On Extensions of Superconformal Algebras

Starting from vector fields that preserve a differential form on a Riemann sphere with Grassmann variables, one can construct a Superconformal Algebra by considering central extensions of the algebra of vector fields. In this note, the N=4 case is analyzed closely, where the presence of weight zero operators in the field theory forces the introduction of non-central extensions. How this modifies the existing Field Theory, Representation Theory and Gelfand-Fuchs constructions is discussed. It is also discussed how graded Riemann sphere geometry can be used to give a geometrical description of the central charge in the N=1 theory.Comment: 16 Pages, LaTeX2e, references added, typesetting fixed, Journal ref adde

Role of anisotropic impurity scattering in anisotropic superconductors

A theory of nonmagnetic impurities in an anisotropic superconductor including the effect of anisotropic (momentum-dependent) impurity scattering is given. It is shown that for a strongly anisotropic scattering the reduction of the pair-breaking effect of the impurities is large. For a significant overlap between the anisotropy functions of the scattering potential and that of the pair potential and for a large amount of anisotropic scattering rate in impurity potential the superconductivity becomes robust vis a vis impurity concentration. The implications of our result for YBCO high-temperature superconductor are discussed.Comment: 14 pages, RevTeX, 5 PostScript figures, to be published in Phys. Rev. B (December 1, 1996

Microscale Modeling of High-Temperature Heat Transfer in Anisotropic Porous Materials

No abstract availabl

Observation of Ground-State Two-Neutron Decay

Neutron decay spectroscopy has become a successful tool to explore nuclear properties of nuclei with the largest neutron-to-proton ratios. Resonances in nuclei located beyond the neutron dripline are accessible by kinematic reconstruction of the decay products. The development of two-neutron detection capabilities of the Modular Neutron Array (MoNA) at NSCL has opened up the possibility to search for unbound nuclei which decay by the emission of two neutrons. Specifically this exotic decay mode was observed in 16Be and 26O.Comment: To be published in Acta Physica Polonica

Exploring the Low-ZZ Shore of the Island of Inversion at N=19N = 19

The technique of invariant mass spectroscopy has been used to measure, for the first time, the ground state energy of neutron-unbound $^{28}\textrm{F},$ determined to be a resonance in the $^{27}\textrm{F} + n$ continuum at $2\underline{2}0 (\underline{5}0)$ keV. States in $^{28}\textrm{F}$ were populated by the reactions of a 62 MeV/u $^{29}\textrm{Ne}$ beam impinging on a 288 $\textrm{mg/cm}^2$ beryllium target. The measured $^{28}\textrm{F}$ ground state energy is in good agreement with USDA/USDB shell model predictions, indicating that $pf$ shell intruder configurations play only a small role in the ground state structure of $^{28}\textrm{F}$ and establishing a low-$Z$ boundary of the island of inversion for N=19 isotones.Comment: 5 pages, 4 figures, to be published in Phys. Rev. Let

Psychophysical Investigations into the Role of Low-Threshold C Fibres in Non-Painful Affective Processing and Pain Modulation

We recently showed that C low-threshold mechanoreceptors (CLTMRs) contribute to touch-evoked pain (allodynia) during experimental muscle pain. Conversely, in absence of ongoing pain, the activation of CLTMRs has been shown to correlate with a diffuse sensation of pleasant touch. In this study, we evaluated (1) the primary afferent fibre types contributing to positive (pleasant) and negative (unpleasant) affective touch and (2) the effects of tactile stimuli on tonic muscle pain by varying affective attributes and frequency parameters. Psychophysical observations were made in 10 healthy participants. Two types of test stimuli were applied: stroking stimulus using velvet or sandpaper at speeds of 0.1, 1.0 and 10.0 cm/s; focal vibrotactile stimulus at low (20 Hz) or high (200 Hz) frequency. These stimuli were applied in the normal condition (i.e. no experimental pain) and following the induction of muscle pain by infusing hypertonic saline (5%) into the tibialis anterior muscle. These observations were repeated following the conduction block of myelinated fibres by compression of sciatic nerve. In absence of muscle pain, all participants reliably linked velvet-stroking to pleasantness and sandpaper-stroking to unpleasantness (no pain). Likewise, low-frequency vibration was linked to pleasantness and high-frequency vibration to unpleasantness. During muscle pain, the application of previously pleasant stimuli resulted in overall pain relief, whereas the application of previously unpleasant stimuli resulted in overall pain intensification. These effects were significant, reproducible and persisted following the blockade of myelinated fibres. Taken together, these findings suggest the role of low-threshold C fibres in affective and pain processing. Furthermore, these observations suggest that temporal coding need not be limited to discriminative aspects of tactile processing, but may contribute to affective attributes, which in turn predispose individual responses towards excitatory or inhibitory modulation of pain

