486 research outputs found
Elementary operations for quantum logic with a single trapped two-level cold ion beyond Lamb-Dicke limit
A simple alternative scheme for implementing quantum gates with a single
trapped cold two-level ion beyond the Lamb-Dicke (LD) limit is proposed. Basing
on the quantum dynamics for the laser-ion interaction described by a
generalized Jaynes-Cummings model, one can introduce two kinds of elementary
quantum operations i.e., the simple rotation on the bare atomic state,
generated by applying a resonant pulse, and the joint operation on the internal
and external degrees of the ion, performed by using an off-resonant pulse.
Several typical quantum gates, including Hadamard gate, controlled-Z and
controlled-NOT gates , can thus be implemented exactly by using these
elementary operations. The experimental parameters including the LD parameter
and the durations of the applied laser pulses, for these implementation are
derived analytically and numerically. Neither the LD approximation for the
laser-ion interaction nor the auxiliary atomic level is needed in the present
scheme.Comment: 5 pages, no figure, to appear in Opt. Com
Effect of Pin Diameters on the Wear Characteristics of Friction Pairs
The tribological tests are carried out to assess the effect of pin diameters on wear characteristics via changing contact stresses and sliding speeds to provide support for choosing friction pair sizes. The friction couple is set as CuZn pins for medium carbon steel (No. 1045 steel) rings. The differential wear rate and its calculation formula are defined to express the line wear rate or the wear resistance of unit cross-section area. The effect of the pin end surface diameter on differential wear rate and its scale/increased multiplier are investigated. When the product (P×V=0.095) is kept constant, the abrasion loss for the specimens of a small diameter (d1=0.6 mm) is lesser than that of the specimens of a large diameter (d2=4.0 mm). As compared to the sliding speed, the change in contact stresses exerts a greater influence on the wear behavior, especially for small-diameter specimens. The differential wear rate of small-diameter specimens is always higher than that of the specimens of a large diameter. The scale multiplier of the differential wear rate is always larger than that of the contact pressure stress, especially for small-diameter specimens.С целью обоснования выбора размеров пар трения проводятся трибологические испытания по оценке влияния диаметров штифта на характеристики износа путем изменения нагрузок и скорости скольжения. Пара трения представляется в виде штифтов из CuZn к кольцам из среднеуглеродистой стали (сталь 1045). Дифференциальная скорость изнашивания и формула для ее расчета определяются для выражения линейной скорости изнашивания или сопротивления износу единицы площади поперечного сечения. Исследуются влияние различного диаметра торцевой поверхности штифтов, дифференциальная скорость изнашивания и ее увеличенный множитель. Результаты показывают, что при поддержании постоянства произведения P×V=0,095 потери при истирании образцов малого диаметра (d1=0,6 мм) меньше, чем образцов большого диаметра (d2 =4,0 мм). По сравнению со скоростью скольжения изменение нагрузки более существенно влияет на характеристики износа, особенно для образцов малого диаметра. Дифференциальная скорость изнашивания образцов малого диаметра всегда больше, чем образцов большого диаметра. Увеличенный множитель дифференциальной скорости изнашивания всегда превышает увеличенный множитель повышения напряжения контактного давления, особенно для образцов малого диаметра.З метою обґрунтування вибору розмірів пар тертя проводяться трибологичні випробування з оцінки впливу діаметрів штифта на характеристики зносу шляхом зміни навантажень і швидкості ковзання. Пара тертя представляється у вигляді штифтів з СuZn до кілець з середньовуглецевої сталі (сталь 1045). Диференціальна швидкість зношування і формула для її розрахунку визначаються для вираження лінійної швидкості зношування або опору зносу одиниці площі поперечного перерізу. Досліджуються вплив різного діаметру торцевої поверхні штифтів, диференціальна швидкість зношування і її збільшений множник. Результати показують, що при підтримці сталості Р x V = 0,095 втрати при стиранні зразків малого діаметра (d1 = 0,6 мм) менше, ніж зразків великого діаметра (d2 = 4,0 мм). У порівнянні зі швидкістю ковзання зміна навантаження більш істотно впливає на характеристики зносу, особливо для зразків малого діаметра. Диференціальна швидкість зношування зразків малого діаметра завжди більше, ніж зразків великого діаметру. Збільшений множник диференціальної швидкості зношування завжди перевищує збільшений множник підвищення напружень контактного тиску, особливо для зразків малого діаметра
Research on Rapidly Shaped Charge Cutting Technology of Aircraft Damaged Thin-Wall Structure
Shaped charge cutting technology has been introduced into the field of aircraft structure repair to rapidly reshape irregular holes in thin-walled structures. In the present research, numerical calculation of the dynamic cutting process by ANSYS and experiments of shaped charge cutting on a 2A12 aluminum alloy plate with 2 mm thickness have been carried out. It was found that fast kerf is smooth, producing a neat edge and good linearity. The incision fracture section is arranged in neat rows on a corrugated strip, and the lines are clear. Otherwise, the lower part is slightly messy without obvious distribution rules. The target plate separation method of cumulative cutting is a kind of “pre-penetration” and “late tear” method. The application of shaped charge cutting technology can aid in repair of aircrafts’ thin-walled structural damage
