Vanishing of Gravitational Particle Production in the Formation of Cosmic Strings

We consider the gravitationally induced particle production from the quantum vacuum which is defined by a free, massless and minimally coupled scalar field during the formation of a gauge cosmic string. Previous discussions of this topic estimate the power output per unit length along the string to be of the order of $10^{68}$ ergs/sec/cm in the s-channel. We find that this production may be completely suppressed. A similar result is also expected to hold for the number of produced photons.Comment: 10 pages, Plain LaTex. Minor improvements. To appear in PR

Ionization of Rydberg atoms in a low frequency field: modelling by maps of transition to chaotic behavior

We investigate a microwave ionization of highly excited atom in a low frequency field and show that such a process may be studied on the bases of map for the electron energy change during the period of the electron motion between two subsequent passages at aphelion. Simple approximate criterion results to the threshold field for transition to chaotic behavior very close to the numerical results. We show that transition from adiabatic to chaotic ionization mechanism takes place when the field frequency to the electron's Kepler frequency ration approximately equals 0.1.Comment: 5 pages, LaTEX, 37Kb, 2 figures (compressed and uuencoded PostScript) included in text. To be published in Chaos: The interplay between stochastics, classics and quanta, Ed. by P. Garbaczewski, et al. Lecture notes in Physics, 1995

Quenching of spectroscopic factors for proton removal in oxygen isotopes

We present microscopic coupled-cluster calculations of the spectroscopic factors for proton removal from the closed-shell oxygen isotopes $^{14,16,22,24,28}$O with the chiral nucleon-nucleon interaction at next-to-next-to-next-to-leading order. We include coupling-to-continuum degrees of freedom by using a Hartree-Fock basis built from a Woods-Saxon single-particle basis. This basis treats bound and continuum states on an equal footing. We find a significant quenching of spectroscopic factors in the neutron-rich oxygen isotopes, pointing to enhanced many-body correlations induced by strong coupling to the scattering continuum above the neutron emission thresholds.Comment: 3 figure

Synthesis of imide/arylene ether copolymers for adhesives and composite matrices

A series of imide/arylene ether copolymers were prepared from the reaction of an amorphous arylene ether oligomer and a semi-crystalline imide oligomer. These copolymers were thermally characterized and mechanical properties were measured. One block copolymer was endcapped and the molecular weight was controlled to provide a material that displayed good compression moldability and attractive adhesion and composite properties

A LANCASTERIAN APPROACH FOR SPECIFYING DERIVED DEMANDS FOR RECREATIONAL ACTIVITIES

Demand and Price Analysis,

Extension of the item pocket method allowing for response review and revision to a computerized adaptive test using the generalized partial credit model

Computerized Adaptive Testing (CAT) has increased in the last few decades, due in part to the increased use and availability of personal computers, but also partly due to the benefits of CATs. CATs provide increased measurement precision of ability estimates while decreasing the demand on examinees with shorter tests. This is accomplished by tailoring the test to each examinee and selecting items that are not too difficult or too easy based on the examinees’ interim ability estimate and responses to previous items. These benefits come at the cost of the flexibility to move through the test as an examinee would with a Paper and Pencil (P & P) test. The algorithms used in CATs for item selection and ability estimation require restrictions to response review and revision; however, a large portion of examinees desire options for review and revision of responses (Vispoel, Clough, Bleiler, Hendrickson, and Ihrig, 2002). Previous research has examined response review and revision in CATs with limited review and revision options and are limited to after all items had been administered. The development of the Item Pocket (IP) method (Han, 2013) has allowed for response review and revision during the test, relaxing the restrictions, while maintaining an acceptable level of measurement precision. This is achieved by creating an item pocket in which items are placed, which are excluded from use in the interim ability estimation and the item selection procedures. The initial simulation study was conducted by Han (2013) who investigated the use of the IP method using a dichotomously-scored fixed length test. The findings indicated that the IP method does not substantially decrease measurement precision and bias in the ability estimates were within acceptable ranges for operational tests. This simulation study extended the IP method to a CAT using polytomously-scored items using the Generalized Partial Credit model with exposure control and content balancing. The IP method was implemented in tests with three IP sizes (2, 3, and 4), two termination criteria (fixed and variable), two test lengths (15 and 20), and two item completion conditions (forced to answer and ignored) for items remaining in the IP at the end of the test. Additionally, four traditional CAT conditions, without implementing the IP method, were included in the design. Results found that the longer, 20 item IP method conditions using the forced answer method had higher measurement precision, with higher mean correlations between known and estimated theta, lower mean bias and RMSE, and measurement precision increased as IP size increased. The two item completion conditions (forced to answer and ignored) resulted in similar measurement precision. The variable length IP conditions resulted in comparable measurement precision as the corresponding fixed length IP conditions. The implications of the findings and the limitations with suggestions for future research are also discussed.Educational Psycholog

Perimeter Generating Functions For The Mean-Squared Radius Of Gyration Of Convex Polygons

We have derived long series expansions for the perimeter generating functions of the radius of gyration of various polygons with a convexity constraint. Using the series we numerically find simple (algebraic) exact solutions for the generating functions. In all cases the size exponent $\nu=1$.Comment: 8 pages, 1 figur

1/z-renormalization of the mean-field behavior of the dipole-coupled singlet-singlet system HoF_3

The two main characteristics of the holmium ions in HoF_3 are that their local electronic properties are dominated by two singlet states lying well below the remaining 4f-levels, and that the classical dipole-coupling is an order of magnitude larger than any other two-ion interactions between the Ho-moments. This combination makes the system particularly suitable for testing refinements of the mean-field theory. There are four Ho-ions per unit cell and the hyperfine coupled electronic and nuclear moments on the Ho-ions order in a ferrimagnetic structure at T_C=0.53 K. The corrections to the mean-field behavior of holmium triflouride, both in the paramagnetic and ferrimagnetic phase, have been calculated to first order in the high-density 1/z-expansion. The effective medium theory, which includes the effects of the single-site fluctuations, leads to a substantially improved description of the magnetic properties of HoF_3, in comparison with that based on the mean-field approximation.Comment: 26pp, plain-TeX, JJ

Connectivity-Driven Coherence in Complex Networks

We study the emergence of coherence in complex networks of mutually coupled non-identical elements. We uncover the precise dependence of the dynamical coherence on the network connectivity, on the isolated dynamics of the elements and the coupling function. These findings predict that in random graphs, the enhancement of coherence is proportional to the mean degree. In locally connected networks, coherence is no longer controlled by the mean degree, but rather on how the mean degree scales with the network size. In these networks, even when the coherence is absent, adding a fraction s of random connections leads to an enhancement of coherence proportional to s. Our results provide a way to control the emergent properties by the manipulation of the dynamics of the elements and the network connectivity.Comment: 4 pages, 2 figure

Size and area of square lattice polygons

We use the finite lattice method to calculate the radius of gyration, the first and second area-weighted moments of self-avoiding polygons on the square lattice. The series have been calculated for polygons up to perimeter 82. Analysis of the series yields high accuracy estimates confirming theoretical predictions for the value of the size exponent, $\nu=3/4$, and certain universal amplitude combinations. Furthermore, a detailed analysis of the asymptotic form of the series coefficients provide the firmest evidence to date for the existence of a correction-to-scaling exponent, $\Delta = 3/2$.Comment: 12 pages 3 figure