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1.
We are interested in noise-induced firings of subthreshold neurons which may be used for encoding environmental stimuli. Noise-induced population synchronization was previously studied only for the case of global coupling, unlike the case of subthreshold spiking neurons. Hence, we investigate the effect of complex network architecture on noise-induced synchronization in an inhibitory population of subthreshold bursting Hindmarsh–Rose neurons. For modeling complex synaptic connectivity, we consider the Watts–Strogatz small-world network which interpolates between regular lattice and random network via rewiring, and investigate the effect of small-world connectivity on emergence of noise-induced population synchronization. Thus, noise-induced burst synchronization (synchrony on the slow bursting time scale) and spike synchronization (synchrony on the fast spike time scale) are found to appear in a synchronized region of the J–D plane (J: synaptic inhibition strength and D: noise intensity). As the rewiring probability p is decreased from 1 (random network) to 0 (regular lattice), the region of spike synchronization shrinks rapidly in the J–D plane, while the region of the burst synchronization decreases slowly. We separate the slow bursting and the fast spiking time scales via frequency filtering, and characterize the noise-induced burst and spike synchronizations by employing realistic order parameters and statistical-mechanical measures introduced in our recent work. Thus, the bursting and spiking thresholds for the burst and spike synchronization transitions are determined in terms of the bursting and spiking order parameters, respectively. Furthermore, we also measure the degrees of burst and spike synchronizations in terms of the statistical-mechanical bursting and spiking measures, respectively. 相似文献
2.
Yubing Gong Yinghang Hao Yanhang Xie Xiaoguang Ma Chuanlu Yang 《Biophysical chemistry》2009,144(1-2):88-93
In this paper, we numerically study how the NGN's deviation q from Gaussian noise (q = 1) affects the spike coherence and synchronization of 60 coupled Hodgkin–Huxley (HH) neurons driven by a periodic sinusoidal stimulus on random complex networks. It is found that the effect of the deviation depends on the network randomness p (the fraction of random shortcuts): for larger p (p > 0.15), the spiking regularity keeps being improved with increasing q; while, for smaller p (p < 0.15), the spiking regularity can reach the best performance at an optimal intermediate q value, indicating the occurrence of “deviation-optimized spike coherence”. The synchronization becomes enhanced with decreasing q, and the enhancing extent for a random HH neuron network is stronger than for a regular one. These behaviors show that the spike coherence and synchronization of the present HH neurons on random networks can be more strongly enhanced by various other types of external noise than by Gaussian noise, whereby the neuron firings may behave more periodically in time and more synchronously in space. Our results provide the constructive roles of the NGN on the spiking activity of the present system of HH neuron networks. 相似文献
3.
We study an excitatory all-to-all coupled network of N spiking neurons with synaptically filtered background noise and slow activity-dependent hyperpolarization currents. Such
a system exhibits noise-induced burst oscillations over a range of values of the noise strength (variance) and level of cell
excitability. Since both of these quantities depend on the rate of background synaptic inputs, we show how noise can provide
a mechanism for increasing the robustness of rhythmic bursting and the range of burst frequencies. By exploiting a separation
of time scales we also show how the system dynamics can be reduced to low-dimensional mean field equations in the limit N → ∞. Analysis of the bifurcation structure of the mean field equations provides insights into the dynamical mechanisms for
initiating and terminating the bursts. 相似文献
4.
Accurate assessments of pollen counts are valuable to allergy sufferers, the medical industry, and health researchers; however,
monitoring stations do not exist in most areas. In addition, the degree of spatial reliability provided by the limited number
of monitoring stations is poorly understood. We developed and compared spatial models to estimate pollen concentrations in
locations without monitoring stations. Daily Acer, Quercus, and overall tree, grass, and weed pollen counts, in grains/m3, were obtained from 14 aeroallergen monitoring stations located in the northeastern and mid-Atlantic region of the United
States from 2003 to 2006. Pollen counts were spatially interpolated using ordinary kriging. Mixed effects and generalized
estimating equations incorporating daily and seasonal weather characteristics, pollen season characteristics and land-cover
information were also developed to estimate daily pollen concentrations. We then compared observed values from a monitoring
station to model estimates for that location. Observed counts and kriging estimates for tree pollen differed (p = 0.04), but not when peak periods were removed (p = 0.29). No differences between observed and kriging estimates of Acer (p = 0.46), Quercus (p = 0.24), grass (p = 0.31) or weed pollen (p = 0.29) were found. Estimates from longitudinal models also demonstrated good agreement with observed counts, except for
the extremes of pollen distributions. Our results demonstrate that spatial interpolation techniques as well as regression
methods incorporating both weather and land-cover characteristics can provide reliable estimates of daily pollen concentrations
in areas where monitors do not exist for all but periods of extremely high pollen. 相似文献
5.
