4,954 research outputs found
Near-horizon geometries of supersymmetric AdS(5) black holes
We provide a classification of near-horizon geometries of supersymmetric,
asymptotically anti-de Sitter, black holes of five-dimensional U(1)^3-gauged
supergravity which admit two rotational symmetries. We find three
possibilities: a topologically spherical horizon, an S^1 \times S^2 horizon and
a toroidal horizon. The near-horizon geometry of the topologically spherical
case turns out to be that of the most general known supersymmetric,
asymptotically anti-de Sitter, black hole of U(1)^3-gauged supergravity. The
other two cases have constant scalars and only exist in particular regions of
this moduli space -- in particular they do not exist within minimal gauged
supergravity. We also find a solution corresponding to the near-horizon
geometry of a three-charge supersymmetric black ring held in equilibrium by a
conical singularity; when lifted to type IIB supergravity this solution can be
made regular, resulting in a discrete family of warped AdS(3) geometries.
Analogous results are presented in U(1)^n gauged supergravity.Comment: Latex, 29 pages. v2: minor improvements, references adde
Two-flux Colliding Plane Waves in String Theory
We construct the two-flux colliding plane wave solutions in higher
dimensional gravity theory with dilaton, and two complementary fluxes. Two
kinds of solutions has been obtained: Bell-Szekeres(BS) type and homogeneous
type. After imposing the junction condition, we find that only Bell-Szekeres
type solution is physically well-defined. Furthermore, we show that the future
curvature singularity is always developed for our solutions.Comment: 16 pages, Latex; typoes corrected; references added, minor
modification
Impression Creep Behavior of Sn-3.5Ag-0.7Cu/Cu Brazed
AbstractBrazing, as one of the major connection technology, has been widely used in different areas such as aviation, aerospace, electronics and chemical industries etc. Sometimes creep fracture can be found in the brazed joints when they are used at high temperature. The conventional characterized method for creep properties cannot be used to study the brazed joints due to their small size. The impression technology has the potential to be used to study the creep properties of brazed joints, since no special requirements are needed for the size and shape of to-be-measured materials. In this investigation, Sn-3.5Ag-0.7Cu/Cu brazed joint is created and its creep properties is measured by impression creep testing. The effect of punching stress and temperature is studied on the impressing depth, which change from 70 to 100MPa and 80-130 oC, respectively. The microstructure of Sn-3.5Ag-0.7Cu/Cu is examined by Optical Microscope (OM), Scanning Electron Microscope (SEM) and Energy Dispersive Spectra (EDS). The results show that the impressing creep depth increases with the rise of temperature and punching stress. Creep resistance of the diffusion region has obvious effect on the creep resistance of the weld. The experimental results can provide the basis for the structural integrity analysis of brazed joints
Teaching Tip: What You Need to Know about Gamification Process of Cybersecurity Hands-on Lab Exercises: Lessons and Challenges
Cybersecurity education is becoming increasingly important in modern society, and hands-on practice is an essential element. Although instructors provide hands-on labs in their cybersecurity courses, traditional lab exercises often fail to effectively motivate students. Hence, many instructors desire to incorporate gamification in hands-on training to engage and motivate cybersecurity students, especially beginner learners. Given the dearth of guiding examples, this paper aims to describe the holistic process of converting traditional cybersecurity hands-on lab exercises to gamified lab exercises in an undergraduate network security course. We find that the gamified cybersecurity lab promotes students’ engagement, learning experience, and learning outcomes. The results show the positive acceptance of gamification by students as well as instructors. While gamification has been used in competitions and training, the success in the classroom and students’ desire for more gamification show that further investment in gamification will be more important in the classroom. We expect this paper to help instructors who are interested in gamification 1) convert traditional lab exercises to gamified labs; 2) estimate the extra workload and potential benefits; and 3) plan resources for implementation. This process is applicable to any cybersecurity courses with hands-on assignments
Optimal unstirred state of a passive scalar
This work was supported by Leverhulme Trust grant PRG-2017-169.Given a passive tracer distribution, what is the simplest unstirred pattern that may be reached under incompressible advection? This question is partially motivated by recent studies of three-dimensional (3-D) magnetic reconnection, in which the patterns of a topological invariant called the field line helicity greatly simplify until reaching a relaxed state. We test two approaches: a variational method with minimal constraints, and a magnetic relaxation scheme where the velocity is determined explicitly by the pattern of. Both methods achieve similar convergence for simple test cases. However, the magnetic relaxation method guarantees a monotonic decrease in the Dirichlet seminorm of, and is numerically more robust. We therefore apply the latter method to two complex mixed patterns modelled on the field line helicity of 3-D magnetic braids. The unstirring separates into a small number of large-scale regions determined by the initial topology, which is well preserved during the computation. Interestingly, the velocity field is found to have the same large-scale topology as. Similarity to the simplification found empirically in 3-D magnetic reconnection simulations supports the idea that advection is an important principle for field line helicity evolution.Publisher PDFPeer reviewe
Metamaterials proposed as perfect magnetoelectrics
Magnetoelectric susceptibility of a metamaterial built from split ring
resonators have been investigated both experimentally and within an equivalent
circuit model. The absolute values have been shown to exceed by two orders of
magnitude that of classical magnetoelectric materials. The metamaterial
investigated reaches the theoretically predicted value of the magnetoelectric
susceptibility which is equal to the geometric average of the electric and
magnetic susceptibilities.Comment: 5 pages, 3 figure
Qcompiler: quantum compilation with CSD method
In this paper, we present a general quantum computation compiler, which maps
any given quantum algorithm to a quantum circuit consisting a sequential set of
elementary quantum logic gates based on recursive cosine-sine decomposition.
The resulting quantum circuit diagram is provided by directly linking the
package output written in LaTex to Qcircuit.tex
. We illustrate the use of the Qcompiler
package through various examples with full details of the derived quantum
circuits. Besides its generality and simplicity, Qcompiler produces quantum
circuits which reflect the symmetry of the systems under study
Roper Resonance and S_{11}(1535) from Lattice QCD
Using the constrained curve fitting method and overlap fermions with the
lowest pion mass at , we observe that the masses of the first
positive and negative parity excited states of the nucleon tend to cross over
as the quark masses are taken to the chiral limit. Both results at the physical
pion mass agree with the experimental values of the Roper resonance
() and (). This is seen for the first
time in a lattice QCD calculation. These results are obtained on a quenched
Iwasaki lattice with . We also extract the
ghost states (a quenched artifact) which are shown to decouple from
the nucleon interpolation field above . From the
quark mass dependence of these states in the chiral region, we conclude that
spontaneously broken chiral symmetry dictates the dynamics of light quarks in
the nucleon.Comment: 10 pages, 5 figures, revised version to appear in PL
Hawking radiation of scalar particles from accelerating and rotating black holes
Hawking radiation of uncharged and charged scalars from accelerating and
rotating black holes is studied. We calculate the tunneling probabilities of
these particles from the rotation and acceleration horizons of these black
holes. Using the tunneling method we recover the correct Hawking temperature as
well
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