AQP9 and AQP10 are all able to induce robust, saturable, phloretin-sensitive silicon transport activity in the range that was observed for low silicon rice 1 (lsi1), a silicon transporter in plant. Furthermore, we show that the aquaglyceroporins appear as relevant silicon permeation pathways in both mice and humans based on 1) the kinetics of substrate transport, 2) their presence in tissues where silicon is presumed to play key roles and 3) their transcriptional responses to changes in dietary silicon. Taken together, our data provide new evidence that silicon is a potentially important biological element in animals and that its body distribution is regulated. They should open up original areas of investigations aimed at deciphering the true physiological role of silicon in vertebrates.
Aquaporins Mediate Silicon Transport in Humans.
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Alexandre P Garneau
Full Text Available In animals, silicon is an abundant and differentially distributed trace element that is believed to play important biological functions. One would thus expect silicon concentrations in body fluids to be regulated by silicon transporters at the surface of many cell types. Curiously, however, and even though they exist in plants and algae, no such transporters have been identified to date in vertebrates. Here, we show for the first time that the human aquaglyceroporins, i.e., AQP3, AQP7, AQP9 and AQP10 can act as silicon transporters in both Xenopus laevis oocytes and HEK-293 cells. In particular, heterologously expressed AQP7, AQP9 and AQP10 are all able to induce robust, saturable, phloretin-sensitive silicon transport activity in the range that was observed for low silicon rice 1 (lsi1, a silicon transporter in plant. Furthermore, we show that the aquaglyceroporins appear as relevant silicon permeation pathways in both mice and humans based on 1 the kinetics of substrate transport, 2 their presence in tissues where silicon is presumed to play key roles and 3 their transcriptional responses to changes in dietary silicon. Taken together, our data provide new evidence that silicon is a potentially important biological element in animals and that its body distribution is regulated. They should open up original areas of investigations aimed at deciphering the true physiological role of silicon in vertebrates.
Reversing hypomyelination in BACE1-null mice with Akt-DD overexpression.
Hu, Xiangyou; Schlanger, Rita; He, Wanxia; Macklin, Wendy B; Yan, Riqiang
2013-05-01
β-Site amyloid precursor protein convertase enzyme 1 (BACE1), a type I transmembrane aspartyl protease required to cleave amyloid precursor protein for releasing a toxic amyloid peptide, also cleaves type I and type III neuregulin-1 (Nrg-1). BACE1 deficiency in mice causes hypomyelination during development and impairs remyelination if injured. In BACE1-null mice, the abolished cleavage of neuregulin-1 by BACE1 is speculated to cause reduced myelin sheath thickness in both the central nervous system and peripheral nervous system because reduced cleavage of Nrg-1 correlates with reduced Akt phosphorylation, a downstream signaling molecule of the Nrg-1/ErbB pathway. Here we tested specifically whether increasing Akt activity alone in oligodendrocytes would be sufficient to reverse the hypomyelination phenotype in BACE1-null mice. BACE1-null mice were bred with transgenic mice expressing constitutively active Akt (Akt-DD; mutations with D(308)T and D(473)S) in oligodendrocytes. Relative to littermate BACE1-null controls, BACE1(-/-)/Akt-DD mice exhibited enhanced expression of myelin basic protein and promoter of proteolipid protein. The elevated expression of myelin proteins correlated with a thicker myelin sheath in optic nerves; comparison of quantified g ratios with statistic significance was used to confirm this reversion. However, it appeared that myelin sheath thickness in the sciatic nerves was not increased in BACE1(-/-)/Akt-DD mice, as the g ratio was not significantly different from the control. Hence, increased Akt activity in BACE1-null myelinating cells only compensates for the loss of BACE1 activity in the central nervous system, which is consistent with the observation that overexpression of Akt-DD in Schwann cells did not induce hypermyelination. Our results suggest that signaling activity other than Akt may also contribute to proper myelination in peripheral nerves.
Effects of Lipoxygenase Null Genes of Soybean in Controlling Beany-flavor of Soymilk and Soyflour
Institute of Scientific and Technical Information of China (English)
MA Hao; GUAN Chun-yun; HE Xiao-ling; ZHANG Guo-zheng; DIN An-lin
2002-01-01
The flavor of the soymilk and soyflour obtained from the lipoxygenase mutant isolines was concentrated by simultaneous distillation and extraction (SDE), and its constituents were identified by gas chromatography (GC) and gas chromatography-mass spectrometry. Results showed that the same 24 flavor constituents were isolated in both soymilk and soyflour, and most of them were aldehydes and alcohols. Lox2 was most responsible for the production of the volatile and beany-flavor components, and Lox1 less responsible.Lox3 was least responsible and can reduce the yield of hexanal. Either Lx1 or Lx2 could significantly reduce the volatile and beany-flavor, and Lx3 could significantly increase the yield of hexanal. Primary and secondary interactions existed among the null mutant genes, and the major effects and interactions could be affected by processing conditions. The isoline with triple lipoxygenase null genes yielded the least volatile and beany-flavor components, and the isoline without the lipoxygenase gene Lx3 produced the greatest amount of the volatile and beany-flavor components. The amounts of volatile and beany-flavor components produced by the other isolines were between that of the isoline with triple lipoxygenase null genes and the isoline without lipoxygenase gene Lx3. According to the correlation analysis, the hexanal amount could be used as an index in evaluating the importance of lipoxygenase isozymes in the yield of beany-flavor compounds, and the effects of the different types of lipoxygenase null mutants in controlling beany-flavor compounds. The cultivars with triple lipoxygenase null genes will be a quality raw material for soyfood processing.
