Evaporative Cooling of a Two-Component Degenerate Fermi Gas

We derive a quantum theory of evaporative cooling for a degenerate Fermi gas with two constituents and show that the optimum cooling trajectory is influenced significantly by the quantum statistics of the particles. The cooling efficiency is reduced at low temperatures due to Pauli blocking of available final states in each binary collision event. We compare the theoretical optimum trajectory with experimental data on cooling a quantum degenerate cloud of potassium-40, and show that temperatures as low as 0.3 times the Fermi temperature can now be achieved.Comment: 6 pages, 4 figure

Scattering of short laser pulses from trapped fermions

We investigate the scattering of intense short laser pulses off trapped cold fermionic atoms. We discuss the sensitivity of the scattered light to the quantum statistics of the atoms. The temperature dependence of the scattered light spectrum is calculated. Comparisons are made with a system of classical atoms who obey Maxwell-Boltzmann statistics. We find the total scattering increases as the fermions become cooler but eventually tails off at very low temperatures (far below the Fermi temperature). At these low temperatures the fermionic degeneracy plays an important role in the scattering as it inhibits spontaneous emission into occupied energy levels below the Fermi surface. We demonstrate temperature dependent qualitative changes in the differential and total spectrum can be utilized to probe quantum degeneracy of trapped Fermi gas when the total number of atoms are sufficiently large $(\geq 10^6)$. At smaller number of atoms, incoherent scattering dominates and it displays weak temperature dependence.Comment: updated figures and revised content, submitted to Phys.Rev.

Sympathetic cooling of an atomic Bose-Fermi gas mixture

Sympathetic cooling of an atomic Fermi gas by a Bose gas is studied by solution of the coupled quantum Boltzmann equations for the confined gas mixture. Results for equilibrium temperatures and relaxation dynamics are presented, and some simple models developed. Our study illustrate that a combination of sympathetic and forced evaporative cooling enables the Fermi gas to be cooled to the degenerate regime where quantum statistics, and mean field effects are important. The influence of mean field effects on the equilibrium spatial distributions is discussed qualitatively.Comment: 8 pages, 9 figures, accepted for publication in Phys.Rev.Let

Simultaneous Magneto-Optical Trapping of Two Lithium Isotopes

We confine 4 10^8 fermionic 6Li atoms simultaneously with 9 10^9 bosonic 7Li atoms in a magneto-optical trap based on an all-semiconductor laser system. We optimize the two-isotope sample for sympathetic evaporative cooling. This is an essential step towards the production of a quantum-degenerate gas of fermionic lithium atoms.Comment: 4 pages, 3 figure

Ecosystem Resilience and Threshold Response in the Galápagos Coastal Zone

Background: The Intergovernmental Panel on Climate Change (IPCC) provides a conservative estimate on rates of sea-level rise of 3.8 mm yr⁻¹ at the end of the 21st century, which may have a detrimental effect on ecologically important mangrove ecosystems. Understanding factors influencing the long-term resilience of these communities is critical but poorly understood. We investigate ecological resilience in a coastal mangrove community from the Galápagos Islands over the last 2700 years using three research questions: What are the 'fast and slow' processes operating in the coastal zone? Is there evidence for a threshold response? How can the past inform us about the resilience of the modern system?Methodology/Principal Findings: Palaeoecological methods (AMS radiocarbon dating, stable carbon isotopes (δ13C)) were used to reconstruct sedimentation rates and ecological change over the past 2,700 years at Diablas lagoon, Isabela, Galápagos. Bulk geochemical analysis was also used to determine local environmental changes, and salinity was reconstructed using a diatom transfer function. Changes in relative sea level (RSL) were estimated using a glacio-isostatic adjustment model. Non-linear behaviour was observed in the Diablas mangrove ecosystem as it responded to increased salinities following exposure to tidal inundations. A negative feedback was observed which enabled the mangrove canopy to accrete vertically, but disturbances may have opened up the canopy and contributed to an erosion of resilience over time. A combination of drier climatic conditions and a slight fall in RSL then resulted in a threshold response, from a mangrove community to a microbial mat.Conclusions/Significance: Palaeoecological records can provide important information on the nature of non-linear behaviour by identifying thresholds within ecological systems, and in outlining responses to 'fast and slow' environmental change between alternative stable states. This study highlights the need to incorporate a long-term ecological perspective when designing strategies for maximizing coastal resilience.</p

