UML Deficiencies from the perspective of Automatic Performance Model Generation

A discussion surrounding the use of UML for distributed system design

A new approach to the evolution of cosmological perturbations on large scales

We discuss the evolution of linear perturbations about a Friedmann-Robertson-Walker background metric, using only the local conservation of energy-momentum. We show that on sufficiently large scales the curvature perturbation on spatial hypersurfaces of uniform-density is conserved when the non-adiabatic pressure perturbation is negligible. This is the first time that this result has been demonstrated independently of the gravitational field equations. A physical picture of long-wavelength perturbations as being composed of separate Robertson-Walker universes gives a simple understanding of the possible evolution of the curvature perturbation, in particular clarifying the conditions under which super-horizon curvature perturbations may vary.Comment: 8 pages, revtex, 1 figure, version to appear in Phys Rev D. Sign errors in original version corrected plus other minor addition

The Transition from School to Work: The Experiences of Blacks and Whites

Because much of the concern about youth unemployment is motivated by the large differences between the rates for blacks and whites, we have pursued our earlier work by analyzing separately for black and white youth the relationship between high school preparation and early labor force experience. We find no striking differences between the determinants of weeks worked by whites and non-whites upon graduation from high school. Although vocational training in high school bears little relationship to weeks worked upon graduation, hours worked while in high school bear a strong relationship to later employment for students and non-students, white and non-white. Academic performanceas measured by standardized test scores and high school class rank isalso positively related to later weeks worked by non-students, both white and non-white. Young persons find jobs in large part through friends and relatives or through direct application to employers orpossibly a combination of the two. Persons who are not looking forwork--and would then be classified as out of the labor force, according to standard definitions--are apparently quite distinct from personswho are looking for work. Those out of the labor force seem not tobe "discouraged workers" for the most part. Controlling for other individual attributes, non-whites are much more likely than whites to be in a post-secondary school full-time (although without controlling for these attributes the reverse is true). A large proportion of young men in school are also working part-time and a significant number are working full-time. A sizeable proportion of persons in post-secondary schools would be classified as unemployed based on official definitions. Indeed the unemployment rate among these full-time students is generally more than twice the rate among young men not inschool. Few high school graduates are chronically unemployed.

Five degree-of-freedom control of an ultra-precision magnetically-suspended linear bearing

The authors constructed a high precision linear bearing. A 10.7 kg platen measuring 125 mm by 125 mm by 350 mm is suspended and controlled in five degrees of freedom by seven electromagnets. The position of the platen is measured by five capacitive probes which have nanometer resolution. The suspension acts as a linear bearing, allowing linear travel of 50 mm in the sixth degree of freedom. In the laboratory, this bearing system has demonstrated position stability of 5 nm peak-to-peak. This is believed to be the highest position stability yet demonstrated in a magnetic suspension system. Performance at this level confirms that magnetic suspensions can address motion control requirements at the nanometer level. The experimental effort associated with this linear bearing system is described. Major topics are the development of models for the suspension, implementation of control algorithms, and measurement of the actual bearing performance. Suggestions for the future improvement of the bearing system are given

Analysis of Quark Mixing Using Binary Tetrahedral Flavor Symmetry

Using the binary tetrahedral group $T^{'}$, the three angles and phase of the quark CKM mixing matrix are pursued by symmetry-breaking which involves $T^{'}$-doublet VEVs and the Chen-Mahanthappa CP-violation mechanism. The NMRT$^{'}$M, Next-to-Minimal-Renormalizable -T$^{'}$-Model is described, and its one parameter comparison to experimental data is explored.Comment: 14 pages latex. Two .eps figures include

Non-gaussianity from the second-order cosmological perturbation

Several conserved and/or gauge invariant quantities described as the second-order curvature perturbation have been given in the literature. We revisit various scenarios for the generation of second-order non-gaussianity in the primordial curvature perturbation \zeta, employing for the first time a unified notation and focusing on the normalisation f_{NL} of the bispectrum. When the classical curvature perturbation first appears a few Hubble times after horizon exit, |f_{NL}| is much less than 1 and is, therefore, negligible. Thereafter \zeta (and hence f_{NL}) is conserved as long as the pressure is a unique function of energy density (adiabatic pressure). Non-adiabatic pressure comes presumably only from the effect of fields, other than the one pointing along the inflationary trajectory, which are light during inflation (`light non-inflaton fields'). During single-component inflation f_{NL} is constant, but multi-component inflation might generate |f_{NL}| \sim 1 or bigger. Preheating can affect f_{NL} only in atypical scenarios where it involves light non-inflaton fields. The curvaton scenario typically gives f_{NL} \ll -1 or f_{NL} = +5/4. The inhomogeneous reheating scenario can give a wide range of values for f_{NL}. Unless there is a detection, observation can eventually provide a limit |f_{NL}| \lsim 1, at which level it will be crucial to calculate the precise observational limit using second order theory.Comment: Latex file in Revtex style. 13 pages, 1 figure. v2: minor changes. Discussion in Subsection VI-A enlarged. References added. Conclusions unchanged. v3: minor typographic changes. Correlated and uncorrelated \chi^2 non-gaussianity concepts and consequences introduced. Section VI-A enlarged. Small change in Table I. References updated and added. Conclusions unchanged. Version to appear in Physical Review

Peeling Back the Onion of Cyber Espionage after Tallinn 2.0

Tallinn 2.0 represents an important advancement in the understanding of international law’s application to cyber operations below the threshold of force. Its provisions on cyber espionage will be instrumental to states in grappling with complex legal problems in the area of digital spying. The law of cyber espionage as outlined by Tallinn 2.0, however, is substantially based on rules that have evolved outside of the digital context, and there exist serious ambiguities and limitations in its framework. This Article will explore gaps in the legal structure and consider future options available to states in light of this underlying mismatch

Pensions, The Option Value of Work, and Retirement

The paper develops a model of retirement based on the option value of continuing to work. Continuing to work maintains the option of retiring on more advantageous terms later. The model is used to estimate the effects on retirement of firm pension plan provisions. Typical defined benefit pension plans in the United States provide very substantial incentives to remain with the firm until some age, often the early retirement age, and then a strong incentive to leave the firm thereafter. (This may be a major reason for the rapidly declining labor force participation rates of older workers in the United States.) The model fits firm retirement data very well; it captures very closely the sharp discontinuous jumps in retirement rates at specific ages. The model is used to simulate the effect on retirement of potential changes in pension plan provisions. Increasing the age of early retirement from 55 to 60, for example, would reduce firm departure rates between ages 50 and 59 by almost forty percent.