3,305 research outputs found
A method for the analysis of the benefits and costs for aeronautical research and technology
A relatively simple, consistent, and reasonable methodology for performing cost-benefit analyses which can be used to guide, justify, and explain investments in aeronautical research and technology is presented. The elements of this methodology (labeled ABC-ART for the Analysis of the Benefits and Costs of Aeronautical Research and Technology) include estimation of aircraft markets; manufacturer costs and return on investment versus aircraft price; airline costs and return on investment versus aircraft price and passenger yield; and potential system benefits--fuel savings, cost savings, and noise reduction. The application of this methodology is explained using the introduction of an advanced turboprop powered transport aircraft in the medium range market in 1978 as an example
Viscoplasticity and large-scale chain relaxation in glassy-polymeric strain hardening
A simple theory for glassy polymeric mechanical response which accounts for
large scale chain relaxation is presented. It captures the crossover from
perfect-plastic response to strong strain hardening as the degree of
polymerization increases, without invoking entanglements. By relating
hardening to interactions on the scale of monomers and chain segments, we
correctly predict its magnitude. Strain activated relaxation arising from the
need to maintain constant chain contour length reduces the dependence of
the characteristic relaxation time by a factor during
active deformation at strain rate . This prediction is consistent
with results from recent experiments and simulations, and we suggest how it may
be further tested experimentally.Comment: The theoretical treatment of the mechanical response has been
significantly revised, and the arguments for coherent relaxation during
active deformation made more transparen
Higher Education Professionals Navigating Anti-Immigration Policy for Undocumented Students
Higher education professionals are critical to undocumented students’ educational success as their access to higher education is heavily dependent on being able to interpret and navigate policies. This study presents an analysis of policies that impact higher education access for undocumented students coupled with a qualitative case study that examines how anti-immigration policy affects the experiences of higher education professionals who worked directly with undocumented students in the state of Indiana. The authors help readers understand the experiences and challenges facing these “pathfinders” as they attempt to navigate the mazes of federal, state, and institutional policy to help their undocumented students
Parallel-Processing Equalizers for Multi-Gbps Communications
Architectures have been proposed for the design of frequency-domain least-mean-square complex equalizers that would be integral parts of parallel- processing digital receivers of multi-gigahertz radio signals and other quadrature-phase-shift-keying (QPSK) or 16-quadrature-amplitude-modulation (16-QAM) of data signals at rates of multiple gigabits per second. Equalizers as used here denotes receiver subsystems that compensate for distortions in the phase and frequency responses of the broad-band radio-frequency channels typically used to convey such signals. The proposed architectures are suitable for realization in very-large-scale integrated (VLSI) circuitry and, in particular, complementary metal oxide semiconductor (CMOS) application- specific integrated circuits (ASICs) operating at frequencies lower than modulation symbol rates. A digital receiver of the type to which the proposed architecture applies (see Figure 1) would include an analog-to-digital converter (A/D) operating at a rate, fs, of 4 samples per symbol period. To obtain the high speed necessary for sampling, the A/D and a 1:16 demultiplexer immediately following it would be constructed as GaAs integrated circuits. The parallel-processing circuitry downstream of the demultiplexer, including a demodulator followed by an equalizer, would operate at a rate of only fs/16 (in other words, at 1/4 of the symbol rate). The output from the equalizer would be four parallel streams of in-phase (I) and quadrature (Q) samples
Use of the Global Alliance for Musculoskeletal Health survey module for estimating the population prevalence of musculoskeletal pain: Findings from the Solomon Islands
Background: Musculoskeletal (MSK) conditions are common and the biggest global cause of physical disability. The objective of the current study was to estimate the population prevalence of MSK-related pain using a standardized global MSK survey module for the first time. Methods: A MSK survey module was constructed by the Global Alliance for Musculoskeletal Health Surveillance Taskforce and the Global Burden of Disease MSK Expert Group. The MSK module was included in the 2015 Solomon Islands Demographic and Health Survey. The sampling design was a two-stage stratified, nationally representative sample of households. Results: A total of 9214 participants aged 15-49 years were included in the analysis. The age-standardized four-week prevalence of activity-limiting low back pain, neck pain, and hip and/or knee pain was 16.8, 8.9, and 10.8%, respectively. Prevalence tended to increase with age, and be higher in those with lower levels of education. Conclusions: Prevalence of activity-limited pain was high in all measured MSK sites. This indicates an important public health issue for the Solomon Islands that needs to be addressed. Efforts should be underpinned by integration with strategies for other non-communicable diseases, aging, disability, and rehabilitation, and with other sectors such as social services, education, industry, and agriculture. Primary prevention strategies and strategies aimed at self-management are likely to have the greatest and most cost-effective impact
Strain Hardening of Polymer Glasses: Entanglements, Energetics, and Plasticity
Simulations are used to examine the microscopic origins of strain hardening
in polymer glasses. While stress-strain curves for a wide range of temperature
can be fit to the functional form predicted by entropic network models, many
other results are fundamentally inconsistent with the physical picture
underlying these models. Stresses are too large to be entropic and have the
wrong trend with temperature. The most dramatic hardening at large strains
reflects increases in energy as chains are pulled taut between entanglements
rather than a change in entropy. A weak entropic stress is only observed in
shape recovery of deformed samples when heated above the glass transition.
