Antidepressant Treatment Duration in Pediatric Depressive and Anxiety Disorders: How Long is Long Enough?

Anxiety and depressive disorders are common in the pediatric primary care setting, and respond to both psychotherapeutic and psychopharmacologic treatment. However, there are limited data regarding the optimal treatment duration. This article systematically reviews guidelines and clinical trial data related to antidepressant treatment duration in pediatric patients with depressive and anxiety disorders. The extant literature suggests 9-12 months of antidepressant treatment for youth with major depressive disorder. For generalized, separation and social anxiety disorders, 6-9 months of antidepressant treatment may be sufficient, though many clinicians extend treatment to 12 months based on extrapolation of data from adults with anxiety disorders. Such extended treatment periods may decrease the risk of long-term morbidity and recurrence; however, the goal of treatment is ultimately remission, rather than duration of antidepressant pharmacotherapy. Moreover, while evidence-based guidelines represent a starting point, appropriate treatment duration varies and patient-specific response, psychological factors, and timing of discontinuation must be considered for individual pediatric patients

Coulomb Explosion and Thermal Spikes

A fast ion penetrating a solid creates a track of excitations. This can produce displacements seen as an etched track, a process initially used to detect energetic particles but now used to alter materials. From the seminal papers by Fleischer et al. [Phys. Rev. 156, 353 (1967)] to the present [C. Trautmann, S. Klaumunzer and H. Trinkaus, Phys. Rev. Lett. 85, 3648 (2000)], `Coulomb explosion' and thermal spike models are treated as conflicting models for describing ion track effects. Here molecular dynamics simulations of electronic-sputtering, a surface manifestation of ion track formation, show that `Coulomb explosion' produces a `heat' spike so that these are early and late aspects of the same process. Therefore, differences in scaling are due to the use of incomplete spike models.Comment: Submitted to PRL. 4 pages, 3 figures. For related movies see: http://dirac.ms.virginia.edu/~emb3t/coulomb/coulomb.html PACS added in new versio

Analytic, Group-Theoretic Density Profiles for Confined, Correlated N-Body Systems

Confined quantum systems involving $N$ identical interacting particles are to be found in many areas of physics, including condensed matter, atomic and chemical physics. A beyond-mean-field perturbation method that is applicable, in principle, to weakly, intermediate, and strongly-interacting systems has been set forth by the authors in a previous series of papers. Dimensional perturbation theory was used, and in conjunction with group theory, an analytic beyond-mean-field correlated wave function at lowest order for a system under spherical confinement with a general two-body interaction was derived. In the present paper, we use this analytic wave function to derive the corresponding lowest-order, analytic density profile and apply it to the example of a Bose-Einstein condensate.Comment: 15 pages, 2 figures, accepted by Physics Review A. This document was submitted after responding to a reviewer's comment

Theory of the Eigler-swith

We suggest a simple model to describe the reversible field-induced transfer of a single Xe-atom in a scanning tunneling microscope, --- the Eigler-switch. The inelasticly tunneling electrons give rise to fluctuating forces on and damping of the Xe-atom resulting in an effective current dependent temperature. The rate of transfer is controlled by the well-known Arrhenius law with this effective temperature. The directionality of atom transfer is discussed, and the importance of use of non-equlibrium-formalism for the electronic environment is emphasized. The theory constitutes a formal derivation and generalization of the so-called Desorption Induced by Multiple Electron Transitions (DIMET) point of view.Comment: 13 pages (including 2 figures in separate LaTeX-files with ps-\specials), REVTEX 3.

Relation between inelastic electron tunneling and vibrational excitation of single adsorbates on metal surfaces

We analyse theoretically a relation between the vibrational generation rate of a single adsorbate by tunneling electrons and the inelastic tunneling (IET) current in scanning tunneling microscope, and the influence of the vibrational excitations on the rate of adsorbate motions. Special attention is paid to the effects of finite lifetime of the vibrational excitations. We show that in the vicinity and below the IET threshold the rate of adsorbate motion deviates from a simple power-law dependence on the bias voltage due to the effects of bath temperature and adsorbate vibrational lifetime broadenings. The temperature broadening appears to be confined near the threshold voltage within a narrow region of several $k_B T$, whereas the lifetime broadening manifests itself in a much wider region of applied voltages below the IET threshold.Comment: 8 pages including 4 figure

Surface Screening Charge and Effective Charge

The charge on an atom at a metallic surface in an electric field is defined as the field-derivative of the force on the atom, and this is consistent with definitions of effective charge and screening charge. This charge can be found from the shift in the potential outside the surface when the atoms are moved. This is used to study forces and screening on surface atoms of Ag(001) c$(2\times 2)$ -- Xe as a function of external field. It is found that at low positive (outward) fields, the Xe with a negative effective charge of -0.093 $|{e}|$ is pushed into the surface. At a field of 2.3 V \AA$^{-1}$ the charge changes sign, and for fields greater than 4.1 V \AA$^{-1}$ the Xe experiences an outward force. Field desorption and the Eigler switch are discussed in terms of these results.Comment: 4 pages, 1 figure, RevTex (accepted by PRL

STM induced hydrogen desorption via a hole resonance

We report STM-induced desorption of H from Si(100)-H(2$\times1$) at negative sample bias. The desorption rate exhibits a power-law dependence on current and a maximum desorption rate at -7 V. The desorption is explained by vibrational heating of H due to inelastic scattering of tunneling holes with the Si-H 5$\sigma$ hole resonance. The dependence of desorption rate on current and bias is analyzed using a novel approach for calculating inelastic scattering, which includes the effect of the electric field between tip and sample. We show that the maximum desorption rate at -7 V is due to a maximum fraction of inelastically scattered electrons at the onset of the field emission regime.Comment: 4 pages, 4 figures. To appear in Phys. Rev. Let

Atomic Tunneling from a STM/AFM tip: Dissipative Quantum Effects from Phonons

We study the effects of phonons on the tunneling of an atom between two surfaces. In contrast to an atom tunneling in the bulk, the phonons couple very strongly, and qualitatively change the tunneling behavior. This is the first example of {\it ohmic} coupling from phonons for a two-state system. We propose an experiment in which an atom tunnels from the tip of an STM, and show how its behavior would be similar to the Macroscopic Quantum Coherence behavior predicted for SQUIDS. The ability to tune and calculate many parameters would lead to detailed tests of the standard theories. (For a general intro to this work on the on the World-Wide-Web: http://www.lassp.cornell.edu. Click on ``Entertaining Science Done Here'' and ``Quantum Tunneling of Atoms'')Comment: 12 pages, ReVTex3.0, two figures (postscript). This is a (substantially) revised version of cond-mat/9406043. More info (+ postscript text) at : http://www.lassp.cornell.edu/ardlouis/publications.htm

Non-Lorentzian single-molecule line shape: Pseudolocal phonons and coherence transfer

The excitation line shape of a single terrylene molecule in a naphthalene crystal has been investigated. In addition to the conventional Lorentzian, it consists of a dispersive component in the core region and a sideband. This is due to a pseudolocal phonon caused by the substitution of a host molecule with the chromophore. When the pseudolocal phonon is excited, the resonance frequency of the chromophore slightly changes, resulting in the appearance of a second, quasiresonant transition. Coherence transfer between these two optical transitions causes the deviation from the purely Lorentzian line shape