Single and double slit scattering of wave packets

The scattering of wave packets from a single slit and a double slit with the Schr\"odinger equation, is studied numerically and theoretically. The phenomenon of diffraction of wave packets in space and time in the backward region, previously found for barriers and wells, is encountered here also. A new phenomenon of forward diffraction that occurs only for packets thiner than the slit, or slits, is calculated numerically as well as, in a theoretical approximation to the problem. This diffraction occurs at the opposite end of the usual diffraction phenomena with monochromatic waves.Comment: Latex format, 35 pages, 15 eps (some colored) figure

A local density functional for the short-range part of the electron-electron interaction

Motivated by recent suggestions --to split the electron-electron interaction into a short-range part, to be treated within the density functional theory, and a long-range part, to be handled by other techniques-- we compute, with a diffusion Monte Carlo method, the ground-state energy of a uniform electron gas with a modified, short-range-only electron-electron interaction \erfc(\mu r)/r, for different values of the cutoff parameter $\mu$ and of the electron density. After deriving some exact limits, we propose an analytic representation of the correlation energy which accurately fits our Monte Carlo data and also includes, by construction, these exact limits, thus providing a reliable ``short-range local-density functional''.Comment: 7 pages, 3 figure

Hall magnetohydrodynamics of partially ionized plasmas

The Hall effect arises in a plasma when electrons are able to drift with the magnetic field but ions cannot. In a fully-ionized plasma this occurs for frequencies between the ion and electron cyclotron frequencies because of the larger ion inertia. Typically this frequency range lies well above the frequencies of interest (such as the dynamical frequency of the system under consideration) and can be ignored. In a weakly-ionized medium, however, the Hall effect arises through a different mechanism -- neutral collisions preferentially decouple ions from the magnetic field. This typically occurs at much lower frequencies and the Hall effect may play an important role in the dynamics of weakly-ionised systems such as the Earth's ionosphere and protoplanetary discs. To clarify the relationship between these mechanisms we develop an approximate single-fluid description of a partially ionized plasma that becomes exact in the fully-ionized and weakly-ionized limits. Our treatment includes the effects of ohmic, ambipolar, and Hall diffusion. We show that the Hall effect is relevant to the dynamics of a partially ionized medium when the dynamical frequency exceeds the ratio of ion to bulk mass density times the ion-cyclotron frequency, i.e. the Hall frequency. The corresponding length scale is inversely proportional to the ion to bulk mass density ratio as well as to the ion-Hall beta parameter.Comment: 11 page, 1 figure, typos removed, numbers in tables revised; accepted for publication in MNRA

A novel algorithm for determining the contextual characteristics of movement behaviors by combining accelerometer features and wireless beacons: development and implementation

Background: Unfortunately, global efforts to promote “how much” physical activity people should be undertaking have been largely unsuccessful. Given the difficulty of achieving a sustained lifestyle behavior change, many scientists are re-examining their approaches. One such approach is to focus on understanding the context of the lifestyle behavior (i.e., where, when, and with whom) with a view to identifying promising intervention targets. Objective: The aim of this study was to develop and implement an innovative algorithm to determine “where” physical activity occurs using proximity sensors coupled with a widely used physical activity monitor. Methods: A total of 19 Bluetooth beacons were placed in fixed locations within a multilevel, mixed-use building. In addition, 4 receiver-mode sensors were fitted to the wrists of a roving technician who moved throughout the building. The experiment was divided into 4 trials with different walking speeds and dwelling times. The data were analyzed using an original and innovative algorithm based on graph generation and Bayesian filters. Results: Linear regression models revealed significant correlations between beacon-derived location and ground-truth tracking time, with intraclass correlations suggesting a high goodness of fit (R2=.9780). The algorithm reliably predicted indoor location, and the robustness of the algorithm improved with a longer dwelling time (>100 s; error <10%, R2=.9775). Increased error was observed for transitions between areas due to the device sampling rate, currently limited to 0.1 Hz by the manufacturer. Conclusions: This study shows that our algorithm can accurately predict the location of an individual within an indoor environment. This novel implementation of “context sensing” will facilitate a wealth of new research questions on promoting healthy behavior change, the optimization of patient care, and efficient health care planning (e.g., patient-clinician flow, patient-clinician interaction)

Fear of falling and activities of daily living function: mediation effect of dual-task ability

Objective: The aim of the study was to explore the association between fear of falling (FOF), dual-task ability during a mobility task, and the activities of daily living (ADL) in a sample of older adults. Methods: Seventy-six older adults (mean age M = 70.87 ± 5.16 years) participated in the study. Data on FOF (using the Falls Self-Efficacy Scale-International), walking ability during both single- and dual-task performances and ADL were collected. Results: Mediation analysis demonstrated the mediation effect of dual-task ability (β = 0.238, p = 0.011) between FOF and ADL level (β = 0.559, p < 0.001). Moreover, significantly lower performances were observed during dual-task condition [F (2, 73) = 7.386, p < 0.001], and lower ADL levels were also found in older adults with FOF [F (2, 73) = 13.734, p < 0.001]. Conclusion: The study underlines the relationship between FOF, dual-task ability and ADL level. These results could be used to develop specific intervention programmes for successful ageing

Quantum creation of an Inhomogeneous universe

In this paper we study a class of inhomogeneous cosmological models which is a modified version of what is usually called the Lema\^itre-Tolman model. We assume that we have a space with 2-dimensional locally homogeneous spacelike surfaces. In addition we assume they are compact. Classically we investigate both homogeneous and inhomogeneous spacetimes which this model describe. For instance one is a quotient of the AdS$_4$ space which resembles the BTZ black hole in AdS$_3$. Due to the complexity of the model we indicate a simpler model which can be quantized easily. This model still has the feature that it is in general inhomogeneous. How this model could describe a spontaneous creation of a universe through a tunneling event is emphasized.Comment: 21 pages, 5 ps figures, REVTeX, new subsection include

Myelodysplastic syndromes: the pediatric point of view.

