1,339 research outputs found
Assessment of Subjective Experiences of Boys Entering the Community From a Correctional School
The purpose of this study was to explore, classify, and evaluate the personal experiences of juvenile offenders following release from a state training school.
During a two month period beginning in the fall of 1967, a group of twenty-three releasees from the MacLaren School for Boys in Woodburn, Oregon were interviewed on a weekly basis in the Portland metropolitan area. The boys, ranging in age from thirteen to seventeen were contacted in their homes, schools, and other settings to learn of positive, negative, and critical experiences encountered in the community.
Open ended questions based upon a twenty- seven item schedule were administered to the boys, focusing upon personal experiences in six major areas: school, family, peer group, community, work and authority. Responses were recorded verbatim and classified according to the boys\u27 judgments of positive and negative connotations. Critical experiences were also recorded to determine specific incidents which brought the boys into contact with legal authorities or otherwise seriously affected their parole status.
Positive, negative, and critical experiences from this study were analyzed both descriptively and statistically. Null hypotheses were tested to determine the quality, quantity, and intensity of experiences with respect to such major variables as age of the boys, race, length of stay in the community, records of school attendance, and personality inventory characteristics. Experiences were similarly related with respect to other variables found to be present as a result of the interviewing experience.
Findings yielded evidence to indicate a predominance of negative experiences in the boys’ contacts with the community following release. The highest proportion of these occurred within the boys’ families, followed by contacts with authority and school, respectively. Peer group relationships for the boys indicated the highest proportion of positive experiences when compared with other major categories
Measuring kinetic coefficients by molecular dynamics simulation of zone melting
Molecular dynamics simulations are performed to measure the kinetic
coefficient at the solid-liquid interface in pure gold. Results are obtained
for the (111), (100) and (110) orientations. Both Au(100) and Au(110) are in
reasonable agreement with the law proposed for collision-limited growth. For
Au(111), stacking fault domains form, as first reported by Burke, Broughton and
Gilmer [J. Chem. Phys. {\bf 89}, 1030 (1988)]. The consequence on the kinetics
of this interface is dramatic: the measured kinetic coefficient is three times
smaller than that predicted by collision-limited growth. Finally,
crystallization and melting are found to be always asymmetrical but here again
the effect is much more pronounced for the (111) orientation.Comment: 8 pages, 9 figures (for fig. 8 : [email protected]). Accepted for
publication in Phys. Rev.
Paramagnetic reentrant effect in high purity mesoscopic AgNb proximity structures
We discuss the magnetic response of clean Ag coated Nb proximity cylinders in
the temperature range 150 \mu K < T < 9 K. In the mesoscopic temperature
regime, the normal metal-superconductor system shows the yet unexplained
paramagnetic reentrant effect, discovered some years ago [P. Visani, A. C.
Mota, and A. Pollini, Phys. Rev. Lett. 65, 1514 (1990)], superimposing on full
Meissner screening. The logarithmic slope of the reentrant paramagnetic
susceptibility chi_para(T) \propto \exp(-L/\xi_N) is limited by the condition
\xi_N=n L, with \xi_N=\hbar v_F/2 \pi k_B T, the thermal coherence length and
n=1,2,4. In wires with perimeters L=72 \mu m and L=130 \mu m, we observe
integer multiples n=1,2,4. At the lowest temperatures, \chi_para compensates
the diamagnetic susceptibility of the \textit{whole} AgNb structure.Comment: 4 pages, 4 figures (color
Superconducting proximity effect in a mesoscopic ferromagnetic wire
We present an experimental study of the transport properties of a
ferromagnetic metallic wire (Co) in metallic contact with a superconductor
(Al). As the temperature is decreased below the Al superconducting transition,
the Co resistance exhibits a significant dependence on both temperature and
voltage. The differential resistance data show that the decay length for the
proximity effect is much larger than we would simply expect from the exchange
field of the ferromagnet.Comment: 4 pages, 6 included epsf figures, published version with small
change
On the verge of Umdeutung in Minnesota: Van Vleck and the correspondence principle (Part One)
In October 1924, the Physical Review, a relatively minor journal at the time,
published a remarkable two-part paper by John H. Van Vleck, working in virtual
isolation at the University of Minnesota. Van Vleck combined advanced
techniques of classical mechanics with Bohr's correspondence principle and
Einstein's quantum theory of radiation to find quantum analogues of classical
expressions for the emission, absorption, and dispersion of radiation. For
modern readers Van Vleck's paper is much easier to follow than the famous paper
by Kramers and Heisenberg on dispersion theory, which covers similar terrain
and is widely credited to have led directly to Heisenberg's "Umdeutung" paper.
