6,351 research outputs found
Quantum phase transitions in bilayer SU(N) anti-ferromagnets
We present a detailed study of the destruction of SU(N) magnetic order in
square lattice bilayer anti-ferromagnets using unbiased quantum Monte Carlo
numerical simulations and field theoretic techniques. We study phase
transitions from an SU(N) N\'eel state into two distinct quantum disordered
"valence-bond" phases: a valence-bond liquid (VBL) with no broken symmetries
and a lattice-symmetry breaking valence-bond solid (VBS) state. For finite
inter-layer coupling, the cancellation of Berry phases between the layers has
dramatic consequences on the two phase transitions: the N\'eel-VBS transition
is first order for all accesible in our model, whereas the N\'eel-VBL
transition is continuous for N=2 and first order for N>= 4; for N=3 the
N\'eel-VBL transition show no signs of first-order behavior
Logarithmic correction to the Bekenstein-Hawking entropy of the BTZ black hole
We derive an exact expression for the partition function of the Euclidean BTZ
black hole. Using this, we show that for a black hole with large horizon area,
the correction to the Bekenstein-Hawking entropy is , in
agreement with that for the Schwarzschild black hole obtained in the canonical
gravity formalism and also in a Lorentzian computation of BTZ black hole
entropy. We find that the right expression for the logarithmic correction in
the context of the BTZ black hole comes from the modular invariance associated
with the toral boundary of the black hole.Comment: LaTeX, 10 pages, typos corrected, clarifications adde
Carbon budgets and carbon sequestration potential of Indian forests
Keywords: Carbon uptake, Forest biomass, Bioenergy, Land use change, Indian forests, Deforestation, Afforestation, Rotation length, Trees outside forests. Global climate change is a widespread and growing concern that has led to extensive international discussions and negotiations. Responses to this concern have focused on reducing emissions of greenhouse gases, especially carbon dioxide, and on measuring carbon absorbed by and stored in forests and soils. Forests are a significant part of the global carbon cycle. The amount of carbon stored, however, changes over time as forests grow and mature. Land use changes, especially afforestation and deforestation may have major impacts on carbon storage. An option for mitigating the accumulation of CO2 in the atmosphere is the enhanced sequestration of carbon by the biosphere through massive reforestation or sustainable afforestation programs. Reducing the rate of deforestation reduces carbon losses from the biosphere. Establishing plantations on former agricultural land may have less of an impact on increasing carbon sequestration than restoring natural forests. The focus of this study was to estimate the carbon budgets and carbon sequestration potential of Indian forests, assessing the possible impacts of land-use changes and climate change on carbon stocks of Indian forests, and the mitigation potential of using forest-based bioenergy for fossil fuel substitution. The results from this study show that over a 10-year period from 1992-2002, Indian forests have acted as a small carbon sink. Thus, India with high population density, low forest cover per capita, high dependence of a large part of human population on forests, and a predominantly agrarian economy, has been able to reduce deforestation rate and increase its forest cover and associated carbon sink in the terrestrial biosphere. Due to fast growth rate and adaptability to a range of environments, short rotation plantations, in addition to carbon storage, rapidly produce biomass for energy and contribute to reduced greenhouse gas emissions. India has the potential to create additional carbon sinks using marginal lands, while at the same time balancing economic development and environmental concerns. </p
Towards a mathematical system for extension education - II
A brief description is given of a mathematical model for use in extension education regarding fisheries in developing countries
Quantum criticality of U(1) gauge theories with fermionic and bosonic matter in two spatial dimensions
We consider relativistic U(1) gauge theories in 2+1 dimensions, with N_b
species of complex bosons and N_f species of Dirac fermions at finite
temperature. The quantum phase transition between the Higgs and Coulomb phases
is described by a conformal field theory (CFT). At large N_b and N_f, but for
arbitrary values of the ratio N_b/N_f, we present computations of various
critical exponents and universal amplitudes for these CFTs. We make contact
with the different spin-liquids, charge-liquids and deconfined critical points
of quantum magnets that these field theories describe. We compute physical
observables that may be measured in experiments or numerical simulations of
insulating and doped quantum magnets.Comment: 30 pages, 8 figure
Tadpole Method and Supersymmetric O(N) Sigma Model
We examine the phase structures of the supersymmetric O(N) sigma model in two
and three dimensions by using the tadpole method. Using this simple method, the
calculation is largely simplified and the characteristics of this theory become
clear. We also examine the problem of the fictitious negative energy state.Comment: Plain Latex(12pages), No figur
Minimizing the Age of Information in Wireless Networks with Stochastic Arrivals
We consider a wireless network with a base station serving multiple traffic
streams to different destinations. Packets from each stream arrive to the base
station according to a stochastic process and are enqueued in a separate (per
stream) queue. The queueing discipline controls which packet within each queue
is available for transmission. The base station decides, at every time t, which
stream to serve to the corresponding destination. The goal of scheduling
decisions is to keep the information at the destinations fresh. Information
freshness is captured by the Age of Information (AoI) metric.
In this paper, we derive a lower bound on the AoI performance achievable by
any given network operating under any queueing discipline. Then, we consider
three common queueing disciplines and develop both an Optimal Stationary
Randomized policy and a Max-Weight policy under each discipline. Our approach
allows us to evaluate the combined impact of the stochastic arrivals, queueing
discipline and scheduling policy on AoI. We evaluate the AoI performance both
analytically and using simulations. Numerical results show that the performance
of the Max-Weight policy is close to the analytical lower bound
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