21,870 research outputs found
Optimal Capacitive Load Matching of Micro Electret Power Generators
This paper presents a model of micro-electret power generators. This model uses two capacitors with fixed charge density and variable area to model the actual micro electret power generator. Simulations of power output with capacitive loads and resistive loads are presented. The power output decreases as the load capacitance increases while it increases as the resistive load increases. To verify the model and simulation results, power output generation experiments are performed and the results confirm the simulation. To collect useful energy from the power generator, a small capacitive load, rather than a resistive load, is required
Field-induced structure transformation in electrorheological solids
We have computed the local electric field in a body-centered tetragonal (BCT)
lattice of point dipoles via the Ewald-Kornfeld formulation, in an attempt to
examine the effects of a structure transformation on the local field strength.
For the ground state of an electrorheological solid of hard spheres, we
identified a novel structure transformation from the BCT to the face-centered
cubic (FCC) lattices by changing the uniaxial lattice constant c under the hard
sphere constraint. In contrast to the previous results, the local field
exhibits a non-monotonic transition from BCT to FCC. As c increases from the
BCT ground state, the local field initially decreases rapidly towards the
isotropic value at the body-centered cubic lattice, decreases further, reaching
a minimum value and increases, passing through the isotropic value again at an
intermediate lattice, reaches a maximum value and finally decreases to the FCC
value. An experimental realization of the structure transformation is
suggested. Moreover, the change in the local field can lead to a generalized
Clausius-Mossotti equation for the BCT lattices.Comment: Submitted to Phys. Rev.
Simple Proof of Security of the BB84 Quantum Key Distribution Protocol
We prove the security of the 1984 protocol of Bennett and Brassard (BB84) for
quantum key distribution. We first give a key distribution protocol based on
entanglement purification, which can be proven secure using methods from Lo and
Chau's proof of security for a similar protocol. We then show that the security
of this protocol implies the security of BB84. The entanglement-purification
based protocol uses Calderbank-Shor-Steane (CSS) codes, and properties of these
codes are used to remove the use of quantum computation from the Lo-Chau
protocol.Comment: 5 pages, Latex, minor changes to improve clarity and fix typo
A simple proof of the unconditional security of quantum key distribution
Quantum key distribution is the most well-known application of quantum
cryptography. Previous proposed proofs of security of quantum key distribution
contain various technical subtleties. Here, a conceptually simpler proof of
security of quantum key distribution is presented. The new insight is the
invariance of the error rate of a teleportation channel: We show that the error
rate of a teleportation channel is independent of the signals being
transmitted. This is because the non-trivial error patterns are permuted under
teleportation. This new insight is combined with the recently proposed quantum
to classical reduction theorem. Our result shows that assuming that Alice and
Bob have fault-tolerant quantum computers, quantum key distribution can be made
unconditionally secure over arbitrarily long distances even against the most
general type of eavesdropping attacks and in the presence of all types of
noises.Comment: 13 pages, extended abstract. Comments will be appreciate
Security proof of a three-state quantum key distribution protocol without rotational symmetry
Standard security proofs of quantum key distribution (QKD) protocols often
rely on symmetry arguments. In this paper, we prove the security of a
three-state protocol that does not possess rotational symmetry. The three-state
QKD protocol we consider involves three qubit states, where the first two
states, |0_z> and |1_z>, can contribute to key generation and the third state,
|+>=(|0_z>+|1_z>)/\sqrt{2}, is for channel estimation. This protocol has been
proposed and implemented experimentally in some frequency-based QKD systems
where the three states can be prepared easily. Thus, by founding on the
security of this three-state protocol, we prove that these QKD schemes are, in
fact, unconditionally secure against any attacks allowed by quantum mechanics.
The main task in our proof is to upper bound the phase error rate of the qubits
given the bit error rates observed. Unconditional security can then be proved
not only for the ideal case of a single-photon source and perfect detectors,
but also for the realistic case of a phase-randomized weak coherent light
source and imperfect threshold detectors. Our result on the phase error rate
upper bound is independent of the loss in the channel. Also, we compare the
three-state protocol with the BB84 protocol. For the single-photon source case,
our result proves that the BB84 protocol strictly tolerates a higher quantum
bit error rate than the three-state protocol; while for the coherent-source
case, the BB84 protocol achieves a higher key generation rate and secure
distance than the three-state protocol when a decoy-state method is used.Comment: 10 pages, 3 figures, 2 column
Similarity transformations approach for a generalized Fokker-Planck equation
By using similarity transformations approach, the exact propagator for a
generalized one-dimensional Fokker-Planck equation, with linear drift force and
space-time dependent diffusion coefficient, is obtained. The method is simple
and enables us to recover and generalize special cases studied through the Lie
algebraic approach and the Green function technique.Comment: 8 pages, no figure
KINEMATICS OF UPPER LIMB AND TRUNK IN TENNIS PLAYERS USING SINGLE HANDED BACKHAND STROKES
INTRODUCTION: Tennis injuries caused by improper drives or overuse of the upper limb are very common in tennis. They may be prevented by using correct movement patterns. The purpose of this study was to analyze the threedimensional kinematics of the upper limb and trunk associated with performances of the single-handed backhand tennis stroke.
