Efficiency optimization for Atomic Frequency Comb storage

We study the efficiency of the Atomic Frequency Comb storage protocol. We show that for a given optical depth, the preparation procedure can be optimize to significantly improve the retrieval. Our prediction is well supported by the experimental implementation of the protocol in a \TMYAG crystal. We observe a net gain in efficiency from 10% to 17% by applying the optimized preparation procedure. In the perspective of high bandwidth storage, we investigate the protocol under different magnetic fields. We analyze the effect of the Zeeman and superhyperfine interaction

A post-Keplerian parameter to test gravito-magnetic effects in binary pulsar systems

We study the pulsar timing, focusing on the time delay induced by the gravitational field of the binary systems. In particular, we study the gravito-magnetic correction to the Shapiro time delay in terms of Keplerian and post-Keplerian parameters, and we introduce a new post-Keplerian parameter which is related to the intrinsic angular momentum of the stars. Furthermore, we evaluate the magnitude of these effects for the binary pulsar systems known so far. The expected magnitude is indeed small, but the effect is important per se.Comment: 6 pages, RevTeX, 1 eps figure, accepted for publication in Physical Review D; references adde

Chaotic Accretion in a Non-Stationary Electromagnetic Field of a Slowly Rotating Compact Star

We investigate charge accretion in vicinity of a slowly rotating compact star with a non-stationary electromagnetic field. Exact solutions to the general relativistic Maxwell equations are obtained for a star formed of a highly degenerate plasma with a gravitational field given by the linearized Kerr metric. These solutions are used to formulate and then to study numerically the equations of motion for a charged particle in star's vicinity using the gravitoelectromagnetic force law. The analysis shows that close to the star charge accretion does not always remain ordered. It is found that the magnetic field plays the dominant role in the onset of chaos near the star's surface.Comment: 9 pages, 4 figure

High-resolution DCE-MRI of the pituitary gland using radial k-space acquisition with compressed sensing reconstruction

BACKGROUND AND PURPOSE: The pituitary gland is located outside of the blood-brain barrier. Dynamic T1 weighted contrast enhanced sequence is considered to be the gold standard to evaluate this region. However, it does not allow assessment of intrinsic permeability properties of the gland. Our aim was to demonstrate the utility of radial volumetric interpolated brain examination with the golden-angle radial sparse parallel technique to evaluate permeability characteristics of the individual components (anterior and posterior gland and the median eminence) of the pituitary gland and areas of differential enhancement and to optimize the study acquisition time. MATERIALS AND METHODS: A retrospective study was performed in 52 patients (group 1, 25 patients with normal pituitary glands; and group 2, 27 patients with a known diagnosis of microadenoma). Radial volumetric interpolated brain examination sequences with goldenangle radial sparse parallel technique were evaluated with an ROI-based method to obtain signal-time curves and permeability measures of individual normal structures within the pituitary gland and areas of differential enhancement. Statistical analyses were performed to assess differences in the permeability parameters of these individual regions and optimize the study acquisition time. RESULTS: Signal-time curves from the posterior pituitary gland and median eminence demonstrated a faster wash-in and time of maximum enhancement with a lower peak of enhancement compared with the anterior pituitary gland (P .005). Time-optimization analysis demonstrated that 120 seconds is ideal for dynamic pituitary gland evaluation. In the absence of a clinical history, differences in the signal-time curves allow easy distinction between a simple cyst and a microadenoma. CONCLUSIONS: This retrospective study confirms the ability of the golden-angle radial sparse parallel technique to evaluate the permeability characteristics of the pituitary gland and establishes 120 seconds as the ideal acquisition time for dynamic pituitary gland imaging

Absence of exposed bone following dental extraction in beagle dogs treated with 9 months of high-dose zoledronic acid combined with dexamethasone

Purpose: Factors contributing to osteonecrosis of the jaw with anti-remodeling drug treatment are unclear. Epidemiologic and experimental studies have suggested the combination of bisphosphonates and dexamethasone results in osteonecrosis of the jaw more often than either agent alone. The goal of this study was to assess the combination of these 2 drugs in a large animal model previously shown to be susceptible to exposed bone in the oral cavity when treated with bisphosphonates. Materials and Methods: Skeletally mature beagle dogs were untreated controls or treated with zoledronic acid (ZOL), dexamethasone (DEX), or ZOL plus DEX. ZOL and DEX were given at doses based on those used in humans. All animals underwent single molar extraction at 7 and 8 months after the start of the study. Extraction sites were obtained at month 9 for assessment of osseous healing using micro-computed tomography and histology. Results: No animals were observed to have exposed bone after dental extraction, yet 1 animal treated with ZOL and 1 treated with ZOL plus DEX had severely disrupted extraction sites as viewed by computed tomography and histology. These 2 animals had an intense periosteal reaction that was less obvious but still present in all ZOL-treated animals and absent from untreated animals. There was no significant difference in bone volume within the socket among groups at 4 or 8 weeks after healing, yet the ratio of surface to volume was significantly higher in animals treated with ZOL plus DEX at 8 weeks compared with control animals. Conclusions: These findings suggest a more complex pathophysiology to osteonecrosis of the jaw than is implied by previous epidemiologic studies and those in rodents and raise questions about the potential role of DEX in its etiology.© 2013 American Association of Oral and Maxillofacial Surgeons

Concomitant polymorphism and the martensitic-like transformation of an organic crystal.

Crystalline polymorphism is a phenomenon that occurs in many molecular solids, resulting in a diverse range of possible bulk structures. Temperature and pressure can often be used to thermodynamically control which crystal form is preferred, and the associated transitions between polymorphic phases are often discontinuous and complete. N-Methyl-4-carboxypyridinium chloride is a solid that undergoes an apparent continuous temperature-dependent phase transition from an orthorhombic to a monoclinic polymorph. However, a hybrid characterization approach using single-crystal X-ray diffraction, terahertz time-domain spectroscopy, and solid-state density functional theory reveals the transformation to be actually a slowly changing ratio of the two discrete polymorphic forms. The potential energy surface of this process can be directly accessed using terahertz radiation, and the data show that a very low barrier (43.3 J mol-1) exists along the polymorph transformation coordinate

Efficient light storage in a crystal using an Atomic Frequency Comb

We demonstrate efficient and reversible mapping of a light field onto a thulium-doped crystal using an atomic frequency comb (AFC). Thanks to an accurate spectral preparation of the sample, we reach an efficiency of 9%. Our interpretation of the data is based on an original spectral analysis of the AFC. By independently measuring the absorption spectrum, we show that the efficiency is both limited by the available optical thickness and the preparation procedure at large absorption depth for a given bandwidth. The experiment is repeated with less than one photon per pulse and single photon counting detectors. We clearly observe that the AFC protocol is compatible with the noise level required for weak quantum field storage