Hardening electronic devices against very high total dose radiation environments

The possibilities and limitations of hardening silicon semiconductor devices to the high neutron and gamma radiation levels and greater than 10 to the eighth power rads required for the NERVA nuclear engine development are discussed. A comparison is made of the high dose neutron and gamma hardening potential of bipolar, metal insulator semiconductors and junction field effect transistors. Experimental data is presented on device degradation for the high neutron and gamma doses. Previous data and comparisons indicate that the JFET is much more immune to the combined neutron displacement and gamma ionizing effects than other transistor types. Experimental evidence is also presented which indicates that p channel MOS devices may be able to meet the requirements

The Information Geometry of the One-Dimensional Potts Model

In various statistical-mechanical models the introduction of a metric onto the space of parameters (e.g. the temperature variable, $\beta$, and the external field variable, $h$, in the case of spin models) gives an alternative perspective on the phase structure. For the one-dimensional Ising model the scalar curvature, ${\cal R}$, of this metric can be calculated explicitly in the thermodynamic limit and is found to be ${\cal R} = 1 + \cosh (h) / \sqrt{\sinh^2 (h) + \exp (- 4 \beta)}$. This is positive definite and, for physical fields and temperatures, diverges only at the zero-temperature, zero-field ``critical point'' of the model. In this note we calculate ${\cal R}$ for the one-dimensional $q$-state Potts model, finding an expression of the form ${\cal R} = A(q,\beta,h) + B (q,\beta,h)/\sqrt{\eta(q,\beta,h)}$, where $\eta(q,\beta,h)$ is the Potts analogue of $\sinh^2 (h) + \exp (- 4 \beta)$. This is no longer positive definite, but once again it diverges only at the critical point in the space of real parameters. We remark, however, that a naive analytic continuation to complex field reveals a further divergence in the Ising and Potts curvatures at the Lee-Yang edge.Comment: 9 pages + 4 eps figure

Electromagnetic self-force on a charged particle on Kerr spacetime: equatorial circular orbits

We calculate the self-force acting on a charged particle on a circular geodesic orbit in the equatorial plane of a rotating black hole. We show by direct calculation that the dissipative self-force balances with the sum of the flux radiated to infinity and through the black hole horizon. Prograde orbits are found to stimulate black hole superradiance, but we confirm that the condition for floating orbits cannot be met. We calculate the conservative component of the self-force by application of the mode sum regularization method, and we present a selection of numerical results. By numerical fitting, we extract the leading-order coefficients in post-Newtonian expansions. The self-force on the innermost stable circular orbits of the Kerr spacetime is calculated, and comparisons are drawn between the electromagnetic and gravitational self forces.Comment: 41 pages, 10 figures, 1 tabl

Persistent pain after caesarean section and its association with maternal anxiety and socioeconomic background

Background: Pain, both from the surgical site, and from other sources such as musculoskeletal backache, can persist after caesarean section. In this study of a predominantly socially deprived population we have sought to prospectively examine the association between antenatal maternal anxiety and socioeconomic background and the development of persistent pain of all sources after caesarean section. Methods: Demographic details and an anxiety questionnaire were completed by 205 women before elective caesarean section. On the first postoperative day, pain scores were recorded, and at four months patients were asked to complete a Brief Pain Inventory and an Edinburgh Postnatal Depression Score. Results: Of 205 parturients recruited, 186 records were complete at the hospital admission phase and 98 (52.7%) were complete at the four-month follow-up phase. At recruitment, 15.1% reported pain. At four months 41.8% (95% CI 32.1 to 51.6%) reported pain, of whom pain was a new finding in 35.7% (95% CI 26.2 to 45.2%). Antenatal anxiety was not a significant predictor of severity of new pain at four months (P=0.43 for state anxiety, P=0.52 for trait anxiety). However, four-month pain severity did correlate with social deprivation (P=0.011), postnatal depression (P<0.001) and pain at 24 h (P=0.018). Conclusion: Persistent pain from a variety of sources after caesarean section is common. Our findings do not support the use of antenatal anxiety scoring to predict persistent pain in this setting, but suggest that persistent pain is influenced by acute pain, postnatal depression and socioeconomic deprivation

Study of thermal protection requirements for a lifting body entry vehicle suitable for near-earth missions Final report

Reentry and abort trajectory analyses, and thermal protection requirements for lifting body entry vehicle

Effective Action of Spontaneously Broken Gauge Theories

The effective action of a Higgs theory should be gauge-invariant. However, the quantum and/or thermal contributions to the effective potential seem to be gauge-dependent, posing a problem for its physical interpretation. In this paper, we identify the source of the problem and argue that in a Higgs theory, perturbative contributions should be evaluated with the Higgs fields in the polar basis, not in the Cartesian basis. Formally, this observation can be made from the derivation of the Higgs theorem, which we provide. We show explicitly that, properly defined, the effective action for the Abelian Higgs theory is gauge invariant to all orders in perturbation expansion when evaluated in the covariant gauge in the polar basis. In particular, the effective potential is gauge invariant. We also show the equivalence between the calculations in the covariant gauge in the polar basis and the unitary gauge. These points are illustrated explicitly with the one-loop calculations of the effective action. With a field redefinition, we obtain the physical effective potential. The SU(2) non-Abelian case is also discussed.Comment: Expanded version, 32 pages, figures produced by LaTeX, plain LaTe