A modified parallel tree code for N-body simulation of the Large Scale Structure of the Universe

N-body codes to perform simulations of the origin and evolution of the Large Scale Structure of the Universe have improved significantly over the past decade both in terms of the resolution achieved and of reduction of the CPU time. However, state-of-the-art N-body codes hardly allow one to deal with particle numbers larger than a few 10^7, even on the largest parallel systems. In order to allow simulations with larger resolution, we have first re-considered the grouping strategy as described in Barnes (1990) (hereafter B90) and applied it with some modifications to our WDSH-PT (Work and Data SHaring - Parallel Tree) code. In the first part of this paper we will give a short description of the code adopting the Barnes and Hut algorithm \cite{barh86} (hereafter BH), and in particular of the memory and work distribution strategy applied to describe the {\it data distribution} on a CC-NUMA machine like the CRAY-T3E system. In the second part of the paper we describe the modification to the Barnes grouping strategy we have devised to improve the performance of the WDSH-PT code. We will use the property that nearby particles have similar interaction list. This idea has been checked in B90, where an interaction list is builded which applies everywhere within a cell C_{group} containing a little number of particles N_{crit}. B90 reuses this interaction list for each particle $p \in C_{group}$ in the cell in turn. We will assume each particle p to have the same interaction list. Thus it has been possible to reduce the CPU time increasing the performances. This leads us to run simulations with a large number of particles (N ~ 10^7/10^9) in non-prohibitive times.Comment: 13 pages and 7 Figure

A Pilot Study to Measure Upper Extremity H-reflexes Following Neuromuscular Electrical Stimulation Therapy after Stroke

Upper extremity (UE) hemiparesis persists after stroke, limiting hand function. Neuromuscular electrical stimulation (NMES) is an effective intervention to improve UE recovery, although the underlying mechanisms are not fully understood. Our objective was to establish a reliable protocol to measure UE agonist–antagonist forearm monosynaptic reflexes in a pilot study to determine if NMES improves wrist function after stroke. We established the between-day reliability of the H-reflex in the extensor carpi radialis longus (ECRL) and flexor carpi radialis (FCR) musculature for individuals with prior stroke (n = 18). The same-day generation of ECRL/FCR H-reflex recruitment curves was well tolerated, regardless of age or UE spasticity. The between-day reliability of the ECRL H-reflex was enhanced above FCR, similar to healthy subjects [20], with the Hmax the most reliable parameter quantified in both muscles. H-reflex and functional measures following NMES show the potential for NMES-induced increases in ECRL Hmax, but confirmation requires a larger clinical study. Our initial results support the safe, easy, and efficacious use of in-home NMES, and establish a potential method to measure UE monosynaptic reflexes after stroke