The role of relative spike timing on sensory coding and stochastic dynamics of small pulse-coupled oscillator networks is
investigated physiologically and mathematically, based on the small biological eye network of the marine invertebrate Hermissenda. Without network interactions, the five inhibitory photoreceptors of the eye network exhibit quasi-regular rhythmic spiking;
in contrast, within the active network, they display more irregular spiking but collective network rhythmicity. We investigate
the source of this emergent network behavior first analyzing the role of relative input to spike–timing relationships in individual
cells. We use a stochastic phase oscillator equation to model photoreceptor spike sequences in response to sequences of inhibitory
current pulses. Although spike sequences can be complex and irregular in response to inputs, we show that spike timing is
better predicted if relative timing of spikes to inputs is accounted for in the model. Further, we establish that greater
noise levels in the model serve to destroy network phase-locked states that induce non-monotonic stimulus rate-coding, as
predicted in Butson and Clark (J Neurophysiol 99:146–154, 2008a; J Neurophysiol 99:155–165, 2008b). Hence, rate-coding can
function better in noisy spiking cells relative to non-noisy cells. We then study how relative input to spike–timing dynamics
of single oscillators contribute to network-level dynamics. Relative timing interactions in the network sharpen the stimulus
window that can trigger a spike, affecting stimulus encoding. Also, we derive analytical inter-spike interval distributions
of cells in the model network, revealing that irregular Poisson-like spike emission and collective network rhythmicity are
emergent properties of network dynamics, consistent with experimental observations. Our theoretical results generate experimental
predictions about the nature of spike patterns in the Hermissenda eye. 相似文献
6.
By using an oligonucleotide mixture corresponding to a region highly conserved among alternative sigma factors we identified
a new σ factor gene (rpoH) from Rhodobacter capsulatus. This gene encodes a protein of 34 kDa with strong similarity to the RpoH (σ
32) factors from other bacterial species. It was not possible to inactivate the R. capsulatusrpoH gene by introducing a resistance cassette, implying that it is essential for growth. The 5′ ends of the mRNAs were mapped
to two sequences with similarity to an rpoH- and an rpoD-dependent promoter, respectively. The amounts of both these mRNAs increased after heat shock, but were unaffected by a decrease
in oxygen tension. Western analysis using a σ factor-specific antibody revealed the accumulation of a protein of about 34 kDa after heat shock, and an increase in the
amounts of a protein with the same size after reduction of oxygen tension in R. capsulatus cultures.
Received: 16 March 1998 / Accepted: 28 July 1998 相似文献
7.
R. Krahe B. Ronacher 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1993,173(4):425-434
Auditory receptors of the locust (Locusta migratoria) were investigated with respect to the directionality cues which are present in their spiking responses, with special emphasis on how directional cues are influenced by the rise time of sound signals. Intensity differences between the ears influence two possible cues in the receptor responses, spike count and response latency. Variation in rise time of sound pulses had little effect on the overall spike count; however, it had a substantial effect on the temporal distribution of the receptor's spiking response, especially on the latencies of first spikes. In particular, with ramplike stimuli the slope of the latency vs. intensity curves was steeper as compared to stimuli with steep onsets (Fig. 3). Stimuli with flat ramplike onsets lead to an increase of the latency differences of discharges between left and right tympanic receptors. This type of ramplike stimulus could thus facilitate directional hearing. This hypothesis was corroborated by a Monte Carlo simulation in which the probability of incorrect directional decisions was determined on the basis of the receptor latencies and spike counts. Slowly rising ramps significantly improved the decisions based on response latency, as compared to stimuli with sudden onsets (Fig. 4). These results are compared to behavioural results obtained with the grasshopper Ch. biguttulus. The stridulation signals of the females of this species consist of ramplike pulses, which could be an adaptation to facilitate directional hearing of phonotactically approaching males.Abbreviations HFR
high frequency receptor
- ILD
interaural level difference
- LFR
low frequency receptor
- SPL
sound pressure level
- WN
white noise 相似文献
8.