Manfroi, Silvia; Scarcello, Antonio; Pagliaro, Pasqualepaolo
2015-10-01
Molecular genetic studies on Duffy blood group antigens have identified mutations underlying rare FY*Null and FY*X alleles. FY*Null has a high frequency in Blacks, especially from sub-Saharan Africa, while its frequency is not defined in Caucasians. FY*X allele, associated with Fy(a-b+w) phenotype, has a frequency of 2-3.5% in Caucasian people while it is absent in Blacks. During the project of extensive blood group genotyping in patients affected by hemoglobinopathies, we identified FY*X/FY*Null and FY*A/FY*Null genotypes in a Caucasian thalassemic family from Sardinia. We speculate on the frequency of FY*X and FY*Null alleles in Caucasian and Black people; further, we focused on the association of FY*X allele with weak Fyb antigen expression on red blood cells and its identification performing high sensitivity serological typing methods or genotyping.
Pieper, J; Johansson, S; Snir, O; Linton, L; Rieck, M; Buckner, J H; Winqvist, O; van Vollenhoven, R; Malmström, V
2014-02-01
Proinflammatory CD4(+) CD28(null) T cells are frequently found in the circulation of patients with rheumatoid arthritis (RA), but are less common in the rheumatic joint. In the present study, we sought to identify functional differences between CD4(+) CD28(null) T cells from blood and synovial fluid in comparison with conventional CD28-expressing CD4(+) T cells. Forty-four patients with RA, displaying a distinct CD4(+) CD28(null) T cell population in blood, were recruited for this study; the methylation status of the IFNG locus was examined in isolated T cell subsets, and intracellular cytokine production (IFN-γ, TNF, IL-17) and chemokine receptor expression (CXCR3, CCR6 and CCR7) were assessed by flow cytometry on T cells from the two compartments. Circulating CD4(+) CD28(null) T cells were significantly more hypomethylated in the CNS-1 region of the IFNG locus than conventional CD4(+) CD28(+) T cells and produced higher levels of both IFN-γ and TNF after TCR cross-linking. CD4(+) CD28(null) T cells from the site of inflammation expressed significantly more CXCR3 and CCR6 compared to their counterparts in blood. While IL-17A production could hardly be detected in CD4(+) CD28(null) cells from the blood, a significant production was observed in CD4(+) CD28(null) T cells from synovial fluid. CD4(+) CD28(null) T cells were not only found to differ from conventional CD4(+) CD28(+) T cells in the circulation, but we could also demonstrate that synovial CD4(+) CD28(null) T cells showed additional effector functions (IL-17 coproduction) as compared to the same subset in peripheral blood, suggesting an active role for these cells in the perpetuation of inflammation in the subset of patients having a CD28(null) population.
Is the 3-D magnetic null point with a convective electric field an efficient particle accelerator?
Guo, J.-N.; Büchner, J.; Otto, A.; Santos, J.; Marsch, E.; Gan, W.-Q.
2010-04-01
Aims: We study the particle acceleration at a magnetic null point in the solar corona, considering self-consistent magnetic fields, plasma flows and the corresponding convective electric fields. Methods: We calculate the electromagnetic fields by 3-D magnetohydrodynamic (MHD) simulations and expose charged particles to these fields within a full-orbit relativistic test-particle approach. In the 3-D MHD simulation part, the initial magnetic field configuration is set to be a potential field obtained by extrapolation from an analytic quadrupolar photospheric magnetic field with a typically observed magnitude. The configuration is chosen so that the resulting coronal magnetic field contains a null. Driven by photospheric plasma motion, the MHD simulation reveals the coronal plasma motion and the self-consistent electric and magnetic fields. In a subsequent test particle experiment the particle energies and orbits (determined by the forces exerted by the convective electric field and the magnetic field around the null) are calculated in time. Results: Test particle calculations show that protons can be accelerated up to 30 keV near the null if the local plasma flow velocity is of the order of 1000 km s-1 (in solar active regions). The final parallel velocity is much higher than the perpendicular velocity so that accelerated particles escape from the null along the magnetic field lines. Stronger convection electric field during big flare explosions can accelerate protons up to 2 MeV and electrons to 3 keV. Higher initial velocities can help most protons to be strongly accelerated, but a few protons also run the risk to be decelerated. Conclusions: Through its convective electric field and due to magnetic nonuniform drifts and de-magnetization process, the 3-D null can act as an effective accelerator for protons but not for electrons. Protons are more easily de-magnetized and accelerated than electrons because of their larger Larmor radii. Notice that macroscopic MHD
Charles, Hanot; Stefan, Martin; Kurt, Liewer; Frank, Loya; Dimitri, Mawet; Pierre, Riaud; Olivier, Absil; Eugene, Serabyn; 10.1088/0004-637X/729/2/110
2011-01-01
A new "self-calibrated" statistical analysis method has been developed for the reduction of nulling interferometry data. The idea is to use the statistical distributions of the fluctuating null depth and beam intensities to retrieve the astrophysical null depth (or equivalently the object's visibility) in the presence of fast atmospheric fluctuations. The approach yields an accuracy much better (about an order of magnitude) than is presently possible with standard data reduction methods, because the astrophysical null depth accuracy is no longer limited by the magnitude of the instrumental phase and intensity errors but by uncertainties on their probability distributions. This approach was tested on the sky with the two-aperture fiber nulling instrument mounted on the Palomar Hale telescope. Using our new data analysis approach alone-and no observations of calibrators-we find that error bars on the astrophysical null depth as low as a few 10-4 can be obtained in the near-infrared, which means that null depths...
