Quantum Cryptography II: How to re-use a one-time pad safely even if P=NP

When elementary quantum systems, such as polarized photons, are used to transmit digital information, the uncertainty principle gives rise to novel cryptographic phenomena unachievable with traditional transmission media, e.g. a communications channel on which it is impossible in principle to eavesdrop without a high probability of being detected. With such a channel, a one-time pad can safely be reused many times as long as no eavesdrop is detected, and, planning ahead, part of the capacity of these uncompromised transmissions can be used to send fresh random bits with which to replace the one-time pad when an eavesdrop finally is detected. Unlike other schemes for stretching a one-time pad, this scheme does not depend on complexity-theoretic assumptions such as the difficulty of factoring.Comment: Original 1982 submission to ACM Symposium on Theory of Computing with spelling and typographical corrections, and comments by the authors 32 years later. Submitted to Natural Computin

Effect of Sensory Feedback from the Proximal Upper Limb on Voluntary Isometric Finger Flexion and Extension in Hemiparetic Stroke Subjects

This study investigated the potential influence of proximal sensory feedback on voluntary distal motor activity in the paretic upper limb of hemiparetic stroke survivors and the potential effect of voluntary distal motor activity on proximal muscle activity. Ten stroke subjects and 10 neurologically intact control subjects performed maximum voluntary isometric flexion and extension, respectively, at the metacarpophalangeal (MCP) joints of the fingers in two static arm postures and under three conditions of electrical stimulation of the arm. The tasks were quantified in terms of maximum MCP torque [MCP flexion (MCPflex) or MCP extension (MCPext)] and activity of targeted (flexor digitorum superficialis or extensor digitorum communis) and nontargeted upper limb muscles. From a previous study on the MCP stretch reflex poststroke, we expected stroke subjects to exhibit a modulation of voluntary MCP torque production by arm posture and electrical stimulation and increased nontargeted muscle activity. Posture 1 (flexed elbow, neutral shoulder) led to greater MCPflex in stroke subjects than posture 2 (extended elbow, flexed shoulder). Electrical stimulation did not influence MCPflex or MCPext in either subject group. In stroke subjects, posture 1 led to greater nontargeted upper limb flexor activity during MCPflex and to greater elbow flexor and extensor activity during MCPext. Stroke subjects exhibited greater elbow flexor activity during MCPflex and greater elbow flexor and extensor activity during MCPext than control subjects. The results suggest that static arm posture can modulate voluntary distal motor activity and accompanying muscle activity in the paretic upper limb poststroke

From Classical State-Swapping to Quantum Teleportation

The quantum teleportation protocol is extracted directly out of a standard classical circuit that exchanges the states of two qubits using only controlled-NOT gates. This construction of teleportation from a classically transparent circuit generalizes straightforwardly to d-state systems.Comment: Missing daggers added to Figures 13, 14, and 15. Otherwise this is the version that appeared in Physical Revie

Strengths and Weaknesses of Quantum Computing

Recently a great deal of attention has focused on quantum computation following a sequence of results suggesting that quantum computers are more powerful than classical probabilistic computers. Following Shor's result that factoring and the extraction of discrete logarithms are both solvable in quantum polynomial time, it is natural to ask whether all of NP can be efficiently solved in quantum polynomial time. In this paper, we address this question by proving that relative to an oracle chosen uniformly at random, with probability 1, the class NP cannot be solved on a quantum Turing machine in time $o(2^{n/2})$. We also show that relative to a permutation oracle chosen uniformly at random, with probability 1, the class $NP \cap coNP$ cannot be solved on a quantum Turing machine in time $o(2^{n/3})$. The former bound is tight since recent work of Grover shows how to accept the class NP relative to any oracle on a quantum computer in time $O(2^{n/2})$.Comment: 18 pages, latex, no figures, to appear in SIAM Journal on Computing (special issue on quantum computing

Early onset preeclampsia is characterized by altered placental lipid metabolism and a premature increase in circulating FABP4

Preeclampsia is a pregnancy-associated disorder that manifests as a sudden increase in maternal blood pressure accompanied by proteinuria. Because the placenta is a key organ in preeclampsia, we used proteomic and lipidomic analyses to compare placentae from preeclamptic and gestational age matched control pregnancies. Fatty acid binding protein 4 (FABP4), enoyl-CoA dehydrogenase and delta-3,5-delta-2,4-dienoyl-CoA isomerase had altered abundance in preeclamptic placentae compared to controls. FABP4 placental protein and RNA and plasma levels were all increased in early-onset preeclampsia (prior to 28 weeks gestation) compared to controls (6-fold, 3.3-fold and 3.5-fold respectively). After 28 weeks, FABP4 protein in control placenta and plasma increased to the same concentrations as in preeclampsia. Total tetracosapentaenoic acid in preeclamptic placentae was decreased to 0.6 of control levels before 28 weeks. The data indicate a disruption of fatty acid transport and metabolism in the placenta in early onset preeclampsia that is reflected in the maternal plasma

Towards An Optimal Level Of Participation Of The Intermediary In The User-system Interface Of Bibliographic Online Search Services

The present research project focuses on the user/system interface of on-line bibliographic search services and more specifically on the role of the human intermediary in the context of on-line searching. A quasi-experimental study was designed with 34 end-users and 22 intermediaries who performed 102 online searches in 6 different organizations (3 academic and 3 special libraries). Each end-user was given a one-day training session and then prepared three different search questions. An on-line search was performed for each question: one direct search (the end-user alone), one delegated search (the intermediary alone) and one combined search (the end-user and intermediary together).;Numerous characteristics of end-users, intermediaries and search questions were assessed. Nine outcome measures were recorded from evaluation questionnaires, printouts and output citations assessed for relevance. Results can be summarized as follows: The direct mode was found superior for total search time, overall user satisfaction and three specific satisfaction measures (number of citations, search mode, search utility), search efficiency, cost effectiveness, cost efficiency and search effort. The delegated mode showed best results on total search cost, connect time, connect cost, search effectiveness and searching efficiency. Finally, the combined mode was best for user satisfaction with the relevance of citations retrieved, and search utility.;Discriminant functions were computed to predict the search mode which would optimize each of the nine performance measures. The best predictor variables were: end-user\u27s age, one specific search purpose (e.g. preparing a class project or term paper), the previous use of secondary journals (indexes or abstracts) by end-users, the previous use of the search service center by end-users, and end-users\u27 experience (level) with online searching