Life in the Cold

Preface; First and Corresponding Author Contact Information; An Evolutionary Framework for Studies of Hibernation and Short-term Torpor -- Gordon C. Grigg; Was Adaptive Hypothermia a Prerequisite for the Colonization of Madagascar By Mammals? -- Barry G. Lovegrove; No Evidence for Torpor in a Small African Mainland Primate: The Lesser Bushbaby, Galago moholi -- Nomakwezi Mzilikazi, Barry G. Lovegrove, and Judith C. Masters; The Origin of Mammalian Heterothermy: A Case for Perpetual Youth? -- Michael B. Harris, Link E. Olson, and William K. Milsom; Passive Rewarming from Torpor in Mammals and Birds: Energetic, Ecological and Evolutionary Implications -- Fritz Geiser, Rebecca L. Drury, Gerhard Kortner, Christopher Turbill, Chris R. Pavey, and R. Mark Brigham; Solar Radiation and the Energetic Cost of Rewarming from Torpor -- Andrew M. McKechnie and Blair O. Wolf; The Role of α-Linolenic Acid (18:3) in Mammalian Torpor -- Craig L. Frank, Wendy R. Hood, and Mary C. Donnelly; Heat Transfer in Humans: Lessons from Large Hibernators -- Dennis Grahn and H. Craig Heller; Factors Influencing the Timing of Dormancy in the Pocket Mouse,Perognathus longimembris -- Alan R. French; The Energetic State-dependency of Autumn Immergence in Eastern Chipmunks -- Murray M. Humphries and Brandon Rodgers; Seasonal Timing of Reproduction and Hibernation in the Edible Dormouse (Glis glis) -- Claudia Bieber and Thomas Ruf; Reproduction and Hibernation in Females: A Comparison of Two Sympatric Ground-Dwelling Rodents -- Eva Millesi, Ilse E. Hoffmann, Anna Aschauer, and Claudia Franceschini; How the Photoperiod Times the Annual Reproductive and Hibernation Cycles -- P. Pevet, M. Saboureau, and P. Klosen; Behaviour, Body Temperature, and Hibernation in Tasmanian Echidnas (Tachyglossus aculeatus) -- Stewart Nicol, Christina Vedel-Smith, and Niels A. Andersen; Metabolic Diversity in Yellow-Bellied Marmots -- Kenneth B. Armitage; Metabolic Rate Reduction During Hibernation and Daily Torpor -- Fritz Geiser; How to Enter Torpor: Thermodynamic and Physiological Mechanisms of Metabolic Depression -- Gerhard Heldmaier and Ralf Elvert; Slow Loss of Protein Integrity During Torpor: A Cause for Arousal? -- Sandra L. Martin, Timothy Dahl, and L. Elaine Epperson; A Technique for Modelling Thermoregulatory Energy Expenditure in Free-ranging Endotherms -- Craig K. R. Willis, Jeffery E. Lane, Eric T. Liknes, David L. Swanson, and R. Mark Brigham; Sex Differences in the Response of Torpor to Exogenous Corticosterone During the Onset of the Migratory Season in Rufous Hummingbirds -- Sara M. Hiebert, John C. Wingfield, Marilyn Ramenofsky, Leah Deni, and Antoinette Grafin zu Elz; The Avian Enigma: “Hibernation” by Common Poorwills (Phalaenoptilus nuttalli) -- Christopher P. Woods and R. Mark Brigham; Shivering Thermogenesis in Birds and Mammals -- Esa Hohtola; The Impact of Social Interactions on Torpor Use in Hummingbirds -- Donald Powers; The Energetics of the Rewarming Phase of Avian Torpor -- Andrew E. McKechnie and Blair O. Wolf; Insect Cold-Hardiness: New Advances Using Gene Screening Technology -- Kenneth B. Storey and David C. McMullen; Advantages and Disadvantages of Freeze-Tolerance and Freeze-Avoidance Overwintering Strategies -- Karl Erick Zachariassen, Sindre Andre Pedersen, and Erlend Kristiansen; Live and Let Diapause: Cell Cycle Regulation During Insect Overwintering -- Savvas c. Pavlides, Kenneth A. Weir, and Steven P. Tammariello; Vertebrate Freeze Tolerance: Role of Freeze-Responsive Gene Expression -- Kenneth B. Storey; Ice, Antifreeze Proteins, and Antifreeze Genes in Polar Fishes -- Arthur L. DeVries; Overwintering in Submerged Turtles -- Donald C. Jackson; Environmental Physiology of Terrestrial Hibernation in Hatchling Turtles -- Patrick J. Baker, Jon P. Costanzo, and Richard E. Lee, Jr.; Overwintering in Tegu Lizards -- Denis V. Andrade, Colin