Jin, Bin; Dong, Pin; Li, Keyong; Shen, Bin; Xie, Jin
2014-01-01
Glutathione S-transferase T1 (GSTT1) null genotype has been proven to be associated with risks of many cancers. There were also many studies assessing on the association between GSTT1 null genotype and nasopharyngeal carcinoma risk in Chinese, but the findings from those studies were inconsistent. We performed a meta-analysis to provide a more precise assessment on the effect of GSTT1 null genotype on nasopharyngeal carcinoma risk. The PubMed and Wanfang databases were searched to identify eligible case-control studies on the association between GSTT1 null genotype and risk of nasopharyngeal carcinoma in Chinese. The pooled odds ratios (OR) with corresponding 95% confidence intervals (95% CI) were used to assess the association. Eight case-control studies with a total of 3,702 individuals were finally included in the meta-analysis. Meta-analysis of a total of eight studies showed that GSTT1 null genotype was significantly associated with increased risk of nasopharyngeal carcinoma in Chinese (OR = 2.27; 95% CI 1.41-3.67; P = 0.001). The finding from cumulative meta-analysis showed that there was a trend of more obvious association between GSTT1 null genotype and risk of nasopharyngeal carcinoma in Chinese as data accumulated by publication year. Therefore, the GSTT1 null genotype is significantly associated with increased risk of nasopharyngeal carcinoma in Chinese.
Bojovic, B; Ho, H-Y; Wu, J; Crowe, D L
2013-10-24
To examine the role of telomeric repeat-binding factor 2 (TRF2) in epithelial tumorigenesis, we characterized conditional loss of TRF2 expression in the basal layer of mouse epidermis. These mice exhibit some characteristics of dyskeratosis congenita, a human stem cell depletion syndrome caused by telomere dysfunction. The epidermis in conditional TRF2 null mice exhibited DNA damage response and apoptosis, which correlated with stem cell depletion. The stem cell population in conditional TRF2 null epidermis exhibited shorter telomeres than those in control mice. Squamous cell carcinomas induced in conditional TRF2 null mice developed with increased latency and slower growth due to reduced numbers of proliferating cells as the result of increased apoptosis. TRF2 null epidermal stem cells were found in both primary and metastatic tumors. Despite the low-grade phenotype of the conditional TRF2 null primary tumors, the number of metastatic lesions was similar to control cancers. Basal cells from TRF2 null tumors demonstrated extreme telomere shortening and dramatically increased numbers of telomeric signals by fluorescence in situ hybridization due to increased genomic instability and aneuploidy in these cancers. DNA damage response signals were detected at telomeres in TRF2 null tumor cells from these mice. The increased genomic instability in these tumors correlated with eightfold expansion of the transformed stem cell population compared with that in control cancers. We concluded that genomic instability resulting from loss of TRF2 expression provides biological advantages to the cancer stem cell population.
Quasinormal modes of nonlinear electromagnetic black holes from unstable null geodesics
Bretón, Nora; López, L. A.
2016-11-01
The expressions for the quasinormal modes (QNM) of black holes with nonlinear electrodynamics, calculated in the eikonal approximation, are presented. In the eikonal limit QNM of black holes are determined by the parameters of the circular null geodesics. The unstable circular null orbits are derived from the effective metric that is the one obeyed by light rays under the influence of a nonlinear electromagnetic field. As an illustration we calculate the QNM of four nonlinear electromagnetic black holes, two singular and two regular, namely, from Euler-Heisenberg and Born-Infeld theories, for singular ones, and the magnetic Bardeen black hole and the one derived by Bronnikov for regular ones. Comparing with the QNM of the linear electromagnetic counterpart, their Reissner-Nordström black hole is done.
Local existence in retarded time under a weak decay on complete null cones
Li, Junbin
2015-01-01
In the previous paper \\cite{L-Z}, for a characteristic problem with not necessarily small initial data given on a complete null cone decaying like that in the work \\cite{Ch-K} of the stability of Minkowski spacetime by Christodoulou and Klainerman, we proved the local existence in retarded time, which means the solution to the vacuum Einstein equations exists in a uniform future neighborhood, while the global existence in retarded time is the weak cosmic censorship conjecture. In this paper, we prove that the local existence in retarded time still holds when the data is assumed to decay slower, like that in Bieri's work \\cite{Bie} on the extension to the stability of Minkowski spacetime. Such decay guarantees the existence of the limit of the Hawking mass on the initial null cone, when approaching to infinity, in an optimal way.
Quasinormal modes of nonlinear electromagnetic black holes from unstable null geodesics
Breton, N
2016-01-01
The expressions for the quasinormal modes (QNMs) of black holes with nonlinear electrodynamics, calculated in the eikonal approximation, are presented. In the eikonal limit QNMs of black holes are determined by the parameters of the circular null geodesics. The unstable circular null orbits are derived from the effective metric that is the one obeyed by light rays under the influence of a nonlinear electromagnetic field. As an illustration we calculate the QNMs of four nonlinear electromagnetic black holes, two singular and two regular, namely from Euler-Heisenberg and Born-Infeld theories, for singular, and the magnetic Bardeen black hole and the one derived by Bronnikov for regular ones. Comparison is shown with the QNMs of the linear electromagnetic counterpart, their Reissner-Nordstr\\"{o}m black hole.
Impact of Electronic Voting Machines on Blank Votes and Null Votes in Brazilian Elections in 1998
Directory of Open Access Journals (Sweden)
Jairo Nicolau
2015-12-01
Full Text Available Electronic voting machines were used for the first time in general elections in Brazil in 1998; in that year, some cities used this new voting method, while others continued to vote using paper ballots. Few studies have demonstrated that the rate of invalid votes for federal deputy was significantly lower in cities that used electronic voting machines. This article analyzes the frequency of null votes and blank votes for four posts—federal deputy, state deputy, the president and governor. Based on a comparison of the results from the 1998 elections with the results from previous elections (1994, the article demonstrates that electronic voting machines reduced the percentage of blank votes for federal deputy, state deputies, the president and governor. Meanwhile, null votes reduced the competition for the posts of federal deputy and state deputy; however, it increased the competition for posts with greater visibility in the Brazilian political system: the governor and president.
