Matveev V.,University Heights |
Bertram R.,Florida State University |
Sherman A.,U.S. National Institutes of Health
Brain Research | Year: 2011
The number of Ca 2+ channels contributing to the exocytosis of a single neurotransmitter vesicle in a presynaptic terminal has been a question of significant interest and debate, and is important for a full understanding of localized Ca 2+ signaling in general, and synaptic physiology in particular. This is usually estimated by measuring the sensitivity of the neurotransmitter release rate to changes in the synaptic Ca 2+ current, which is varied using appropriate voltage-clamp protocols or via pharmacological Ca 2+ channel block under the condition of constant single-channel Ca 2+ current. The slope of the resulting log-log plot of transmitter release rate versus presynaptic Ca 2+ current is termed Ca 2+ current cooperativity of exocytosis, and provides indirect information about the underlying presynaptic morphology. In this review, we discuss the relationship between the Ca 2+ current cooperativity and the average number of Ca 2+ channels participating in the exocytosis of a single vesicle, termed the Ca 2+channel cooperativity. We relate these quantities to the morphology of the presynaptic active zone. We also review experimental studies of Ca 2+ current cooperativity and its modulation during development in different classes of synapses.
Zhang C.,University of Florida |
Zhang Y.,University Heights |
Fang Y.,University of Florida
IEEE Transactions on Mobile Computing | Year: 2010
After a wireless sensor network (WSN) is deployed, sensor nodes are usually left unattended for a long period of time. There is an inevitable devolution of the connected coverage of the WSN due to battery exhaustion of sensor nodes, intended physical destruction attacks on sensor nodes, unpredictable node movement by physical means like wind, and so on. It is, therefore, critical that the base station (BS) learns in real time how well the WSN performs the given sensing task (i.e., what is the current connected coverage) under a dynamically changing network topology. In this paper, we propose a coverage inference protocol (CIP), which can provide the BS an accurate and in-time measurement of the current connected coverage in an energy-efficient way. Especially, we show that the scheme called BOND, which our CIP requires to be implemented on each sensor node, enables each node to locally self-detect whether it is a boundary node with the minimal communication and computational overhead. The BOND can also be exploited to seamlessly integrate multiple functionalities with low overhead. Moreover, we devise extensions to CIP that can tolerate location errors and actively predict the change of the connected coverage based on residual energy of sensor nodes. © 2010 IEEE.
Boubendir Y.,University Heights |
Antoine X.,University of Lorraine |
Geuzaine C.,University of Liège
Journal of Computational Physics | Year: 2012
This paper presents a new non-overlapping domain decomposition method for the Helmholtz equation, whose effective convergence is quasi-optimal. These improved properties result from a combination of an appropriate choice of transmission conditions and a suitable approximation of the Dirichlet to Neumann operator. A convergence theorem of the algorithm is established and numerical results validating the new approach are presented in both two and three dimensions. © 2011 Elsevier Inc.
Stamatis D.,New Jersey Institute of Technology |
Stamatis D.,University Heights |
Dreizin E.L.,New Jersey Institute of Technology |
Dreizin E.L.,University Heights |
Higa K.,U.S. Navy
Journal of Propulsion and Power | Year: 2011
Two types of nanocomposite reactive materials with the same bulk compositions 8Al·MoO3 were prepared and compared with each other. One of the materials was manufactured by arrested reactive milling and the other so-called metastable interstitial composite was manufactured by mixing of nanoscaled individual powders. The materials were characterized using differential scanning calorimetry, thermogravimetric, as well as ignition, experiments using an electrically heated filament and laser as heat sources. The experiments were interpreted using simplified models describing heat transfer in the heated material samples in different experimental configurations. Clear differences in the low-temperature redox reactions, well detectable by differential scanning calorimetry, were established between metastable interstitial composite and arrested-reactive-milling-prepared materials. However, the materials did not differ significantly from each other in the ignition experiments. In the heated filament ignition tests, their ignition temperatures were nearly identical to each other and were in the range of 750-800 K. These ignition temperatures coincided with the temperatures at which main exothermic processes were detected in differential scanning calorimetry experiments. In laser ignition experiments performed with consolidated pellets of both materials, metastable interstitial composite pellets produced consistently stronger pressure pulses. The ignition delays were similar for the pellets of both materials prepared with the same porosity. Analysis of the heat transfer in the pellets heated by the laser suggested that the laser-exposed pellet surfaces were heated to approximately the same temperature before ignition for both materials. This temperature was estimated to be close to 500 K, neglecting the exothermic reactions preceding ignition and possible fragmentation of the heated pellets. Taking into account both phenomena is expected to result in a higher surface temperature, which would better represent the experimental situation. It is proposed that the ignition of both metastable interstitial composite and arrested-reactive-millingprepared materials at the same temperature can be explained by a thermodynamically driven transformation of a protective amorphous alumina into a crystalline polymorph. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc.
