9,683 research outputs found
Upper critical dimension of the KPZ equation
Numerical results for the Directed Polymer model in 1+4 dimensions in various
types of disorder are presented. The results are obtained for system size
considerably larger than that considered previously. For the extreme strong
disorder case (Min-Max system), associated with the Directed Percolation model,
the expected value of the meandering exponent, zeta = 0.5 is clearly revealed,
with very week finite size effects. For the week disorder case, associated with
the KPZ equation, finite size effects are stronger, but the value of seta is
clearly seen in the vicinity of 0.57. In systems with "strong disorder" it is
expected that the system will cross over sharply from Min-Max behavior at short
chains to weak disorder behavior at long chains. This is indeed what we find.
These results indicate that 1+4 is not the Upper Critical Dimension (UCD) in
the week disorder case, and thus 4+1 does not seem to be the upper critical
dimension for the KPZ equation
Airbag vent valve and system
An energy absorbing airbag system includes one or more vent valve assemblies for controlling the release of airbag inflation gases to maintain inflation gas pressure within an airbag at a substantially constant pressure during a ride-down of an energy absorbing event. Each vent valve assembly includes a cantilever spring that is flat in an unstressed condition and that has a free end portion. The cantilever spring is secured to an exterior surface of the airbag housing and flexed to cause the second free end portion of the cantilever spring to be pressed, with a preset force, against a vent port or a closure covering the vent port to seal the vent port until inflation gas pressure within the airbag reaches a preselected value determined by the preset force whereupon the free end portion of the cantilever spring is lifted from the vent port by the inflation gases within the airbag to vent the inflation gases from within the airbag. The resilience of the cantilever spring maintains a substantially constant pressure within the airbag during a ride-down portion of an energy absorbing event by causing the cantilever spring to vent gases through the vent port whenever the pressure of the inflation gases reaches the preselected value and by causing the cantilever spring to close the vent port whenever the pressure of the inflation gases falls below the preselected value
Coherence-enhanced imaging of a degenerate Bose gas
We present coherence-enhanced imaging, an in situ technique that uses Raman
superradiance to probe the spatial coherence properties of an ultracold gas.
Applying this method, we obtain a spatially resolved measurement of the
condensate number and more generally, of the first-order spatial correlation
function in a gas of Rb atoms. We observe the enhanced decay of
propagating spin gratings in high density regions of a Bose condensate, a decay
we ascribe to collective, non-linear atom-atom scattering. Further, we directly
observe spatial inhomogeneities that arise generally in the course of extended
sample superradiance.Comment: 4 pages, 4 figure
High-Resolution Magnetometry with a Spinor Bose-Einstein Condensate
We demonstrate a precision magnetic microscope based on direct imaging of the
Larmor precession of a Rb spinor Bose-Einstein condensate. This
magnetometer attains a field sensitivity of 8.3 pT/Hz over a
measurement area of 120 m, an improvement over the low-frequency field
sensitivity of modern SQUID magnetometers. The corresponding atom shot-noise
limited sensitivity is estimated to be 0.15 pT/Hz for unity duty cycle
measurement. The achieved phase sensitivity is close to the atom shot-noise
limit suggesting possibilities of spatially resolved spin-squeezed
magnetometry. This magnetometer marks a significant application of degenerate
atomic gases to metrology
Mapping the cellular electrophysiology of rat sympathetic preganglionic neurones to their roles in cardiorespiratory reflex integration:A whole cell recording study in situ
Sympathetic preganglionic neurones (SPNs) convey sympathetic activity flowing from the CNS to the periphery to reach the target organs. Although previous in vivo and in vitro cell recording studies have explored their electrophysiological characteristics, it has not been possible to relate these characteristics to their roles in cardiorespiratory reflex integration. We used the working heartâbrainstem preparation to make whole cell patch clamp recordings from T3â4 SPNs (n = 98). These SPNs were classified by their distinct responses to activation of the peripheral chemoreflex, diving response and arterial baroreflex, allowing the discrimination of muscle vasoconstrictor-like (MVC(like), 39%) from cutaneous vasoconstrictor-like (CVC(like), 28%) SPNs. The MVC(like) SPNs have higher baseline firing frequencies (2.52 ± 0.33 Hz vs. CVC(like) 1.34 ± 0.17 Hz, P = 0.007). The CVC(like) have longer after-hyperpolarisations (314 ± 36 ms vs. MVC(like) 191 ± 13 ms, P < 0.001) and lower input resistance (346 ± 49  MΩ vs. MVC(like) 496 ± 41 MΩ, P < 0.05). MVC(like) firing was respiratory-modulated with peak discharge in the late inspiratory/early expiratory phase and this activity was generated by both a tonic and respiratory-modulated barrage of synaptic events that were blocked by intrathecal kynurenate. In contrast, the activity of CVC(like) SPNs was underpinned by rhythmical membrane potential oscillations suggestive of gap junctional coupling. Thus, we have related the intrinsic electrophysiological properties of two classes of SPNs in situ to their roles in cardiorespiratory reflex integration and have shown that they deploy different cellular mechanisms that are likely to influence how they integrate and shape the distinctive sympathetic outputs
Pisatin demethylation by fungal pathogens and nonpathogens of pea: Association with pisatin tolerance and virulence
Previous studies have indicated that detoxification of their hostsâ phytoalexins is a tolerance mechanism for some true fungi, but not the fungus-like Oomycota, and may be involved in determining the virulence of a pathogen. In the present study, the associations between demethylation of the pea phytoalexin pisatin, tolerance to pisatin, and viruÂlence on pea were examined for 50 fungal isolates which represent 17 species of pathogens and nonpathogens of pea. All isolates of Pythium coloratum and P. irregulare failed to metabolize and were sensitive to pisatin, consistent with previous observations that members of the Oomycota generally lack the ability to metabolize and are sensitive to their hostsâ phytoalexins. Among true fungi tested, the ability to demethylate pisatin was common, regardless of whether the particular isolate was pathogenic on pea or not. However, when the rate of pisatin demethylation was compared to virulence, all but one of the moderate to highly virulent isolates rapidly demethylated pisatin. In addition, the more rapidly demethylating isolates were generally more tolerant of pisatin. These results suggest that a specialized enÂzyme system for quickly detoxifying pisatin might be present in most pea pathogens. In previous studies a specific cyÂtochrome P450 enzyme for demethylating pisatin was identified in the pea pathogen Nectria haematococca mating popÂulation VI, and genes (PDA genes) encoding that enzyme have been cloned from this fungus. When DNA specific for these genes was used to probe genomic DNA from other fungi that demethylate pisatin, significant hybridization was detected with only one fungus, the pea pathogen Fusarium oxysporum f. sp. pisi. If the other pea pathogens possess a specific cytochrome P450 system for detoxification of pisatin, the genes encoding these enzymes apparently share limÂited nucleotide similarity with N. haematococca PDA genes
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