DAMA confronts null searches in the effective theory of dark matter-nucleon interactions
Catena, Riccardo; Wild, Sebastian
2016-01-01
We examine the dark matter interpretation of the modulation signal reported by the DAMA experiment from the perspective of effective field theories displaying Galilean invariance. We consider the most general effective coupling leading to the elastic scattering of a dark matter particle with a nucleon, and we analyze the compatibility of the DAMA signal with the null results from other direct detection experiments, as well as with the non-observation of a high energy neutrino flux in the direction of the Sun from dark matter annihilation. Assuming the standard halo model, we find a strong tension between the dark matter interpretation of the DAMA modulation signal and the null result experiments. We also list possible ways-out to this conclusion.
Internalizing Null Extraterrestrial "Signals": An Astrobiological App for a Technological Society
Chaisson, Eric J
2014-01-01
One of the beneficial outcomes of searching for life in the Universe is that it grants greater awareness of our own problems here on Earth. Lack of contact with alien beings to date might actually comprise a null "signal" pointing humankind toward a viable future. Astrobiology has surprising practical applications to human society; within the larger cosmological context of cosmic evolution, astrobiology clarifies the energetic essence of complex systems throughout the Universe, including technological intelligence that is intimately dependent on energy and likely will be for as long as it endures. The "message" contained within the "signal" with which today's society needs to cope is reasonably this: Only solar energy can power our civilization going forward without soiling the environment with increased heat yet robustly driving the economy with increased per capita energy usage. The null "signals" from extraterrestrials also offer a rational solution to the Fermi paradox as a principle of cosmic selection l...
DAMA confronts null searches in the effective theory of dark matter-nucleon interactions
Energy Technology Data Exchange (ETDEWEB)
Catena, Riccardo [Department of Physics, Chalmers University of Technology,Kemigården 1, Gothenburg (Sweden); Ibarra, Alejandro; Wild, Sebastian [Physik-Department T30d, Technische Universität München,James-Franck-Straße, 85748 Garching (Germany)
2016-05-17
We examine the dark matter interpretation of the modulation signal reported by the DAMA experiment from the perspective of effective field theories displaying Galilean invariance. We consider the most general effective coupling leading to the elastic scattering of a dark matter particle with spin 0 or 1/2 off a nucleon, and we analyze the compatibility of the DAMA signal with the null results from other direct detection experiments, as well as with the non-observation of a high energy neutrino flux in the direction of the Sun from dark matter annihilation. To this end, we develop a novel semi-analytical approach for comparing experimental results in the high-dimensional parameter space of the non-relativistic effective theory. Assuming the standard halo model, we find a strong tension between the dark matter interpretation of the DAMA modulation signal and the null result experiments. We also list possible ways-out of this conclusion.
Asymptotic Properties of Parabolic Systems for Null-Recurrent Switching Diffusions
Institute of Scientific and Technical Information of China (English)
R.Z.Khasminskii; C.Zhu; G.Yin
2007-01-01
This work is concerned with the asymptotic behavior of systems of parabolic equations arising from null-recurrent switching diffusions,which are diffusion processes modulated by continuous-time Markov chains.A sufficient condition for null recurrence is presented.Moreover,convergence rate of the solutions of systems of homogeneous parabolic equations under suitable conditions is established.Then a case study on verifying one of the conditions proposed is provided with the use of a two-state Markov chain.To verify the condition,boundary value problems(BVPs)for parabolic systems are treated,which are not the usual two-point BVP type.An extra condition in the interior is needed resulting in jump discontinuity of the derivative of the corresponding solution.
The removal of shear-ellipticity correlations from the cosmic shear signal by nulling techniques
Joachimi, B
2008-01-01
In order to render cosmic shear an astronomical tool of high precision, it is essential to eliminate systematic effects upon its signal, one of the most significant ones being correlations between the gravitational shear and the intrinsic ellipticity of source galaxies. Regarding the crudeness of current models of intrinsic alignment, we have developed a model-independent, purely geometrical method to remove shear-ellipticity correlations. We eliminate the contributions to a tomographic cosmic shear signal that may be subject to contamination by shear-ellipticity correlations, making use of the characteristic dependence of these correlations on redshift. By introducing an appropriately chosen weight function to the lensing efficiency that nulls signals stemming from certain distances, new second-order measures of cosmic shear, free from intrinsic alignment, can be constructed. The loss of information induced by this nulling technique and the subsequent degradation of constraints on cosmological parameters is ...
Reconnection at 3D Magnetic Null Points: Effect of Current Sheet Asymmetry
Wyper, Peter F
2013-01-01
Asymmetric current sheets are likely to be prevalent in both astrophysical and laboratory plasmas with complex three dimensional (3D) magnetic topologies. This work presents kinematic analytical models for spine and fan reconnection at a symmetric 3D null with asymmetric current sheets. Asymmetric fan reconnection is characterized by an asymmetric reconnection of flux past each spine line and a bulk flow of plasma across the null point. In contrast, asymmetric spine reconnection is inherently equal and opposite in how flux is reconnected across the fan plane. The higher modes of spine reconnection also include localized wedges of vortical flux transport in each half of the fan. In this situation, two definitions for reconnection rate become appropriate: a local reconnection rate quantifying how much flux is genuinely reconnected across the fan plane and a global rate associated with the net flux driven across each semi-plane. Through a scaling analysis it is shown that when the ohmic dissipation in the layer ...
