Age-related Changes in the Mechanical Properties of Human Skin

The mechanical properties of skin have been studied both in vivo and in vitro by a variety of test methods. These properties are well matched to the function of the skin, and they depend on the geometry of the collagen and elastin networks of the dermis. The time dependence of these properties is thought to be related to the “ground substance” components of the dermis. Age-related changes in the mechanical properties are a function of the degradation of the elastin network and of some as yet undefined changes in the viscoelastic properties of the “ground substance.

Ratio-Balanced Maximum Flows

When a loan is approved for a person or company, the bank is subject to \emph{credit risk}; the risk that the lender defaults. To mitigate this risk, a bank will require some form of \emph{security}, which will be collected if the lender defaults. Accounts can be secured by several securities and a security can be used for several accounts. The goal is to fractionally assign the securities to the accounts so as to balance the risk. This situation can be modelled by a bipartite graph. We have a set $S$ of securities and a set $A$ of accounts. Each security has a \emph{value} $v_i$ and each account has an \emph{exposure} $e_j$. If a security $i$ can be used to secure an account $j$, we have an edge from $i$ to $j$. Let $f_{ij}$ be part of security $i$'s value used to secure account $j$. We are searching for a maximum flow that send at most $v_i$ units out of node $i \in S$ and at most $e_j$ units into node $j \in A$. Then $s_j = e_j - \sum_i f_{ij}$ is the unsecured part of account $j$. We are searching for the maximum flow that minimizes $\sum_j s_j^2/e_j$

Proton tracking in a high-granularity Digital Tracking Calorimeter for proton CT purposes

Radiation therapy with protons as of today utilizes information from x-ray CT in order to estimate the proton stopping power of the traversed tissue in a patient. The conversion from x-ray attenuation to proton stopping power in tissue introduces range uncertainties of the order of 2-3% of the range, uncertainties that are contributing to an increase of the necessary planning margins added to the target volume in a patient. Imaging methods and modalities, such as Dual Energy CT and proton CT, have come into consideration in the pursuit of obtaining an as good as possible estimate of the proton stopping power. In this study, a Digital Tracking Calorimeter is benchmarked for proof-of-concept for proton CT purposes. The Digital Tracking Calorimeteris applied for reconstruction of the tracks and energies of individual high energy protons. The presented prototype forms the basis for a proton CT system using a single technology for tracking and calorimetry. This advantage simplifies the setup and reduces the cost of a proton CT system assembly, and it is a unique feature of the Digital Tracking Calorimeter. Data from the AGORFIRM beamline at KVI-CART in Groningen in the Netherlands and Monte Carlo simulation results are used to in order to develop a tracking algorithm for the estimation of the residual ranges of a high number of concurrent proton tracks. The range of the individual protons can at present be estimated with a resolution of 4%. The readout system for this prototype is able to handle an effective proton frequency of 1 MHz by using 500 concurrent proton tracks in each readout frame, which is at the high end range of present similar prototypes. A future further optimized prototype will enable a high-speed and more accurate determination of the ranges of individual protons in a therapeutic beam.Comment: 21 pages, 8 figure

