1,025 research outputs found
Organic Ring Oscillators with Sub-200 ns Stage Delay Based on a Solution-Processed p-type Semiconductor Blend
High-frequency ring oscillators with sub-microsecond stage delay fabricated from spin-coated films of a specially formulated small-molecule/host-polymer blend are reported. Contacts and interconnects are patterned by photolithography with plasma etching used for creating vias and removing excess material to reduce parasitic effects. The characteristics of transistors with 4.6 μm channel length scale linearly with channel width over the range 60�2160 μm. Model device parameters extracted using Silvaco's Universal Organic Thin Film Transistor (UOTFT) Model yield values of hole mobility increasing from 1.9 to 2.6 cm2 Vs�1 as gate voltage increased. Simulated and fabricated Vgs = 0 inverters predict that the technology is capable of fabricating 5-stage ring oscillators operating above 100 kHz. Initial designs operated mainly at frequencies in the range 250�300 kHz, due to smaller parasitic gate overlap capacitances and higher supply voltages than assumed in the simulations. A design incorporating graded inverter sizes operates at frequencies above 400 kHz with the best reaching 529 kHz. The corresponding stage delay of 189 ns is the shortest reported to date for a solution-processed p-type semiconductor and compares favorably with similar circuits based on evaporated small molecules. Significant further improvements are identified which could lead to the fabrication of digital circuits that operate at much higher bit rates than previously reported
N identical particles under quantum confinement: A many-body dimensional perturbation theory approach
Systems that involve N identical interacting particles under quantum
confinement appear throughout many areas of physics, including chemical,
condensed matter, and atomic physics. In this paper, we present the methods of
dimensional perturbation theory, a powerful set of tools that uses symmetry to
yield simple results for studying such many-body systems. We present a detailed
discussion of the dimensional continuation of the N-particle Schrodinger
equation, the spatial dimension D -> infinity equilibrium (D^0) structure, and
the normal-mode (D^{-1}) structure. We use the FG matrix method to derive
general, analytical expressions for the many-body normal-mode vibrational
frequencies, and we give specific analytical results for three confined N-body
quantum systems: the N-electron atom, N-electron quantum dot, and N-atom
inhomogeneous Bose-Einstein condensate with a repulsive hardcore potential
Effects of Strong Magnetic Fields in Strange Baryonic Matter
We investigate the effects of very strong magnetic fields upon the equation
of state of dense bayonic matter in which hyperons are present. In the presence
of a magnetic field, the equation of state above nuclear density is
significantly affected both by Landau quantization and magnetic moment
interactions, but only for field strengths G. The former
tends to soften the EOS and increase proton and lepton abundances, while the
latter produces an overall stiffening of the EOS. Each results in a supression
of hyperons relative to the field-free case. The structure of a neutron star
is, however, primarily determined by the magnetic field stress. We utilize
existing general relativistic magneto-hydrostatic calculations to demonstrate
that maximum average fields within a stable neutron are limited to values G. This is not large enough to significantly influence
particle compositions or the matter pressure, unless fluctuations dominate the
average field strengths in the interior or configurations with significantly
larger field gradients are considered.Comment: 12 pages, 3 figures. To be submitted to Phys. Lett.
q-Newton binomial: from Euler to Gauss
A counter-intuitive result of Gauss (formulae (1.6), (1.7) below) is made
less mysterious by virtue of being generalized through the introduction of an
additional parameter
Intake of herbage and infective parasitic larvae by goats and sheep grazing annual pastures
Stabilization of Extra Dimensions and The Dimensionality of the Observed Space
We present a simple model for the late time stabilization of extra
dimensions. The basic idea is that brane solutions wrapped around extra
dimensions, which is allowed by string theory, will resist expansion due to
their winding mode. The momentum modes in principle work in the opposite way.