Single Past Null Geodesic in the Lemaitre-Tolman-Bondi Cosmology
Nogueira, Felipe A M G
2013-01-01
This work provides a general discussion of the spatially inhomogeneous Lema\\^itre-Tolman-Bondi (LTB) cosmology, as well as its basic properties and many useful relevant quantities, such as the cosmological distances. We apply the concept of the single null geodesic to produce some simple analytical solutions for observational quantities such as the redshift. As an application of the single null geodesic technique, we carry out a fractal approach to the parabolic LTB model, comparing it to the spatially homogeneous Einstein-de Sitter cosmology. The results obtained indicate that the standard model, in this case represented by the Einstein-de Sitter cosmology, can be equivalently described by a fractal distribution of matter, as we found that different single fractal dimensions describe different scale ranges of the parabolic LTB matter distribution. It is shown that at large ranges the parabolic LTB model with fractal dimension equal to 0.5 approximates the matter distribution of the Einstein-de Sitter univers...
Null Dust Solution in Ho\\v{r}ava-Lifshitz Gravity
Goldoni, O; Chan, R; Satheeshkumar, V H; da Rocha, J F Villas
2016-01-01
Non-stationary null dust in a spherically symmetric spacetime is studied in the context of a general-covariant Ho\\v{r}ava-Lifshitz gravity. The non-minimal coupling to matter is considered in the post-Newtonian approximation (PPN) in the infrared limit. The aim of this paper is to see if a general relativistic spacetime of a shearing null dust-like fluid can be a solution of Ho\\v{r}ava-Lifshitz theory in the infrared limit. We have shown that this solution admits the process of gravitational collapse leaving a singularity at the end. These solutions have, qualitatively, the same temporal behavior as the dust collapse in Einstein theory. We have also found other possible solutions, representing an expansion behavior that is not found in General Relativity (GR). This solution might represent a repulsive phantom energy in GR.
Interaction between filaggrin null mutations and tobacco smoking in relation to asthma
DEFF Research Database (Denmark)
Husemoen, Lise Lotte N; Thuesen, Betina Heinsbæk; Hersoug, Lars-Georg;
2012-01-01
BACKGROUND: The mechanisms underlying the association between filaggrin (FLG) deficiency and asthma are not known. It has been hypothesized that FLG deficiency leads to enhanced percutaneous exposure to environmental substances that might trigger immune responses. We hypothesized that interactions...... between FLG deficiency and environmental exposures play a role in asthma development. OBJECTIVE: We sought to investigate possible interactions between FLG null mutations and tobacco smoking in relation to asthma. METHODS: A total of 3471 adults from a general population sample participated in a health...... examination. Lung function and serum specific IgE levels to inhalant allergens were measured, and information on asthma and smoking was obtained by means of questionnaire. Participants were genotyped for the 2 most common FLG null mutations in white subjects: R501X and 2282del4. Another Danish population...
Common-path lateral-shearing nulling interferometry with a Savart plate for exoplanet detection.
Murakami, Naoshi; Baba, Naoshi
2010-09-15
We propose a common-path lateral-shearing nulling interferometer for direct detection of exoplanets. A Savart plate is placed between crossed polarizers to produce a lateral shear and realize fully achromatic and highly stable nulling interference for starlight. We construct a double-shearing interferometer using two Savart plates for implementing orthogonal x and y shears. A laboratory demonstration is carried out using a broadband light source with a bandwidth of Δλ/λ(0)=0.33 (Δλ=0.2 μm and λ(0)=0.6 μm). As a result, achieved extinction levels are 4 × 10(-4) at peak and 4 × 10(-7) at 10λ(0)/D(L) (D(L) is the diameter of a Lyot stop).
Space filling in the World Trade Web: measures and null models
Ruzzenenti, Franco; Garlaschelli, Diego; Basosi, Riccardo
2012-01-01
It is here proposed global and local, bynary and weighted measures of space filling, to detect the degree of stretching of a network within its embedding space. Measures are normalized indexes that vary from zero - a maximally shrunk network, to one -a maximally expanded network. We evaluated the indexes according to three different null models an propose an unbiased measure of network filling, suitable for confrontation of different (cross sectional) embedded networks or historical trends of the same network. We further develop a local measure of filling and thereby of vertex assortativity. Finally, we showed that in the WTW metric distances seem to have determined the links' allocation more than the present null models tend to have predicted and that this burden upon links has been changing in time. However, surprisingly, our analysis seems to indicate that during globalization the WTW expanded merely because of topology and contrary to expectations it actually shrunk.
Numerical Simulations of Solar Spicule Jets at a Magnetic Null-Point
Smirnova, V.; Konkol, P. M.; Solov'ev, A. A.; Murawski, K.
2016-11-01
Two-dimensional numerical simulations of jet-like structures in the solar atmosphere are performed. These structures result from a pressure pulse that is launched at the null point of a potential magnetic arcade. The plasma jet exhibits a double structure with two components: (a) dense, cool, and short vertical stream and (b) a less dense, hot and tall part of the jet. The upper part of the hot and tall jet may represent a direct response of the system to the pressure pulse launched at the null point, and the second, slower cool and dense part of the jet is formed later through the stretching up of the stream as a result of plasma evacuation from the top of the magnetic arcade. Numerical results show that jet-like structures mimic some properties of both type I and type II spicules, according to the classification provided by De Pontieu et al. ( Publ. Astron. Soc. Japan 59, S655, 2007).
