Quantum Effects in the Mechanical Properties of Suspended Nanomechanical Systems

We explore the quantum aspects of an elastic bar supported at both ends and subject to compression. If strain rather than stress is held fixed, the system remains stable beyond the buckling instability, supporting two potential minima. The classical equilibrium transverse displacement is analogous to a Ginsburg-Landau order parameter, with strain playing the role of temperature. We calculate the quantum fluctuations about the classical value as a function of strain. Excitation energies and quantum fluctuation amplitudes are compared for silicon beams and carbon nanotubes.Comment: RevTeX4. 5 pages, 3 eps figures. Submitted to Physical Review Letter

Quasielastic 12C(e,e'p) Reaction at High Momentum Transfer

We measured the 12C(e,e'p) cross section as a function of missing energy in parallel kinematics for (q,w) = (970 MeV/c, 330 MeV) and (990 MeV/c, 475 MeV). At w=475 MeV, at the maximum of the quasielastic peak, there is a large continuum (E_m > 50 MeV) cross section extending out to the deepest missing energy measured, amounting to almost 50% of the measured cross section. The ratio of data to DWIA calculation is 0.4 for both the p- and s-shells. At w=330 MeV, well below the maximum of the quasielastic peak, the continuum cross section is much smaller and the ratio of data to DWIA calculation is 0.85 for the p-shell and 1.0 for the s-shell. We infer that one or more mechanisms that increase with $\omega$ transform some of the single-nucleon-knockout into multinucleon knockout, decreasing the valence knockout cross section and increasing the continuum cross section.Comment: 14 pages, 7 figures, Revtex (multicol, prc and aps styles), to appear in Phys Rev

Nuclear Transparency to Intermediate-Energy Protons

Nuclear transparency in the (e,e'p) reaction for 135 < Tp < 800 MeV is investigated using the distorted wave approximation. Calculations using density-dependent effective interactions are compared with phenomenological optical potentials. Nuclear transparency is well correlated with proton absorption and neutron total cross sections. For Tp < 300 MeV there is considerable sensitivity to the choice of optical model, with the empirical effective interaction providing the best agreement with transparency data. For Tp > 300 MeV there is much less difference between optical models, but the calculations substantially underpredict transparency data and the discrepancy increases with A. The differences between Glauber and optical model calculations are related to their respective definitions of the semi-inclusive cross section. By using a more inclusive summation over final states the Glauber model emphasizes nucleon-nucleon inelasticity, whereas with a more restrictive summation the optical model emphasizes nucleon-nucleus inelasticity; experimental definitions of the semi-inclusive cross section lie between these extremes.Comment: uuencoded gz-compressed tar file containing revtex and bbl files and 5 postscript figures, totalling 31 pages. Uses psfi

Recoil Polarization Measurements for Neutral Pion Electroproduction at Q^2=1 (GeV/c)^2 Near the Delta Resonance

We measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q^2 = 1.0 (GeV/c)^2 in 10 bins of W across the Delta resonance. A total of 16 independent response functions were extracted, of which 12 were observed for the first time. Comparisons with recent model calculations show that response functions governed by real parts of interference products are determined relatively well near 1.232 GeV, but variations among models is large for response functions governed by imaginary parts and for both increases rapidly with W. We performed a nearly model-independent multipole analysis that adjusts complex multipoles with high partial waves constrained by baseline models. Parabolic fits to the W dependence of the multipole analysis around the Delta mass gives values for SMR = (-6.61 +/- 0.18)% and EMR = (-2.87 +/- 0.19)% that are distinctly larger than those from Legendre analysis of the same data. Similarly, the multipole analysis gives Re(S0+/M1+) = (+7.1 +/- 0.8)% at W=1.232 GeV, consistent with recent models, while the traditional Legendre analysis gives the opposite sign because its truncation errors are quite severe. Finally, using a unitary isobar model (UIM), we find that excitation of the Roper resonance is dominantly longitudinal with S1/2 = (0.05 +/- 0.01) GeV^(-1/2) at Q^2=1. The ReS0+ and ReE0+ multipoles favor pseudovector coupling over pseudoscalar coupling or a recently proposed mixed-coupling scheme, but the UIM does not reproduce the imaginary parts of 0+ multipoles well.Comment: 60 pages, 54 figure

The Quasielastic 3He(e,e'p)d Reaction at Q^2 = 1.5 GeV^2 for Recoil Momenta up to 1 GeV/c

