String-like behaviour of 4d SU(3) Yang-Mills flux tubes

We present here results on the fine structure of the static q\bar q potential in d=4 SU(3) Yang-Mills theory. The potential is obtained from Polyakov loop correlators having separations between 0.3 and 1.2 fermi. Measurements were carried out on lattices of spatial extents of about 4 and 5.4 fermi. The temporal extent was 5.4 fermi in both cases. The results are analyzed in terms of the force between a q\bar q pair as well as in terms of a scaled second derivative of the potential. The data is accurate enough to distinguish between different effective string models and it seems to favour the expression for ground state energy of a Nambu-Goto string.Comment: 9 pages in LaTeX with 2 figures and 2 tables in JHEP style. Replaced to match with shortened published versio

Hitting time for the continuous quantum walk

We define the hitting (or absorbing) time for the case of continuous quantum walks by measuring the walk at random times, according to a Poisson process with measurement rate $\lambda$. From this definition we derive an explicit formula for the hitting time, and explore its dependence on the measurement rate. As the measurement rate goes to either 0 or infinity the hitting time diverges; the first divergence reflects the weakness of the measurement, while the second limit results from the Quantum Zeno effect. Continuous-time quantum walks, like discrete-time quantum walks but unlike classical random walks, can have infinite hitting times. We present several conditions for existence of infinite hitting times, and discuss the connection between infinite hitting times and graph symmetry.Comment: 12 pages, 1figur

Quantum walks on quotient graphs

A discrete-time quantum walk on a graph is the repeated application of a unitary evolution operator to a Hilbert space corresponding to the graph. If this unitary evolution operator has an associated group of symmetries, then for certain initial states the walk will be confined to a subspace of the original Hilbert space. Symmetries of the original graph, given by its automorphism group, can be inherited by the evolution operator. We show that a quantum walk confined to the subspace corresponding to this symmetry group can be seen as a different quantum walk on a smaller quotient graph. We give an explicit construction of the quotient graph for any subgroup of the automorphism group and illustrate it with examples. The automorphisms of the quotient graph which are inherited from the original graph are the original automorphism group modulo the subgroup used to construct it. We then analyze the behavior of hitting times on quotient graphs. Hitting time is the average time it takes a walk to reach a given final vertex from a given initial vertex. It has been shown in earlier work [Phys. Rev. A {\bf 74}, 042334 (2006)] that the hitting time can be infinite. We give a condition which determines whether the quotient graph has infinite hitting times given that they exist in the original graph. We apply this condition for the examples discussed and determine which quotient graphs have infinite hitting times. All known examples of quantum walks with fast hitting times correspond to systems with quotient graphs much smaller than the original graph; we conjecture that the existence of a small quotient graph with finite hitting times is necessary for a walk to exhibit a quantum speed-up.Comment: 18 pages, 7 figures in EPS forma

Parity Violating Gravitational Coupling Of Electromagnetic Fields

A manifestly gauge invariant formulation of the coupling of the Maxwell theory with an Einstein Cartan geometry is given, where the space time torsion originates from a massless Kalb-Ramond field augmented by suitable U(1) Chern Simons terms.We focus on the situation where the torsion violates parity, and relate it to earlier proposals for gravitational parity violation.Comment: 7 Pages, Latex . no figures, Replaced with Revtex version, many references added and typos correcte

Alat Perangkap Hama Serangga Padi Sawah Menggunakan Cahaya dari Tenaga Surya

Untuk mengendalikan hama serangga yang ramah lingkungan, dirancang sebuah alat perangkap hama serangga pada padi sawah dengan menggunakan cahaya dari tenaga surya dengan sumber listrik dari tenaga surya. Alat ini menggunakan panel surya 10 Wp - 12 V dengan baterai 12 V - 7 Ah. Alat ini menggunakan lampu LED 5 watt dan dapat bertahan selama 14 jam. Alat ini bekerja secara otomatis karena menggunakan sensor LDR (cahaya) untuk menghidupkan lampu secara otomatis. Alat memanfaatkan keterkaitan hama serangga yang tertarik dengan cahaya. Secara alami hama serangga mudah tertarik dengan cahaya. Berdasarkan pengujian yang dilakukan di persawahan warga di Kandang Lamo, Kec. Harau, hama serangga yang tertangkap adalah walang sangit (leptocorica acuta), kepinding tanah (scotinophora coarctata), kepik hijau (nezara viridula), penggerek batang padi putih (scripophaga innotata) dan belalang (caelifera)

