The Pion in Electromagnetic and Weak Neutral Current Nuclear Response Functions

The impact of pionic correlations and meson--exchange currents in determining the (vector) response functions for electroweak quasielastic lepton scattering from nuclei is discussed. The approach taken builds on previous work where the Fermi gas model is used to maintain consistency in treating forces and currents (gauge invariance) and to provide a Lorentz covariant framework. Results obtained in first-order perturbation theory are compared with infinite-order summation schemes (HF and RPA) and found to provide quite successful approximations for the quasielastic response functions. The role of pionic correlations in hardening the responses R_L and R_T is investigated in some detail, including studies of the relative importance of central and tensor pieces of the force and of exchange and self-energy diagrams; in addition, their role in significantly modifying the longitudinal parity-violating response R_{AV}^L is explored. The MEC are shown to provide a small, but non-negligible, contribution in determining the vector responses.Comment: TeX, 21 figures (Postscript, available from the authors), MIT preprint CTP\#219

Comparison of Anterior Cruciate Ligament Graft Materials and Risk of Rupture/Reinjury in Young Athletes

The anterior cruciate ligament tear is a standard surgical injury seen with young athletes competing at elite, amateur, and recreational capacities. The purpose of this literature review is to determine the rehabilitation guidelines and risks associated with anterior cruciate ligament reconstruction, as well as determining the role of rehabilitation in graft rupture. This literature review also serves to determine if graft choice for surgical repair plays a role in an increased risk of rupture or reinjury. This literature review used various online databases, including Dynamed, Cochran, and Pubmed, with the utilization of MeSH terms listed below in “keywords” in order to identify applicable data. A systematic review of the literature was then completed. Data showed that athletes near or younger than the age of 25 were at a higher risk of graft rupture. The patellar tendon graft shows a decreased risk of rupture and instability when compared to hamstring grafts. Allografts were found to have an increased risk of rupture in young athletes when compared to hamstring grafts and should not be considered for young athletes. Failure to complete a rehabilitation program was also determined to play a role in graft rupture. Keywords

Best Practices in the use of Employee Assessment Instruments in Leadership Development

Companies both large and small have been interested for decades in offering skill, talent and leadership development opportunities for their employees. These experiences can take place through a variety of talent management methods through selection, formal and informal training, performance management and succession planning. One of the most common ways to begin or enhance any development for teams or individuals is through the use of assessments, surveys and instruments employees complete online or fill out in paper format. Utilization of assessment instruments is a beneficial practice in creating a foundation where individuals begin to understand differences in leadership styles, decision making approaches and work preferences. This study focused on defining best practices for companies using assessment instruments across the spectrum of talent management systems and in particular leadership development

Meson-exchange contributions to the nuclear charge operator

The role of the meson-exchange current correction to the nuclear charge operator is studied in electron scattering processes involving the excitation of medium and heavy nuclei to energies up to the quasi-elastic peak. The effect of these contributions in the quasi-free electron scattering process is a reduction of at most a 3% in the longitudinal response at the energy of the peak, a value which is below the experimental error and must not be taken into account in calculations in this energy region. On the other hand, the excitation of low-lying nuclear levels of neutronic character shows, with respect to the protonic ones, a considerable effect due to the inclusion of the two-body term in the charge operator. More realistic calculations, such as those performed in the random-phase approximation framework, give rise to a mixing of one particle-one hole configurations of both kinds which reduce these effects. However, it has been found that the excitation of some of these levels is sizeably affected by the meson-exchange contribution. More precise experimental data concerning some of these states, such as e.g. the high-spin states in 208Pb, could throw some light in the problem of a more feasible determination of these effects and, as a consequence, could provide an alternative procedure to obtain the charge neutron form factor.Comment: 26 pages, 10 figures, LateX file and Postscript figure

The Ins and Outs of Undergraduate Research and Leadership: A Student\u27s Perspective