It is this interplay that leads to dynamical stabilization. We use the idea of
democratic wrapping \cite{art5}-\cite{art6}, where in a given decimation of
extra dimensions, all possible winding cases are considered. To simplify the
study further we assumed a symmetric decimation in which the total number of
extra dimensions is taken to be where N can be called the order of the
decimation. We also assumed that extra dimensions all have the topology of
tori. We show that with these rather conservative assumptions, there exists
solutions to the field equations in which the extra dimensions are stabilized
and that the conditions do not depend on . This fact means that there exists
at least one solution to the asymmetric decimation case. If we denote the
number of observed space dimensions (excluding time) by , the condition for
stabilization is for pure Einstein gravity and for dilaton
gravity massaged by string theory parameters.Comment: Final versio
Hyperthermic Fatigue Precedes a Rapid Reduction in Serum Sodium in an Ironman Triathlete: A Case Report
Purpose: To monitor the hydration, core temperature, and speed (pace) of a triathlete performing an Ironman triathlon. Methods: A 35-year-old experienced male triathlete participated in the Western Australian Ironman triathlon on December 1, 2006. The participant was monitored for blood Na+ concentration before the race (PRE), at the transitions (T1 and T2), halfway through the run (R21), and after the race (POST; 2hPOST). Core body temperature (Tc; pill telemetry) was recorded continuously, and running speed (s3 stride sensor) was measured during the run. Results: The participant completed the race in 11 h 38 min, in hot conditions (26.6 ± 5.8°C; 42 ± 19% rel. humidity). His Tc increased from 37.0 to 38.6°C during the 57-min swim, and averaged 38.4°C during the 335-min bike (33.5 km·h−1). After running at 12.4 km·h−1 for 50 min in the heat (33.1°C), Tc increased to 39.4°C, before slowing to 10.0 km·h−1 for 20 min. Tc decreased to 38.9°C until he experienced severe leg cramps, after which speed diminished to 6 km·h−1 and Tc fell to 38.0°C. The athlete’s blood Na+ was constant from PRE to T2 (139–140 mEq·L−1, but fell to 131 mEq·L−1 at R21, 133 mEq·L−1 at POST, and 128 mEq·L−1 at 2hPOST. The athlete consumed 9.25 L of fluid from PRE to T2, 6.25 L from T2 to POST, and lost 2% of his body mass, indicating sweat losses greater than 15.5 L. Conclusion: This athlete slowed during the run phase following attainment of a critically high Tc and experienced an unusually rapid reduction in blood Na+ that preceded cramping, despite presenting with signs of dehydration
What are communities of practice? A comparative review of four seminal works
This paper is a comparative review of four seminal works on communities of practice. It is argued that the ambiguities of the terms community and practice are a source of the concept's reusability allowing it to be reappropriated for different purposes, academic and practical. However, it is potentially confusing that the works differ so markedly in their conceptualizations of community, learning, power and change, diversity and informality. The three earlier works are underpinned by a common epistemological view, but Lave and Wenger's 1991 short monograph is often read as primarily about the socialization of newcomers into knowledge by a form of apprenticeship, while the focus in Brown and Duguid's article of the same year is, in contrast, on improvising new knowledge in an interstitial group that forms in resistance to management. Wenger's 1998 book treats communities of practice as the informal relations and understandings that develop in mutual engagement on an appropriated joint enterprise, but his focus is the impact on individual identity. The applicability of the concept to the heavily individualized and tightly managed work of the twenty-first century is questionable. The most recent work by Wenger – this time with McDermott and Snyder as coauthors – marks a distinct shift towards a managerialist stance. The proposition that managers should foster informal horizontal groups across organizational boundaries is in fact a fundamental redefinition of the concept. However it does identify a plausible, if limited, knowledge management (KM) tool. This paper discusses different interpretations of the idea of 'co-ordinating' communities of practice as a management ideology of empowerment
High-Spin Stretched States in Nuclei Excited via (p,n) Reactions
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Looking Beyond Inflationary Cosmology
In spite of the phenomenological successes of the inflationary universe
scenario, the current realizations of inflation making use of scalar fields
lead to serious conceptual problems which are reviewed in this lecture. String
theory may provide an avenue towards addressing these problems. One particular
approach to combining string theory and cosmology is String Gas Cosmology. The
basic principles of this approach are summarized.Comment: invited talk at "Theory Canada 1" (Univ. of British Columbia,
Vancouver, Canada, June 2 - 4, 2005) (references updated
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