Sanders, William K. Milsom, and Augusto S. Abe; Overwintering in Cold-Submerged Frogs -- Glenn J. Tattersall; Effect of Temperature on Regular and Modified Circannual Rhythms in the European Ground Squirrel Under Free-Running Conditions -- Radoslav K. Andjus, Marina Marjanovic, and Dragoslava Zivadinovic; The Role of the Suprachiasmatic Pacemaker (SCN) in Energy Expenditure During Hibernation of Golden-mantled Ground Squirrels -- Patricia J. DeCoursey; Does Hibernation Violate Biological Laws? -- Andre Malan; The Suprachiasmatic Nucleus Influences Energy Balance of Golden-mantled Ground Squirrels During Hibernation -- Norman E. Ruby; Pesticide Effects on Body Temperature of Torpid/Hibernating Rodents (Peromyscus leucopus and Spermophilus tridecemlineatus) -- Thomas E. Tomasi, Peta Elsken-Lacy, Jean A. Perry, and Kerry Withers; Steroidogenesis and the HPA Axis During Hibernation: Differential Expression of the StAR Protein -- Matthew T. Andrews, Meaghan M. Tredrea, and Aubie K. Shaw; A Quest for the Origin of Mammalian Uncoupling Proteins -- Marton Jastroch, Sigrid Stohr, Kerry Withers, and Martine Klingenspor; Brown-Fat-Derived and Thyroid-Hormone Thermogenesis: Mechanisms and Interactions -- Jan Nedergaard, Valeria Golozoubova, and Barbara Cannon; Alterations in Localization of Hippocampal Protein Kinase Cγ (PKCγ), but Not PKCα, -β1, or –β2, in European Ground Squirrels During Hibernation -- Eddy A. Van der Zee, Jens Stieler, Roelof A. Hut, Martin de Wilde, and Arjen M. Strijkstra; The Role of the Medial Septum in the Control of Hibernation -- Irina Yu. Popova and Yurii M. Kokoz; Proteolysis in Hibernators -- Frank can Breukelen; Post-genomic Approaches to the Mechanisms of Cold Response in Fish and Hibernating Small Mammals -- Daryl Williams, L. Elaine Epperson, Andrew R. Cossins, Jane Fraser, Weizhong Li, Sandra Martin, and Andrew Y. Gracey; Use of Suppression Subtractive Hybridization to Elucidate Novel Gene Products Related to Physiological Events in a Hibernator -- Gregory L. Florant, Chris Pittman, and Scott A. Summers; Clinical Applications and Limitations of Hypothermia -- Philip E. bickler; Hibernation in Mammals: A Model for Alzheimer-type Phosphorylation of the Microtubule-associated Protein Tau -- Thomas Arendt, Jens Stieler, Arjen M. Strijkstriam Roelof A. Hut, Eddy A. Van der Zee, max Holzer, and Woldfgang Hartig; Resistance of Livers to Cold Ischemia/Reperfusion Injury During Hibernation: Involvement of Matrix Metalloproteinase and Nitric Oxide Synthase -- Hannah V. Carey, Timothy M. Piazza, Sarah E. Davis, Susanne L. Lindell, Anna Durranis, Kieran Clarke, and James H. Southard; Anti-Proliferative Effects of Plasma from Hibernating Rodents -- Donna G. Sieckmann, Decheng Cai, Howard Jaffe, John Hallenbeck, and Richard M. McCarron; Antifreeze Proteins in Terrestrial Arthropods -- John G. Duman, Valerie A. Bennett, N. Li, L. Wang, L. Huang, T. Sformo, and B.M. Barnes; Cardiac Conduction and Resistance to Ventricular Fibrillation in Siberian Hibernator Ground Squirrel Citellus undulatus -- Vadim V. Fedorov, Rubin R. Aliev, Alexey V. Glukhov, Andrey V. Resnik, Andrey Anufriev, Irina A. Ivanova, Olga V. Nakipova, Stella G. Kolaeva, Leonid V. Rosenshtraukh, and Igor R. Efimov; The Correlation Between Akt Activity and Hibernation -- Decheng Cai, Richard M. McCarron, Donna Sieckmann, and John M. Hallenbeck; Protection from Traumatic Brain Injury During Hibernation -- Kelly L. Drew, Fang Zhou, Xiongwei Zhu, Rudy J. Castellani, and Mark A. Smith; δ-Opioid Agonists Protect the Rat Liver From Cold Storage and Ischemia/Reperfusion Injury -- Thomas L. Husted, Wen-Jian Chang, Alex B. Lentsch, Steven M. Rudich;Animal Adaptability to Oxidative Stress: Gastropod Estivation and Mammalian Hibernation -- Marcelo Hermes-Lima, Gabriella R. Ramos-Vasconcelos, Luciano A. Cardoso, Adrienne l. Orr, Patricia M. Rivera, and Kelly L. Drew

