3,173 research outputs found
A robust empirical seasonal prediction of winter NAO and surface climate
A key determinant of winter weather and climate in Europe and North America is the North Atlantic Oscillation (NAO), the dominant mode of atmospheric variability in the Atlantic domain. Skilful seasonal forecasting of the surface climate in both Europe and North America is reflected largely in how accurately models can predict the NAO. Most dynamical models, however, have limited skill in seasonal forecasts of the winter NAO. A new empirical model is proposed for the seasonal forecast of the winter NAO that exhibits higher skill than current dynamical models. The empirical model provides robust and skilful prediction of the December-January-February (DJF) mean NAO index using a multiple linear regression (MLR) technique with autumn conditions of sea-ice concentration, stratospheric circulation, and sea-surface temperature. The predictability is, for the most part, derived from the relatively long persistence of sea ice in the autumn. The lower stratospheric circulation and sea-surface temperature appear to play more indirect roles through a series of feedbacks among systems driving NAO evolution. This MLR model also provides skilful seasonal outlooks of winter surface temperature and precipitation over many regions of Eurasia and eastern North America
Time-Symmetric Quantum Theory of Smoothing
Smoothing is an estimation technique that takes into account both past and
future observations, and can be more accurate than filtering alone. In this
Letter, a quantum theory of smoothing is constructed using a time-symmetric
formalism, thereby generalizing prior work on classical and quantum filtering,
retrodiction, and smoothing. The proposed theory solves the important problem
of optimally estimating classical Markov processes coupled to a quantum system
under continuous measurements, and is thus expected to find major applications
in future quantum sensing systems, such as gravitational wave detectors and
atomic magnetometers.Comment: 4 pages, 1 figure, v2: accepted by PR
Vertical Variability and Lateral Distribution of Late Wisconsinan Sediments Parallel to theAxis of the Buried Valley of Mud Brook North of Akron, Summit County, Ohio
Author Institution: Department of Geology & Environmental Science, University of AkronThe buried valley of Mud Brook in northern Summit County, OH, contains sediments associated with the late
Wisconsinan glaciation. The vertical variability and lateral distribution of these sediments can be ascertained from information
derived from logs from highway borings and water wells along a 15-km north-south transect parallel to the axis of the buried
valley. Textural, carbonate, clay mineral, and lithologic analyses of samples from roadcuts, geological borings, and some highway
department borings provide additional information to assign lithofacies units to specific glaciations. Cross sections show that
nearly similar depositional environments existed before each late Wisconsinan glacial advance. The proglacial sediments consist
of outwash and lacustrine deposits overridden by ice that deposited an overlying till. Sediments associated with the Lavery and
Hiram advances overlie a Kent-aged kame plateau within the Summit County Morainic Complex at the southern end of the study
area. Farther north meltwater accumulated and drowned ground moraine to form post-glacial lakes that were eventually drained
as the drainage network of Mud Brook became better integrated
Bellman equations for optimal feedback control of qubit states
Using results from quantum filtering theory and methods from classical
control theory, we derive an optimal control strategy for an open two-level
system (a qubit in interaction with the electromagnetic field) controlled by a
laser. The aim is to optimally choose the laser's amplitude and phase in order
to drive the system into a desired state. The Bellman equations are obtained
for the case of diffusive and counting measurements for vacuum field states. A
full exact solution of the optimal control problem is given for a system with
simpler, linear, dynamics. These linear dynamics can be obtained physically by
considering a two-level atom in a strongly driven, heavily damped, optical
cavity.Comment: 10 pages, no figures, replaced the simpler model in section
Changes in biomechanical properties of chemotherapy bone cement after a year in saline storage
Introduction: Acrylic based bone cements are a versatile treatment modality in Orthopaedic surgery due to their wide variety of uses and tolerance to high degree of customization. Bone cement can be used to repair and stabilize pathologic fractures and may potentially prevent recurrence post tumor resection. Chemotherapeutic bone cements are favorable because they can potentially minimize systemic side effects and the need for radiation. Cements can be combined with soluble fillers such as polyethylene glycol (PEG) to optimize drug elution. Even though studies have measured the mechanical properties of bone cement in dry state, the exact change in the mechanical properties of bone cement after drug/soluble filler elution is largely unknown. This study investigates the change in mechanical properties of commercially available bone cements modified with PEG fillers after one year of storage in drug elution medium.
