19,013 research outputs found
A statistical mechanics framework for multi-particle production in high energy reactions
We deduce the particle distributions in particle collisions with
multihadron-production in the framework of mechanical statistics. They are
derived as functions of x, P_T^2 and the rest mass of different species for a
fixed total number of all produced particles, inelasticity and total transverse
energy. For P_T larger than the mass of each particle we get the behaviour
\frac{dn_i}{dP_T} \sim \sqrt{P_T} e^{-\frac{P_T}{T_H}} Values of _\pi,
_K, and _{\bar{p}} in agreement with experiment are found by taking
T_H=180MeV (the Hagedorn temperature).Comment: 9 pages, RevTe
Hydrodynamic mean field solutions of 1D exclusion processes with spatially varying hopping rates
We analyze the open boundary partially asymmetric exclusion process with
smoothly varying internal hopping rates in the infinite-size, mean field limit.
The mean field equations for particle densities are written in terms of Ricatti
equations with the steady-state current as a parameter. These equations are
solved both analytically and numerically. Upon imposing the boundary conditions
set by the injection and extraction rates, the currents are found
self-consistently. We find a number of cases where analytic solutions can be
found exactly or approximated. Results for from asymptotic analyses for
slowly varying hopping rates agree extremely well with those from extensive
Monte Carlo simulations, suggesting that mean field currents asymptotically
approach the exact currents in the hydrodynamic limit, as the hopping rates
vary slowly over the lattice. If the forward hopping rate is greater than or
less than the backward hopping rate throughout the entire chain, the three
standard steady-state phases are preserved. Our analysis reveals the
sensitivity of the current to the relative phase between the forward and
backward hopping rate functions.Comment: 12 pages, 4 figure
Surface roughness during depositional growth and sublimation of ice crystals
Full version of an earlier discussion paper (Chou et al. 2018)Ice surface properties can modify the scattering properties of atmospheric ice crystals and therefore affect the radiative properties of mixed-phase and cirrus clouds. The Ice Roughness Investigation System (IRIS) is a new laboratory setup designed to investigate the conditions under which roughness develops on single ice crystals, based on their size, morphology and growth conditions (relative humidity and temperature). Ice roughness is quantified through the analysis of speckle in 2-D light-scattering patterns. Characterization of the setup shows that a supersaturation of 20 % with respect to ice and a temperature at the sample position as low as-40 °C could be achieved within IRIS. Investigations of the influence of humidity show that higher supersaturations with respect to ice lead to enhanced roughness and irregularities of ice crystal surfaces. Moreover, relative humidity oscillations lead to gradual ratcheting-up of roughness and irregularities, as the crystals undergo repeated growth-sublimation cycles. This memory effect also appears to result in reduced growth rates in later cycles. Thus, growth history, as well as supersaturation and temperature, influences ice crystal growth and properties, and future atmospheric models may benefit from its inclusion in the cloud evolution process and allow more accurate representation of not just roughness but crystal size too, and possibly also electrification properties.Peer reviewe
^{59}Co NMR evidence for charge ordering below T_{CO}\sim 51 K in Na_{0.5}CoO_2
The CoO layers in sodium-cobaltates NaCoO may be viewed as
a spin triangular-lattice doped with charge carriers. The underlying
physics of the cobaltates is very similar to that of the high cuprates.
We will present unequivocal Co NMR evidence that below ,
the insulating ground state of the itinerant antiferromagnet
NaCoO () is induced by charge ordering.Comment: Phys. Rev. Lett. 100 (2008), in press. 4 figure
The infrared conductivity of NaCoO: evidence of gapped states
We present infrared ab-plane conductivity data for the layered cobaltate
NaCoO at three different doping levels (, and 0.75). The
Drude weight increases monotonically with hole doping, . At the lowest
hole doping level =0.75 the system resembles the normal state of underdoped
cuprate superconductors with a scattering rate that varies linearly with
frequency and temperature and there is an onset of scattering by a bosonic mode
at 600 \cm. Two higher hole doped samples ( and 0.25) show two
different-size gaps (110 \cm and 200 \cm, respectively) in the optical
conductivities at low temperatures and become insulators. The spectral weights
lost in the gap region of 0.50 and 0.25 samples are shifted to prominent peaks
at 200 \cm and 800 \cm, respectively. We propose that the two gapped states of
the two higher hole doped samples (=0.50 and 0.25) are pinned charge ordered
states.Comment: 4 pages, 3 figure
Sodium vacancy ordering and the co-existence of localized spins and itinerant charges in NaxCoO2
The sodium cobaltate family (NaxCoO2) is unique among transition metal oxides
because the Co sits on a triangular lattice and its valence can be tuned over a
wide range by varying the Na concentration x. Up to now detailed modeling of
the rich phenomenology (which ranges from unconventional superconductivity to
enhanced thermopower) has been hampered by the difficulty of controlling pure
phases. We discovered that certain Na concentrations are specially stable and
are associated with superlattice ordering of the Na clusters. This leads
naturally to a picture of co-existence of localized spins and itinerant charge
carriers. For x = 0.84 we found a remarkably small Fermi energy of 87 K. Our
picture brings coherence to a variety of measurements ranging from NMR to
optical to thermal transport. Our results also allow us to take the first step
towards modeling the mysterious ``Curie-Weiss'' metal state at x = 0.71. We
suggest the local moments may form a quantum spin liquid state and we propose
experimental test of our hypothesis.Comment: 16 pages, 5 figure
Deep shower interpretation of the cosmic ray events observed in excess of the Greisen-Zatsepin-Kuzmin energy
We consider the possibility that the ultra-high-energy cosmic ray flux has a
small component of exotic particles which create showers much deeper in the
atmosphere than ordinary hadronic primaries. It is shown that applying the
conventional AGASA/HiRes/Auger data analysis procedures to such exotic events
results in large systematic biases in the energy spectrum measurement. SubGZK
exotic showers may be mis-reconstructed with much higher energies and mimick
superGZK events. Alternatively, superGZK exotic showers may elude detection by
conventional fluorescence analysis techniques.Comment: 22 pages, 5 figure
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