8,523 research outputs found
Simulated acoustic emissions from coupled strings
We consider traveling transverse waves on two identical uniform taut strings that are elastically coupled through springs that gradually decrease their stiffness over a region of finite length. The wave system can be decomposed into two modes: an in-phase mode ( + ) that is transparent to the coupling springs, and an out-of-phase mode ( − ) that engages the coupling springs and can resonate at a particular location depending on the excitation frequency. The system exhibits linear mode conversion whereby an incoming ( + ) wave is reflected back from the resonance location both as a propagating ( + ) wave and an evanescent ( − ) wave, while both types emerge as propagating forward through the resonance location. We match a local transition layer expansion to the WKB expansion to obtain estimates of the reflection and transmission coefficients. The reflected waves may be an analog for stimulated emissions from the ear
Timescales of carbon turnover in soils with mixed crystalline mineralogies
Organic matter–mineral associations stabilize much of the carbon
(C) stored globally in soils. Metastable short-range-order (SRO) minerals
such as allophane and ferrihydrite provide one mechanism for long-term
stabilization of organic matter in young soil. However, in soils with few SRO
minerals and a predominance of crystalline aluminosilicate or Fe (and
Al) oxyhydroxide, C turnover should
be governed by chemisorption with those minerals. Here, we correlate mineral
composition from soils containing small amounts of SRO minerals with mean
turnover time (TT) of C estimated from radiocarbon (<sup>14</sup>C) in bulk soil,
free light fraction and mineral-associated organic matter. We varied the
mineral amount and composition by sampling ancient soils formed on different
lithologies in arid to subhumid climates in Kruger National Park (KNP), South
Africa. Mineral contents in bulk soils were assessed using chemical
extractions to quantify Fe oxyhydroxides and SRO minerals. Because of our
interest in the role of silicate clay mineralogy, particularly smectite
(2 : 1) and kaolinite (1 : 1), we separately quantified the mineralogy of
the clay-sized fraction using X-ray diffraction (XRD) and measured <sup>14</sup>C
on the same fraction.
<br><br>
Density separation demonstrated that mineral associated C accounted for
40–70 % of bulk soil organic C in A and B1 horizons for granite,
nephelinite and arid-zone gabbro soils, and > 80 % in other
soils. Organic matter strongly associated with the isolated clay-sized
fraction represented only 9–47 % of the bulk soil C. The mean TT of C
strongly associated with the clay-sized fraction increased with the amount of
smectite (2 : 1 clays); in samples with > 40 % smectite it
averaged 1020 ± 460 years. The C not strongly associated with
clay-sized minerals, including a combination of low-density C, the C
associated with minerals of sizes between 2 µm and 2 cm (including
Fe oxyhydroxides as coatings), and C removed from clay-sized material by
2 % hydrogen peroxide had TTs averaging 190 ± 190 years in surface
horizons. Summed over the bulk soil profile, we found that smectite content
correlated with the mean TT of bulk soil C across varied lithologies. The SRO
mineral content in KNP soils was generally very low, except for the soils
developed on gabbros under more humid climate that also had very high Fe and
C contents with a surprisingly short, mean C TTs. In younger landscapes, SRO
minerals are metastable and sequester C for long timescales. We hypothesize
that in the KNP, SRO minerals represent a transient stage of mineral
evolution and therefore lock up C for a shorter time.
<br><br>
Overall, we found crystalline Fe-oxyhydroxides (determined as the difference
between Fe in dithionate citrate and oxalate extractions) to be the strongest
predictor for soil C content, while the mean TT of soil C was best predicted
from the amount of smectite, which was also related to more easily measured
bulk properties such as cation exchange capacity or pH. Combined with
previous research on C turnover times in 2 : 1 vs. 1 : 1 clays, our
results hold promise for predicting C inventory and persistence based on
intrinsic timescales of specific carbon–mineral
interactions
Initial Experiences of Building Secure Access to Patient Confidential Data via the Internet
A project to enable health care professionals (GPs, practice nurses and diabetes nurse specialists) to access, via the Internet, confidential patient data held on a secondary care (hospital) diabetes information system, has been implemented. We describe the application that we chose to distribute (a diabetes register); the security mechanisms we used to protect the data (a public key infrastructure with strong encryption and digitally signed messages, plus a firewall); the reasons for the implementation decisions we made; the validation testing that we performed and the preliminary results of the pilot implementation
The impact of boundary conditions on CO2 capacity estimation in aquifers
The boundary conditions of an aquifer determine the extent to which fluids (including formation water
and CO2) and pressure can be transferred into adjacent geological formations, either laterally or vertically.
Aquifer boundaries can be faults, lithological boundaries, formation pinch-outs, salt walls, or outcrop. In
many cases compliance with regulations preventing CO2 storage influencing areas outside artificial
boundaries defined by non-geological criteria (international boundaries; license limits) may be necessary.
A bounded aquifer is not necessarily a closed aquifer.
The identification of an aquifer’s boundary conditions determines how CO2 storage capacity is estimated
in the earliest screening and characterization stages. There are different static capacity estimation methods
in use for closed systems and open systems. The method used has a significant impact on the final
capacity estimate.
The recent EU Directive (2009/31/EC) stated that where more than one storage site within a single
“hydraulic unit” (bounded aquifer volume) is being considered, the characterization process should
account for potential pressure interactions. The pressure interplay of multiple sites (or even the pressure
footprint of just one site) is heavily influenced by boundary conditions
Female Health Networks in Yemen: an Examination of the Impact of Conflict on Health Infrastructure and the Role of Women in Yemen’s Health System
This project aims to establish the existence of informal community female-led health networks within Yemen and understand the functions of these health networks and how they have been impacted by the ongoing internal conflict in the country. Female health networks exist globally in both informal and formal sectors. But, the extent to which female health networks function and their importance is unique to Yemen, and there has been no scholarly work focusing on this phenomenon. This paper will use the information gained from 52 interviews with Yemeni women and available literature to understand the current formal and informal health systems in Yemen. I found that informal community female-led health networks have been strengthened to support communities that lack adequate health systems and have evolved instinctively as a necessary response to provide mutual aid. Women from all sects of life participate in these networks and have taken on roles that are unsubsidized in order to aid in the maintenance of community health. Women in Yemen have organized effectively to create a profusion of support networks across the country at various levels to improve the quality of life for other women and Yemeni society at large. In regions that experience heightened levels of conflict and health infrastructure destruction, informal community female-led health networks have grown and are more heavily relied upon by other women and the community
- …