Wang H.,University Heights |
Liu C.,University Heights
Astrophysical Journal | Year: 2012
Solar flare emissions in the chromosphere often appear as elongated ribbons on both sides of the magnetic polarity inversion line (PIL), which has been regarded as evidence of a typical configuration of magnetic reconnection. However, flares having a circular ribbon have rarely been reported, although it is expected in the fan-spine magnetic topology involving reconnection at a three-dimensional (3D) coronal null point. We present five circular ribbon flares with associated surges, using high-resolution and high-cadence Hα blue wing observations obtained from the recently digitized films of Big Bear Solar Observatory. In all the events, a central parasitic magnetic field is encompassed by the opposite polarity, forming a circular PIL traced by filament material. Consequently, a flare kernel at the center is surrounded by a circular flare ribbon. The four homologous jet-related flares on 1991 March 17 and 18 are of particular interest, as (1) the circular ribbons brighten sequentially, with cospatial surges, rather than simultaneously, (2) the central flare kernels show an intriguing "round-trip" motion and become elongated, and (3) remote brightenings occur at a region with the same magnetic polarity as the central parasitic field and are co-temporal with a separate phase of flare emissions. In another flare on 1991 February 25, the circular flare emission and surge activity occur successively, and the event could be associated with magnetic flux cancellation across the circular PIL. We discuss the implications of these observations combining circular flare ribbons, homologous jets, and remote brightenings for understanding the dynamics of 3D magnetic restructuring. © 2012. The American Astronomical Society. All rights reserved.
Ihde E.S.,Hackensack University Medical Center |
Loh J.M.,University Heights |
Rosen L.,Hackensack University Medical Center
BMC Endocrine Disorders | Year: 2015
Background: The prevalence of pediatric hormonal disorders and hormonally-sensitive cancers are rising. Chemicals including bisphenol A (BPA), phthalates, parabens, 4-nonylphenol (4NP) and triclosan have been linked to disruption of endocrine pathways and altered hormonal status in both animal and human studies. Additionally, changes in estrogen metabolism have been associated with pediatric endocrine disorders and linked to estrogen-dependent cancers. The main objective of the study was to measure the presence of these environmental chemicals in prepubescent children and assess the relationship between chemical metabolites and estrogen metabolism. Methods: 50 subjects (25 male, 25 female) were recruited from the principal investigator's existing patient population at his pediatric primary care office. The first 5 boys and 5 girls in each age group (4 through 8 years old inclusive) who presented for annual examinations were included, as long as they were Tanner Stage I (prepubertal) on physical exam, without diagnosis of hormonally-related condition and/or cancer and able to give a urine sample. Urine samples were collected in glass containers for analysis of chemical and estrogen metabolites. Study kits and lab analysis were provided by Genova Diagnostics (Duluth, GA). Summary statistics for the concentrations of each chemical metabolite as well as estrogen metabolites were computed (minimum, maximum, median and inter-quartile range) for males only, for females only and for all subjects. Comparisons between groups (e.g. males v. females) were assessed using the nonparametric Wilcoxon test, since the data was skewed. The correlation between concentrations of chemical metabolites and estrogen metabolites in prepubescent children were examined by the Spearman's correlation coefficient (ρ). Results: 100 % of subjects had detectable levels of at least one chemical in their urine, and 74 % had detectable levels of eight or more chemicals. 28 % of subjects had measurable levels of 4NP. No associations were found between the urine levels of chemicals and estrogen metabolites. Conclusions: Endocrine disrupting environmental chemicals were detected in all children in the study, with measurable levels of 4NP in nearly 1/3 of subjects. This is the first known published study of 4NP levels in American children. No associations were found between the urine levels of chemicals tested and estrogen metabolites. The presence of multiple chemicals in a majority of children's urine coupled with increasing prevalence of pediatric hormonal disorders warrants further research to elucidate potential causal mechanisms in pre- and post-pubertal children. © 2015 Ihde et al.