Water uptake by roots of maize and sunflower affects the radial transport of abscisic acid and its concentration in the xylem 总被引:13,自引:0,他引:13
The radial movement of cis-abscisic acid (ABA) has been investigated in young excised roots of Zea mays L. and Helianthus annuus L. which were grown hydroponically. In addition to the symplastic path, ABA was largely translocated across the root apoplast
by solvent drag with the water in the transpiration stream. On the apoplastic path ABA may even cross the endodermis. Depending
on the ABA concentration of the medium (range: 5–500 nM) and in the root apoplast, the solvent-drag component of the flow
of ABA counteracted the dilution of ABA in the xylem caused by transpirational water flow. Acidification of the rhizosphere
and of the root apoplast increased the apoplastic transport component. In sunflower, the apoplastic flow of ABA was significantly
weaker than in maize roots. This was also indicated by the larger apparent reflection coefficient (σABA) of sunflower roots for ABA (sunflower: σABA = 0.97 ± 0.02, n = 6 roots; maize: σABA = 0.68 ± 0.06, n = 6 roots; ±SD). For both species, σABA was smaller than unity. Root reflection coefficients were affected by factors such as pH, ABA concentration of the medium,
and by the suction force applied to excised root systems. Due to the complex composite structure of the permeation barrier
in the root, the reflection coefficient estimated from solvent drag is also complex. Since unstirred layers affected the absolute
value of the reflection coefficient, σABA has been termed `apparent'. It is concluded that the pH and ABA concentration of the soil solution as well as the transpiration
rate (suction force) modify the intensity of the root-to-shoot signal which is influenced by an apoplastic bypass flow of
ABA. The latter may be substantially affected by the existence of Casparian bands in the exodermis, which were lacking in
the roots studied in this paper.
Received: 25 February 1998 / Accepted: 16 July 1998 相似文献
9.
Kizilpinar I Civelek E Tuncer A Dogan C Karabulut E Sahiner UM Yavuz ST Sackesen C 《International journal of biometeorology》2011,55(4):623-631
Pollen plays an important role in the development and exacerbation of allergic diseases. We aimed to investigate the days
with highest counts of the most allergenic pollens and to identify the meteorological factors affecting pollen counts in the
atmosphere of Ankara, Turkey. Airborne pollen measurements were carried out from 2005 to 2008 with a Burkard volumetric 7-day
spore trap. Microscope counts were converted into atmospheric concentrations and expressed as pollen grains/m3. Meteorological parameters were obtained from the State Meteorological Service. All statistical analyses were done with pollen
counts obtained from March to October for each year. The percentages of tree, grass and weed pollens were 72.1% (n = 24,923), 12.8% (n = 4,433) and 15.1% (n = 5,219), respectively. The Pinaceae family from tree taxa (39% to 57%) and the Chenopodiaceae/Amaranthaceae family from weed taxa, contributed the highest percentage of pollen (25% to 43%), while from the grass taxa, only the Poaceae family was detected from 2005 to 2008. Poaceae and Chenopodiaceae/Amaranthaceae families, which are the most allergenic pollens, were found in high numbers from May to August in Ankara. In multiple logistic
regression analysis, wind speed (OR = 1.18, CI95% = 1.02–1.36, P = 0.023) for tree pollen, daily mean temperature (OR = 1.10, CI95% = 1.04–1.17, P = 0.001) and sunshine hours (OR = 1.15, CI95% = 1.01–1.30, P = 0.033) for grass pollen, and sunshine hours (OR = 3.79, CI95% = 1.03–13.92, P = 0.044) for weed pollen were found as significant risk factors for high pollen count. The pollen calendar and its association
with meteorological factors depend mainly on daily temperature, sunshine hours and wind speed, which may help draw the attention
of physicians and allergic patients to days with high pollen counts. 相似文献
10.