This manuscript is a reflective write-up of Regina Hockert’s experience in completing KINE 462, Honors Kinesiology Senior Project, during the 2022 Fall Quarter. It describes their experience as an undergraduate research leader, including specific milestones and artifacts related to a broader replication study and the daily activities of Dr. Jafrā Thomas’ lab. This essay was designed to be a written reflection around their senior project presentation and the insights shared through that medium about the senior project experience. It is created to showcase lessons learned in relationship with the tasks and responsibilities required of working in-depth on student-led research. There are a series of appendices to this manuscript that include images, documents, and other artifacts that were collected and analyzed for the end-of-course presentation. This essay mirrors that presentation. Specifically, it focuses on three main milestones of (a) turning a literature review into a manuscript, (b) creating a recruitment sign-up form, and (c) creating recruitment tabling material to sign up participants for the broader replication study. The overarching goal of this essay submission was to provide information on the inner workings of a senior project and student research, as well as personal insight into challenges and skills developed through unexpected hurdles whilst working on the components of the senior project experience. This information contained within the insights presented can be used to advise the creation of future senior projects, assist in designing student-led research experiences, and allow people to become familiar with how student-led research may unfold

Delta-isobar relativistic meson exchange currents in quasielastic electron scattering

We study the role of the $\Delta$-isobar current on the response functions for high energy inclusive quasielastic electron scattering from nuclei. We consider a general Lagrangian which is compatible with contact invariance and perform a fully relativistic calculation in first-order perturbation theory for one-particle emission. The dependence of the responses upon off-shell parametrizations is analyzed and found to be mild. A discussion of scaling behaviour and a comparison with various non-relativistic approaches are also presented.Comment: 26 pages, 9 figures; one page of text added; corrected errors in eq

Consistent Treatment of Relativistic Effects in Electrodisintegration of the Deuteron

The influence of relativistic contributions to deuteron electrodisintegration is systematically studied in various kinematic regions of energy and momentum transfer. As theoretical framework the equation-of-motion and the unitarily equivalent S-matrix approaches are used. In a (p/M)-expansion, all leading order relativistic $\pi$-exchange contributions consistent with the Bonn OBEPQ model are included. In addition, static heavy meson exchange currents including boost terms, $\gamma\pi\rho/\omega$-currents, and $\Delta$-isobar contributions are considered. Sizeable effects from the various relativistic two-body contributions, mainly from $\pi$-exchange, have been found in inclusive form factors and exclusive structure functions for a variety of kinematic regions.Comment: 41 pages revtex including 15 postscript figure

Exchange Current Corrections to Neutrino--Nucleus Scattering

Relativistic exchange current corrections to neutrino--nucleus cross sections are presented assuming non--vanishing strange quark form factors for the constituent nucleons. For charged current processes the exchange current corrections can lower the impulse approximation results by 10\% while these corrections are found to be sensitive to both the nuclear density and the strange quark axial form factor of the nucleon for neutral current processes. Implications on the LSND experiment to determine this form factor are discussed.Comment: 11 pages, 2 figures, revtex 3.0, full postscript version of the file and figures available at http://www.nikhefk.nikhef.nl/projects/Theory/preprints/preprints.html To appear in Phys. Rev. Lett

Threshold Electrodisintegration of ^3He

Cross sections were measured for the near-threshold electrodisintegration of ^3He at momentum transfer values of q=2.4, 4.4, and 4.7 fm^{-1}. From these and prior measurements the transverse and longitudinal response functions R_T and R_L were deduced. Comparisons are made against previously published and new non-relativistic A=3 calculations using the best available NN potentials. In general, for q<2 fm^{-1} these calculations accurately predict the threshold electrodisintegration of ^3He. Agreement at increasing q demands consideration of two-body terms, but discrepancies still appear at the highest momentum transfers probed, perhaps due to the neglect of relativistic dynamics, or to the underestimation of high-momentum wave-function components.Comment: 9 pages, 7 figures, 1 table, REVTEX4, submitted to Physical Review