1,144 research outputs found
Scintillation observations of satellite signals
Scintillation observations of satellite signal
Prototype ultrasonic instrument for quantitative testing
Ultrasonic instrument has been developed for use in quantitative nondestructive evaluation of material defects such as cracks, voids, inclusions, and unbonds. Instrument is provided with standard pulse source and transducer for each frequency range selected and includes integral aids that allow calibration to prescribed standards
Dark matter within high surface brightness spiral galaxies
We present results from a detailed dynamical analysis of five high surface
brightness, late type spirals, studied with the aim to quantify the
luminous-to-dark matter ratio inside their optical radii. The galaxies' stellar
light distribution and gas kinematics have been observed and compared to
hydrodynamic gas simulations, which predict the 2D gas dynamics arising in
response to empirical gravitational potentials, which are combinations of
differing stellar disk and dark halo contributions. The gravitational potential
of the stellar disk was derived from near-infrared photometry, color-corrected
to constant (M/L); the dark halo was modelled by an isothermal sphere with a
core. Hydrodynamic gas simulations were performed for each galaxy for a
sequence of five different mass fractions of the stellar disk and for a wide
range of spiral pattern speeds. These two parameters mainly determine the
modelled gas distribution and kinematics. The agreement between the
non-axisymmetric part of the simulated and observed gas kinematics permitted us
to conclude that the galaxies with the highest rotation velocities tend to
possess near-maximal stellar disks. In less massive galaxies, with v_max<200
km/s, the mass of the dark halo at least equals the stellar mass within 2-3
R_disk. The simulated gas morphology provides a powerful tool to determine the
dominant spiral pattern speed. The corotation radius for all galaxies was found
to be constant at R_corotation ~ 3 R_disk and encloses the strong part of the
stellar spiral in all cases.Comment: 28 pages, 7 figures; to appear in the Astrophysical Journal, Vol.
586, March 200
Oral Health Activities of Early Head Start and Migrant and Seasonal Head Start Programs
Guidelines recommend that Migrant and Seasonal Head Start programs (MSHS) address the dental needs of children of migrant and seasonal farmworkers. This study describes parent- and child-oriented oral health activities of North Carolinaâs MSHS programs and compares them with non-migrant Early Head Start (EHS) programs using data collected from a questionnaire completed by teachers and family services staff. MSHS staff reported engaging in more oral health activities than EHS staff, which was confirmed by results of logit and ordered logit regression models. Despite promising findings about the engagement of MSHS staff, participation in oral health activities is lower than recommended. Differences between EHS and MSHS programs might be due to differing needs of enrolled children and families or to different approaches to meeting the needs of families
Oral Health Activities of Early Head Start Teachers Directed toward Children and Parents
ObjectivesâThis cross-sectional study examined Early Head Start (EHS) teachersâ oral health
program activities and their association with teacher and program characteristics.
MethodsâSelf-complete questionnaires were distributed to staff in all EHS programs in North
Carolina. Variables for dental health activities for parents (4 items) and children (4 items) were
constructed as the sum of responses to a 0-4 Likert-type scale (never to very frequently). Ordinary
least squares regression models examined the association between teachersâ oral health program
activities and modifiable teacher (oral health knowledge, values, self-efficacy, dental health
training, perceived barriers to dental activities) and program (director and health coordinator
knowledge and perceived barriers to dental activities) characteristics.
ResultsâTeachers in the parent (n=260) and child (n=231) analyses were a subset of the 485
staff respondents (98% response rate). Teachers engaged in child oral health activities
(range=0-16; mean=9.0) more frequently than parent activities (range=0-16; mean=6.9). Teachersâ
oral health values, perceived oral health self-efficacy, dental training, and director and health
coordinator knowledge were positively associated with oral health activities (P<0.05). Perceived
barriers were negatively associated with child activities (P<0.05).
ConclusionâThe level of oral health activity in EHS programs is less than optimal. Several
characteristics of EHS staff were identified that can be targeted with education interventions.