Chen, Jian; Dutton, Zachary; Lazarus, Richard; Guha, Saikat
2011-01-01
The quantum states of two laser pulses---coherent states---are never mutually orthogonal, making perfect discrimination impossible. Even so, coherent states can achieve the ultimate quantum limit for capacity of a classical channel, the Holevo capacity. Attaining this requires the receiver to make joint-detection measurements on long codeword blocks, optical implementations of which remain unknown. We report the first experimental demonstration of a joint-detection receiver, demodulating quaternary pulse-position-modulation (PPM) codewords at a word error rate of up to 40% (2.2 dB) below that attained with direct-detection, the largest error-rate improvement over the standard quantum limit reported to date. This is accomplished with a conditional nulling receiver, which uses optimized-amplitude coherent pulse nulling, single photon detection and quantum feedforward. We further show how this translates into coding complexity improvements for practical PPM systems, such as in deep-space communication. We antici...
Herpes simplex virus type 1 ribonucleotide reductase null mutants induce lesions in guinea pigs.
Turk, S R; Kik, N A; Birch, G M; Chiego, D J; Shipman, C
1989-12-01
Two herpes simplex virus type 1 ribonucleotide reductase null mutants, hrR3 and ICP6 delta, produced cutaneous lesions in guinea pigs as severe as those of wild-type strains. The lesions induced by hrR3 resulted from in vivo replication of the mutant virus, suggesting that this virus-encoded enzyme is nonessential for virus replication in guinea pigs.
Einstein equations in the null quasi-spherical gauge III: numerical algorithms
Bartnik, Robert A.; Norton, Andrew H.
1999-01-01
We describe numerical techniques used in the construction of our 4th order evolution for the full Einstein equations, and assess the accuracy of representative solutions. The code is based on a null gauge with a quasi-spherical radial coordinate, and simulates the interaction of a single black hole with gravitational radiation. Techniques used include spherical harmonic representations, convolution spline interpolation and filtering, and an RK4 "method of lines" evolution. For sample initial ...
A musculoskeletal shoulder model based on pseudo-inverse and null-space optimization
Terrier, Alexandre; Aeberhard, Martin; Michellod, Yvan; Müllhaupt, Philippe; Gillet, Denis; Farron, Alain; Pioletti, Dominique P.
2010-01-01
The goal of the present work was assess the feasibility of using a pseudo-inverse and null-space optimization approach in the modeling of the shoulder biomechanics. The method was applied to a simplified musculoskeletal shoulder model. The mechanical system consisted in the arm, and the external forces were the arm weight, 6 scapulohumeral muscles and the reaction at the glenohumeral joint, which was considered as a spherical joint. The muscle wrapping was considered around the humeral head a...
Fonction constante et d\\'eriv\\'ee nulle : un r\\'esultat si trivial..
Delcroix, Antoine
2008-01-01
We study various proofs of the caracterization of constant functions, more precisely of the theorem: a derivable function, defined on a real interval, is constant if, and only if, its derivative is null. Our aim is to study the relationships of these proofs with the mathematical curriculum of secondary schools and the begining of undergraduate studies in France, from various point of views (epistemological, historical, didactical).
EXACT NULL CONTROLLABILITY OF NON-AUTONOMOUS FUNCTIONAL EVOLUTION SYSTEMS WITH NONLOCAL CONDITIONS
Institute of Scientific and Technical Information of China (English)
Xianlong FU; Yu ZHANG
2013-01-01
In this article,by using theory of linear evolution system and Schauder fixed point theorem,we establish a sufficient result of exact null controllability for a non-autonomous functional evolution system with nonlocal conditions.In particular,the compactness condition or Lipschitz condition for the function g in the nonlocal conditions appearing in various literatures is not required here.An example is also provided to show an application of the obtained result.
Magnetic damping forces in figure-eight-shaped null-flux coil suspension systems
Energy Technology Data Exchange (ETDEWEB)
He, Jianliang; Coffey, H.
1997-08-01
This paper discusses magnetic damping forces in figure-eight-shaped null-flux coil suspension systems, focusing on the Holloman maglev rocket system. The paper also discusses simulating the damping plate, which is attached to the superconducting magnet by two short-circuited loop coils in the guideway. Closed-form formulas for the magnetic damping coefficient as functions of heave-and-sway displacements are derived by using a dynamic circuit model. These formulas are useful for dynamic stability studies.
Influence of near null magnetic field on in vitro growth of potato and wild Solanum species.
Rakosy-Tican, Lenuta; Aurori, C M; Morariu, V V
2005-10-01
The influence of near null magnetic field on in vitro growth of different cultures of potato and related Solanum species was investigated for various exposure times and dates. Potato (Solanum tuberosum L. cv. Désirée) in vitro cultures of shoot tips or nodal segments were used. Three different exposure periods revealed either stimulation or inhibition of root, stem, or leaf in vitro growth after 14 or 28 days of exposure. In one experiment the significant stimulation of leaf growth was also demonstrated at biochemical level, the quantity of chlorophyll a and b and carotenoids increasing more than two-fold. For the wild species Solanum chacoense, S. microdontum, and S. verrucosum, standardized in vitro cultures of nodal stem segments were used. Root and stem growth was either stimulated or slightly inhibited after 9 days exposure to near null magnetic field. Callus cultures obtained from potato dihaploid line 120/19 were maintained in near null magnetic field in 2 different months. For these experiments as well as for Solanum verrucosum, callus cultures recorded either slight inhibition or no effect on fresh weight. For all experiments significant growth variation was brought about only when geomagnetic activity (AP index) showed variations at the beginning of in vitro growth and when the explant had at least one meristematic tissue. Moreover longer maintenance in near null magnetic field, 28 days as compared to 14 days or the controls, can also make a difference in plant growth in response to geomagnetic field variations when static component was reduced to zero value. These results of in vitro plant growth stimulation by variable component of geomagnetic field also sustain the so-called seasonal "window" effect.
