2,288 research outputs found
Optical nonlinear dynamics with cold atoms in a cavity
This paper presents the nonlinear dynamics of laser cooled and trapped cesium
atoms placed inside an optical cavity and interacting with a probe light beam
slightly detuned from the 6S1/2(F=4) to 6P3/2(F=5) transition. The system
exhibits very strong bistability and instabilities. The origin of the latter is
found to be a competition between optical pumping and non-linearities due to
saturation of the optical transition.Comment: 6 pages, 7 figures, LaTe
Late Glacial to Holocene relative sea level change in Assynt, northwest Scotland, UK
Relative sea-level change (RSL), from the Late Glacial through to the late Holocene, is reconstructed for the Assynt region, northwest Scotland, based on bio- and lithostratigraphical analysis. Four new radiocarbon-dated sea-level index points help constrain RSL change for the Late Glacial to late Holocene. These new data, in addition to published material, capture the RSL fall during the Late Glacial and the rise and fall associated with the mid-Holocene highstand. Two of these index points constrain the Late Glacial RSL history in Assynt for the first time, reconstructing RSL falling from 2.47 ± 0.59 m OD to 0.15 ± 0.59 m OD at c. 14000 - 15000 cal yr BP. These new data test model predictions of glacial isostatic adjustment (GIA), particularly during the early deglacial period which is currently poorly constrained throughout the British Isles. While the empirical data from the mid- to late-Holocene to present matches quite well with recent GIA model output, there is a relatively poor fit between the timing of the Late Glacial RSL fall and early Holocene RSL rise. This mismatch, also evident elsewhere in northwest Scotland, may result from uncertainties associated with both the global and local ice components of GIA models
The Ricci flow on noncommutative two-tori
In this paper we construct a version of Ricci flow for noncommutative 2-tori,
based on a spectral formulation in terms of the eigenvalues and eigenfunction
of the Laplacian and recent results on the Gauss-Bonnet theorem for
noncommutative tori.Comment: 18 pages, LaTe
A note on the universality of the Hagedorn behavior of pp-wave strings
Following on from recent studies of string theory on a one-parameter family
of integrable deformations of proposed by Lunin and
Maldacena, we carry out a systematic analysis of the high temperature
properties of type IIB strings on the associated pp-wave geometries. In
particular, through the computation of the thermal partition function and free
energy we find that not only does the theory exhibit a Hagedorn transition in
both the and class of pp-waves, but that the Hagedorn
temperature is insensitive to the deformation suggesting an interesting
universality in the high temperature behaviour of the pp-wave string theory. We
comment also on the implications of this universality on the
confinement/deconfinement transition in the dual
Leigh-Strassler deformation of Yang-Mills theory.Comment: 25 pages; fixed minor typo; added reference
Excursions beyond the horizon: Black hole singularities in Yang-Mills theories (I)
We study black hole singularities in the AdS/CFT correspondence. These
singularities show up in CFT in the behavior of finite-temperature correlation
functions. We first establish a direct relation between space-like geodesics in
the bulk and momentum space Wightman functions of CFT operators of large
dimensions. This allows us to probe the regions inside the horizon and near the
singularity using the CFT. Information about the black hole singularity is
encoded in the exponential falloff of finite-temperature correlators at large
imaginary frequency. We construct new gauge invariant observables whose
divergences reflect the presence of the singularity. We also find a UV/UV
connection that governs physics inside the horizon. Additionally, we comment on
the possible resolution of the singularity.Comment: 34 page, 10 figures, uses harvmac, references adde
On the positive mass theorem for manifolds with corners
We study the positive mass theorem for certain non-smooth metrics following
P. Miao's work. Our approach is to smooth the metric using the Ricci flow. As
well as improving some previous results on the behaviour of the ADM mass under
the Ricci flow, we extend the analysis of the zero mass case to higher
dimensions.Comment: 21 pages, incorporated referee's comment
Single-top Wt-channel production matched with parton showers using the POWHEG method
We present results for the next-to-leading order calculation of single-top
Wt-channel production interfaced to Shower Monte Carlo programs, implemented
according to the POWHEG method. A comparison with MC@NLO is carried out.
Results obtained using the PYTHIA shower are also shown and the effect of
typical cuts is briefly discussed.Comment: 23 pages, 9 figure
Time series forecasting with the WARIMAX-GARCH method
It is well-known that causal forecasting methods that include appropriately chosen Exogenous Variables (EVs) very often present improved forecasting performances over univariate methods. However, in practice, EVs are usually difficult to obtain and in many cases are not available at all. In this paper, a new causal forecasting approach, called Wavelet Auto-Regressive Integrated Moving Average with eXogenous variables and Generalized Auto-Regressive Conditional Heteroscedasticity (WARIMAX-GARCH) method, is proposed to improve predictive performance and accuracy but also to address, at least in part, the problem of unavailable EVs. Basically, the WARIMAX-GARCH method obtains Wavelet âEVsâ (WEVs) from Auto-Regressive Integrated Moving Average with eXogenous variables and Generalized Auto-Regressive Conditional Heteroscedasticity (ARIMAX-GARCH) models applied to Wavelet Components (WCs) that are initially determined from the underlying time series. The WEVs are, in fact, treated by the WARIMAX-GARCH method as if they were conventional EVs. Similarly to GARCH and ARIMA-GARCH models, the WARIMAX-GARCH method is suitable for time series exhibiting non-linear characteristics such as conditional variance that depends on past values of observed data. However, unlike those, it can explicitly model frequency domain patterns in the series to help improve predictive performance. An application to a daily time series of dam displacement in Brazil shows the WARIMAX-GARCH method to remarkably outperform the ARIMA-GARCH method, as well as the (multi-layer perceptron) Artificial Neural Network (ANN) and its wavelet version referred to as Wavelet Artificial Neural Network (WANN) as in [1], on statistical measures for both in-sample and out-of-sample forecasting
Gulf Stream remote forcing of shelfbreak currents in the MidâAtlantic Bight
The âSlope Seaâ is a narrow band of ocean that lies between the Gulf Stream and the continental shelf edge in the MidâAtlantic Bight. It is composed primarily of slopewater, and a closed cyclonic gyre circulates within the upper few hundred meters of its western end. A twoâyear time series of current measurements in this region has shown that the southwestward flowing shelfbreak currents along the shoreward flank of the gyre are directly related to the position of the Gulf Stream, which is typically some 150 to 300 km seaward of the shelfbreak. The mean monthly shelfbreak currents are strongest, towards the southwest at about 30â40 cm sâ1, when the Stream is within 150 km of the shelf edge, whereas those currents are close to zero when the Stream is about 300 km away
Information ontrol and the exercise of power in the obstetrical encounter
Interactions between doctor and patient involve participants with unequal power and possibly different interests. While a number of studies have focused upon the doctor/patient relationship, few have examined the utility of the concept of power and its capacity to help us understand the outcome of these interactions. The information sought by pregnant women from their obstetricians is used to provide a case study of one conceptualization and test of the utility of the concept of power. Pregnant women and their obstetricians are found to have different perceptions of the information that should be exchanged during their interactions. Women generally fail to obtain the information they want. Lower social class patients desire more and obtain less information than their higher status counterparts
- âŠ