Using the cell pressure probe, the effects of temperature on hydraulic conductivity (Lp; osmotic water permeability), solute
permeability (permeability coefficient, Ps), and reflection coefficients (σs) were measured on internodes of Chara corallina, Klein ex Willd., em R.D.W.. For the first time, complete sets of transport coefficients were obtained in the range between
10 and 35 °C which provided evidence about pathways of water and solutes as they move across the plasma membrane (water channel
and bilayer arrays). Test solutes used to check for the selectivity of water channels were monohydric alcohols of different
molecular size and shape (ethanol, n-propanol, iso-propanol, and tert-butanol) and heavy water (HDO). Within the limits of accuracy, Q10 values for Lp and for the diffusive water permeability (Pd) were identical (Q10 for Lp = 1.29 ± 0.17 (± SD; n = 15 cells) and Q10 for Pd = 1.25 ± 0.16 (n = 5 cells)). The Q10 values were equivalent to activation energies of Ea = 16.8 ± 6.4 and 16.6 ± 10.0 kJ · mol−1, respectively, which is similar to that of self-diffusion or of viscous flow of water. The Q10 values and activation energies for Ps of the alcohols were significantly larger (ethanol: Q10 = 1.68 ± 0.16, Ea = 37.1 ± 5.9 kJ · mol−1; n-propanol: Q10 = 1.75 ± 0.40, Ea = 43.1 ± 15.3 kJ · mol−1; iso-propanol: Q10 = 2.12 ± 0.42, Ea = 52.2 ± 14.6 kJ · mol−1; tert-butanol: Q10 = 2.13 ± 0.56, Ea = 51.6 ± 17.1 kJ · mol−1; ±SD; n = 5 to 6 cells). Effects of temperature on reflection coefficients were most pronounced. With increasing temperature, σs values of the alcohols decreased and those of HDO increased. The data indicate that water and solutes use different pathways
when crossing the membrane. Ordinary and isotopic water use water channels and the other test solutes use the bilayer array
(composite transport model of membrane). Changes in σs values with temperature were found to be a sensitive measure for the open/closed state of water channels. The decrease of
σs with temperature was theoretically predicted from the temperature dependence of Ps and Lp. Differences between predicted and measured values of σs allowed estimation of the bypass flow (slippage) of solutes through water channels which did not completely exclude test
solutes. The permeability of channels depended on the structure and size of test solutes. It is concluded that water channels
are much less selective than is usually thought. Since water channels represent single-file or no-pass pores, solutes drag
along considerable amounts of water as they diffuse across channels. This results in low overall values of σs. The σs of HDO was extremely low. Its response to temperature was opposite to that for the σs of the alcohols. This suggested a stronger effect of temperature on the hydraulic (osmotic) than on the diffusive water flow
across individual water channels, i.e. a differential sensitivity of different mechanisms to temperature.
Received: 10 October 1996 / Accepted: 2 December 1996 相似文献
11.
Aarnink A Garchon HJ Puissant-Lubrano B Blancher-Sardou M Apoil PA Blancher A 《Immunogenetics》2011,63(2):95-102
While the number of peripheral blood T lymphocytes and of their two main subsets (CD4+CD8− and CD4−CD8+) varies little in
a given healthy individual, substantial variation is observed between individuals. It was proposed that these counts could
be influenced by MHC polymorphisms because of the well-established role of MHC molecules in thymic T lymphocyte maturation
and presentation of antigenic peptides to peripheral T lymphocytes. To test this hypothesis, we have chosen the crab-eating
macaque (Macaca fascicularis), an animal model phylogenetically close to man. We selected the Philippine macaque population because of a restriction of
the MHC polymorphism in this islander population. Peripheral blood lymphocytes were counted with an automated analyzer and
T lymphocyte subsets were assessed by immunolabeling and flow cytometry. The MHC polymorphism was investigated in 200 unrelated
subjects using 14 microsatellites markers distributed across the MHC and the DRB locus that was genotyped by denaturing gradient gel electrophoresis and sequencing. All markers were in Hardy–Weinberg equilibrium.
Allelic associations were tested with the UNPHASED software. We revealed a significant influence of the MHC class II region
on CD4+ T lymphocyte blood count with the largest effect associated with a two-locus haplotypes combining the DRACA allele 274 and the DRB haplotype #8a (p < 8 × 10−7). Our data should stimulate a similar association study of the CD4+ T cell counts in humans. 相似文献
12.