Carleman estimates and null controllability of degenerate/singular parabolic systems
Directory of Open Access Journals (Sweden)
Abdelkarim Hajjaj
2016-11-01
Full Text Available We study null controllability properties for parabolic coupled systems with degeneracy and singularity occurring in the interior of the spatial domain. This article is the first to consider a problem with singular coupling terms; previous result cannot be adapted to this situation. In particular, we focus on the well posedness of the problem and then we prove Carleman estimates for the associated adjoint problem.
Null Geodesic Congruences, Asymptotically-Flat Spacetimes and Their Physical Interpretation
Directory of Open Access Journals (Sweden)
Timothy M. Adamo
2009-09-01
Full Text Available A priori, there is nothing very special about shear-free or asymptotically shear-free null geodesic congruences. Surprisingly, however, they turn out to possess a large number of fascinating geometric properties and to be closely related, in the context of general relativity, to a variety of physically significant effects. It is the purpose of this paper to try to fully develop these issues. This work starts with a detailed exposition of the theory of shear-free and asymptotically shear-free null geodesic congruences, i.e., congruences with shear that vanishes at future conformal null infinity. A major portion of the exposition lies in the analysis of the space of regular shear-free and asymptotically shear-free null geodesic congruences. This analysis leads to the space of complex analytic curves in complex Minkowski space. They in turn play a dominant role in the applications. The applications center around the problem of extracting interior physical properties of an asymptotically-flat spacetime directly from the asymptotic gravitational (and Maxwell field itself, in analogy with the determination of total charge by an integral over the Maxwell field at infinity or the identification of the interior mass (and its loss by (Bondi’s integrals of the Weyl tensor, also at infinity. More specifically, we will see that the asymptotically shear-free congruences lead us to an asymptotic definition of the center-of-mass and its equations of motion. This includes a kinematic meaning, in terms of the center-of-mass motion, for the Bondi three-momentum. In addition, we obtain insights into intrinsic spin and, in general, angular momentum, including an angular-momentum–conservation law with well-defined flux terms. When a Maxwell field is present, the asymptotically shear-free congruences allow us to determine/define at infinity a center-of-charge world line and intrinsic magnetic dipole moment.
Zn2+ Uptake in Streptococcus pyogenes: Characterization of adcA and lmb Null Mutants.
Tedde, Vittorio; Rosini, Roberto; Galeotti, Cesira L
2016-01-01
An effective regulation of metal ion homeostasis is essential for the growth of microorganisms in any environment and in pathogenic bacteria is strongly associated with their ability to invade and colonise their hosts. To gain a better insight into zinc acquisition in Group A Streptococcus (GAS) we characterized null deletion mutants of the adcA and lmb genes of Streptococcus pyogenes strain MGAS5005 encoding the orthologues of AdcA and AdcAII, the two surface lipoproteins with partly redundant roles in zinc homeostasis in Streptococcus pneumoniae. Null adcA and lmb mutants were analysed for their capability to grow in zinc-depleted conditions and were found to be more susceptible to zinc starvation, a phenotype that could be rescued by the addition of Zn2+ ions to the growth medium. Expression of AdcA, Lmb and HtpA, the polyhistidine triad protein encoded by the gene adjacent to lmb, during growth under conditions of limited zinc availability was examined by Western blot analysis in wild type and null mutant strains. In the wild type strain, AdcA was always present with little variation in expression levels between conditions of excess or limited zinc availability. In contrast, Lmb and HtpA were expressed at detectable levels only during growth in the presence of low zinc concentrations or in the null adcA mutant, when expression of lmb is required to compensate for the lack of adcA expression. In the latter case, Lmb and HtpA were overexpressed by several fold, thus indicating that also in GAS AdcA is a zinc-specific importer and, although it shares this function with Lmb, the two substrate-binding proteins do not show fully overlapping roles in zinc homeostasis.
Optic-null space medium for cover-up cloaking without any negative refraction index materials
Fei Sun; Sailing He
2016-01-01
With the help of optic-null medium, we propose a new way to achieve invisibility by covering up the scattering without using any negative refraction index materials. Compared with previous methods to achieve invisibility, the function of our cloak is to cover up the scattering of the objects to be concealed by a background object of strong scattering. The concealed object can receive information from the outside world without being detected. Numerical simulations verify the performance of our...
Null Geodesic Congruences, Asymptotically-Flat Spacetimes and Their Physical Interpretation
Directory of Open Access Journals (Sweden)
Timothy M. Adamo
2012-01-01
Full Text Available A priori, there is nothing very special about shear-free or asymptotically shear-free null geodesic congruences. Surprisingly, however, they turn out to possess a large number of fascinating geometric properties and to be closely related, in the context of general relativity, to a variety of physically significant effects. It is the purpose of this paper to try to fully develop these issues. This work starts with a detailed exposition of the theory of shear-free and asymptotically shear-free null geodesic congruences, i.e., congruences with shear that vanishes at future conformal null infinity. A major portion of the exposition lies in the analysis of the space of regular shear-free and asymptotically shear-free null geodesic congruences. This analysis leads to the space of complex analytic curves in an auxiliary four-complex dimensional space, H-space. They in turn play a dominant role in the applications. The applications center around the problem of extracting interior physical properties of an asymptotically-flat spacetime directly from the asymptotic gravitational (and Maxwell field itself, in analogy with the determination of total charge by an integral over the Maxwell field at infinity or the identification of the interior mass (and its loss by (Bondi's integrals of the Weyl tensor, also at infinity. More specifically, we will see that the asymptotically shear-free congruences lead us to an asymptotic definition of the center-of-mass and its equations of motion. This includes a kinematic meaning, in terms of the center-of-mass motion, for the Bondi three-momentum. In addition, we obtain insights into intrinsic spin and, in general, angular momentum, including an angular-momentum--conservation law with well-defined flux terms. When a Maxwell field is present, the asymptotically shear-free congruences allow us to determine/define at infinity a center-of-charge world line and intrinsic magnetic dipole moment.