Methods: Confidence Ultra, Vertebroplastic, and Palacos cement were used and mixed with varying amounts (0–50%) of PEG and chemotherapy agents (methotrexate or doxorubicin). Bone cement specimens were stored in a saline solution for one year after which they were tested in compression at 1 mm/min until failure.
Results: The modulus and compression strength of bone cements decreased with increase in soluble filler composition. Although soluble fillers were shown to weaken the mechanical properties of the bone cement, Palacos and Vertebroplastic cements retained their mechanical properties better than Confidence.
Discussion: When using chemotherapeutic bone cements, combining soluble fillers enhances drug elution at the expense of mechanical properties. However, the results showed that mechanical properties of different commercially available bone cements behave differently with similar percentages of soluble filler and drug added making it difficult to predict changes in mechanical properties of bone cement intraoperatively. This elucidates the need for well characterized bone cement optimized for chemotherapy drug delivery
Characterization of gsp-Mediated Growth Hormone Excess in the Context of McCune-Albright Syndrome
McCune-Albright syndrome (MAS) is a disorder characterized by the triad of café-au-lait skin pigmentation, polyostotic fibrous dysplasia of bone, and hyperfunctioning endocrinopathies, including GH excess. The molecular etiology of the disease is postzygotic activating mutations of the GNAS1 gene product, Gsα. The term gsp oncogene has been assigned to these mutations due to their association with certain neoplasms. The aim of this study was to estimate the prevalence of GH excess in MAS, characterize the clinical and endocrine manifestations, and describe the response to treatment. Fifty-eight patients with MAS were screened, and 22 with stigmata of acromegaly and/or elevated GH or IGF-I underwent oral glucose tolerance testing. Twelve patients (21%) had GH excess, based on failure to suppress serum GH on oral glucose tolerance test, and underwent a TRH test, serial GH sampling from 2000-0800 h, and magnetic resonance imaging of the sella. We found that vision and hearing deficits were more common in patients with GH excess (4 of 12, 33%) than those without (2 of 56, 4%). Of interest, patients with a history of precocious puberty and GH excess who had reached skeletal maturity achieved normal adult height despite a history of early epiphyseal fusion. All 9 patients tested had an increase in serum GH after TRH, 11 of 12 (92%) had hyperprolactinemia, and all 8 tested had detectable or elevated nighttime GH levels. Pituitary adenoma was detected in 4 of 12 (33%) patients. All patients with elevated IGF-I levels were treated with cabergoline (7 patients), long-acting octreotide (LAO; 8 patients), or a combination of cabergoline and LAO (4 patients). In six of the seven patients (86%) treated with cabergoline, serum IGF-I decreased, but not to the normal range. In the eight patients treated with LAO alone, IGF-I decreased, and, in four, returned to the normal range. The remaining 4 patients were treated with a combination of cabergoline and LAO. For them, symptoms of GH excess diminished, and IGF-I decreased further, but did not enter the normal range. GH excess is common in MAS and results in a distinct clinical phenotype characterized by inappropriately normal stature, TRH responsiveness, prolactin cosecretion, small or absent pituitary tumors, a consistent but inadequate response to treatment with cabergoline, and an intermediate response to LAO
Self-Averaging Scaling Limits of Two-Frequency Wigner Distribution for Random Paraxial Waves
Two-frequency Wigner distribution is introduced to capture the asymptotic
behavior of the space-frequency correlation of paraxial waves in the radiative
transfer limits. The scaling limits give rises to deterministic transport-like
equations. Depending on the ratio of the wavelength to the correlation length
the limiting equation is either a Boltzmann-like integral equation or a
Fokker-Planck-like differential equation in the phase space. The solutions to
these equations have a probabilistic representation which can be simulated by
Monte Carlo method. When the medium fluctuates more rapidly in the longitudinal
direction, the corresponding Fokker-Planck-like equation can be solved exactly.Comment: typos correcte
A fully-discrete scheme for systems of nonlinear Fokker-Planck-Kolmogorov equations
We consider a system of Fokker-Planck-Kolmogorov (FPK) equations, where the
dependence of the coefficients is nonlinear and nonlocal in time with respect
to the unknowns. We extend the numerical scheme proposed and studied recently
by the authors for a single FPK equation of this type. We analyse the
convergence of the scheme and we study its applicability in two examples. The
first one concerns a population model involving two interacting species and the
second one concerns two populations Mean Field Games
Comparison of Ventricular Refractory Periods Determined by Incremental and Decremental Scanning of an Extrastimulus
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73345/1/j.1540-8159.1989.tb02699.x.pd
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