2,688 research outputs found
Crossover from a square to a hexagonal pattern in Faraday surface waves
We report on surface wave pattern formation in a Faraday experiment operated
at a very shallow filling level, where modes with a subharmonic and harmonic
time dependence interact. Associated with this distinct temporal behavior are
different pattern selection mechanisms, favoring squares or hexagons,
respectively. In a series of bifurcations running through a pair of
superlattices the surface wave pattern transforms between the two incompatible
symmetries. The close analogy to 2D and 3D crystallography is pointed out.Comment: 4 pages, 4 figure
Phase relaxation of Faraday surface waves
Surface waves on a liquid air interface excited by a vertical vibration of a
fluid layer (Faraday waves) are employed to investigate the phase relaxation of
ideally ordered patterns. By means of a combined frequency-amplitude modulation
of the excitation signal a periodic expansion and dilatation of a square wave
pattern is generated, the dynamics of which is well described by a Debye
relaxator. By comparison with the results of a linear theory it is shown that
this practice allows a precise measurement of the phase diffusion constant.Comment: 5 figure
Characterization of Cytokine Induction and Effects of Antiviral Treatment in Four Murine Models of Poxvirus Infection
Cytokine profiles during cowpox virus (CPV) strain Brighton and vaccinia virus (VV) strain Western Reserve infections were characterized in intranasal (i.n.) and intraperitoneal (i .p.) models in BALB/c mice. The time-course of induction and effects of cidofovir treatment on interferon (IFN)-γ, IFN-γ inducible protein (IP)-10, interleukin (IL)-6, and monocyte chemoattractant protein (MCP)-1 were determined. The four models have distinct patterns of cytokine induction. CPV i.p. and VV i.n. infections showed increased induction throughout the time studied. CPV i.n. infection resulted in delayed induction of IFN-γ and IP-10. Cytokine levels were fairly constant during VV i.p. infections. Cidofovir treatment (100 mg/kg/day i.p. for 2 days) significantly reduced certain cytokine levels in the four models. Treatment did not affect IP-10 in the CPV i.n. model; IFN-γ and IP-10 in the CPV i.p. model; or IL-6, IP- 10, and MCP-1 in the VV i.p. model. Characterization of cytokine responses has implications for understanding the immune responses and pathogeneses of viral infections in these models
Determinants and predictability of global wildfire emissions
Biomass burning is one of the largest sources of atmospheric trace gases and aerosols globally. These emissions have a major impact on the radiative balance of the atmosphere and on air quality, and are thus of significant scientific and societal interest. Several datasets have been developed that quantify those emissions on a global grid and offered to the atmospheric modelling community. However, no study has yet attempted to systematically quantify the dependence of the inferred pyrogenic emissions on underlying assumptions and input data. Such a sensitivity study is needed for understanding how well we can currently model those emissions and what the factors are that contribute to uncertainties in those emission estimates. <br><br> Here, we combine various satellite-derived burned area products, a terrestrial ecosystem model to simulate fuel loads and the effect of fire on ecosystem dynamics, a model of fuel combustion, and various emission models that relate combusted biomass to the emission of various trace gases and aerosols. We carry out simulations with varying parameters for combustion completeness and fuel decomposition rates within published estimates, four different emissions models and three different global burned-area products. We find that variations in combustion completeness and simulated fuel loads have the largest impact on simulated global emissions for most species, except for some with highly uncertain emission factors. Variation in burned-area estimates also contribute considerably to emission uncertainties. We conclude that global models urgently need more field-based data for better parameterisation of combustion completeness and validation of simulated fuel loads, and that further validation and improvement of burned area information is necessary for accurately modelling global wildfire emissions. The results are important for chemical transport modelling studies, and for simulations of biomass burning impacts on the atmosphere under future climate change scenarios
Liquid n-hexane condensed in silica nanochannels: A combined optical birefringence and vapor sorption isotherm study
The optical birefringence of liquid n-hexane condensed in an array of
parallel silica channels of 7nm diameter and 400 micrometer length is studied
as a function of filling of the channels via the vapor phase. By an analysis
with the generalized Bruggeman effective medium equation we demonstrate that
such measurements are insensitive to the detailed geometrical (positional)
arrangement of the adsorbed liquid inside the channels. However, this technique
is particularly suitable to search for any optical anisotropies and thus
collective orientational order as a function of channel filling. Nevertheless,
no hints for such anisotropies are found in liquid n-hexane. The n-hexane
molecules in the silica nanochannels are totally orientationally disordered in
all condensation regimes, in particular in the film growth as well as in the
the capillary condensed regime. Thus, the peculiar molecular arrangement found
upon freezing of liquid n-hexane in nanochannel-confinement, where the
molecules are collectively aligned perpendicularly to the channels' long axes,
does not originate in any pre-alignment effects in the nanoconfined liquid due
to capillary nematization.Comment: 7 pages, 5 figure
Real-time observation of interfering crystal electrons in high-harmonic generation
Accelerating and colliding particles has been a key strategy to explore the
texture of matter. Strong lightwaves can control and recollide electronic
wavepackets, generating high-harmonic (HH) radiation which encodes the
structure and dynamics of atoms and molecules and lays the foundations of
attosecond science. The recent discovery of HH generation in bulk solids
combines the idea of ultrafast acceleration with complex condensed matter
systems and sparks hope for compact solid-state attosecond sources and
electronics at optical frequencies. Yet the underlying quantum motion has not
been observable in real time. Here, we study HH generation in a bulk solid
directly in the time-domain, revealing a new quality of strong-field
excitations in the crystal. Unlike established atomic sources, our solid emits
HH radiation as a sequence of subcycle bursts which coincide temporally with
the field crests of one polarity of the driving terahertz waveform. We show
that these features hallmark a novel non-perturbative quantum interference
involving electrons from multiple valence bands. The results identify key
mechanisms for future solid-state attosecond sources and next-generation
lightwave electronics. The new quantum interference justifies the hope for
all-optical bandstructure reconstruction and lays the foundation for possible
quantum logic operations at optical clock rates
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