Herbonnet, Ricardo; Buddendiek, Axel; Kuijken, Konrad
2017-03-01
Context. Current optical imaging surveys for cosmology cover large areas of sky. Exploiting the statistical power of these surveys for weak lensing measurements requires shape measurement methods with subpercent systematic errors. Aims: We introduce a new weak lensing shear measurement algorithm, shear nulling after PSF Gaussianisation (SNAPG), designed to avoid the noise biases that affect most other methods. Methods: SNAPG operates on images that have been convolved with a kernel that renders the point spread function (PSF) a circular Gaussian, and uses weighted second moments of the sources. The response of such second moments to a shear of the pre-seeing galaxy image can be predicted analytically, allowing us to construct a shear nulling scheme that finds the shear parameters for which the observed galaxies are consistent with an unsheared, isotropically oriented population of sources. The inverse of this nulling shear is then an estimate of the gravitational lensing shear. Results: We identify the uncertainty of the estimated centre of each galaxy as the source of noise bias, and incorporate an approximate estimate of the centroid covariance into the scheme. We test the method on extensive suites of simulated galaxies of increasing complexity, and find that it is capable of shear measurements with multiplicative bias below 0.5 percent.
Gravitational Field equations near an Arbitrary Null Surface expressed as a Thermodynamic Identity
Chakraborty, Sumanta; Padmanabhan, T
2015-01-01
Previous work has demonstrated that the gravitational field equations in all Lanczos-Lovelock models imply a thermodynamic identity TdS=dE+PdV (where the variations are interpreted as changes due to virtual displacement along the affine parameter) in the near-horizon limit in static spacetimes. Here we generalize this result to any arbitrary null surface in an arbitrary spacetime and show that certain components of the Einstein's equations can be expressed in the form of the above thermodynamic identity. We also obtain an explicit expression for the thermodynamic energy associated with the null surface. Under appropriate limits, our expressions reduce to those previously derived in the literature. The components of the field equations used in obtaining the current result are orthogonal to the components used previously to obtain another related result, viz. that some components of the field equations reduce to a Navier-Stokes equation on any null surface, in any spacetime. We also describe the structure of Ei...
Energy Technology Data Exchange (ETDEWEB)
Smith, J. Torquil; Morrison, H. Frank; Doolittle, Lawrence R.; Tseng, Hung-Wen
2005-10-17
Equivalent dipole polarizabilities are a succinct way tosummarize the inductive response of an isolated conductive body atdistances greater than the scale of the body. Their estimation requiresmeasurement of secondary magnetic fields due to currents induced in thebody by time varying magnetic fields in at least three linearlyindependent (e.g., orthogonal) directions. Secondary fields due to anobject are typically orders of magnitude smaller than the primaryinducing fields near the primary field sources (transmitters). Receivercoils may be oriented orthogonal to primary fields from one or twotransmitters, nulling their response to those fields, but simultaneouslynulling to fields of additional transmitters is problematic. Iftransmitter coils are constructed symmetrically with respect to inversionin a point, their magnetic fields are symmetric with respect to thatpoint. If receiver coils are operated in pairs symmetric with respect toinversion in the same point, then their differenced output is insensitiveto the primary fields of any symmetrically constructed transmitters,allowing nulling to three (or more) transmitters. With a sufficientnumber of receivers pairs, object equivalent dipole polarizabilities canbe estimated in situ from measurements at a single instrument sitting,eliminating effects of inaccurate instrument location on polarizabilityestimates. The method is illustrated with data from a multi-transmittermulti-receiver system with primary field nulling through differencedreceiver pairs, interpreted in terms of principal equivalent dipolepolarizabilities as a function of time.
Internal structure of an optical null Ronchi grating test for a plano-parabolic lens.
Ortega-Vidals, Paula; Juárez-Reyes, Salvador Alejandro; Silva-Ortigoza, Gilberto; Cabrera-Rosas, Omar de J
2016-01-01
In this work we use geometrical optics and the caustic touching theorem, introduced by Berry, to describe the internal structure of the null Ronchi grating for a plano-parabolic lens illuminated by a point light source placed on the optical axis. The aim of this work is to explain the role of the caustic region in the process of morphology change between image and object in computing the null Ronchi grating. To this end, we obtain the analytic expression of the null Ronchi grating, and after that we deeply study the change in morphology between a single straight fringe image at the Ronchigram and the multiple curve rulings that can generate it (one open and one closed). We analyze exactly how multiple rulings generate the same straight image fringe, or how an entire ruling collapses into a single point image. For this analysis, we take different observation planes at different positions with respect to the caustic region. Finally, we characterize this topological change as one of two possible kinds depending on the relative position between the observation plane and the caustic region.
Simulations of 3D Magnetic Merging: Resistive Scalings for Null Point and QSL Reconnection
Effenberger, Frederic
2016-01-01
Starting from an exact, steady-state, force-free solution of the magnetohydrodynamic (MHD) equations, we investigate how resistive current layers are induced by perturbing line-tied three-dimensional magnetic equilibria. This is achieved by the superposition of a weak perturbation field in the domain, in contrast to studies where the boundary is driven by slow motions, like those present in photospheric active regions. Our aim is to quantify how the current structures are altered by the contribution of so called quasi-separatrix layers (QSLs) as the null point is shifted outside the computational domain. Previous studies based on magneto-frictional relaxation have indicated that, despite the severe field line gradients of the QSL, the presence of a null is vital in maintaining fast reconnection. Here, we explore this notion using highly resolved simulations of the full MHD evolution. We show that for the null-point configuration, the resistive scaling of the peak current density is close to $J\\sim\\eta^{-1}$, ...