Path integration in relativistic quantum mechanics

The simple physics of a free particle reveals important features of the path-integral formulation of relativistic quantum theories. The exact quantum-mechanical propagator is calculated here for a particle described by the simple relativistic action proportional to its proper time. This propagator is nonvanishing outside the light cone, implying that spacelike trajectories must be included in the path integral. The propagator matches the WKB approximation to the corresponding configuration-space path integral far from the light cone; outside the light cone that approximation consists of the contribution from a single spacelike geodesic. This propagator also has the unusual property that its short-time limit does not coincide with the WKB approximation, making the construction of a concrete skeletonized version of the path integral more complicated than in nonrelativistic theory.Comment: 14 page

In vivo length oscillations of indirect flight muscles in the fruit fly Drosophila virilis

We have used high-speed video microscopy to measure in vivo length oscillations of the indirect flight muscles of the fruit fly Drosophila virilis during tethered flight. The changes in muscle strain were measured by tracking the deformation of the thoracic exoskeleton at the origin and insertion of both the dorsal longitudinal (DLM) and the dorsal ventral (DVM) muscles. The mean peak-to-peak strain amplitudes were found to be 3.5% for the DLMs and 3.3% for the DVMs, although the strain amplitude within individual cycles ranged from 2 to 5%. These values are consistent with the small number of previous measurements of indirect flight muscle strain in other insects, but almost an order of magnitude greater than the strain amplitudes used in most biophysical studies of skinned Drosophila fibers. The results suggest that serial compliance within this sarcomere would need to relieve approximately 70% of the total strain in order for individual crossbridges to remain attached throughout a complete contraction-extension cycle

Viscous vortical flow calculations over delta wings

Two approaches to calculate turbulent vortical flows over delta wing configurations are illustrated. The first is for a simple delta wing at low speeds using the boundary layer approximation to treat the effects of the secondary separation. The second is for the supersonic case of a generic fighter using the NASA Ames parabolized Navier/Stokes method. Test/theory comparisons are given in both cases

Error Free Perfect Secrecy Systems

Shannon's fundamental bound for perfect secrecy says that the entropy of the secret message cannot be larger than the entropy of the secret key initially shared by the sender and the legitimate receiver. Massey gave an information theoretic proof of this result, however this proof does not require independence of the key and ciphertext. By further assuming independence, we obtain a tighter lower bound, namely that the key entropy is not less than the logarithm of the message sample size in any cipher achieving perfect secrecy, even if the source distribution is fixed. The same bound also applies to the entropy of the ciphertext. The bounds still hold if the secret message has been compressed before encryption. This paper also illustrates that the lower bound only gives the minimum size of the pre-shared secret key. When a cipher system is used multiple times, this is no longer a reasonable measure for the portion of key consumed in each round. Instead, this paper proposes and justifies a new measure for key consumption rate. The existence of a fundamental tradeoff between the expected key consumption and the number of channel uses for conveying a ciphertext is shown. Optimal and nearly optimal secure codes are designed.Comment: Submitted to the IEEE Trans. Info. Theor

Analytical method for designing grating compensated dispersion-managed soliton systems

This paper was published in Journal of Optical Society of America B and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/abstract.cfm?URI=JOSAB-21-4-706. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law. © 2004 The Optical Society.Peer reviewedPublisher PD

Syntheses, Structures, and Photoluminescence of 1-D Lanthanide Coordination Polymers

Five new lanthanide 1-D coordination polymers are reported which are formed from flexible salen type Schiff-base ligands H(2)L and H(2)L' (H(2)L = N, N(1)-ethylene bis(salicylideneimine); H(2)L' = N,N(1)-bis(3-methoxysalicylidene) ethylene-1,2-diamine). The polymeric structures are formed by bridging neutral H(2)L units in the case of {[Ln(2)L(2)(CF(3)SO(3))(H(2)L)(4)(MeOH)]center dot CF(3)SO(3)}(n) (Ln = Eu (1), Nd (2) and Er (3)), and by acetate (OAc(-)) groups in [Yb(2)(L)(2)(OAc)(2)(MeOH)(2)](n) (4) and {[Tb(3)(L')(2)(OAc)(5)]center dot Et(2)O center dot(MeOH)(0.5)}(n) (5). The structures of 1-5 were determined by single crystal X-ray crystallographic studies and the luminescence properties of 1 and 5 in MeOH solution were determined.ong Kong Baptist University FRG/06-07/II-16Hong Kong Research Grants Council HKBU 202407Robert A. Welch Foundation F-816Texas Higher Education Coordinating Board ARP 003658-0010-2006Petroleum Research FundAmerican Chemical Society 47014-AC5Chemistr

