2,912 research outputs found
An exponential open hashing function based on dynamical systems theory
In this paper an efficient open addressing hash function called exponential hashing is developed using concepts from dynamical systems theory and number theory. A comparison of exponential hashing versus a widely used double hash function is performed using an analysis based on Lyapunov exponents and entropy. Proofs of optimal table parameter choices are provided for a number of hash functions. We also demonstrate experimentally that exponential hashing nearly matches the performance of an optimal double hash function for uniform data distributions and performs significantly better for nonuniform data distributions. We show that exponential hashing exhibits a higher integer Lyapunov exponent and entropy than double hashing for initial data probes which offers one explanation for its improved performance on nonuniform data distributions
Dynamical system representation of open address hash functions
This paper demonstrates how a broad collection of hash function families can be expressed as dynamical systems. We then show that this representation can be useful for analysis. In particular, we provide an analysis which proves that a widely-used family of double hash functions will transform any initial distribution of keys into the uniform distribution over the table space
CASTER - a concept for a Black Hole Finder Probe based on the use of new scintillator technologies
The primary scientific mission of the Black Hole Finder Probe (BHFP), part of
the NASA Beyond Einstein program, is to survey the local Universe for black
holes over a wide range of mass and accretion rate. One approach to such a
survey is a hard X-ray coded-aperture imaging mission operating in the 10--600
keV energy band, a spectral range that is considered to be especially useful in
the detection of black hole sources. The development of new inorganic
scintillator materials provides improved performance (for example, with regards
to energy resolution and timing) that is well suited to the BHFP science
requirements. Detection planes formed with these materials coupled with a new
generation of readout devices represent a major advancement in the performance
capabilities of scintillator-based gamma cameras. Here, we discuss the Coded
Aperture Survey Telescope for Energetic Radiation (CASTER), a concept that
represents a BHFP based on the use of the latest scintillator technology.Comment: 12 pages; conference paper presented at the SPIE conference "UV,
X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XIV." To be
published in SPIE Conference Proceedings, vol. 589
Behavioral strategies during incubation influence nest and female survival of Wild Turkeys
Females must balance physiological and behavioral demands of producing offspring with associated expenditures, such as resource acquisition and predator avoidance. Nest success is an important parameter underlying avian population dynamics. Galliforms are particularly susceptible to low nest success due to exposure of ground nests to multiple predator guilds, lengthy incubation periods, and substantive reliance on crypsis for survival. Hence, it is plausible that nesting individuals prioritize productivity and survival differently, resulting in a gradient of reproductive strategies. Fine-scale movement patterns during incubation are not well documented in ground-nesting birds, and the influence of reproductive movements on survival is largely unknown. Using GPS data collected from female wild turkeys (n = 278) across the southeastern United States, we evaluated the influence of incubation recess behaviors on trade-offs between nest and female survival. We quantified daily recess behaviors including recess duration, recess frequency, total distance traveled, and incubation range size for each nest attempt as well as covariates for nest concealment, nest attempt, and nest age. Of 374 nests, 91 (24%) hatched and 39 (14%) females were depredated during incubation. Average nest survival during the incubation period was 0.19, whereas average female survival was 0.78. On average, females took 1.6 daily unique recesses (SD = 1.2), spent 2.1 hr off the nest each day (SD = 1.8), and traveled 357.6 m during recesses (SD = 396.6). Average nest concealment was 92.5 cm (SD = 47). We found that females who took longer recess bouts had higher individual survival, but had increased nest loss. Females who recessed more frequently had lower individual survival. Our findings suggest behavioral decisions made during incubation represent life-history trade-offs between predation risk and reproductive success on an unpredictable landscape
Seminal plasma and prostaglandin E2 up-regulate fibroblast growth factor 2 expression in endometrial adenocarcinoma cells via E-series prostanoid-2 receptor-mediated transactivation of the epidermal growth factor receptor and extracellular signal-regulated kinase pathway
We report a multiwavelength (X-ray, ultraviolet/optical/infrared, radio)
analysis of the relativistic tidal disruption event candidate Sw J2058+05 from
3 months to 3 yr post-discovery in order to study its properties and compare
its behavior with that of Sw J1644+57. Our main results are as follows. (1) The
long-term X-ray light curve of Sw J2058+05 shows a remarkably similar trend to
that of Sw J1644+57. After a prolonged power-law decay, the X-ray flux drops
off rapidly by a factor of within a span of /
0.95. Associating this sudden decline with the transition from super-Eddington
to sub-Eddington accretion, we estimate the black hole mass to be in the range
of M. (2) We detect rapid ( s) X-ray
variability before the dropoff, suggesting that, even at late times, the X-rays
originate from close to the black hole (ruling out a forward-shock origin). (3)
We confirm using HST and VLBA astrometry that the location of the source
coincides with the galaxy's center to within pc (in projection).