Furrow Diking Technology for Agricultural Water Conservation and its Impact on Crop Yields in Texas

Furrow diking is a practical, efficient and low-cost technique to conserve water and increase crop yields. Improvements in diker design and the increased use of herbicides have resulted in the rapid spread of furrow diking in the Texas High Plains and other regions. To quantify the long-term effects of diking on crop yields, a computer simulation approach was used. Three crop models for sorghum, corn and cotton were combined with surface runoff hydrology algorithms, based on the USDA-SCS curve number methodology. The combination models called SORDIKE, CORDIKE and COTDIKE were run to determine the effects of conserving the runoff (by diking) on crop yields. Three scenarios of not diking, diking in the growing season, and diking all year were simulated. Daily weather data for 25 years from five Texas regions were used for the analyses. Depending on the location, furrow diking in the growing season increased average annual sorghum yields by 320 to 570 kg/ha, corn yields by 180 to 570 kg/ha, and cotton lint yields by 10 to 20 kg/ha. Diking the land throughout the year increased mean annual yields by 440 to 1080 kg/ha of sorghum, 210 to 800 kg/ha of corn and 10 to 30 kg/ha of cotton lint. The study indicated that furrow diking can be a valuable management practice for about 3.4 million ha of cropped area in the semi-arid and sub-humid regions of Texas. The practice may be useful in other areas also, to mitigate the effects of short duration moisture stress on crop yields

On the Emergence of the Microcanonical Description from a Pure State

We study, in general terms, the process by which a pure state can ``self-thermalize'' and {\em appear} to be described by a microcanonical density matrix. This requires a quantum mechanical version of the Gibbsian coarse graining that conceptually underlies classical statistical mechanics. We introduce some extra degrees of freedom that are necessary for this. Interaction between these degrees and the system can be understood as a process of resonant absorption and emission of ``soft quanta''. This intuitive picture allows one to state a criterion for when self thermalization occurs. This paradigm also provides a method for calculating the thermalization rate using the usual formalism of atomic physics for calculating decay rates. We contrast our prescription for coarse graining, which is somewhat dynamical, with the earlier approaches that are intrinsically kinematical. An important motivation for this study is the black hole information paradox.Comment: 58 pages, 2 figures. A reference adde

Magneto-thermal phenomena in bulk high temperature superconductors subjected to applied AC magnetic fields

In the present work we study, both theoretically and experimentally, the temperature increase in a bulk high-temperature superconductor subjected to applied AC magnetic fields of large amplitude. We calculate analytically the equilibrium temperatures of the bulk sample as a function of the experimental parameters using a simple critical-state model for an infinitely long type-II superconducting slab or cylinder. The results show the existence of a limit heat transfer coefficient (AUlim) separating two thermal regimes with different characteristics. The theoretical analysis predicts a "forbidden" temperature window within which the temperature of the superconductor can never stabilize when the heat transfer coefficient is small. In addition, we determine an analytical expression of two threshold fields Htr1 and Htr2 characterizing the importance of magneto-thermal effects and show that a thermal runaway always occurs when the field amplitude is larger than Htr2. The theoretical predictions of the temperature evolution of the bulk sample during a self-heating process agree well with the experimental data. The simple analytical study presented in this paper enables order of magnitude thermal effects to be estimated for simple superconductor geometries under applied AC magnetic fields and can be used to predict the influence of experimental parameters on the self-heating characteristics of bulk type-II superconductors.Comment: 32 pages, 6 figure

An AC susceptometer for the characterization of large, bulk superconducting samples

The main purpose of this work was to design, develop and construct a simple, low-cost AC susceptometer to measure large, bulk superconducting samples (up to 32 mm in diameter) in the temperature range 78-120 K. The design incorporates a double heating system that enables a high heating rate (25 K/hour) while maintaining a small temperature gradient (< 0.2 K) across the sample. The apparatus can be calibrated precisely using a copper coil connected in series with the primary coil. The system has been used successfully to measure the temperature dependence of the AC magnetic properties of entire RE-Ba-Cu-O [(RE)BCO] bulk superconducting domains. A typical AC susceptibility measurement run from 78 K to 95 K takes about 2 hours, with excellent temperature resolution (temperature step ~ 4 mK) around the critical temperature, in particular.Comment: 25 pages, 7 figures. Accepted for publication in Measurement Science and Technolog