214 research outputs found
Investigating feedforward neural regulation of circulation from analysis of spontaneous arterial pressure and heart rate fluctuations in conscious rats.
Investigating feedforward neural regulation
of circulation from analysis of spontaneous arterial pressure and
heart rate fluctuations in conscious rats. Am J Physiol Heart Circ
Physiol 296: H202âH210, 2009. First published November 14, 2008;
doi:10.1152/ajpheart.00358.2008.âIt has been suggested in anesthetized
animals that the occurrence of sequences of consecutive beats
characterized by systolic arterial pressure (SAP) and RR or pulse
interval (PI) changing in the opposite direction (SAP /RR and
SAP /RR , nonbaroreflex sequences) might represent the expression
of neural cardiovascular regulatory mechanisms operating with feedforward
characteristics. The aim of the present study was to study
nonbaroreflex sequences in a more physiological experimental model,
i.e., in conscious freely moving rats. We studied conscious rats before
and after 1) complete autonomic blockade (n 12), 2) sympathetic
blockade (n 10), 3) (n 7)- and (n 8)-adrenergic blockade,
and 4) parasympathetic blockade (n 10). Nonbaroreflex sequences
were defined as three or more beats in which SAP and PI of the
following beat changed in the opposite direction. Complete autonomic
blockade reduced the number of nonbaroreflex sequences (95.6 9.0
vs. 45.2 4.1, P 0.001), as did sympathetic blockade (80.9 12.6
vs. 30.9 6.1, P 0.001). The selective -receptor blockade did not
induce significant changes (80.9 12.5 in baseline vs. 79.0 14.7
after prazosin), whereas -receptor blockade significantly reduced
nonbaroreflex sequence occurrence (80.9 12.5 in baseline vs.
48.9 15.3 after propranolol). Parasympathetic blockade produced a
significant increase of nonbaroreflex sequences (95.1 6.9 vs.
136.0 12.4, P 0.01). These results demonstrate the physiological
role of the nonbaroreflex sequences as an expression of a feedforward
type of short-term cardiovascular regulation able to interact dynamically
with the feedback mechanisms of baroreflex origin in the neural
control of the sinus node
Changes in Cardiac Autonomic Regulation after Acute Lung Exposure to Carbon Nanotubes: Implications for Occupational Exposure
Carbon nanotubes (CNTs) are among the most relevant engineered nanomaterials (ENMs). Given the expected rise of exposure to ENMs, there is concern that they may adversely affect health of exposed people. Aim of the study was to test the hypothesis that single wall carbon nanotubes (SWCNTs) pulmonary exposure acutely affect the autonomic cardiovascular regulation in conscious rats. We studied Wistar-Kyoto rats in which a telemetry transmitter for continuous arterial pressure (AP) and heart rate (HR) recordings was surgically implanted. SWCNTs dispersed in phosphate buffer saline (PBS) or PBS alone were randomly administered intratracheally. Immediately before, and 24 hours after each instillation a 30 min AP recording was performed. The sequence analysis was performed to evaluate the baroreflex function. In the control group, PBS instillation did not induce any significant changes. At variance the SWCNT exposure induced a significant reduction of baroreflex system (BRS) (3.5 \ub1 0.6 versus 2.6 \ub1 0.40\u2009msec/mmHg) without significant changes in the occurrence of baroreflex sequences (7.5 \ub1 0.47 % versus 7.4 \ub1 0.38 %). Our results show that SWCNT pulmonary exposure might affect the cardiovascular autonomic regulation thus contributing to cardiac and arrhythmic events
Sampling Scarab Beetles in Tropical Forests: The Effect of Light Source and Night Sampling Periods
Light traps have been used widely to sample insect abundance and diversity, but their performance for sampling scarab beetles in tropical forests based on light source type and sampling hours throughout the night has not been evaluated. The efficiency of mercury-vapour lamps, cool white light and ultraviolet light sources in attracting Dynastinae, Melolonthinae and Rutelinae scarab beetles, and the most adequate period of the night to carry out the sampling was tested in different forest areas of Costa Rica. Our results showed that light source wavelengths and hours of sampling influenced scarab beetle catches. No significant differences were observed in trap performance between the ultraviolet light and mercury-vapour traps, whereas these two methods caught significantly more species richness and abundance than cool white light traps. Species composition also varied between methods. Large differences appear between catches in the sampling period, with the first five hours of the night being more effective than the last five hours. Because of their high efficiency and logistic advantages, we recommend ultraviolet light traps deployed during the first hours of the night as the best sampling method for biodiversity studies of those scarab beetles in tropical forests
