10,878 research outputs found
Molecular determinants of enterotoxigenic Escherichia coli heat-stable toxin secretion and delivery
Field Work Reflections: Journeys in Knowing and Not-Knowing
In this paper, I retrace my interest in narrative forms of inquiry. I begin by revisiting a series of research projects that I conducted early in my career, describing some of my own dissatisfactions with the methods I used at the time. I move on to a detailed reexamination of my first piece of narrative research, completed during my PhD. In that project I used a narrative pointed psychosocial method in an attempt to develop new knowledge in the field of drugs, ‘race’ and ethnicity. In the final section, I consider what I have learned from this approach in terms of knowing and not-knowing and how I have used this experience to explore different approaches to narrative inquiry. I finish by drawing out some lessons I have learned from these different studies, which I hope might be of relevance to other social work researchers
Coalescing at 8 GeV in the Fermilab Main Injector
For Project X, it is planned to inject a beam of 3 10**11 particles per bunch
into the Main Injector. To prepare for this by studying the effects of higher
intensity bunches in the Main Injector it is necessary to perform coalescing at
8 GeV. The results of a series of experiments and simulations of 8 GeV
coalescing are presented. To increase the coalescing efficiency adiabatic
reduction of the 53 MHz RF is required, resulting in ~70% coalescing efficiency
of 5 initial bunches. Data using wall current monitors has been taken to
compare previous work and new simulations for 53 MHz RF reduction, bunch
rotations and coalescing, good agreement between experiment and simulation was
found. Possible schemes to increase the coalescing efficiency and generate even
higher intensity bunches are discussed. These require improving the timing
resolution of the low level RF and/or tuning the adiabatic voltage reduction of
the 53 MHz.Comment: 3 pp. 3rd International Particle Accelerator Conference (IPAC 2012)
20-25 May 2012, New Orleans, Louisian
The design and evaluation of grazing incidence relay optics
X-ray astronomy, both solar and celestial, has many needs for high spatial resolution observations which have to be performed with electronic detectors. If the resolution is not to be detector limited, plate scales in excess of 25 microns arc/sec, corresponding to focal lengths greater than 5 m, are required. In situations where the physical size is restricted, the problem can be solved by the use of grazing incidence relay optics. A system was developed which employs externally polished hyperboloid-hyperboloid surfaces to be used in conjunction with a Wolter-Schwarzschild primary. The secondary is located in front of the primary focus and provides a magnification of 4, while the system has a plate scale of 28 microns arc/sec and a length of 1.9 m. The design, tolerance specification, fabrication and performance at visible and X-ray wavelengths of this optical system are described
Vacuum-UV negative photoion spectroscopy of CF3Cl, CF3Br and CF3I
Using synchrotron radiation negative ions have been detected by mass spectrometry following vacuum-UV photoexcitation of trifluorochloromethane (CFCl), trifluorobromomethane (CFBr) and trifluoroiodomethane (CFI). The anions F, X, F, FX, CF, CF and CF were observed from all three molecules, where X = Cl, Br or I, and their ion yields recorded in the range 8-35 eV. With the exception of Br and I, the anions observed show a linear dependence of signal with pressure, showing that they arise from unimolecular ion-pair dissociation. Dissociative electron attachment, following photoionization of CFBr and CFI as the source of low-energy electrons, is shown to dominate the observed Br and I signals, respectively. Cross sections for ion-pair formation are put on to an absolute scale by calibrating the signal strengths with those of F from both SF and CF. These anion cross sections are normalized to vacuum-UV absorption cross sections, where available, and the resulting quantum yields are reported. Anion appearance energies are used to calculate upper limits to 298 K bond dissociation energies for (CF-X) which are consistent with literature values. We report new data for (CFI-F) ≤ 2.7 ± 0.2 eV and (CFI) ≤ (598 ± 22) kJ mol. No ion-pair formation is observed below the ionization energy of the parent molecule for CFCl and CFBr, and only weak signals (in both I and F) are detected for CFI. These observations suggest neutral photodissociation is the dominant exit channel to Rydberg state photoexcitation at these lower energies
Is there more to glycaemic control than meets the eye?
Tight glycaemic control has emerged as a major focus in critical care. However, the struggle to repeat, improve and standardize the results of the initial landmark studies is ongoing. The prospective computerized glycaemic control study by Shulman et al. highlights two emerging and often overlooked aspects of intensive insulin therapy protocols beyond simple glycaemic performance. First, the clinical ergonomics and ability to integrate into the critical care unit workflow must be considered as they may impact results and definitely affect uptake. Second, the real lessons of any protocol's performance are likely to be best realized by comparison with other results, a task that is very difficult without a consensus method of reporting that allows such comparisons across studies. Embracing these issues will take the field closer to accepted, repeatable approaches to tight glycaemic control
Collective processes of an ensemble of spin-1/2 particles
When the dynamics of a spin ensemble are expressible solely in terms of
symmetric processes and collective spin operators, the symmetric collective
states of the ensemble are preserved. These many-body states, which are
invariant under particle relabeling, can be efficiently simulated since they
span a subspace whose dimension is linear in the number of spins. However, many
open system dynamics break this symmetry, most notably when ensemble members
undergo identical, but local, decoherence. In this paper, we extend the
definition of symmetric collective states of an ensemble of spin-1/2 particles
in order to efficiently describe these more general collective processes. The
corresponding collective states span a subspace which grows quadratically with
the number of spins. We also derive explicit formulae for expressing arbitrary
identical, local decoherence in terms of these states.Comment: 12 pages, see 0805.2910 for simulations using these method
Efficient feedback controllers for continuous-time quantum error correction
We present an efficient approach to continuous-time quantum error correction
that extends the low-dimensional quantum filtering methodology developed by van
Handel and Mabuchi [quant-ph/0511221 (2005)] to include error recovery
operations in the form of real-time quantum feedback. We expect this paradigm
to be useful for systems in which error recovery operations cannot be applied
instantaneously. While we could not find an exact low-dimensional filter that
combined both continuous syndrome measurement and a feedback Hamiltonian
appropriate for error recovery, we developed an approximate reduced-dimensional
model to do so. Simulations of the five-qubit code subjected to the symmetric
depolarizing channel suggests that error correction based on our approximate
filter performs essentially identically to correction based on an exact quantum
dynamical model
- …