We have studied the quasielastic 3He(e,e'p)d reaction in perpendicular coplanar kinematics, with the energy and momentum transferred by the electron fixed at 840 MeV and 1502 MeV/c, respectively. The 3He(e,e'p)d cross section was measured for missing momenta up to 1000 MeV/c, while the A_TL asymmetry was extracted for missing momenta up to 660 MeV/c. For missing momenta up to 150 MeV/c, the measured cross section is described well by calculations that use a variational ground-state wave function of the 3He nucleus derived from a potential that includes three-body forces. For missing momenta from 150 to 750 MeV/c, strong final-state interaction effects are observed. Near 1000 MeV/c, the experimental cross section is more than an order of magnitude larger than predicted by available theories. The A_TL asymmetry displays characteristic features of broken factorization, and is described reasonably well by available models.Comment: 5 pages, 3 figures, submitted to Physical Review Letters, v3: changed conten

The Impact of Major Events on the Lives of Family Caregivers of Children with Disabilities

Copyright 1996 Families International, Inc.The authors examine the family caregiving experience among families with children with severe emotional disabilities from a perspective that recognizes the importance of the family's views and feelings. This viewpoint anticipates the occurrence of both positive and negative experiences and seeks to illuminate the caregiving process from the perspective of outcomes achieved. Family caregivers of 164 children with serious emotional disorders were asked to identify major pleasant and stressful events that had occurred in the past 12 months. The most frequently described pleasant events related to children's behavior, school activities, and interactions with professionals and friends. Frequently described problem areas included children's behavior, professionals/services, and difficulty with school. The impact of these pleasant and stressful events was examined with respect to caregivers' perceived well-being: (I) overall stress, (2) the ability to fulfill responsibilities, and (3) pleasure experienced in various life domains. Implications of the study findings for supporting family caregivers in their roles are discussed

Measurement of the 3He(e,e'p)pn reaction at high missing energies and momenta

Results of the Jefferson Lab Hall A quasielastic 3He(e,e'p)pn measurements are presented. These measurements were performed at fixed transferred momentum and energy, q = 1502 MeV/c and omega = 840 MeV, respectively, for missing momenta p_m up to 1 GeV/c and missing energies in the continuum region, up to pion threshold; this kinematic coverage is much more extensive than that of any previous experiment. The cross section data are presented along with the effective momentum density distribution and compared to theoretical models.Comment: 5 pages, 3 figures, updated to reflect published paper: minor text changes from previous version along with updated and added reference

A Measurement of the Interference Structure Function, R_LT, for the 12C(e,e'p) reaction in the Quasielastic Region

The coincidence cross-section and the interference structure function, R_LT, were measured for the 12C(e,e'p) 11B reaction at quasielastic kinematics and central momentum transfer of q=400 MeV/c. The measurement was at an opening angle of theta_pq=11 degrees, covering a range in missing energy of E_m = 0 to 65 MeV. The R_LT structure function is found to be consistent with zero for E_m > 50 MeV, confirming an earlier study which indicated that R_L vanishes in this region. The integrated strengths of the p- and s-shell are compared with a Distorted Wave Impulse Approximation calculation. The s-shell strength and shape are compared with a Hartree Fock-Random Phase Approximation calculation. The DWIA calculation overestimates the cross sections for p- and s-shell proton knockout as expected, but surprisingly agrees with the extracted R_LT value for both shells. The HF-RPA calculation describes the data more consistently, which may be due to the inclusion of 2-body currents in this calculation.Comment: 8 Pages LaTex, 5 postscript figures. Submitted to Phys. Rev.

The reaction dynamics of the 16O(e,e'p) cross section at high missing energies

We measured the cross section and response functions (R_L, R_T, and R_LT) for the 16O(e,e'p) reaction in quasielastic kinematics for missing energies 25 <= E_miss <= 120 MeV at various missing momenta P_miss <= 340 MeV/c. For 25 < E_miss < 50 MeV and P_miss \approx 60 MeV/c, the reaction is dominated by single-nucleon knockout from the 1s1/2-state. At larger P_miss, the single-particle aspects are increasingly masked by more complicated processes. For E_miss > 60 MeV and P_miss > 200 MeV/c, the cross section is relatively constant. Calculations which include contributions from pion exchange currents, isobar currents and short-range correlations account for the shape and the transversity but only for half of the magnitude of the measured cross section.Comment: 6 pages, 4 figures, submitted to Phys Rev Lett, formatting error fixe

Large Momentum Transfer Measurements of the Deuteron Elastic Structure Function A(Q^2) at Jefferson Laboratory

The deuteron elastic structure function A(Q^2) has been extracted in the Q^2 range 0.7 to 6.0 (GeV/c)^2 from cross section measurements of elastic electron-deuteron scattering in coincidence using the Hall A Facility of Jefferson Laboratory. The data are compared to theoretical models based on the impulse approximation with inclusion of meson-exchange currents, and to predictions of quark dimensional scaling and perturbative quantum chromodynamicsComment: Submitted to Physical Review Letter