Plasma photoemission from string theory
Leading 't Hooft coupling corrections to the photoemission rate of the planar
limit of a strongly-coupled {\cal {N}}=4 SYM plasma are investigated using the
gauge/string duality. We consider the full order \alpha'^3 type IIB string
theory corrections to the supergravity action, including higher order terms
with the Ramond-Ramond five-form field strength. We extend our previous results
presented in arXiv:1110.0526. Photoemission rates depend on the 't Hooft
coupling, and their curves suggest an interpolating behaviour from strong
towards weak coupling regimes. Their slopes at zero light-like momentum give
the electrical conductivity as a function of the 't Hooft coupling, in full
agreement with our previous results of arXiv:1108.6306. Furthermore, we also
study the effect of corrections beyond the large N limit.Comment: 36 pages, 5 figures, paragraph added in the conclusions, references
added, typos correcte
The evolutionary history of the stearoyl-CoA desaturase gene family in vertebrates
<p/> <p>Background</p> <p>Stearoyl-CoA desaturases (SCDs) are key enzymes involved in <it>de novo </it>monounsaturated fatty acid synthesis. They catalyze the desaturation of saturated fatty acyl-CoA substrates at the delta-9 position, generating essential components of phospholipids, triglycerides, cholesterol esters and wax esters. Despite being crucial for interpreting SCDs roles across species, the evolutionary history of the SCD gene family in vertebrates has yet to be elucidated, in particular their isoform diversity, origin and function. This work aims to contribute to this fundamental effort.</p> <p>Results</p> <p>We show here, through comparative genomics and phylogenetics that the SCD gene family underwent an unexpectedly complex history of duplication and loss events. Paralogy analysis hints that SCD1 and SCD5 genes emerged as part of the whole genome duplications (2R) that occurred at the stem of the vertebrate lineage. The SCD1 gene family expanded in rodents with the parallel loss of SCD5 in the Muridae family. The SCD1 gene expansion is also observed in the Lagomorpha although without the SCD5 loss. In the amphibian <it>Xenopus tropicalis </it>we find a single SCD1 gene but not SCD5, though this could be due to genome incompleteness. In the analysed teleost species no SCD5 is found, while the surrounding SCD5-less locus is conserved in comparison to tetrapods. In addition, the teleost SCD1 gene repertoire expanded to two copies as a result of the teleost specific genome duplication (3R). Finally, we describe clear orthologues of SCD1 and SCD5 in the chondrichthian, <it>Scyliorhinus canicula</it>, a representative of the oldest extant jawed vertebrate clade. Expression analysis in <it>S. canicula </it>shows that whilst SCD1 is ubiquitous, SCD5 is mainly expressed in the brain, a pattern which might indicate an evolutionary conserved function.</p> <p>Conclusion</p> <p>We conclude that the SCD1 and SCD5 genes emerged as part of the 2R genome duplications. We propose that the evolutionary conserved gene expression between distinct lineages underpins the importance of SCD activity in the brain (and probably the pancreas), in a yet to be defined role. We argue that an expression independent of an external stimulus, such as diet induced activity, emerged as a novel function in vertebrate ancestry allocated to the SCD5 isoform in various tissues (e.g. brain and pancreas), and it was selectively maintained throughout vertebrate evolution.</p
Thermal quenches in N=2* plasmas
We exploit gauge/gravity duality to study `thermal quenches' in a plasma of
the strongly coupled N=2* gauge theory. Specifically, we consider the response
of an initial thermal equilibrium state of the theory under variations of the
bosonic or fermionic mass, to leading order in m/T<<1. When the masses are made
to vary in time, novel new counterterms must be introduced to renormalize the
boundary theory. We consider transitions the conformal super-Yang-Mills theory
to the mass deformed gauge theory and also the reverse transitions. By
construction, these transitions are controlled by a characteristic time scale
\calt and we show how the response of the system depends on the ratio of this
time scale to the thermal time scale 1/T. The response shows interesting
scaling behaviour both in the limit of fast quenches with T\calt<<1 and slow
quenches with T\calt>>1. In the limit that T\calt\to\infty, we observe the
expected adiabatic response. For fast quenches, the relaxation to the final
equilibrium is controlled by the lowest quasinormal mode of the bulk scalar
dual to the quenched operator. For slow quenches, the system relaxes with a