Photodiode read-out of the ALICE photon spectrometer PbWO4PbWO_{4} crystals

Proposal of abstract for LEB99, Snowmass, Colorado, 20-24 September 1999The PHOton Spectrometer of the ALICE experiment is an electromagnetic calorimeter of high granularity consisting of 17280 lead-tungstate (PWO) crystals of dimensions 22x22x180 mm3, read out by large-area PIN-diodes with very low-noise front-end electronics. The crystal assembly is operated at -25C to increase the PWO light yield. A 16.1x17.1 mm2 photodiode, optimized for the PWO emissio spectrum at 400-500 nm, has been developed. The 20x20 mm2 preamplifier PCB is attached to the back side of the diode ceramic frame. The charge sensitive preamplifier is built in discrete logic with two input JFETs for optimum matching with the ~150pF PIN-diode. A prototype shaper has been designed and built in discrete logic. For a detector matrix of 64 units the measured ENCs are between 450-550e at -25C. Beam tests demonstrate that the required energy resolution is reached.Summary:The PHOton Spectrometer of the ALICE experiment is an electromagnetic calorimeter of high granularity consisting of 17280 lead-tungstate (PWO) crystals of dimensions 22x22x180 mm3, coupled to large-area PIN-diodes with matching low-noise preamplifiers. PHOS is optimized for measuring photons, pi0s and eta mesons in the momentum ranges 0.5-10, 1-10 and 2-10 GeV/c, respectively, and is designed for the expected large number of particles that will be produced in central Pb-Pb collisions. Lead tungstate (PWO) is a fast scintillating crystal with a rather complex emission spectrum, consisting of two components: a blue component peaking at 420 nm and a green component peaking at 480-520 nm. The light yield of PWO at room temperature is low compared with other heavy scintillating crystals, for instance BGO. However, the yield depends strongly on the temperature with a coefficient of ~-2 degree. At the selected operating temperature of -25C the yield is about a factor of 3 higher compared to room temperature. Still, in order to reach the required energy resolution for a PHOS channel, an ENC noise of less than 600e for the PIN-diode-preamplifier-shaper stage is required. This is a very low value taking into account the high capacitance of 150-200 pF of the large area PIN-diodes. In collaboration with the PHOS project, the company AME (Horten, Norway) has designed and produced a PIN-photodiode optimized for the cross-section and spectral responsivity of the PHOS PWO crystal. The photodiode has an active area of 17.1x16.1 mm2 and is fabricated on n-type silicon material of thickness 280 um. The wafer specific resistivity is between 3000 and 6000 ohm-cm, which corresponds to a depletion voltage of 70V. The photodiode response is optimized for the spectral region 400-500 nm in order to match the PWO emission spectrum. The PIN-diode is mounted on a ceramic substrate 0.65 mm thick. On this substrate the diode is surrounded by a ceramic frame. The preamplifier PCB of dimension 20x20 mm2 is attached to the back side of the frame. The PIN-diode and bondings to ground and preamplifier input are protected by an optically transparent epoxy layer. The front side of the PIN-diode is glued onto the endface of the PWO crystal with optically transparent glue (Melt-Mount Quick-Stick, Cargille Laboratories, USA). Each crystal is wrapped in White Tyvek to ensure maximum light collection efficiency and optical insulation between the crystals. The PHOS detector consists of four independent modules, each with 4320 channels. The crystal assembly with the photo detectors are operated at -25 +/- 0.3C. The power dissipation per module is ~1 kW. The charge sensitive preamplifier is an operational amplifier built in discrete logic and with two input JFETs (BF861A). Using two JFETs in parallel gives the lowest noise for detector capacitance >100 pF. A prototype shaper, comprising three amplification stages, has been designed and built in discrete logic. For a PIN-diode with capacitance ~150 pF and a leakage current <1 nA under cooling, calculations give optimum time differentiation and integration constants around 3 microsec. For a detector matrix of 64 units the measured ENCs are between 450-550 e at -25C. Beam tests of this matrix show that the required energy resolution for the PHOS is reached

Prenatal exposure to DDT in malaria endemic region following indoor residual spraying and in non-malaria coastal regions of South Africa