(4) We modeled Sw J2058+05's ultraviolet/optical/infrared spectral energy
distribution with a single-temperature blackbody and find that while the radius
remains more or less constant at a value of AU (
cm) at all times during the outburst, the blackbody temperature drops
significantly from 30,000 K at early times to a value of 15,000 K
at late times (before the X-ray dropoff). Our results strengthen Sw J2058+05's
interpretation as a tidal disruption event similar to Sw J1644+57.Comment: Replaced with the published version of the manuscrip
Electrical Stimulation Modulates High γ Activity and Human Memory Performance.
Direct electrical stimulation of the brain has emerged as a powerful treatment for multiple neurological diseases, and as a potential technique to enhance human cognition. Despite its application in a range of brain disorders, it remains unclear how stimulation of discrete brain areas affects memory performance and the underlying electrophysiological activities. Here, we investigated the effect of direct electrical stimulation in four brain regions known to support declarative memory: hippocampus (HP), parahippocampal region (PH) neocortex, prefrontal cortex (PF), and lateral temporal cortex (TC). Intracranial EEG recordings with stimulation were collected from 22 patients during performance of verbal memory tasks. We found that high γ (62-118 Hz) activity induced by word presentation was modulated by electrical stimulation. This modulatory effect was greatest for trials with poor memory encoding. The high γ modulation correlated with the behavioral effect of stimulation in a given brain region: it was negative, i.e., the induced high γ activity was decreased, in the regions where stimulation decreased memory performance, and positive in the lateral TC where memory enhancement was observed. Our results suggest that the effect of electrical stimulation on high γ activity induced by word presentation may be a useful biomarker for mapping memory networks and guiding therapeutic brain stimulation
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Human Verbal Memory Encoding Is Hierarchically Distributed in a Continuous Processing Stream.
Processing of memory is supported by coordinated activity in a network of sensory, association, and motor brain regions. It remains a major challenge to determine where memory is encoded for later retrieval. Here, we used direct intracranial brain recordings from epilepsy patients performing free recall tasks to determine the temporal pattern and anatomical distribution of verbal memory encoding across the entire human cortex. High γ frequency activity (65-115 Hz) showed consistent power responses during encoding of subsequently recalled and forgotten words on a subset of electrodes localized in 16 distinct cortical areas activated in the tasks. More of the high γ power during word encoding, and less power before and after the word presentation, was characteristic of successful recall and observed across multiple brain regions. Latencies of the induced power changes and this subsequent memory effect (SME) between the recalled and forgotten words followed an anatomical sequence from visual to prefrontal cortical areas. Finally, the magnitude of the memory effect was unexpectedly found to be the largest in selected brain regions both at the top and at the bottom of the processing stream. These included the language processing areas of the prefrontal cortex and the early visual areas at the junction of the occipital and temporal lobes. Our results provide evidence for distributed encoding of verbal memory organized along a hierarchical posterior-to-anterior processing stream
High Temperature Boost (HTB) Power Processing Unit (PPU) Formulation Study
This technical memorandum is to summarize the Formulation Study conducted during fiscal year 2012 on the High Temperature Boost (HTB) Power Processing Unit (PPU). The effort is authorized and supported by the Game Changing Technology Division, NASA Office of the Chief Technologist. NASA center participation during the formulation includes LaRC, KSC and JPL. The Formulation Study continues into fiscal year 2013. The formulation study has focused on the power processing unit. The team has proposed a modular, power scalable, and new technology enabled High Temperature Boost (HTB) PPU, which has 5-10X improvement in PPU specific power/mass and over 30% in-space solar electric system mass saving
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alters the connectivity of olfactory neurons in the absence of amyloid plaques in vivo
The amyloid beta peptide aggregates into amyloid plaques at presymptomatic stages of Alzheimer's disease, but the temporal relationship between plaque formation and neuronal dysfunction is poorly understood. Here we demonstrate that the connectivity of the peripheral olfactory neural circuit is perturbed in mice overexpressing human APPsw (Swedish mutation) before the onset of plaques. Expression of human APPsw exclusively in olfactory sensory neurons also perturbs connectivity with associated reductions in odour-evoked gene expression and olfactory acuity. By contrast, olfactory sensory neuron axons project correctly in mice overexpressing wild-type human amyloid precursor protein throughout the brain and in mice overexpressing M671V human APP, a missense mutation that reduces amyloid beta production, exclusively in olfactory sensory neurons. Furthermore, expression of Aβ40 or Aβ42 solely in the olfactory epithelium disrupts the olfactory sensory neuron axon targeting. Our data indicate that altering the structural connectivity and function of highly plastic neural circuits is one of the pleiotropic actions of soluble human amyloid beta
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