1,552 research outputs found
Cost and price estimate of Brayton and Stirling engines in selected production volumes
The methods used to determine the production costs and required selling price of Brayton and Stirling engines modified for use in solar power conversion units are presented. Each engine part, component and assembly was examined and evaluated to determine the costs of its material and the method of manufacture based on specific annual production volumes. Cost estimates are presented for both the Stirling and Brayton engines in annual production volumes of 1,000, 25,000, 100,000 and 400,000. At annual production volumes above 50,000 units, the costs of both engines are similar, although the Stirling engine costs are somewhat lower. It is concluded that modifications to both the Brayton and Stirling engine designs could reduce the estimated costs
The reported use and effectiveness of Hypericum (St John’s wort) on affective symptoms in a depression self-help group
A recent meta-analysis suggested that Hypericum
perforatum (St John’s wort) is an effective
treatment for mild to moderate depression and
may have a superior side-effect profile to some
antidepressant drugs. The aim of this study was to
assess the use of herbal remedies in treating
depressive and anxiety symptoms, as reported by
members of the UK self-help organization
Depression Alliance using self-completed
questionnaires. More than 50% of the 452
respondents reported using Hypericum, onequarter
of whom also reported concurrent use of
traditional antidepressants. Most of the sample
reported sufficient symptoms for warranting a
diagnosis of major depression, with the majority
also describing symptoms suggestive of co-morbid
psychiatric conditions. One-half of the Hypericum
users experienced symptom improvement, which
for most occurred within the first 4 weeks of use.
Response was better for those with mild as
compared to severe symptoms and poorer for
those taking Hypericum alongside other
antidepressants. The responders were generally
older than non-responders. Adverse effects were
reported by one-quarter of users and were mostly
psychological in nature. This retrospective survey
indicated that use of herbal remedies was
common in this population. Although often helpful
in relieving symptoms, particularly in those with
mild depression, there is a risk of adverse events
and drug interaction
Theoretical investigation of electron-hole complexes in anisotropic two-dimensional materials
Trions and biexcitons in anisotropic two-dimensional materials are
investigated within an effective mass theory. Explicit results are obtained for
phosphorene and arsenene, materials that share features such as a direct
quasi-particle gap and anisotropic conduction and valence bands. Trions are
predicted to have remarkably high binding energies and an elongated
electron-hole structure with a preference for alignment along the armchair
direction, where the effective masses are lower. We find that biexciton binding
energies are also notably large, especially for monolayer phosphorene, where
they are found to be twice as large as those for typical monolayer transition
metal dichalcogenides.Comment: 3 figures, 5 pages + Supplementary Material, accepted for publication
in Phys. Rev.
Counterfactual Quantum Cryptography
Quantum cryptography allows one to distribute a secret key between two remote
parties using the fundamental principles of quantum mechanics. The well-known
established paradigm for the quantum key distribution relies on the actual
transmission of signal particle through a quantum channel. This paper shows
that the task of a secret key distribution can be accomplished even though a
particle carrying secret information is not in fact transmitted through the
quantum channel. The proposed protocols can be implemented with current
technologies and provide practical security advantages by eliminating the
possibility that an eavesdropper can directly access the entire quantum system
of each signal particle.Comment: 19 pages, 1 figure; a little ambiguity in the version 1 removed;
abstract, text, references, and appendix revised; suggestions and comments
are highly appreciate
Deuteron Momentum Distribution in KD2HPO4
The momentum distribution in KD2PO4(DKDP) has been measured using neutron
Compton scattering above and below the weakly first order
paraelectric-ferroelectric phase transition(T=229K). There is very litte
difference between the two distributions, and no sign of the coherence over two
locations for the proton observed in the paraelectric phase, as in KH2PO4(KDP).
We conclude that the tunnel splitting must be much less than 20mev. The width
of the distribution indicates that the effective potential for DKDP is
significantly softer than that for KDP. As electronic structure calculations
indicate that the stiffness of the potential increases with the size of the
coherent region locally undergoing soft mode fluctuations, we conclude that
there is a mass dependent quantum coherence length in both systems.Comment: 6 pages 5 figure
A deterministic cavity-QED source of polarization entangled photon pairs
We present two cavity quantum electrodynamics proposals that, sharing the
same basic elements, allow for the deterministic generation of entangled
photons pairs by means of a three-level atom successively coupled to two single
longitudinal mode high-Q optical resonators presenting polarization degeneracy.
In the faster proposal, the three-level atom yields a polarization entangled
photon pair via two truncated Rabi oscillations, whereas in the adiabatic
proposal a counterintuitive Stimulated Raman Adiabatic Passage process is
considered. Although slower than the former process, this second method is very
efficient and robust under fluctuations of the experimental parameters and,
particularly interesting, almost completely insensitive to atomic decay.Comment: 5 pages, 5 figure
Effects of detector efficiency mismatch on security of quantum cryptosystems
We suggest a type of attack on quantum cryptosystems that exploits variations
in detector efficiency as a function of a control parameter accessible to an
eavesdropper. With gated single-photon detectors, this control parameter can be
the timing of the incoming pulse. When the eavesdropper sends short pulses
using the appropriate timing so that the two gated detectors in Bob's setup
have different efficiencies, the security of quantum key distribution can be
compromised. Specifically, we show for the Bennett-Brassard 1984 (BB84)
protocol that if the efficiency mismatch between 0 and 1 detectors for some
value of the control parameter gets large enough (roughly 15:1 or larger), Eve
can construct a successful faked-states attack causing a quantum bit error rate
lower than 11%. We also derive a general security bound as a function of the
detector sensitivity mismatch for the BB84 protocol. Experimental data for two
different detectors are presented, and protection measures against this attack
are discussed.Comment: v3: identical to the journal version. However, after publication we
have discovered that Eq. 11 is incorrect: the available bit rate after
privacy amplification is reduced even in the case (QBER)=0 [see Quant. Inf.
Comp. 7, 73 (2007)
Cestodes in Four Species of Euryhaline Stingrays from Colombia
Seven species of cestodes are reported from coastal stingrays in the vicinity of Cartagena, Colombia, Acanthobothrium colombianum sp,n. from Aetobatis narinari resembles A . paulum and A. mathiasi but differs by having relatively shorter, more squared proglottids at the end of the strobila, a pre-equatorial genital pore, relatively less elongate ovarian lobes in terminal proglottids, and less prominent apical suckers and pads. Acanthobothrium urotrygoni sp.n. from Urotrygon venezuelae most closely resembles A . olseni in bothridial hook length but differs in cirrus sac size, resembles A. southwelli in cirrus sac size but differs in bothridial hook length, and differs from the former two and resembles A. lineatum by having a long and spinose cephalic peduncle; the new species differs from A, lineatum by possessing smaller bothridial hooks and cirrus sacs, Acanthobothrium cartagenensis sp.n, from UrolophliS jamaicensis most closely resembles A. llrolophi but differs in bothridial hook length, length of cirrus sac, number of testes and proglottids, and position of genital pore, Rhinebothrium magniphallum infected the new hosts Urolophus jamaicensis, Urotrygon veneZllelae , and Dasyatis americana in the new locality of Cartagena, Colombia. Phyllobothrium cf. kingae occurred in Dasyatis americana and Urolophus jamaicensis. Polypocephalus medusius and Lecanicephalum peltatum infected the new host Dasyatis americana . Cartagena is a new locality for both cestode species, A host-parasite checklist for cestodes collected from 121 stingrays examined in Colombia during 1975 and 1976 is presented
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