Time Domain Studies of X-ray Shot Noise in Cygnus X-1

We investigate the variability of Cygnus X-1 in the context of shot moise models, and employ a peak detection algorithm to select individual shots. For a long observation of the low, hard state, the distribution of time intervals between shots is found to be consistent with a purely random process, contrary to previous claims in the literature. The detected shots are fit to several model templates and found to have a broad range of shapes. The fitted shots have a distribution of timescales from below 10 milliseconds to above 1 second. The coherence of the cross spectrum of light curves of these data in different energy bands is also studied. The observed high coherence implies that the transfer function between low and high energy variability is uniform. The uniformity of the tranfer function implies that the observed distribution of shot widths cannot have been acquired through Compton scattering. Our results in combination with other results in the literature suggest that shot luminosities are correlated with one another. We discuss how our experimental methodology relates to non-linear models of variability.Comment: Accepted for publication in Astrophysical Journal on July 16, 200

Trade liberalization, employment flows, and wage inequality in Brazil

Using nationally representative, economywide data, this paper investigates the relative importance of trade-mandated effects on industry wage premia; industry and economywide skill premia; and employment flows in accounting for changes in the wage distribution in Brazil during the 1988-95 trade liberalization. Unlike in other Latin American countries, trade liberalization appears to have made a significant contribution toward a reduction in wage inequality. These effects have not occurred through changes in industry-specific (wage or skill) premia. Instead, they appear to have been channeled through substantial employment flows across sectors and formality categories. Changes in the economywide skill premium are also important.Economic Theory&Research,Free Trade,Labor Markets,Trade Policy,Trade Law

Distributed Concurrent Persistent Languages: An Experimental Design and Implementation

A universal persistent object store is a logical space of persistent objects whose localities span over machines reachable over networks. It provides a conceptual framework in which, on one hand, the distribution of data is transparent to application programmers and, on the other, store semantics of conventional languages is preserved. This means the manipulation of persistent objects on remote machines is both syntactically and semantically the same as in the case of local data. Consequently, many aspects of distributed programming in which computation tasks cooperate over different processors and different stores can be addressed within the confines of persistent programming. The work reported in this thesis is a logical generalization of the notion of persistence in the context of distribution. The concept of a universal persistent store is founded upon a universal addressing mechanism which augments existing addressing mechanisms. The universal addressing mechanism is realized based upon remote pointers which although containing more locality information than ordinary pointers, do not require architectural changes. Moreover, these remote pointers are transparent to the programmers. A language, Distributed PS-algol, is designed to experiment with this idea. The novel features of the language include: lightweight processes with a flavour of distribution, mutexes as the store-based synchronization primitive, and a remote procedure call mechanism as the message-based interprocess communication mechanism. Furthermore, the advantages of shared store programming and network architecture are obtained with the introduction of the programming concept of locality in an unobtrusive manner. A characteristic of the underlying addressing mechanism is that data are never copied to satisfy remote demands except where efficiency can be attained without compromising the semantics of data. A remote store operation model is described to effect remote updates. It is argued that such a choice is the most natural given that remote store operations resemble remote procedure calls

Cyclin F Is Degraded during G2-M by Mechanisms Fundamentally Different from Other Cyclins

Cyclin F, a cyclin that can form SCF complexes and bind to cyclin B, oscillates in the cell cycle with a pattern similar to cyclin A and cyclin B. Ectopic expression of cyclin F arrests the cell cycle in G2/M. How the level of cyclin F is regulated during the cell cycle is completely obscure. Here we show that, similar to cyclin A, cyclin F is degraded when the spindle assembly checkpoint is activated and accumulates when the DNA damage checkpoint is activated. Cyclin F is a very unstable protein throughout much of the cell cycle. Unlike other cyclins, degradation of cyclin F is independent of ubiquitination and proteasome-mediated pathways. Interestingly, proteolysis of cyclin F is likely to involve metalloproteases. Rapid destruction of cyclin F does not require the N-terminal F-box motif but requires the COOH-terminal PEST sequences. The PEST region alone is sufficient to interfere with the degradation of cyclin F and confer instability when fused to cyclin A. These data show that although cyclin F is degraded at similar time as the mitotic cyclins, the underlying mechanisms are entirely distinct