10,339 research outputs found
Systematics of fusion probability in "hot" fusion reactions
The fusion probability in "hot" fusion reactions leading to the synthesis of
super-heavy nuclei is investigated systematically. The quasi-fission barrier
influences the formation of the super-heavy nucleus around the "island of
stability" in addition to the shell correction. Based on the quasi-fission
barrier height obtained with the Skyrme energy-density functional, we propose
an analytical expression for the description of the fusion probability, with
which the measured evaporation residual cross sections can be reproduced
acceptably well. Simultaneously, some special fusion reactions for synthesizing
new elements 119 and 120 are studied. The predicted evaporation residual cross
sections for 50Ti+249Bk are about 10-150fb at energies around the
entrance-channel Coulomb barrier. For the fusion reactions synthesizing element
120 with projectiles 54Cr and 58Fe, the cross sections fall to a few femtobarns
which seems beyond the limit of the available facilities.Comment: 5 figures, 1 tabl
On Revenue Maximization with Sharp Multi-Unit Demands
We consider markets consisting of a set of indivisible items, and buyers that
have {\em sharp} multi-unit demand. This means that each buyer wants a
specific number of items; a bundle of size less than has no value,
while a bundle of size greater than is worth no more than the most valued
items (valuations being additive). We consider the objective of setting
prices and allocations in order to maximize the total revenue of the market
maker. The pricing problem with sharp multi-unit demand buyers has a number of
properties that the unit-demand model does not possess, and is an important
question in algorithmic pricing. We consider the problem of computing a revenue
maximizing solution for two solution concepts: competitive equilibrium and
envy-free pricing.
For unrestricted valuations, these problems are NP-complete; we focus on a
realistic special case of "correlated values" where each buyer has a
valuation v_i\qual_j for item , where and \qual_j are positive
quantities associated with buyer and item respectively. We present a
polynomial time algorithm to solve the revenue-maximizing competitive
equilibrium problem. For envy-free pricing, if the demand of each buyer is
bounded by a constant, a revenue maximizing solution can be found efficiently;
the general demand case is shown to be NP-hard.Comment: page2
Pegasus: A New Hybrid-Kinetic Particle-in-Cell Code for Astrophysical Plasma Dynamics
We describe Pegasus, a new hybrid-kinetic particle-in-cell code tailored for
the study of astrophysical plasma dynamics. The code incorporates an
energy-conserving particle integrator into a stable, second-order--accurate,
three-stage predictor-predictor-corrector integration algorithm. The
constrained transport method is used to enforce the divergence-free constraint
on the magnetic field. A delta-f scheme is included to facilitate a
reduced-noise study of systems in which only small departures from an initial
distribution function are anticipated. The effects of rotation and shear are
implemented through the shearing-sheet formalism with orbital advection. These
algorithms are embedded within an architecture similar to that used in the
popular astrophysical magnetohydrodynamics code Athena, one that is modular,
well-documented, easy to use, and efficiently parallelized for use on thousands
of processors. We present a series of tests in one, two, and three spatial
dimensions that demonstrate the fidelity and versatility of the code.Comment: 27 pages, 12 figures, accepted for publication in Journal of
Computational Physic
Random close packing revisited: How many ways can we pack frictionless disks?
We create collectively jammed (CJ) packings of 50-50 bidisperse mixtures of
smooth disks in 2d using an algorithm in which we successively compress or
expand soft particles and minimize the total energy at each step until the
particles are just at contact. We focus on small systems in 2d and thus are
able to find nearly all of the collectively jammed states at each system size.
We decompose the probability for obtaining a collectively jammed
state at a particular packing fraction into two composite functions: 1)
the density of CJ packing fractions , which only depends on
geometry and 2) the frequency distribution , which depends on the
particular algorithm used to create them. We find that the function
is sharply peaked and that depends exponentially on
. We predict that in the infinite system-size limit the behavior of
in these systems is controlled by the density of CJ packing
fractions--not the frequency distribution. These results suggest that the
location of the peak in when can be used as a
protocol-independent definition of random close packing.Comment: 9 pages, 14 figure
New Approach on the General Shape Equation of Axisymmetric Vesicles
The general Helfrich shape equation determined by minimizing the curvature
free energy describes the equilibrium shapes of the axisymmetric lipid bilayer
vesicles in different conditions. It is a non-linear differential equation with
variable coefficients. In this letter, by analyzing the unique property of the
solution, we change this shape equation into a system of the two differential
equations. One of them is a linear differential equation. This equation system
contains all of the known rigorous solutions of the general shape equation. And
the more general constraint conditions are found for the solution of the
general shape equation.Comment: 8 pages, LaTex, submit to Mod. Phys. Lett.
Respon Pemberian Hormon Tumbuh Dan Mikoriza Terhadap Pertumbuhan Stek Ramin (Gonystylus Bancanus (Miq.) Kurz)
This study was conducted to determine the effect of growth hormones and mycorhyza application on the growth of ramin cuttings. A Completely Randomized Design with 5 replicates was used in this study. The experiment consisted of two stages i.e hormon treatments (control, Rapid root, Root Up, IBA 250 mg/l, IBA 500 mg/l, IBA 1000 mg/l), Fusarium and mycorhyza applications. The result showed that the highest number of root was obtained from Root Up (12,83 cm), while the lowest was from Fusarium treatments (4,67 cm). IBA 250 mg/l enhanced the number of roots and the length of root significantly but not stimulate the development of new leaf. While mycorhyza application improving the growth of the new leaf and the root development of ramin
Gate Tunable Dissipation and "Superconductor-Insulator" Transition in Carbon Nanotube Josephson Transistors
Dissipation is ubiquitous in quantum systems, and its interplay with
fluctuations is critical to maintaining quantum coherence. We experimentally
investigate the dissipation dynamics in single-walled carbon nanotubes coupled
to superconductors. The voltage-current characteristics display gate-tunable
hysteresis, with sizes that perfectly correlate with the normal state
resistance RN, indicating the junction undergoes a periodic modulation between
underdamped and overdamped regimes. Surprisingly, when a device's Fermi-level
is tuned through a local conductance minimum, we observe a gate-controlled
transition from superconducting-like to insulating-like states, with a
"critical" R_N value of about 8-20 kohm.Comment: Figures revised to improve clarity. Accepted for publication by
Physical Review Letter
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