Zhang S.,University Heights |
Schoenitz M.,University Heights |
Dreizin E.L.,University Heights
Journal of Physical Chemistry C | Year: 2010
Multifunctional materials combining the high energy density of metal fuels with the ability to generate biocidal combustion products are of interest for defeat of stockpiles of biological weapons. In this study, new Al-I composites are prepared and investigated, which are expected to combust similarly to Al powder while releasing biocidal iodine-containing reaction products. Materials are prepared by mechanical milling of pure Al powder and iodine at cryogenic temperatures. Prepared materials are stable at room temperature and contain more than 10 wt % of iodine. Two samples with the same nominal compositions were prepared using different milling conditions. Thermogravimetric measurements at different heating rates were used to characterize reactions of iodine release and oxidation of the prepared materials. Oxidation was studied with O 2 serving as an oxidizer. Ignition of the prepared materials was studied by coating them onto an electrically heated filament and using optical diagnostics to identify ignition temperatures at different heating rates. It was observed that iodine is released from the prepared materials in several steps. At low temperatures, iodine release is similar to volatilization of elemental iodine and AlI3. Substantial amounts of iodine are retained to higher temperatures and begin to volatilize when the sample temperature approaches the Al melting point. Oxidation of the prepared materials in O2 begins at lower temperatures than that for pure Al. Melting of Al accelerates both oxidation and iodine release rates. Prepared materials ignite at substantially lower temperatures than pure Al, and a correlation between ignition and iodine release is identified. © 2010 American Chemical Society.
Sakarindr P.,University Heights |
Ansari N.,University Heights
IET Information Security | Year: 2010
Secure group communication (SGC) has attracted much attention, as group-oriented communications have been increasingly facilitating many emerging applications that require packet delivery from one or more sender(s) to multiple receivers. Of all proposals reported, most have focused on addressing the issue of key management to SGC systems. The authors, however, advocate that security services are also needed to satisfy different security requirements of various applications. The authors also present here a survey on recent advances in several security requirements and security services in group communication systems (GCSs), illustrate some outstanding GCSs that deploy these security services, and describe challenges for any future research works in designing a secure GCS. © 2010 The Institution of Engineering and Technology.
Moore R.O.,University Heights
Optics Letters | Year: 2014
We demonstrate a trade-off between linewidth and loss-of-lock rate in a mode-locked laser employing active feedback to control the carrier-envelope offset phase difference. In frequency metrology applications, the linewidth translates directly to uncertainty in the measured frequency, whereas the impact of lock loss and recovery on the measured frequency is less well understood. We reduce the dynamics to stochastic differential equations, specifically diffusion processes, and compare the linearized linewidth to the rate of lock loss determined by the mean time to exit, as calculated from large deviation theory. © 2014 Optical Society of America.
Chou P.B.,University Heights
International Journal of Information Technology and Management | Year: 2011
This paper develops a game-theoretical model to address different levels of cooperation between two firms that share their knowledge/information systems as a local public good. The model shows that the collaboration between two firms can lead to the creation of new knowledge/information technology, and that a higher speed of creating new knowledge can change the structure of the game from a prisoners' dilemma game to a coordination game as an evolutionary process. Therefore, despite the knowledge-sharing dilemma, it is possible for both firms to reach the stable and more efficient full-collaboration equilibrium than the Nash collaboration equilibrium. © 2011 Inderscience Enterprises Ltd.