While short chains do not form an entangled network, they exhibit partial shape
recovery, orientation, and strain hardening. Stresses for all chain lengths
collapse when plotted against a microscopic measure of chain stretching rather
than the macroscopic stretch. The thermal contribution to the stress is
directly proportional to the rate of plasticity as measured by breaking and
reforming of interchain bonds. These observations suggest that the correct
microscopic theory of strain hardening should be based on glassy state physics
rather than rubber elasticity.Comment: 15 pages, 12 figures: significant revision
Hyperuricaemia, gout and allopurinol in the CKD Queensland registry
Introduction There is scant data on the role of hyperuricaemia, gout and allopurinol treatment in chronic kidney disease (CKD). Therefore, our aim is to investigate the possible associations between hyperuricaemia, gout, prescription of allopurinol and renal outcomes in patients with CKD.
Methods The retrospective cohort study involved 1123 Royal Brisbane and Women’s Hospital (RBWH) patients, enrolled in the CKD.QLD registry from May 2011 to August 2017. Patients were divided into two uric acid categories, with uric acid ≤ 0.36 mmol/L and > 0.36 mmol/L. Association of delta estimated glomerular filtration rate (eGFR) with gout, allopurinol treatment and hyperuricaemia were analysed.
Results Patients with an entry urate > 0.36 mmol/L were older, had higher body mass index (BMI) and worse baseline kidney function. Proportion of patients with gout, hyperuricaemia and allopurinol treatment increased with advanced CKD stages. Age-adjusted analysis revealed a significant association between serum urate level and delta eGFR, with no significant association between gout, treatment with allopurinol and delta eGFR. Furthermore, neither gout nor the prescription of allopurinol had a significant effect on the time to renal death (composite end point of kidney replacement therapy or death).
Conclusion Hyperuricaemia seemed to be independently associated with faster CKD progression or renal death. This was not observed with gout or prescription of allopurinol. Furthermore, allopurinol was not associated with decreased incidence of cardiovascular events. These data suggest that hyperuricaemia is likely the effect and not the cause of CKD or CKD progression
Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements and Crazing
Large-scale molecular simulations are performed to investigate tensile
failure of polymer interfaces as a function of welding time . Changes in the
tensile stress, mode of failure and interfacial fracture energy are
correlated to changes in the interfacial entanglements as determined from
Primitive Path Analysis. Bulk polymers fail through craze formation, followed
by craze breakdown through chain scission. At small welded interfaces are
not strong enough to support craze formation and fail at small strains through
chain pullout at the interface. Once chains have formed an average of about one
entanglement across the interface, a stable craze is formed throughout the
sample. The failure stress of the craze rises with welding time and the mode of
craze breakdown changes from chain pullout to chain scission as the interface
approaches bulk strength. The interfacial fracture energy is calculated
by coupling the simulation results to a continuum fracture mechanics model. As
in experiment, increases as before saturating at the average
bulk fracture energy . As in previous simulations of shear strength,
saturation coincides with the recovery of the bulk entanglement density. Before
saturation, is proportional to the areal density of interfacial
entanglements. Immiscibiltiy limits interdiffusion and thus suppresses
entanglements at the interface. Even small degrees of immisciblity reduce
interfacial entanglements enough that failure occurs by chain pullout and
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