Bloch Equations and Completely Positive Maps

The phenomenological dissipation of the Bloch equations is reexamined in the context of completely positive maps. Such maps occur if the dissipation arises from a reduction of a unitary evolution of a system coupled to a reservoir. In such a case the reduced dynamics for the system alone will always yield completely positive maps of the density operator. We show that, for Markovian Bloch maps, the requirement of complete positivity imposes some Bloch inequalities on the phenomenological damping constants. For non-Markovian Bloch maps some kind of Bloch inequalities involving eigenvalues of the damping basis can be established as well. As an illustration of these general properties we use the depolarizing channel with white and colored stochastic noise.Comment: Talk given at the Conference "Quantum Challenges", Falenty, Poland, September 4-7, 2003. 21 pages, 3 figure

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Inequivalence of pure state ensembles for open quantum systems: the preferred ensembles are those that are physically realizable

An open quantum system in steady state $\hat\rho_{ss}$ can be represented by a weighted ensemble of pure states $\hat\rho_{ss}=\sum_{k}\wp_{k}\ket{\psi_k} \bra{\psi_k}$ in infinitely many ways. A physically realizable (PR) ensemble is one for which some continuous measurement of the environment will collapse the system into a pure state $\ket{\psi(t)}$, stochastically evolving such that the proportion of time for which $\ket{\psi(t)} = \ket{\psi_{k}}$ equals $\wp_{k}$. Some, but not all, ensembles are PR. This constitutes the preferred ensemble fact, with the PR ensembles being the preferred ensembles. We present the necessary and sufficient conditions for a given ensemble to be PR, and illustrate the method by showing that the coherent state ensemble is not PR for an atom laser.Comment: 5 pages, no figure

The Star Formation History of the Large Magellanic Cloud

Using WFPC2 aboard the Hubble Space Telescope, we have created deep color-magnitude diagrams in the V and I passbands for approximately 100,000 stars in a field at the center of the LMC bar and another in the disk. The main--sequence luminosity functions (LFs) from 19 mag < V < 23.5 mag, the red clump and horizontal branch morphologies, and the differential Hess diagram of the two fields all strongly imply that the disk and bar have significantly different star-formation histories (SFHs). The disk's SFH has been relatively smooth and continuous over the last 15 Gyr while the bar's SFH was dominated by star formation episodes at intermediate ages. Comparison of the LF against predictions based on Padova theoretical stellar evolution models and an assumed age-metallicity relationship allows us to identify the dominant stellar populations in the bar with episodes of star formation that occurred from 4 to 6 and 1 to 2 Gyr ago. These events accounted, respectively, for approximately 25% and 15% of its stellar mass. The disk field may share a mild enhancement in SF for the younger episode, and thus we identify the 4 to 6 Gyr episode with the formation of the LMC bar.Comment: 14 pages, 5 figures, Latex, also available at http://www.ps.uci.edu/physics/smeckerhane.html. Accepted for publication in Ap

Evaluation of routes to chiral core dendrimers

Dendrimers are macromolecules with a highly branched three-dimensional shape, produced in an iterative sequence of reaction steps, in which each reaction results in a new generation. Dendrimers have stimulated wide interest in the field of chemistry and biology, particularly with respect to applications to drug delivery and more recently imaging. They have also been of growing interest as macromolecular hosts, potential catalysts and have been attached to surfaces and polymeric materials, and have significant potential in new materials development. Dendrimers can have comparable molecular dimensions to some proteins and could potentially have internal microenvironments akin to the active site of an enzyme. Encapsulation within dendrimers has significant potential biomedical applications, whilst dendrimer surface behavior is of interest to evaluate interactions of dendrimer surface functionality (its most accessible region) with biological molecules. Exploiting many of these areas are dependent on generating chirality in dendrimers

A Study of the Persistence of Mycobacterium bovis in the Environment under Natural Weather Conditions in Michigan, USA

Reisolation of Mycobacterium bovis from inoculated substrates was used to follow the persistence of viable M. bovis bacteria exposed to natural weather conditions over a 12-month period. Environmental factors were recorded continuously, and factors affecting M. bovis persistence (i.e., temperature, season, and substrate) were studied using survival analysis and Cox's proportional hazards regression. Persistence of M. bovis in the environment was significantly shorter in the spring/summer season, characterized by the highest average daily temperatures over the 12-month period. M. bovis persisted up to 88 days in soil, 58 days in water and hay, and 43 days on corn. These studies demonstrate that M. bovis bacteria persist long enough to represent a risk of exposure for cattle and/or wildlife and strengthen evidence that suggests cattle farm biosecurity and efforts to eliminate supplemental feeding of white-tailed deer will decrease the risk of bovine TB transmission among and between cattle and deer populations