This makes Van Vleck's paper extremely valuable for the reconstruction of the
genesis of matrix mechanics. It also makes it tempting to ask why Van Vleck did
not take the next step and develop matrix mechanics himself.Comment: 82 page
Structural and electrical transport properties of superconducting Au{0.7}In{0.3} films: A random array of superconductor-normal metal-superconductor (SNS) Josephson junctions
The structural and superconducting properties of Au{0.7}In{0.3} films, grown
by interdiffusion of alternating Au and In layers, have been studied. The films
were found to consist of a uniform solid solution of Au{0.9}In{0.1}, with
excess In precipitated in the form of In-rich grains of various Au-In phases
(with distinct atomic compositions), including intermetallic compounds. As the
temperature was lowered, these individual grains became superconducting at a
particular transition temperature (Tc), determined primarily by the atomic
composition of the grain, before a fully superconducting state of zero
resistance was established. From the observed onset Tc, it was inferred that up
to three different superconducting phases could have formed in these
Au{0.7}In{0.3} films, all of which were embedded in a uniform Au{0.9}In{0.1}
matrix. Among these phases, the Tc of a particular one, 0.8 K, is higher than
any previously reported for the Au-In system. The electrical transport
properties were studied down to low temperatures. The transport results were
found to be well correlated with those of the structural studies. The present
work suggests that Au{0.7}In{0.3} can be modeled as a random array of
superconductor-normal metal-superconductor (SNS) Josephson junctions. The
effect of disorder and the nature of the superconducting transition in these
Au{0.7}In{0.3} films are discussed.Comment: 8 text pages, 10 figures in one separate PDF file, submitted to PR
Performance of a quasi-steady, multi megawatt, coaxial plasma thruster
The Los Alamos National Laboratory Coaxial Thruster Experiment (CTX) has been upgraded to enable the quasisteady operation of magnetoplasmadynamic (MPD) type thrusters at power levels from 2 to 40 MW for 10 ms. Diagnostics include an eight position, three axis magnetic field probe to measure magnetic field fluctuations during the pulse; a triple Langmuir probe to measure ion density, electron temperature, and plasma potential; and a time-of-flight neutral particle spectrometer to measure specific impulse. Here we report on the experimental observations and associated analysis and interpretation of long-pulse, quasisteady, coaxial thruster performance in the CTX device
Relationship between Structure, Entropy and Diffusivity in Water and Water-like Liquids
Anomalous behaviour of the excess entropy () and the associated scaling
relationship with diffusivity are compared in liquids with very different
underlying interactions but similar water-like anomalies: water (SPC/E and
TIP3P models), tetrahedral ionic melts (SiO and BeF) and a fluid with
core-softened, two-scale ramp (2SRP) interactions. We demonstrate the presence
of an excess entropy anomaly in the two water models. Using length and energy
scales appropriate for onset of anomalous behaviour, the density range of the
excess entropy anomaly is shown to be much narrower in water than in ionic
melts or the 2SRP fluid. While the reduced diffusivities () conform to the
excess entropy scaling relation, for all the systems
(Y. Rosenfeld, Phys. Rev. A {\bf 1977}, {\it 15}, 2545), the exponential
scaling parameter, , shows a small isochore-dependence in the case of
water. Replacing by pair correlation-based approximants accentuates the
isochore-dependence of the diffusivity scaling. Isochores with similar
diffusivity scaling parameters are shown to have the temperature dependence of
the corresponding entropic contribution. The relationship between diffusivity,
excess entropy and pair correlation approximants to the excess entropy are very
similar in all the tetrahedral liquids.Comment: 24 pages, 4 figures, to be published in Journal of Physical Chemistry
Nucleation and Bulk Crystallization in Binary Phase Field Theory
We present a phase field theory for binary crystal nucleation. In the
one-component limit, quantitative agreement is achieved with computer
simulations (Lennard-Jones system) and experiments (ice-water system) using
model parameters evaluated from the free energy and thickness of the interface.
The critical undercoolings predicted for Cu-Ni alloys accord with the
measurements, and indicate homogeneous nucleation. The Kolmogorov exponents
deduced for dendritic solidification and for "soft-impingement" of particles
via diffusion fields are consistent with experiment.Comment: 4 pages, 4 figures, accepted to PR
The medical student
The Medical Student was published from 1888-1921 by the students of Boston University School of Medicine
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