Magnetic reversal processes and critical thickness in FePt/{\alpha}-Fe/FePt trilayers
Magnetic reversal processes of a FePt/{\alpha}-Fe/FePt trilayer system with
in-plane easy axes have been investigated within a micromagnetic approach. It
is found that the magnetic reversal process consists of three steps: nucleation
of a prototype of domain wall in the soft phase, the evolution as well as the
motion of the domain wall from the soft to the hard phase and finally, the
magnetic reversal of the hard phase. For small soft layer thickness Ls, the
three steps are reduced to one single step, where the magnetizations in the two
phases reverse simultaneously and the hysteresis loops are square with
nucleation as the coercivity mechanism. As Ls increases, both nucleation and
pinning fields decrease. In the meantime, the single-step reversal expands to a
standard three-step one and the coercivity mechanism changes from nucleation to
pinning. The critical thickness where the coercivity mechanism alters, could be
derived analytically, which is found to be inversely proportional to the square
root of the crystalline anisotropy of the hard phase. Further increase of Ls
leads to the change of the coercivity mechanism from pinning to nucleation.Comment: 21 pages, 5 figures, pdf file, figures include
Fractional Quantum Hall Effect via Holography: Chern-Simons, Edge States, and Hierarchy
We present three holographic constructions of fractional quantum Hall effect
(FQHE) via string theory. The first model studies edge states in FQHE using
supersymmetric domain walls in N=6 Chern-Simons theory. We show that D4-branes
wrapped on CP^1 or D8-branes wrapped on CP^3 create edge states that shift the
rank or the level of the gauge group, respectively. These holographic edge
states correctly reproduce the Hall conductivity. The second model presents a
holographic dual to the pure U(N)_k (Yang-Mills-)Chern-Simons theory based on a
D3-D7 system. Its holography is equivalent to the level-rank duality, which
enables us to compute the Hall conductivity and the topological entanglement
entropy. The third model introduces the first string theory embedding of
hierarchical FQHEs, using IIA string on C^2/Z_n.Comment: 36 pages, 6 figures; v2: with an improved derivation of Hall
conductivity in section 3.2, typo corrections, and additional references; v3:
explanations and comments adde
Probing interaction and spatial curvature in the holographic dark energy model
In this paper we place observational constraints on the interaction and
spatial curvature in the holographic dark energy model. We consider three kinds
of phenomenological interactions between holographic dark energy and matter,
i.e., the interaction term is proportional to the energy densities of dark
energy (), matter (), and matter plus dark energy
(). For probing the interaction and spatial curvature in
the holographic dark energy model, we use the latest observational data
including the type Ia supernovae (SNIa) Constitution data, the shift parameter
of the cosmic microwave background (CMB) given by the five-year Wilkinson
Microwave Anisotropy Probe (WMAP5) observations, and the baryon acoustic
oscillation (BAO) measurement from the Sloan Digital Sky Survey (SDSS). Our
results show that the interaction and spatial curvature in the holographic dark
energy model are both rather small. Besides, it is interesting to find that
there exists significant degeneracy between the phenomenological interaction
and the spatial curvature in the holographic dark energy model.Comment: 11 pages, 5 figures; to appear in JCA
Lepton flavor violation decays in the topcolor-assisted technicolor model and the littlest Higgs model with parity
The new particles predicted by the topcolor-assisted technicolor ()
model and the littlest Higgs model with T-parity (called model) can
induce the lepton flavor violation () couplings at tree level or one loop
level, which might generate large contributions to some processes. Taking
into account the constraints of the experimental data on the relevant free
parameters, we calculate the branching ratios of the decay processes
with = , and
in the context of these two kinds of new physics models. We find
that the model and the model can indeed produce significant
contributions to some of these decay processes.Comment: 24 pages, 7 figure
Direct Measurements of the Branching Fractions for and and Determinations of the Form Factors and
The absolute branching fractions for the decays and
are determined using singly
tagged sample from the data collected around 3.773 GeV with the
BES-II detector at the BEPC. In the system recoiling against the singly tagged
meson, events for and events for decays are observed. Those yield
the absolute branching fractions to be and . The
vector form factors are determined to be
and . The ratio of the two form
factors is measured to be .Comment: 6 pages, 5 figure
Measurements of J/psi Decays into 2(pi+pi-)eta and 3(pi+pi-)eta
Based on a sample of 5.8X 10^7 J/psi events taken with the BESII detector,
the branching fractions of J/psi--> 2(pi+pi-)eta and J/psi-->3(pi+pi-)eta are
measured for the first time to be (2.26+-0.08+-0.27)X10^{-3} and
(7.24+-0.96+-1.11)X10^{-4}, respectively.Comment: 11 pages, 6 figure
BESII Detector Simulation
A Monte Carlo program based on Geant3 has been developed for BESII detector
simulation. The organization of the program is outlined, and the digitization
procedure for simulating the response of various sub-detectors is described.
Comparisons with data show that the performance of the program is generally
satisfactory.Comment: 17 pages, 14 figures, uses elsart.cls, to be submitted to NIM
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