Guided random walk calculation of energies and <\sq {r^2} > values of the 1Σg^1\Sigma_g state of H_2 in a magnetic field

Energies and spatial observables for the $^1\Sigma_g$ state of the hydrogen molecule in magnetic fields parallel to the proton-proton axis are calculated with a guided random walk Feynman-Kac algorithm. We demonstrate that the accuracy of the results and the simplicity of the method may prove it a viable alternative to large basis set expansions for small molecules in applied fields.Comment: 10 pages, no figure

Disrupting the wall accumulation of human sperm cells by artificial corrugation

Many self-propelled microorganisms are attracted to surfaces. This makes their dynamics in restricted geometries very different from that observed in the bulk. Swimming along walls is beneficial for directing and sorting cells, but may be detrimental if homogeneous populations are desired, such as in counting microchambers. In this work, we characterize the motion of human sperm cells $60 \mu m$ long, strongly confined to $25 \mu m$ shallow chambers. We investigate the nature of the cell trajectories between the confining surfaces and their accumulation near the borders. Observed cell trajectories are composed of a succession of quasi-circular and quasi-linear segments. This suggests that the cells follow a path of intermittent trappings near the top and bottom surfaces separated by stretches of quasi-free motion in between the two surfaces, as confirmed by depth resolved confocal microscopy studies. We show that the introduction of artificial petal-shaped corrugation in the lateral boundaries removes the tendency of cells to accumulate near the borders, an effect which we hypothesize may be valuable for microfluidic applications in biomedicine.Comment: 9 pages, latex. In accepted version on April 14, v2: abstract modified, information added to Sec. II.A and experiments added to Sec. III.A and Fig.3. Sec. III.C was deleted. Requested references adde

Abnormal negative feedback processing in first episode schizophrenia: evidence from an oculomotor rule switching task

Background. Previous studies have shown that patients with schizophrenia are impaired on executive tasks, where positive and negative feedbacks are used to update task rules or switch attention. However, research to date using saccadic tasks has not revealed clear deficits in task switching in these patients. The present study used an oculomotor ‘ rule switching ’ task to investigate the use of negative feedback when switching between task rules in people with schizophrenia. Method. A total of 50 patients with first episode schizophrenia and 25 healthy controls performed a task in which the association between a centrally presented visual cue and the direction of a saccade could change from trial to trial. Rule changes were heralded by an unexpected negative feedback, indicating that the cue-response mapping had reversed. Results. Schizophrenia patients were found to make increased errors following a rule switch, but these were almost entirely the result of executing saccades away from the location at which the negative feedback had been presented on the preceding trial. This impairment in negative feedback processing was independent of IQ. Conclusions. The results not only confirm the existence of a basic deficit in stimulus–response rule switching in schizophrenia, but also suggest that this arises from aberrant processing of response outcomes, resulting in a failure to appropriately update rules. The findings are discussed in the context of neurological and pharmacological abnormalities in the conditions that may disrupt prediction error signalling in schizophrenia

Semiclassical time--dependent propagation in three dimensions: How accurate is it for a Coulomb potential?

A unified semiclassical time propagator is used to calculate the semiclassical time-correlation function in three cartesian dimensions for a particle moving in an attractive Coulomb potential. It is demonstrated that under these conditions the singularity of the potential does not cause any difficulties and the Coulomb interaction can be treated as any other non-singular potential. Moreover, by virtue of our three-dimensional calculation, we can explain the discrepancies between previous semiclassical and quantum results obtained for the one-dimensional radial Coulomb problem.Comment: 8 pages, 4 figures (EPS

Strong enhancement of spin fluctuations in the low-temperature-tetragonal phase of antiferromagnetically ordered La_{2-x-y}Eu_ySr_xCuO_4

Measurements of the static magnetization, susceptibility and ESR of Gd spin probes have been performed to study the properties of antiferromagnetically ordered La_{2-x-y}Eu_ySr_xCuO_4 (x less or equal 0.02) with the low temperature tetragonal structure. According to the static magnetic measurements the CuO_2 planes are magnetically decoupled in this structural phase. The ESR study reveals strong magnetic fluctuations at the ESR frequency which are not present in the orthorhombic phase. It is argued that this drastic enhancement of the spin fluctuations is due to a considerable weakening of the interlayer exchange and a pronounced influence of hole motion on the antiferromagnetic properties of lightly hole doped La_2CuO_4. No evidence for the stripe phase formation at small hole doping is obtained in the present study.Comment: 10 pages, LaTeX, 3 EPS figures; to be published in Journal of Physics: Condensed Matte