Addition of allochthonous fungi to a historically contaminated soil affects both remediation efficiency and bacterial diversity 总被引:1,自引:0,他引:1
Federici E Leonardi V Giubilei MA Quaratino D Spaccapelo R D'Annibale A Petruccioli M 《Applied microbiology and biotechnology》2007,77(1):203-211
Botryosphaeria rhodina DABAC P82 and Pleurotus pulmonarius CBS 664.97 were tested for their ability to grow and to degrade aromatic hydrocarbons in an aged contaminated soil. To evaluate
the impact of indigenous microflora on the overall process, incubations were performed on both fumigated and nonfumigated
soils. Fungal colonization by B. rhodina was unexpectedly lower in the fumigated than in the nonfumigated soil while the growth of P. pulmonarius showed an opposite response. Degradation performances and detoxification by both fungi in the nonfumigated soil were markedly
higher than those observed in the fumigated one. Heterotrophic bacterial counts in nonfumigated soil augmented with either
B. rhodina or P. pulmonarius were significantly higher than those of the corresponding incubation control (6.7 ± 0.3 × 108 and 8.35 ± 0.6 × 108, respectively, vs 9.2 ± 0.3 × 107). Bacterial communities of both incubation controls and fungal-augmented soil were compared by numerical analysis of denaturing
gradient gel electrophoresis profiles of polymerase chain reaction (PCR)-amplified 16S ribosomal RNA (rRNA) genes and cloning
and sequencing of PCR-amplified 16S rRNA genes. Besides increasing overall diversity, fungal augmentation led to considerable
qualitative differences with respect to the pristine soil. 相似文献
13.
Bülbül Hizel S Sanli C Bayar Muluk N Albayrak M Ozyazici A Apan A 《Biological trace element research》2008,124(2):129-134
The aim of this study was to investigate the effects of topotecan, a topoisomerase I-inhibiting anticancer agent, on hematologic
parameters and serum levels of trace elements. The study was conducted on three groups consisting of 16 and 18 rabbits in
the study groups and 15 rabbits in the control group. Rabbits in group I (n = 16) received high-dose topotecan intravenously (i.v.; 0.5 mg/kg once daily), while rabbits in group II (n = 18) received low-dose topotecan i.v. (0.25 mg/kg once daily) for 3 days. The 15 rabbits comprising the control group did
not receive topotecan. Serum samples were collected from each rabbit on the first day, before the treatment, and on the 15th
day of treatment. Erithrocytes, hemoglobin, white blood cell count, thrombocyte count, and trace elements such as selenium,
copper, lead, zinc, and cobalt were analyzed. Hemoglobin levels and erythrocyte counts were lower in both study groups than
in the control group. However, thrombocyte and leukocyte counts were similar in all three groups (p > 0.005). Serum trace element levels (copper, lead, zinc, and cobalt) did not differ significantly between groups. However,
serum selenium levels were significantly lower in both study groups than the control group (p < 0.001). The results revealed that topotecan treatment causes a decrease in erythrocyte counts and hemoglobin levels due
to bone marrow suppression, and these effects must be taken into account during treatment. In addition, selenium supplementation
might be helpful in cancer patients receiving topotecan to increase the effect of the chemotherapeutic agent. 相似文献
14.
We studied the influence of noisy stimulation on the Hodgkin-Huxley neuron model. Rather than examining the noise-related
variability of the discharge times of the model – as has been done previously – our study focused on the effect of noise on
the stationary distributions of the membrane potential and gating variables of the model. We observed that a gradual increase
in the noise intensity did not result in a gradual change of the distributions. Instead, we could identify a critical intermediate
noise range in which the shapes of the distributions underwent a drastic qualitative change. Namely, they moved from narrow
unimodal Gaussian-like shapes associated with low noise intensities to ones that spread widely at large noise intensities.
In particular, for the membrane potential and the sodium activation variable, the distributions changed from unimodal to bimodal.