Myelodysplastic syndromes (MDS) are clonal disorders of the multipotent hematopoietic stem cell characterized by ineffective hematopoiesis and associated with marrow hypercellularity, increased intramedullary cell death and peripheral cytopenias of varying severity. Patients with myelodysplasia have a propensity (20% to 30% of cases) to undergo transformation into acute myeloid leakemia (AML), and a large body of evidence indicates that MDS represent steps in the multiphasic evolution of AML. Progression of the disease is characterized by expansion of the abnormal clone and inhibition of normal hematopoiesis leading to deterioration of the blood cell count and/or development of AML. MDS are relatively unusual in childhood, representing only 3% of pediatric hematological malignancies, although it has been reported that up to 17% of pediatric AML cases may have a previous myelodysplastic phase. The first systematic attempt at morphological classification of MDS was provided by the French-American-British (FAB) group. However, the FAB classification of MDS is only partially applicable in children. Some variants are extremely rare or absent (refractory anemia with ring sideroblasts and chronic myelomonocytic leukemia), and other peculiar pediatric disorders, represented by juvenile chronic myelogenous leukemia (JCML) and the monosomy 7 syndrome, are not included. Moreover, since there is a partial overlap between pediatric MDS and myeloproliferative disorders and the variants occurring in young children have rather specific features, some confusion still surrounds the nosographical definition of childhood MDS, so that none of the proposed classifications are widely accepted and used. Characteristically, some genetic conditions such as Fanconi's anemia, Shwachman's and Down's syndromes predispose to the development of MDS in childhood. The most common variants of childhood MDS are represented by JCML and the monosomy 7 syndrome, both disorders typically occurring in young children. JCML is characterized by a spontaneous growth of granulocyte-macrophage progenitors that show a striking hypersensitivity to granulocyte-macrophage colony-stimulating factor. Clinical presentation resembles that of some myeloproliferative disorders, with massive organomegaly usually not observed in the classically reported variants of MDS. Clinical features of the monosomy 7 syndrome resemble those observed in JCML and a differential diagnosis between these two entities relies upon the higher percentage of fetal hemoglobin, the more pronounced decrease in platelet count and, in some cases, the lack of the peculiar cytogenetic abnormality in the latter. With the number of children being cured of cancer constantly rising, a significant increase in secondary or chemotherapy-related myelodysplasia is being observed, and these disorders represent a formidable challenge for pediatric hematologists due to their poor response to chemotherapy. As a matter of fact, owing to their biological heterogeneity and aggressive clinical course in childhood, all MDS variants pose serious difficulties for successful management. If a compatible donor is available, allogeneic bone marrow transplantation (BMT) becomes the treatment of choice and should be performed during the early stages of the disease. Supportive therapy, differentiative treatments and low-dose chemotherapy, while valuable alternative therapeutic options in adults, have limited application in pediatric patients. The role of intensive chemotherapy and autologous BMT has not yet been clearly defined, and the use of hematopoietic growth factors does not seem to have a significant influence on the natural history of the disease. In the future, new insights into the events leading to progressive genetic changes in the clonal population and into the molecular basis of these genetic lesions could result in interesting new therapeutic approaches directed either at the oncogenes involved in the pathogenesis of the disease, or at the cytokines and/or their receptors causing the abnormal differentiation and proliferation of the myelodysplastic clone

Measurement invariance of TGMD-3 in children with and without mental and behavioral disorders

This study evaluated whether the Test of Gross Motor Development 3 (TGMD-3) is a reliable tool to compare children with and without mental and behavioural disorders across gross motor skill domains. A total of 1075 children (aged 3-11 years), 98 with mental and behavioural disorders and 977 without (typically developing), were included in the analyses. The TGMD-3 evaluates fundamental gross motor skills of children across two domains: locomotor skills and ball skills. Two independent testers simultaneously observed children’s performances (agreement over 95%). Each child completed one practice and then two formal trials. Scores were recorded only during the two formal trials. Multigroup Confirmatory Factor Analysis tested the assumption of TGMD-3 measurement invariance across disability groups. According to the magnitude of changes in Root Mean Square Error of Approximation and Comparative Fit Index between nested models, the assumption of measurement invariance across groups was valid. Loadings of the manifest indicators on locomotor and ball skills were significant (p < .001) in both groups. Item Response Theory analysis showed good reliability results across locomotor and the ball skills full latent traits. The present study confirmed the factorial structure of TGMD-3 and demonstrated its feasibility across normally developing children and children with mental and behavioural disorders. These findings provide new opportunities for understanding the effect of specific intervention strategies on this population

Electron scattering from molecules and molecular aggregates of biological relevance

In this Topical Review we survey the current state of the art in the study of low energy electron collisions with biologically relevant molecules and molecular clusters. We briefly describe the methods and techniques used in the investigation of these processes and summarise the results obtained so far for DNA constituents and their model compounds, amino acids, peptides and other biomolecules. The applications of the data obtained is briefly described as well as future required developments