METHODS: Six male national representatives performed tennis single-handed backhand drives in the laboratory. Sixteen reflective markers were placed on the subjects to represent the movements of the upper limb and trunk. They included one each on processus xiphoideus, incisura jugularis, 7th cervical vertebra, acromion, medialis and lateralis epicondylus, ulnar and radial styloid process, 2nd and 4th metacarpal heads, two anterior superior illiac spine and posterior superior illiac spine, and a triad markers on the upper limb. The markers’ positions were collected with the ExpertVision motion analysis system (Motion Analysis Corp., Santa Rosa, CA, USA) in order to estimate the joint movements of the shoulder, elbow, and wrist joints and the trunk. Ten trials were sampled for each subject. Eulerian angles were used to represent joint kinematics.
RESULTS: The joint movements of the upper limbs were consistent while performing the tennis single-handed backhand stroke. The angular velocities of the clockwise rotation of the trunk and ulnar deviation of the wrist reached the maximum values at the middle acceleration phase and then decreased. In addition, the angular velocities of the shoulder external rotation, elbow flexion and wrist extension reached maximum values in the instant subsequent to impact. The results showed that the major movements of the shoulder joint were abduction/adduction (73.6±11.5°), flexion/extension (45.7±20.2°), and internal/external rotation (46.3±13.7°). The major movements of the elbow joint were pronation/supination (71.2±20.8°), and flexion/extension (35.3±14.4°). The results provide basic guidelines for tennis training and tennis evaluation. It is also helpful for the physician and therapist to assist in the diagnosis of sports injuries and to plan clinical treatment.
CONCLUSIONS: In the acceleration phase, the trunk moves with the racket to increase angular momentum for the preparation of the impact. During this period, the movement of the shoulder is small. When the maximum angular velocities of the shoulder external rotation, elbow flexion and wrist extension occur in the instant prior to impact, they then immediately decrease. In this way, the hyperextension of the wrist joint, the cause of tennis elbow, may be prevented. The stability of the elbow joint and forearm is maintained by the contraction of the biceps and triceps
On bit-commitment based quantum coin flipping
In this paper, we focus on a special framework for quantum coin flipping
protocols,_bit-commitment based protocols_, within which almost all known
protocols fit. We show a lower bound of 1/16 for the bias in any such protocol.
We also analyse a sequence of multi-round protocol that tries to overcome the
drawbacks of the previously proposed protocols, in order to lower the bias. We
show an intricate cheating strategy for this sequence, which leads to a bias of
1/4. This indicates that a bias of 1/4 might be optimal in such protocols, and
also demonstrates that a cleverer proof technique may be required to show this
optimality.Comment: The lower bound shown in this paper is superceded by a result of
Kitaev (personal communication, 2001
Intrabodies Binding the Proline-Rich Domains of Mutant Huntingtin Increase Its Turnover and Reduce Neurotoxicity
Although expanded polyglutamine (polyQ) repeats are inherently toxic, causing at least nine neurodegenerative diseases, the protein context determines which neurons are affected. The polyQ expansion that causes Huntington's disease (HD) is in the first exon (HDx-1) of huntingtin (Htt). However, other parts of the protein, including the 17 N-terminal amino acids and two proline (polyP) repeat domains, regulate the toxicity of mutant Htt. The role of the P-rich domain that is flanked by the polyP domains has not been explored. Using highly specific intracellular antibodies (intrabodies), we tested various epitopes for their roles in HDx-1 toxicity, aggregation, localization, and turnover. Three domains in the P-rich region (PRR) of HDx-1 are defined by intrabodies: MW7 binds the two polyP domains, and Happ1 and Happ3, two new intrabodies, bind the unique, P-rich epitope located between the two polyP epitopes. We find that the PRR-binding intrabodies, as well as VL12.3, which binds the N-terminal 17 aa, decrease the toxicity and aggregation of HDx-1, but they do so by different mechanisms. The PRR-binding intrabodies have no effect on Htt localization, but they cause a significant increase in the turnover rate of mutant Htt, which VL12.3 does not change. In contrast, expression of VL12.3 increases nuclear Htt. We propose that the PRR of mutant Htt regulates its stability, and that compromising this pathogenic epitope by intrabody binding represents a novel therapeutic strategy for treating HD. We also note that intrabody binding represents a powerful tool for determining the function of protein epitopes in living cells
Metallic behaviour of carrier-polarized C molecular layers: Experiment and Theory
Although C is a molecular crystal with a bandgap E of ~2.5 eV, we
show that E is strongly affected by injected charge. In sharp contrast to
the Coulomb blockade typical of quantum dots, E is {\it reduced} by the
Coulomb effects. The conductance of a thin C layer sandwiched between
metal (Al, Ag, Au, Mg and Pt) contacts is investigated. Excellent Ohmic
conductance is observed for Al electrodes protected with ultra-thin LiF layers.
First-principles calculations, Hubbard models etc., show that the energy gap of
C is dramatically reduced when electrons hop from C to
C.Comment: 4 PRL style pages, 2 figures. email: [email protected]
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