(nearly) adiabatic response that is governed entirely by the late time profile
of the mass. We describe new renormalization scheme ambiguities in defining
gauge invariant observables for the theory with time dependant couplings.Comment: 78 pages, 17 figure
Discovery of VHE Gamma Radiation from IC443 with the MAGIC Telescope
We report the detection of a new source of very high energy (VHE, E_gamma >=
100GeV) gamma-ray emission located close to the Galactic Plane, MAGIC
J0616+225, which is spatially coincident with SNR IC443. The observations were
carried out with the MAGIC telescope in the periods December 2005 - January
2006 and December 2006 - January 2007. Here we present results from this
source, leading to a VHE gamma-ray signal with a statistical significance of
5.7 sigma in the 2006/7 data and a measured differential gamma-ray flux
consistent with a power law, described as dN_gamma/(dA dt dE) = (1.0 +/-
0.2)*10^(-11)(E/0.4 TeV)^(-3.1 +/- 0.3) cm^(-2)s^(-1)TeV^(-1). We briefly
discuss the observational technique used and the procedure implemented for the
data analysis. The results are put in the perspective of the multiwavelength
emission and the molecular environment found in the region of IC443.Comment: Accepted by ApJ Letter
On holographic thermalization and gravitational collapse of massless scalar fields
In this paper we study thermalization in a strongly coupled system via
AdS/CFT. Initially, the energy is injected into the system by turning on a
spatially homogenous scalar source coupled to a marginal composite operator.
The thermalization process is studied by numerically solving Einstein's
equations coupled to a massless scalar field in the Poincare patch of AdS_5. We
define a thermalization time t_T on the AdS side, which has an interpretation
in terms of a spacelike Wilson loop in CFT. Here T is the thermal
equilibrium temperature. We study both cases with the source turned on in
short(Delta t = 1/T) durations. In the former case,
the thermalization time t_T = g_t/T <= 1/T and the coefficient g_t = 0.73 in
the limit Delta t <= 0.02/T. In the latter case, we find double- and
multiple-collapse solutions, which may be interpreted as the gravity duals of
two- or multi-stage thermalization in CFT. In all the cases our results
indicate that such a strongly coupled system thermalizes in a typical time
scale t_T=O(1)/T.Comment: 25 papers, 13 figures, Minor modifications, details of numerics
added, references added, final version to appear in JHE
Study of the reaction e^{+}e^{-} -->J/psi\pi^{+}\pi^{-} via initial-state radiation at BaBar
We study the process with
initial-state-radiation events produced at the PEP-II asymmetric-energy
collider. The data were recorded with the BaBar detector at center-of-mass
energies 10.58 and 10.54 GeV, and correspond to an integrated luminosity of 454
. We investigate the mass
distribution in the region from 3.5 to 5.5 . Below 3.7
the signal dominates, and above 4
there is a significant peak due to the Y(4260). A fit to
the data in the range 3.74 -- 5.50 yields a mass value
(stat) (syst) and a width value (stat)(syst) for this state. We do not
confirm the report from the Belle collaboration of a broad structure at 4.01
. In addition, we investigate the system
which results from Y(4260) decay
Thermalization with a chemical potential from AdS spaces
The time-scale of thermalization in holographic dual models with a chemical
potential in diverse number of dimensions is systematically investigated using
the gauge/gravity duality. We consider a model with a thin-shell of charged
dust collapsing from the boundary toward the bulk interior of asymptotically
anti-de Sitter (AdS) spaces. In the outer region there is a
Reissner-Nordstr\"om-AdS black hole (RNAdS-BH), while in the inner region there
is an anti-de Sitter space. We consider renormalized geodesic lengths and
minimal area surfaces as probes of thermalization, which in the dual quantum
field theory (QFT) correspond to two-point functions and expectation values of
Wilson loops, respectively. We show how the behavior of these extensive probes
changes for charged black holes in comparison with Schwarzschild-AdS black
holes (AdS-BH), for different values of the black hole mass and charge. The
full range of values of the chemical potential over temperature ratio in the
dual QFT is investigated. In all cases, the structure of the thermalization
curves shares similar features with those obtained from the AdS-BH. On the
other hand, there is an important difference in comparison with the AdS-BH: the
thermalization times obtained from the renormalized geodesic lengths and the
minimal area surfaces are larger for the RNAdS-BH, and they increase as the
black hole charge increases.Comment: 32 pages, 4 figures, references added, appendix added, typos
correcte
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