Detection of non-Gaussian Fluctuations in a Quantum Point Contact

An experimental study of current fluctuations through a tunable transmission barrier, a quantum point contact, are reported. We measure the probability distribution function of transmitted charge with precision sufficient to extract the first three cumulants. To obtain the intrinsic quantities, corresponding to voltage-biased barrier, we employ a procedure that accounts for the response of the external circuit and the amplifier. The third cumulant, obtained with a high precision, is found to agree with the prediction for the statistics of transport in the non-Poissonian regime.Comment: 4 pages, 4 figures; published versio

Symmetric photon-photon coupling by atoms with Zeeman-split sublevels

We propose a simple scheme for highly efficient nonlinear interaction between two weak optical fields. The scheme is based on the attainment of electromagnetically induced transparency simultaneously for both fields via transitions between magnetically split F=1 atomic sublevels, in the presence of two driving fields. Thereby, equal slow group velocities and symmetric cross-coupling of the weak fields over long distances are achieved. By simply tuning the fields, this scheme can either yield giant cross-phase modulation or ultrasensitive two-photon switching.Comment: Modified scheme, 4 pages, 1 figur

Photon-photon correlations and entanglement in doped photonic crystals

We consider a photonic crystal (PC) doped with four-level atoms whose intermediate transition is coupled near-resonantly with a photonic band-gap edge. We show that two photons, each coupled to a different atomic transition in such atoms, can manifest strong phase or amplitude correlations: One photon can induce a large phase shift on the other photon or trigger its absorption and thus operate as an ultrasensitive nonlinear photon-switch. These features allow the creation of entangled two-photon states and have unique advantages over previously considered media: (i) no control lasers are needed; (ii) the system parameters can be chosen to cause full two-photon entanglement via absorption; (iii) a number of PCs can be combined in a network.Comment: Modified, expanded text; added reference

Whole lifespan microscopic observation of budding yeast aging through a microfluidic dissection platform

Important insights into aging have been generated with the genetically tractable and short-lived budding yeast. However, it is still impossible today to continuously track cells by high-resolution microscopic imaging (e.g., fluorescent imaging) throughout their entire lifespan. Instead, the field still needs to rely on a 50-y-old laborious and time-consuming method to assess the lifespan of yeast cells and to isolate differentially aged cells for microscopic snapshots via manual dissection of daughter cells from the larger mother cell. Here, we are unique in achieving continuous and high-resolution microscopic imaging of the entire replicative lifespan of single yeast cells. Our microfluidic dissection platform features an optically prealigned single focal plane and an integrated array of soft elastomer-based micropads, used together to allow for trapping of mother cells, removal of daughter cells, monitoring gradual changes in aging, and unprecedented microscopic imaging of the whole aging process. Using the platform, we found remarkable age-associated changes in phenotypes (e.g., that cells can show strikingly differential cell and vacuole morphologies at the moment of their deaths), indicating substantial heterogeneity in cell aging and death. We envision the microfluidic dissection platform to become a major tool in aging research.

Broadband optical gain via interference in the free electron laser: principles and proposed realizations

We propose experimentally simplified schemes of an optically dispersive interface region between two coupled free electron lasers (FELs), aimed at achieving a much broader gain bandwidth than in a conventional FEL or a conventional optical klystron composed of two separated FELs. The proposed schemes can {\it universally} enhance the gain of FELs, regardless of their design when operated in the short pulsed regime

Gravitational instantons and black plane solutions in 4-d string theory

We consider gauged Wess-Zumino models based on the non compact group $SU(2,1)$. It is shown that by vector gauging the maximal compact subgroup $U(2)$ the resulting backgrounds obey the gravity-dilaton one loop string vacuum equations of motion in four dimensional euclidean space. The torsionless solution is then interpreted as a pseudo-instanton of the $d=4$ Liouville theory coupled to gravity. The presence of a traslational isometry in the model allows to get another string vacuum backgrounds by using target duality that we identify with those corresponding to the axial gauging. We also compute the exact backgrounds. Depending on the value of $k$, they may be interpreted as instantons connecting a highly singular big bang like universe with a static singular or regular black plane geometry.Comment: 29 page

Current-Current Deformations of Conformal Field Theories, and WZW Models

Moduli spaces of conformal field theories corresponding to current-current deformations are discussed. For WZW models, CFT and sigma model considerations are compared. It is shown that current-current deformed WZW models have WZW-like sigma model descriptions with non-bi-invariant metrics, additional B-fields and a non-trivial dilaton.Comment: 30 pages, latex, v2: remarks and references adde

Averages of b-hadron Properties at the End of 2005

This article reports world averages for measurements on b-hadron properties obtained by the Heavy Flavor Averaging Group (HFAG) using the available results as of at the end of 2005. In the averaging, the input parameters used in the various analyses are adjusted (rescaled) to common values, and all known correlations are taken into account. The averages include lifetimes, neutral meson mixing parameters, parameters of semileptonic decays, branching fractions of B meson decays to final states with open charm, charmonium and no charm, and measurements related to CP asymmetries

A Conformal Field Theory of a Rotating Dyon

A conformal field theory representing a four-dimensional classical solution of heterotic string theory is presented. The low-energy limit of this solution has U(1) electric and magnetic charges, and also nontrivial axion and dilaton fields. The low-energy metric contains mass, NUT and rotation parameters. We demonstrate that this solution corresponds to part of an extremal limit of the Kerr-Taub-NUT dyon solution. This limit displays interesting `remnant' behaviour, in that asymptotically far away from the dyon the angular momentum vanishes, but far down the infinite throat in the neighbourhood of the horizon (described by our CFT) there is a non-zero angular velocity. A further natural generalization of the CFT to include an additional parameter is presented, but the full physical interpretation of its role in the resulting low energy solution is unclear.Comment: 43 pages, Plain TEX + epsf.tex for one uuencoded figure

Cohesion, team mental models, and collective efficacy: Towards an integrated framework of team dynamics in sport

A nomological network on team dynamics in sports consisting of a multi-framework perspective is introduced and tested. The aim was to explore the interrelationship among cohesion, team mental models (TMM), collective-efficacy (CE), and perceived performance potential (PPP). Three hundred and forty college-aged soccer players representing 17 different teams (8 female and 9 male) participated in the study. They responded to surveys on team cohesion, TMM, CE and PPP. Results are congruent with the theoretical conceptualization of a parsimonious view of team dynamics in sports. Specifically, cohesion was found to be an exogenous variable predicting both TMM and CE beliefs. TMM and CE were correlated and predicted PPP, which in turn accounted for 59% of the variance of objective performance scores as measured by teams’ season record. From a theoretical standpoint, findings resulted in a parsimonious view of team dynamics, which may represent an initial step towards clarifying the epistemological roots and nomological network of various team-level properties. From an applied standpoint, results suggest that team expertise starts with the establishment of team cohesion. Following the establishment of cohesiveness, teammates are able to advance team-related schemas and a collective sense of confidence. Limitations and key directions for future research are outlined