Thus, our investigation revealed a noise-induced transition in the Hodgkin-Huxley model. In order to further characterize
this phenomenon, we considered a reduced one-dimensional model of an excitable system, namely the active rotator. For this
model, our analysis indicated that the noise-induced transition is associated with a deterministic bifurcation of approximate
equations governing the dynamics of the mean and variance of the state variable. Finally, we shed light on the possible functional
importance of this noise-induced transition in neuronal coding by determining its effect on the spike timing precision in
models of neuronal ensembles.
Received: 19 September 2000 / Accepted in revised form: 4 March 2001 相似文献
15.
We investigated the normalized autocovariance (correlation coefficient) function of the output of an erf( ) function nonlinearity
subject to non-zero mean Gaussian noise input. When the sigmoid is wide compared to the input, or the input mean is close
to the midpoint of the sigmoid, the output correlation coefficient function is very close to the input correlation coefficient
function. When the noise mean and variance are such that there is a significant probability of operating in the saturation
region and the sigmoid is not too flat, the correlation coefficient output function is less than that of the input. This difference
is much greater when the correlation coefficient is negative than when it is positive. The sigmoid partially rectifies the
correlation coefficient function. The analysis does not depend on the spectral properties of the input noise. All that is
required is that the input at times t and (t+τ) be jointly Gaussian with the same mean and autocovariance. The analysis therefore applies equally well to the case of two
identical sigmoids with jointly Gaussian inputs. This correlational rectification could help explain the parameter sensitivity
of "neural network" models. If biological neurons share this property it could explain why few negative correlations between
spike trains have been observed.
Received: 1 July 1992/Accepted in revised form: 6 July 1993 相似文献
16.
Statistical inferences are essentially important in analyzing neural spike trains in computational neuroscience. Current approaches
have followed a general inference paradigm where a parametric probability model is often used to characterize the temporal
evolution of the underlying stochastic processes. To directly capture the overall variability and distribution in the space
of the spike trains, we focus on a data-driven approach where statistics are defined and computed in the function space in
which spike trains are viewed as individual points. To this end, we at first develop a parametrized family of metrics that
takes into account different warpings in the time domain and generalizes several currently used spike train distances. These
new metrics are essentially penalized L
p
norms, involving appropriate functions of spike trains, with penalties associated with time-warping. The notions of means
and variances of spike trains are then defined based on the new metrics when p = 2 (corresponding to the “Euclidean distance”). Using some restrictive conditions, we present an efficient recursive algorithm,
termed Matching-Minimization algorithm, to compute the sample mean of a set of spike trains with arbitrary numbers of spikes.
The proposed metrics as well as the mean spike trains are demonstrated using simulations as well as an experimental recording
from the motor cortex. It is found that all these methods achieve desirable performance and the results support the success
of this novel framework. 相似文献
17.
Tock Y Ljubisavljevic M Thunberg J Windhorst U Inbar GF Johansson H 《Biological cybernetics》2002,87(4):241-248
The information transmission properties of single, de-efferented primary muscle-spindle afferents from the hind limb of the
cat were investigated. The gastrocnemius medialis muscle was stretched randomly while recording spike trains from several
muscle-spindle afferents in the dorsal root. Two classes of input stimuli were used: (i) Gaussian noise with band-limited
flat spectrum, and (ii) Gaussian noise with a more “naturalistic” 1/f
n
spectrum. The “reconstruction” method was used to calculate a lower bound to the information rate (in bits per second) between
the muscle spindles and the spinal cord. Results show that in response to the flat-spectrum input, primary muscle-spindle
afferents transfer information mainly about high frequencies, carrying 2.12 bits/spike. In response to naturalistic-spectrum
inputs, primary muscle-spindle afferents transfer information about both low and high frequencies, with “spiking efficiency”
increasing to 2.67 bits/spike. A simple muscle-spindle simulation model was analyzed with the same method, emphasizing the
important part played by the intrafusal fiber mechanical properties in information transmission.
Received: 22 January 2002 / Accepted in revised form: 17 June 2002
Correspondence to: Y. Tock (e-mail: ytock@tx.technion.ac.il, Fax: +972-4-8323041) 相似文献
18.