Exemption was granted by the Stockholm Convention in 2004 for use of DDT by indoor residual spraying (IRS) as a malaria vector control. South Africa endorsed the use of DDT in its Malaria Control Programmes in malaria endemic regions and IRS remains a primary method of controlling malaria transmitting mosquitoes in this country. This study examines the impact of IRS on the levels of DDT and its metabolites in maternal blood of delivering women as a measure of prenatal exposure. We report on the concentrations of DDT and its metabolites (p,p′- DDE, p,p′-DDT, o,p′-DDE, o,p′-DDD, p,p′-DDD, and o,p′-DDT) in maternal plasma of 255 delivering women residing in three sites along Indian Ocean, namely in malaria endemic where IRS takes place, low risk and non-malaria sites. Concentrations of measured compounds were found to be significantly higher in the malaria endemic site (p = 0.0001): the geometric mean concentration (95% confidence intervals; n = 91) for o,p′-DDE was 9 ng/g lipids (7–10); for p,p′-DDE, 3840 ng/g lipids (3008–4902); for o,p′-DDD, 8 ng/g lipids (6–9); for p,p′-DDD, 26 ng/g lipids (20–32); for o,p′-DDT, 168 ng/g lipids (127–221) and for p,p′-DDT, 2194 ng/g lipids (1706–2823). These compounds were also detected in women residing in other sites but in lower concentrations. The maternal characteristics, age, IRS, number of children and breastfeeding were significantly associated for both p,p′-DDE and p,p′-DDT levels in the malaria area where exposure through IRS is predominant. There was no association between maternal characteristics and DDT levels in the low risk and non-malaria area. Results presented are of particular value to the policy decision makers and regulatory toxicology organizations as they characterise the extent of controlled exposure to DDT used exclusively for IRS purposes. Furthermore, findings of this study will form a base for further investigation of foetal exposure to pollutants.Research Council of Norway and National Research Foundation, South Africa (Grant 64528), the Arctic Monitoring and Assessment Programme (AMAP), the Royal Norwegian Ministry for Foreign Affairs and the SA Medical Research Council.http://www.elsevier.com/locate/scitotenvhb2013ay201

Single-neutron transfer from 11Be gs via the (p,d) reaction with a radioactive beam

The 11Be(p,d)10Be reaction has been performed in inverse kinematics with a radioactive 11Be beam of E/A = 35.3 MeV. Angular distributions for the 0+ ground state, the 2+, 3.37 MeV state and the multiplet of states around 6 MeV in 10Be were measured at angles up to 16 deg CM by detecting the 10Be in a dispersion-matched spectrometer and the coincident deuterons in a silicon array. Distorted wave and coupled-channels calculations have been performed to investigate the amount of 2+ core excitation in 11Be gs. The use of "realistic" 11Be wave functions is emphasised and bound state form factors have been obtained by solving the particle-vibration coupling equations. This calculation gives a dominant 2s component in the 11Be gs wave function with a 16% [2+ x 1d] core excitation admixture. Cross sections calculated with these form factors are in good agreement with the present data. The Separation Energy prescription for the bound state wave function also gives satisfactory fits to the data, but leads to a significantly larger [2 x 1d] component in 11Be gs.Comment: 39 pages, 12 figures. Accepted for publication in Nuclear Physics A. Added minor corrections made in proof to pages 26 and 3

Regional variation in pesticide concentrations in plasma of delivering women residing in rural Indian Ocean coastal regions of South Africa

Exposure to pesticides places pregnant women and the developing foetus at the highest risk. The objective of this study is to obtain an exposure assessment by investigating levels of pesticides in blood plasma of delivering women. We report on the concentrations of a, b, g HCH, endosulfan, HCB and the pyrethroids: cis-permethrin, cyfluthrin, cypermethrin and deltamethrin found in the maternal blood plasma of delivering women (n ¼ 241) in three coastal sites of KwaZulu Natal. g-HCH and endosulfan 1 and 2 were the most dominant pesticides in all three sites. Significantly, higher levels of g-HCH and endosulfan were found in site 3 (vicinity of Empangeni) compared to the other two sites (p < 0.05). The GMlevels for g-HCH, endosulfan 1 and 2 were 956, 141 and 21 ng g 1 lipids in site 3, respectively. The pyrethroid pesticides, HCB, a-HCH and b-HCH were detected in less than 31% of the samples in all sites. g-HCH correlated positively and strongly to both endosulfan 1 and 2 (r > 0.47), indicating a common source of exposure. The high levels of g-HCH and endosulfan in maternal plasma samples in site 3 indicate the current and on-going exposure, which is of great concern for reproductive health and prenatal exposure.Part of this work was presented at the Environmental Health Conference 2011 – Resetting our Priorities, Salvador, Brazil, 6–9 February 2011.The Research Council of Norway and the National Research Foundation, South Africa (Grant 64528), the Arctic Monitoring and Assessment Programme (AMAP), the Royal Norwegian Ministry for Foreign Affairs and the SA Medical Research Council.http://www.rsc.org/jemam2013ay201