Optimal teleportation via thermal entangled states of a two-qubit Heisenberg Chain

We study the optimal teleportation based on Bell measurements via the thermal states of a two-qubit Heisenberg XXX chain in the presence of Dzyaloshinsky-Moriya (DM) anisotropic antisymmetric interaction and obtain the optimal unitary transformation. The explicit expressions of the output state and the teleportation fidelity are presented and compared with those of the standard protocol. It is shown that in this protocol the teleportation fidelity is always larger and unit fidelity is achieved at zero temperature. The DM interaction can enhance the teleportation fidelity at finite temperatures, as opposed to the effect of the interaction in the standard protocol. Cases with other types of anisotropies are also discussed.Comment: Accepted by EP

Various Correlations in Anisotropic Heisenberg XYZ Model with Dzyaloshinski-Moriya Interaction

Various thermal correlations as well as the effect of intrinsic decoherence on the correlations are studied in a two-qubit Heisenberg XYZ spin chain with the Dzyaloshinski--Moriya (DM) interaction along the z direction, i.e. Dz. It is found that tunable parameter Dz may play a constructive role on the concurrence (C), classical correlation (CC) and quantum discord (QD) in thermal equilibrium while it plays a destructive role on the correlations in the intrinsic decoherence case. The entanglement and quantum discord exhibit collapse and revival under the phase decoherence. With a proper combination of the system parameters, the correlations can effectively be kept at high steady state values despite the intrinsic decoherence.Comment: 4 pages, 4 figure

General approach of weak-to-strong measurement transition for Fock-state-based pointer states

The transition from von Neumann's projective strong measurement to Aharonov's weak measurement has recently received large attention, theoretical and experimental. In this work, we present a general approach to describe the weak-to-strong measurement transition for Fock-state-based pointer pointer states, and analyze in some details the case of coherent pointer states. A possible realization of our measurement scheme using trapped ions is also discussed.Comment: 12 pages,11 figure

High Pressure Effects on Superconductivity in the beta-pyrochlore Oxides AOs2O6 (A=K, Rb, Cs)

Recently new pyrochlore oxides superconductors AOs2O6 (A=K,Rb,Cs) were found and we measured the pressure dependence of magnetization up to 1.2 GPa in order to deduce the pressure effect of Tc in the three beta-pyrochlore oxides. It is found that the initial pressure dependence of Tc is positive for all the compounds. Only KOs2O6 exhibits a saturation in Tc at 0.56 GPa and the downturn at higher pressureComment: 7 pages, 2 figure

A Novel Puzzle-Based Framework for Mitigating Distributed Denial of Service Attacks Against Internet Applications

Cryptographic puzzles are promising techniques for mitigating DDoS attacks via decreasing the incoming rate of service eligible requests. However, existing cryptographic puzzle techniques have several shortcomings that make them less appealing as a tool of choice for DDoS defense. These shortcomings include: (1) the lack of accurate models for dynamically determining puzzle hardness; (2) the lack of an efficient and effective counter mechanism for puzzle solution replay attacks; and (3) the wastefulness of the puzzle computations in terms of the clients' computational resources. In this thesis, we provide a puzzle based DDoS defense framework that addresses these shortcomings. Our puzzle framework includes three novel puzzle mechanisms. The first mechanism, called Puzzle+, provides a mathematical model of per-request puzzle hardness. Through extensive experimental study, we show that this model optimizes the effectiveness of puzzle based DDoS mitigation while enabling tight control over the server utilization. In addition, Puzzle+ disables puzzle solution replay attacks by utilizing a novel cache algorithm to detect replays. The second puzzle mechanism, called Productive Puzzles, alleviates the wastefulness of computational puzzles by transforming the puzzle computations into computations of meaningful tasks that provide utility. Our third puzzle mechanism, called Guided Tour Puzzles, eliminates the wasteful puzzle computations all together, and adopts a novel delay-based puzzle construction idea. In addition, it is not affected by the disparity in the computational resources of the client machines that perform the puzzle computations. Through measurement analysis on real network testbeds as well as extensive simulation study, we show that both Productive Puzzles and Guided Tour Puzzles achieve effective mitigation of DDoS attacks while satisfying no wasteful computation requirement. Lastly, we introduce a novel queue management algorithm, called Stochastic Fair Drop Queue (SFDQ), to further strengthen the DDoS protection provided by the puzzle framework. SFDQ is not only effective against DDoS attacks at multiple layers of the protocol stack, it is also simple to configure and deploy. SFDQ is implemented over a novel data structure, called Indexed Linked List, to provide enqueue, dequeue, and remove operations with O(1) time complexity

Age-Related Changes in the Penile Reflex of Rats

The penile reflex in sexually experienced male rats aged 10 and 44 weeks was observed for 20 min following sheath retraction. All 7 males aged 10 weeks showed erections, cups arid flips, while of 5 males aged 44 weeks only 2 showed erections.Frequencies of the above behaviors in aged males were significantly lower than that in young males. The decrease of penile reflexes with aging was similar to that of copulatory behavior with aging, when paired with receptive females. The presentstudy is the first to clearly establish the pattern of penile reflexes in aged rats

Comparison of water consumption of three urban greening trees in a typical arid oasis citiy, northwest China

In order to ensure sustainable development of arid oasis cities, close attention must be paid to the rational use of limited water resources. Since urban vegetation is one important user of water, urban greening activities should be adapted to local environmental conditions. In this study, one native (Morus alba L.) and two introduced urban greening tree species (Fraxinus sogdiana Bunge and Platanus acerifolia Willd.) were selected in Aksu – a typical oasis city in northwest China. Their stem sap flow velocity (SFV) was determined and diel water consumption was calculated. In the meantime, meteorological variables were recorded to analyze the water consumption strategy of these tree species. The results show that the average SFV of M. alba, F. sogdiana and P. acerifolia were 4.1±0.3 cm h-1, 10.5±0.7 cm h-1 and 22.3±2.6 cm h-1, respectively. SFV was positively correlated with solar radiation (Rs), air temperature (Ta), vapor pressure deficit (VPD) and wind speed (Ws), and negatively correlated with air humidity (RH). Stepwise analysis showed that VPD had the highest impact on SFV of F. sogdiana (R²=0.987) and M. alba (R²=0.887), while the impact of RH was highest on P. acerifolia (R²=0.937). P. acerifolia had the highest sap flow daily accumulation (104±7 L tree-1), F. sogdiana was second (52±4 L tree-1), and third was M. alba (16±2 L tree-1). The water use efficiency (WUE) was M. alba (3.61 mmol mol-1) > F. sogdiana (3.33 mmol mol-1) > P. acerifolia (2.90 mmol mol-1). This study showed that native tree species developed certain adaptation strategies to the arid environment and thus consumed less water. Therefore, we recommend that in tree species selection by landscape planners as well as other decision makers, native tree species should be given priority in future urban greening projects