Ono EY Fungaro MH Sofia SH Figueira EL Gerage AC Ichinoe M Sugiura Y Ueno Y Hirooka EY 《Mycopathologia》2004,158(4):451-455
Eleven feed samples associated with six animal (horse and poultry) intoxication outbreaks (1991) in the state of Paraná, Brazil,
were evaluated for fungal and fumonisin contamination. In order to estimate the␣trend of livestock intoxication, fumonisin
contamination was monitored in corn produced both at the commercial level (1991, 1995 crop), and in an experimental field
at a local Agronomy Institute (1997 crop). The total mould count in the feed samples ranged from 2.9 × 103 to 1.9 × 107 CFU/g, with Fusarium verticillioides as the predominant species, at a high count of 2.4 × 104–6.5 × 105 CFU/g. Fumonisins (FB1 + FB2) were detected in all corn-based feed samples at levels ranging from 2.89 to 14.54 μg/g. All 27 Northern corn samples (1991 crop) were contaminated with fumonisins at levels ranging from 2.32 to 16.64 μg/g. Twenty-six (96.3%) out of 27 corn samples from the Central-Southern region (1995 crop) were positive for fumonisins (FB1+FB2), with the range of 0.07–3.66 μg/g, while all 37 Northern samples (1995 crop) were contaminated with fumonisins ranging from 0.57 to 9.97 μg/g. Twenty-one out of 37 corn samples from the Northern region (1997 crop) were positive for fumonisins, but at low level
(range of 0.05–2.67 μg/g). The results showed a decreasing trend in fumonisin contamination over the years. Nowadays animal intoxication outbreaks
rarely occur in this State, as both animal producers and feed industries have become conscious about monitoring of corn and
other raw materials at the quality control level. 相似文献
19.
Noise improves transfer of near-threshold, phase-locked activity of the cochlear nerve: evidence for stochastic resonance? 总被引:2,自引:0,他引:2
K. R. Henry 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1999,184(6):577-584
Stochastic resonance can be described as improved detection of weak periodic stimuli by a dynamic nonlinear system, resulting
from the simultaneous presentation of a restricted dynamic range of low-intensity noise. This property has been reported in
simple physical and biological activities. The present study describes data consistent with the interpretation that stochastic
resonance can be observed in the response of cochlear neurons. These experiments utilized low levels (−5 to 25 dB SPL) of
stimuli and noise (5 to 30 dB SPL). Stimuli consisted of simultaneously presented 8 kHz (F
1) and 8.8 kHz (F
2) tone bursts, which generated an 800 Hz F
2–F
1 cochlear nerve envelope ensemble response in the gerbil. The mean response threshold was approximately −3 dB SPL. Simultaneous
presentation of a low-intensity wideband noise increased the amplitude of this response. This was observed with tonal stimuli
having intensities of 0–5 dB SPL; responses to stimulus levels >10 dB were attenuated by noise. Response amplitude was increased
by noise levels of 10–15 dB; the amplitude was unaffected by lower levels of noise, and decreased in the presence of higher
noise levels. These properties are compatible with those of stochastic resonance.
Accepted: 11 March 1999 相似文献
20.
Vedat Cinar Rasim Mogulkoc Abdulkerim Kasim Baltaci 《Biological trace element research》2010,134(2):130-135
In the present study, experiments were designed to investigate if supplementation with calcium during 4 weeks had an effect
on blood parameters in sedentary male athletes at rest and exhaustion. Thirty healthy subjects of ages ranging from 18 to
22 years were included in the study. The subjects were separated into three groups, as follows: Group 1 consisted sedentary
athletes receiving 35 mg/kg/day calcium gluconate. Group 2 included subjects equally supplemented with calcium training 90 min/day
for 5 days/week. Group 3 were subject to the same exercise regime but did not receive calcium supplements. Blood parameters
were determined in the experimental subjects at rest and after exhaustion. The leukocyte count (WBC) of athletes in groups
2 and 3 were significantly higher at exhaustion (p < 0.05). There were no significant differences in the WBC of the two supplemented groups. The erythrocyte count (RBC) was
increased in the supplemented athletes after training (p < 0.05), but hemoglobin, hematocrit, and trombocyte levels remained unchanged. The mean corpuscular volume increased in the
calcium-supplemented group at rest (p < 0.05). These results suggest that calcium supplementation only causes increases in white and red blood cell counts in athletes
after exhaustion while other hematological parameters remain unchanged. 相似文献