Evidence for effectiveness of EHS interventions needs to be strengthened, but results of this
survey provide encouraging findings about the potential effects of teacher training on their oral
health practices
Impact of measurement backaction on nuclear spin qubits in silicon
Phosphorus donor nuclear spins in silicon couple weakly to the environment
making them promising candidates for high-fidelity qubits. The state of a donor
nuclear spin qubit can be manipulated and read out using its hyperfine
interaction with the electron confined by the donor potential. Here we use a
master equation-based approach to investigate how the backaction from this
electron-mediated measurement affects the lifetimes of single and multi-donor
qubits. We analyze this process as a function of electric and magnetic fields,
and hyperfine interaction strength. Apart from single nuclear spin flips, we
identify an additional measurement-related mechanism, the nuclear spin
flip-flop, which is specific to multi-donor qubits. Although this flip-flop
mechanism reduces qubit lifetimes, we show that it can be effectively
suppressed by the hyperfine Stark shift. We show that using atomic precision
donor placement and engineered Stark shift, we can minimize the measurement
backaction in multi-donor qubits, achieving larger nuclear spin lifetimes than
single donor qubits
Compilation of extended recursion in call-by-value functional languages
This paper formalizes and proves correct a compilation scheme for
mutually-recursive definitions in call-by-value functional languages. This
scheme supports a wider range of recursive definitions than previous methods.
We formalize our technique as a translation scheme to a lambda-calculus
featuring in-place update of memory blocks, and prove the translation to be
correct.Comment: 62 pages, uses pi
Bodies, technologies and action possibilities: when is an affordance?
Borrowed from ecological psychology, the concept of affordances is often said to offer the social study of technology a means of re-framing the question of what is, and what is not, âsocialâ about technological artefacts. The concept, many argue, enables us to chart a safe course between the perils of technological determinism and social constructivism. This article questions the sociological adequacy of the concept as conventionally deployed. Drawing on ethnographic work on the ways technological artefacts engage, and are engaged by, disabled bodies, we propose that the âaffordancesâ of technological objects are not reducible to their material constitution but are inextricably bound up with specific, historically situated modes of engagement and ways of life
Detection of small-molecule enzyme inhibitors with peptides isolated from phage-displayed combinatorial peptide libraries
AbstractBackground: The rapidly expanding list of pharmacologically important targets has highlighted the need for ways to discover new inhibitors that are independent of functional assays. We have utilized peptides to detect inhibitors of protein function. We hypothesized that most peptide ligands identified by phage display would bind to regions of biological interaction in target proteins and that these peptides could be used as sensitive probes for detecting low molecular weight inhibitors that bind to these sites.Results: We selected a broad range of enzymes as targets for phage display and isolated a series of peptides that bound specifically to each target. Peptide ligands for each target contained similar amino acid sequences and competition analysis indicated that they bound one or two sites per target. Of 17 peptides tested, 13 were found to be specific inhibitors of enzyme function. Finally, we used two peptides specific for Haemophilus influenzae tyrosyl-tRNA synthetase to show that a simple binding assay can be used to detect small-molecule inhibitors with potencies in the micromolar to nanomolar range.Conclusions: Peptidic surrogate ligands identified using phage display are preferentially targeted to a limited number of sites that inhibit enzyme function. These peptides can be utilized in a binding assay as a rapid and sensitive method to detect small-molecule inhibitors of target protein function. The binding assay can be used with a variety of detection systems and is readily adaptable to automation, making this platform ideal for high-throughput screening of compound libraries for drug discovery
A bottom-up design framework for CAD tools to support design for additive manufacturing
Additive manufacturing (AM) technology is enabling a platform to produce parts with enhanced shape complexity. Design engineers are exploiting this capability to produce high performance functional parts. The current top-down approach to design for AM requires the designer to develop a design model in CAD software and then use optimization tools to adapt the design for the AM technology, however this approach neglects a number of desired criteria. This paper proposes an alternative bottom-up design framework for a new type of CAD tool which combines the knowledge required to design a part with evolutionary programming in order to design parts specifically for the AM platform.</p
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