Number squeezed and fragmented states of strongly interacting bosons in a double well

We present a systematic study of the phenomena of number squeezing and fragmentation for a repulsive Bose-Einstein condensate (BEC) in a three dimensional double well potential over a range of interaction strengths and barrier heights, including geometries that exhibit appreciable overlap in the one-body wavefunctions localized in the left and right wells. We compute the properties of the condensate with numerically exact, full dimensional path integral ground state (PIGS) Quantum Monte Carlo simulations and compare with results obtained from using two- and eight-mode truncated basis models. The truncated basis models are found to agree with the numerically exact PIGS simulations for weak interactions, but fail to correctly predict the amount of number squeezing and fragmentation exhibited by the PIGS simulations for strong interactions. We find that both number squeezing and fragmentation of the BEC show non-monotonic behavior at large values of interaction strength a. The number squeezing shows a universal scaling with the product of number of particles and interaction strength (Na) but no such universal behavior is found for fragmentation. Detailed analysis shows that the introduction of repulsive interactions not only suppresses number fluctuations to enhance number squeezing, but can also enhance delocalization across wells and tunneling between wells, each of which may suppress number squeezing. This results in a dynamical competition whose resolution shows a complex dependence on all three physical parameters defining the system: interaction strength, number of particles, and barrier height.Comment: 33 pages, 21 figures. Submitted for publication in Physical Review

Superdense objects in general relativity : modeling neutron stars with free quark cores

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2004.Includes bibliographical references (p. 65-66).We present the results of a numerical study of neutron stars made of a color-flavor locked (CFL) quark matter center and a nuclear fluid exterior. CFL quark matter is a theoretical state of matter which may exist at the center of highly dense neutron stars. To verify its existence, we need to make falsifiable predictions about the differences between typical neutron stars and CFL hybrid neutron stars and verify them observationally. This thesis begins this process by modelling the hybrid neutron stars at rest and while undergoing rotation. We show that Newtonian models are insufficient to correctly describe these objects; their treatment must be relativistic. We also put a bound on the upper rotation speed allowed by our approximations. Finally, we note the presence of the backbending instability in our hybrid star model which may constrain the physically accessible parameters of this model. The tools we have developed in this study are a first step in fully investigating the properties of these objects.by Joel C. Corbo.S.B

Unpacking challenges in student-faculty partnerships on Departmental Action Teams

This paper is a case study analysis of one student-faculty partnership working to enact departmental change. Students as Partners (SaP) is an approach in which students and faculty work in partnership on the co-design of a curricular or institutional change effort. Our team implements SaP through Departmental Action Teams (DATs), which are facilitated teams of faculty, students, and staff within a single STEM department working on an issue related to undergraduate education. In our research, we aim to understand the ways in which SaP becomes enacted in DATs. Through analyzing interviews with student and faculty members of a single DAT, we construct a case study of the complexities and challenges of student-faculty partnership. We find that members of a partnership can hold different views of that partnership. Underlying these differences are differing views about their joint work as well as differences in the visibility of power dynamics. In self-critically analyzing the ways in which we mitigated and reproduced power dynamics, we reflect on our project’s areas for growth

A Framework for Transforming Departmental Culture to Support Educational Innovation

This paper provides a research-based framework for promoting institutional change in higher education. To date, most educational change efforts have focused on relatively narrow subsets of the university system (e.g., faculty teaching practices or administrative policies) and have been largely driven by implicit change logics; both of these features have limited the success of such efforts at achieving sustained, systemic change. Drawing from the literature on organizational and cultural change, our framework encourages change agents to coordinate their activities across three key levels of the university and to ground their activities in the various change perspectives that emerge from that literature. We use examples from a change project that we have been carrying out at a large research university to illustrate how our framework can be used as a basis for planning and implementing holistic change.Comment: 15 pages, 0 figures, submitted to Physical Review Special Topics: Physics Education Researc

Developing the DELTA: Capturing cultural changes in undergraduate departments

Departments are now recognized as an important locus for sustainable change on university campuses. Making sustainable changes typically requires a shift in culture, but culture is complex and difficult to measure. For this reason, cultural changes are often studied using qualitative methods that provide rich, detailed data. However, this imposes barriers to measuring culture and studying change at scale (i.e., across many departments). To address this issue, we introduce the Departmental Education and Leadership Transformation Assessment (DELTA), a new survey aimed at capturing cultural changes in undergraduate departments. We describe the survey’s development and validation and provide sugges-tions for its utility for researchers and practitioners

Building Classroom and Organizational Structure Around Positive Cultural Values

The Compass Project is a self-formed group of graduate and undergraduate students in the physical sciences at UC Berkeley. Our goals are to improve undergraduate physics education, provide opportunities for professional development, and increase retention of students-especially those from populations typically underrepresented in the physical sciences. Compass fosters a diverse, collaborative student community by providing a wide range of services, including a summer program and fall/spring seminar courses. We describe Compass's cultural values, discuss how community members are introduced to and help shape those values, and demonstrate how a single set of values informs the structure of both our classroom and organization.We emphasize that all members of the Compass community participate in, and benefit from, our cultural values, regardless of status as student, teacher, or otherwise.Comment: 4 pages, to be submitted to PERC 2012 proceeding

Retrospective evaluation of whole exome and genome mutation calls in 746 cancer samples

Funder: NCI U24CA211006Abstract: The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that ~80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAF < 15%) and clonal heterogeneity contribute up to 68% of private WGS mutations and 71% of private WES mutations. We observe that ~30% of private WGS mutations trace to mutations identified by a single variant caller in WES consensus efforts. WGS captures both ~50% more variation in exonic regions and un-observed mutations in loci with variable GC-content. Together, our analysis highlights technological divergences between two reproducible somatic variant detection efforts

A team-based model that catalyzes sustained department-wide change

We developed a team-based model supporting departmental change and ran 17 change teams at two R1 universities between 2014 and 2021, in a wide variety of STEM academic departments. Change team members included faculty, staff, graduate students, and undergraduates. Teams were externally facilitated by project staff for a period of up to two years, and were supported in training internal facilitators to continue the work. Long-term impacts of the change teams were recently investigated by qualitatively analyzing interviews of former team members that took place 1–4 years following the end of external facilitation. In this presentation, we will describe qualitative coding of these rich interviews that illuminate a wide variety of impacts to individuals and departments. We found that most change teams, or another group in the department, sustained change by continuing to work on the change team’s original project. Sustained change frequently included structural changes to departmental curricula or policies, skill development of team members, and the spread of skills or cultural features from the change team to other departmental groups. Participating departments often experienced department-wide growth around the model’s core principles for change, such as engaging “students as partners” or demonstrating “a commitment to equity and inclusion through their work”. In alignment with the WCSE theme of Belonging, this presentation will include an examination of one change team’s work that resulted in both a substantial increase in the enrollment of underrepresented students and an increase in the sense of belonging among department majors