Restoration of Southern Ecosystems

Restoration of the myriad communities of bottomland hardwood and wetland forests and of the diverse communities of fire-dominated pine forests is the subject of intense interest in the Southern United States. Restoration practice is relatively advanced for bottomland hardwoods and longleaf pine (Pinus palustris Mill.), and less so for swamps and shortleaf pine (P. echinata Mill.). Most bottomland hardwood restoration is taking place on private land, while restoration of swamps and shortleaf pine occurs mostly on public land. Both public and private landowners are involved in the restoration of longleaf pine. Proper matching of species to site is critical to successful restoration of bottomland hardwoods. Techniques for longleaf pine restoration include the reintroduction of growing-season fire and the planting of longleaf pine seedlings and understory species. Safely reintroducing growing-season fire, however, may require initial manipulation of other vegetation by mechanical or chemical means to reduce built-up fuels

A reservoir for inverse power law decoherence of a qubit

The exact dynamics of a Jaynes-Cummings model for a qubit interacting with a continuous distribution of bosons, characterized by a special form of the spectral density, is evaluated analytically. The special reservoir is designed to induce anomalous decoherence, resulting in an inverse power law relaxation, of power 3/2, over an evaluated long time scale. If compared to the exponential-like relaxation obtained from the original Jaynes-Cummings model for Lorentzian-type spectral density functions, decoherence is strongly suppressed. The special reservoir exhibits an upper band edge frequency coinciding with the qubit transition frequency. Known theoretical models of photonic band gap media suitable for the realization of the designed reservoir are proposed.Comment: 5 pages, 2 figure

Long-term Survival Outcomes for Men Who Provided Ejaculate Specimens for Prostate Cancer Research: Implications for Patient Management

Background: Determining whether men diagnosed with early prostate cancer (PCa) will live long enough to benefit from interventions with curative intent is difficult. Although validated instruments for predicting patient survival are available, these do not have clinical utility so are not used routinely in practice. Objective: To test the hypothesis that volunteers who provided ejaculate specimens had a high survival rate at 10 and 15 yr and beyond. Design, setting, and participants: A total of 290 patients investigated because of high serum prostate-specific antigen donated ejaculate specimens for research between January 1992 and May 2003. The median age at the time of ejaculation was 63.5 yr. 153 of the donors were diagnosed with PCa and followed up to December 31, 2013. Outcome measurements and statistical analysis: Survival outcomes were compared with those for the whole population, as indicated by life expectancy tables up to 20 yr. Results and limitations: Men in the PCa group had life expectancies comparable with values listed in life expectancy tables for the whole population. Overall, PCa-specific and relative survival were significantly better for men in the non-PCa and PCa groups in comparison with men diagnosed with PCa in Queensland during the same period. Relative survival for those aged 20-49, 50-64, and ≥65 yr was >100% for ejaculate donors and 81.5%, 82.7%, and 65.2%, respectively, for the Queensland Cancer Registry reference at 10 yr. These findings for this highly selected patient cohort support the hypothesis that an ability to provide an ejaculate specimen is associated with a high likelihood of surviving 10-20 yr after donation, whether or not PCa was detected. Conclusion: Life expectancy tables may serve as a quick and simple life expectancy indicator for biopsy patients who donate ejaculate. Patient summary: Life expectancy tables indicated survival of up to 20 yr for men who provided ejaculate specimens for prostate cancer research. Life expectancy tables indicated survival of up to 20 yr for men who provided ejaculate specimens for prostate cancer research

Master equation for collective spontaneous emission with quantized atomic motion

We derive a markovian master equation for the internal dynamics of an ensemble of two-level atoms including all effects related to the quantization of their motion. Our equation provides a unifying picture of the consequences of recoil and indistinguishability of atoms beyond the Lamb-Dicke regime on both their dissipative and conservative dynamics, and applies equally well to distinguishable and indistinguishable atoms. We give general expressions for the decay rates and the dipole-dipole shifts for any motional states, and we find closed-form formulas for a number of relevant states (Gaussian states, Fock states and thermal states). In particular, we show that dipole-dipole interactions and cooperative photon emission can be modulated through the external state of motion.Comment: 16 pages, 7 figures, minor correction