Exploring the neutron dripline two neutrons at a time: The first observations of the 26O and 16Be ground state resonances

The two-neutron unbound ground state resonances of $^{26}$O and $^{16}$Be were populated using one-proton knockout reactions from $^{27}$F and $^{17}$B beams. A coincidence measurement of 3-body system (fragment + n + n) allowed for the decay energy of the unbound nuclei to be reconstructed. A low energy resonance, $<$ 200 keV, was observed for the first time in the $^{24}$O + n + n system and assigned to the ground state of $^{26}$O. The $^{16}$Be ground state resonance was observed at 1.35 MeV. The 3-body correlations of the $^{14}$Be + n + n system were compared to simulations of a phase-space, sequential, and dineutron decay. The strong correlations in the n-n system from the experimental data could only be reproduced by the dineutron decay simulation providing the first evidence for a dineutron-like decay.Comment: Invited Talk given at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

Task force on immigration and higher education in Central Massachusetts

In August 2007, the Colleges of Worcester Consortium, Inc. created a task force to examine the issue of immigration and higher education in Central Massachusetts. It has become increasingly clear from recent demographic and economic studies and projections that the population in the northeast, and certainly in Central Massachusetts, is showing minimal growth. There is evidence that a decline in the “native-born” population is caused by significant out-migration due to a number of factors, including the high cost of living, limited career opportunities and a declining birth rate. The limited population growth that is evident is due primarily to the recent influx of immigrants to this area, with the most significant numbers in Worcester coming from Ghana, Brazil, the Dominican Republic, Kenya, El Salvador, Albania and Liberia. It is also clear that the area’s economy is becoming more knowledge-based with an increasing percentage of all new jobs requiring some form of postsecondary education. According to the 2007 Massachusetts Department of Workforce Development’s Job Vacancy Survey, 38 percent of current job vacancies in Massachusetts require an associate’s degree or higher. This represents an increase from 30 percent in 2003. Consequently, the level of education that the immigrant population attains is of vital importance to everyone—not only to immigrant students and their families but also to the economic well-being of the entire region. The Task Force was charged with researching the barriers to higher education faced by this new wave of immigrants and suggesting recommendations to address those barriers. The 36-member Task Force was made up of representatives from Consortium member institutions; federal, state and local governments; community and faithbased organizations; the Worcester Public Schools; the Massachusetts Board of Higher Education; and the Massachusetts Immigrant and Refugee Advocacy (MIRA) Coalition. Meetings were held over six months, during which the Task Force identified three main barriers faced by immigrant communities in accessing higher education, and sub-committees were created to work on each of these. Speakers were invited to present on topics of interest. Two public hearings were held, the first of which was conducted at Worcester State College in October. It attracted community representatives, as well as college and high school faculty and administrators. The second hearing, held at the downtown branch of Quinsigamond Community College (QCC) in December, was attended by immigrants (English for Speakers of Other Languages – ESOL and GED) students as well as QCC staff.Published versio

Combined potential and spin impurity scattering in cuprates

We present a theory of combined nonmagnetic and magnetic impurity scattering in anisotropic superconductors accounting for the momentum-dependent impurity potential. Applying the model to the d-wave superconducting state, we obtain a quantitative agreement with the initial suppression of the critical temperature due to Zn and Ni substitutions as well as electron irradiation defects in the cuprates. We suggest, that the unequal pair-breaking effect of Zn and Ni may be related to a different nature of the magnetic moments induced by these impurities.Comment: 5 pages, 3 tables, RevTex, to be published in Phys. Rev.

Effect of anisotropic impurity scattering in superconductors

We discuss the weak-coupling BCS theory of a superconductor with the impurities, accounting for their anisotropic momentum-dependent potential. The impurity scattering process is considered in the t-matrix approximation and its influence on the superconducting critical temperature is studied in the Born and unitary limit for a d- and (d+s)-wave superconductors. We observe a significant dependence of the pair-breaking strength on the symmetry of the scattering potential and classify the impurity potentials according to their ability to alter T_c. A good agreement with the experimental data for Zn doping and oxygen irradiation in the overdoped cuprates is found.Comment: 31 pages, RevTex, 15 PostScript figure