3,450 research outputs found
Rain: Relaxations in the sky
We demonstrate how, from the point of view of energy flow through an open
system, rain is analogous to many other relaxational processes in Nature such
as earthquakes. By identifying rain events as the basic entities of the
phenomenon, we show that the number density of rain events per year is
inversely proportional to the released water column raised to the power 1.4.
This is the rain-equivalent of the Gutenberg-Richter law for earthquakes. The
event durations and the waiting times between events are also characterised by
scaling regions, where no typical time scale exists. The Hurst exponent of the
rain intensity signal . It is valid in the temporal range from
minutes up to the full duration of the signal of half a year. All of our
findings are consistent with the concept of self-organised criticality, which
refers to the tendency of slowly driven non-equilibrium systems towards a state
of scale free behaviour.Comment: 9 pages, 8 figures, submitted to PR
The Impact of Situational Factors On Information System (Is) Managerial Leader Behaviors: What Information Systems Employees Want
Information systems leadership has evolved dramatically over the past 40 years. Early in the era of computing most attention was focused on the technical skills of IS managers. As IS has become ubiquitous in our organizations and increasingly embedded in our everyday lives, the need for a broader approach to IS management has emerged with an increasing emphasis on non-technical skills in business practices and an appreciation of the impact of organizational culture. Further, information systems managers increasingly find themselves in crisis situations that may require different leadership skills to successfully navigate. These crises may be caused by the physical destruction of computer hardware, the loss of critically sensitive data, sophisticated hacking of company computers, or a coding error in a mission critical software program. The research on managerial leadership in crisis situations is relatively sparse; however, the research on managerial leadership behaviors for the information systems sector is essentially nonexistent. This research study attempts to fill that gap, finding that there are a few desired managerial leadership behaviors in common between the information systems group and other studied groups, as well as differences and desired shifts in priorities
Immune-responses to varicella-zoster in the aged
Skin test reactivity and in vitro lymphocyte stimulation responses to varicella-zoster (VZ) were examined in a large normal population ranging in age from 6 months to 93 years. Waning of cellular immunity, as examined by skin delayed hypersensitivity, began at age 40 years. Skin test responses to phytohemagglutinin, however, remained positive into the eighth decade of life. In vitro lymphocyte stimulation responses to VZ were usually positive (stimulation index ≥2.5) until age 60 years, after which time levels, as observed with nonimmune individuals, were often demonstrated. Antibody levels, as measured by fluorescent antibody to membrane antigen, remained positive into the ninth and tenth decades of life. This was especially so with a history of reactivation (zoster) VZ infections, while skin test and in vitro responses were rarely positive in those individuals. Thus cellular, as contrasted with humoral, immunity decreases with advancing age, which may account for a propensity to reactivation of VZ virus
Astrophysical S-factors for fusion reactions involving C, O, Ne and Mg isotopes
Using the Sao Paulo potential and the barrier penetration formalism we have
calculated the astrophysical factor S(E) for 946 fusion reactions involving
stable and neutron-rich isotopes of C, O, Ne, and Mg for center-of-mass
energies E varying from 2 MeV to 18-30 MeV (covering the range below and above
the Coulomb barrier). We have parameterized the energy dependence S(E) by an
accurate universal 9-parameter analytic expression and present tables of fit
parameters for all the reactions. We also discuss the reduced 3-parameter
version of our fit which is highly accurate at energies below the Coulomb
barrier, and outline the procedure for calculating the reaction rates. The
results can be easily converted to thermonuclear or pycnonuclear reaction rates
to simulate various nuclear burning phenomena, in particular, stellar burning
at high temperatures and nucleosynthesis in high density environments.Comment: 30 pages including 11 tables, 4 figures, ADNDT, accepte
Stochastic series expansion method with operator-loop update
A cluster update (the ``operator-loop'') is developed within the framework of
a numerically exact quantum Monte Carlo method based on the power series
expansion of exp(-BH) (stochastic series expansion). The method is generally
applicable to a wide class of lattice Hamiltonians for which the expansion is
positive definite. For some important models the operator-loop algorithm is
more efficient than loop updates previously developed for ``worldline''
simulations. The method is here tested on a two-dimensional anisotropic
Heisenberg antiferromagnet in a magnetic field.Comment: 5 pages, 4 figure
Ultrafast supercontinuum spectroscopy of carrier multiplication and biexcitonic effects in excited states of PbS quantum dots
We examine the multiple exciton population dynamics in PbS quantum dots by
ultrafast spectrally-resolved supercontinuum transient absorption (SC-TA). We
simultaneously probe the first three excitonic transitions over a broad
spectral range. Transient spectra show the presence of first order bleach of
absorption for the 1S_h-1S_e transition and second order bleach along with
photoinduced absorption band for 1P_h-1P_e transition. We also report evidence
of the one-photon forbidden 1S_{h,e}-1P_{h,e} transition. We examine signatures
of carrier multiplication (multiexcitons for the single absorbed photon) from
analysis of the first and second order bleaches, in the limit of low absorbed
photon numbers (~ 10^-2), at pump energies from two to four times the
semiconductor band gap. The multiexciton generation efficiency is discussed
both in terms of a broadband global fit and the ratio between early- to
long-time transient absorption signals.. Analysis of population dynamics shows
that the bleach peak due to the biexciton population is red-shifted respect the
single exciton one, indicating a positive binding energy.Comment: 16 pages, 5 figure
The Physical Origins of Entropy Production, Free Energy Dissipation and their Mathematical Representations
A complete mathematical theory of nonequilibrium thermodynamics of stochastic
systems in terms of master equations is presented. As generalizations of
isothermal entropy and free energy, two functions of states play central roles:
the Gibbs entropy and the relative entropy , which are related via the
stationary distribution of the stochastic dynamics. satisfies the
fundamental entropy balance equation with entropy production
rate and heat dissipation rate , while . For
closed systems that satisfy detailed balance: . For open system
one has where the housekeeping heat
was first introduced in the phenomenological nonequilibrium steady state
thermodynamics. Entropy production consists of free energy dissipation
associated with spontaneous relaxation, , and active energy pumping that
sustains the open system . The amount of excess heat involved in the
relaxation .Comment: 4 pages, no figure
Critical exponents of the quantum phase transition in a planar antiferromagnet
We have performed a large scale quantum Monte Carlo study of the quantum
phase transition in a planar spin-1/2 Heisenberg antiferromagnet with CaV4O9
structure. We obtain a dynamical exponent z=1.018+/-0.02. The critical
exponents beta, nu and eta agree within our errors with the classical 3D O(3)
exponents, expected from a mapping to the nonlinear sigma model. This confirms
the conjecture of Chubukov, Sachdev and Ye [Phys. Rev. B 49, 11919 (1994)] that
the Berry phase terms in the planar Heisenberg antiferromagnet are dangerously
irrelevant.Comment: 5 pages including 4 figures; revised version: some minor changes and
added reference
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