CMS physics technical design report : Addendum on high density QCD with heavy ions

Peer reviewe

Evolutionary awareness: Darwin among the organizational sciences

The purpose of this paper is to propose that organizational scientists can address this problem by embracing “evolutionary awareness” (EA). EA builds on theories and constructs developed in the evolutionary sciences that serve to add depth to theory building. Design/methodology/approach: The design of the paper is first to introduce the concept of EA and identify its four key constructs. Next, the authors apply EA to three areas of research within organizational science: human motivation, interpersonal communication and leadership. The authors’ intent is to show that EA constructs extend and deepen traditional organizational science theorizing. Thereby, the authors show that the problems noted above, i.e., lack of depth and maturing theories, can be addressed by embracing EA. Findings: The findings are that EA substantially enhances and freshens theorizing in the organizational sciences in the areas of human motivation, communication and leadership. By extension, other areas of interest will also benefit by embracing the EA perspective. Research limitations/implications: The implications of the research are many. Organizational scientists can advance theory building, research and practical prescriptions by embracing EA. They can also engage in interdisciplinary research programs with scholars in the evolutionary sciences eager to see their work having practical implications. The limitation of this work is that the authors were only able to show a limited application of EA to three areas of interest to organizational science scholars. Practical implications: The practical implications of this research are potentially far reaching. At this very moment, scholars in a wide array of disciplines are re-casting their views of humanity, cognition, values and other constructs based on the acceptance of evolution and its primary mechanism, variation and selection based on consequences. These changes will usher in new ideas about leadership, work-life balance, organizational purpose and many others. Social implications: A much-needed “consilience” across the human sciences through embracement of the EA perspective may provide insights that will advance human flourishing in organizations and beyond. The authors believe that an increasingly veridical understanding of humanity will produce substantial social impact. Originality/value: This work will provide an encompassing perspective that will assist organizational scholars in advancing their theory building and research questions. A much-needed “consilience” across the human sciences may provide insights that will advance human flourishing in organizations and beyond

Just how miserable is work? A meta-analysis comparing work and non-work affect.

Although we spend much of our waking hours working, the emotional experience of work, versus non-work, remains unclear. While the large literature on work stress suggests that work generally is aversive, some seminal theory and findings portray working as salubrious and perhaps as an escape from home life. Here, we examine the subjective experience of work (versus non-work) by conducting a quantitative review of 59 primary studies that assessed affect on working days. Meta-analyses of within-day studies indicated that there was no difference in positive affect (PA) between work versus non-work domains. Negative affect (NA) was higher for work than non-work, although the magnitude of difference was small (i.e., .22 SD, an effect size comparable to that of the difference in NA between different leisure activities like watching TV versus playing board games). Moderator analyses revealed that PA was relatively higher at work and NA relatively lower when affect was measured using "real-time" measurement (e.g., Experience Sampling Methodology) versus measured using the Day Reconstruction Method (i.e., real-time reports reveal a more favorable view of work as compared to recall/DRM reports). Additional findings from moderator analyses included significant differences in main effect sizes as a function of the specific affect, and, for PA, as a function of the age of the sample and the time of day when the non-work measurements were taken. Results for the other possible moderators including job complexity and affect intensity were not statistically significant

An examination of two positive organizational interventions: For whom do these interventions work?

Owing to the importance of employee psychological well-being for a variety of work- and non-workrelated outcomes, practitioners and scholars have begun to broaden the scope of workplace well-being interventions by incorporating principles from positive psychology. Among such positive interventions, gratitude exercises have arguably emerged as the gold standard practice, with much research pointing to their effectiveness. However, existing workplace interventions lack a true (i.e., no intervention) control group, and effects have been observed for some-but not all-outcomes tested. Therefore, the purpose of this brief report was to conduct a concise but methodologically rigorous evaluation of the effectiveness of 2 positive psychology workplace interventions in improving employee affect, and to examine potential moderators of intervention effectiveness. Ninety-two employees in a large social services agency were assigned to (a) a gratitude intervention, (b) an intervention in which participants alternated between the gratitude activity and one involving increasing social connectedness, or (c) a wait list control condition, for 1 month. Neither intervention produced a main effect on any of the 3 affective outcomes measured. However, agreeableness, conscientiousness, and job tenure were significant moderators of intervention effectiveness. We discuss the implications of these preliminary results in an effort to advance the literature on workplace positive psychology interventions