Scanning Photo-Induced Impedance Microscopy - Resolution studies and polymer characterization

Scanning Photo-Induced Impedance Microscopy (SPIM) is an impedance imaging technique that is based on photocurrent measurements at field-effect structures. The material under investigation is deposited onto a semiconductor-insulator substrate. A thin metal film or an electrolyte solution with an immersed electrode serves as the gate contact. A modulated light beam focused into the space charge region of the semiconductor produces a photocurrent, which is directly related to the local impedance of the material. The absolute impedance of a polymer film can be measured by calibrating photocurrents using a known impedance in series with the sample. Depending on the wavelength of light used, charge carriers are not only generated in the focus but also throughout the bulk of the semiconductor. This can have adverse effects on the lateral resolution. Two-photon experiments were carried out to confine charge carrier generation to the spacecharge layer. The lateral resolution of SPIM is also limited by the lateral diffusion of charge carriers in the semiconductor. This problem can be solved by using thin silicon layers as semiconductor substrates. A resolution of better than 1 mu m was achieved using silicon on sapphire (SOS) substrates with a I l.Lm thick silicon layer

Random walks in random Dirichlet environment are transient in dimension d≥3d\ge 3

We consider random walks in random Dirichlet environment (RWDE) which is a special type of random walks in random environment where the exit probabilities at each site are i.i.d. Dirichlet random variables. On $\Z^d$, RWDE are parameterized by a $2d$-uplet of positive reals. We prove that for all values of the parameters, RWDE are transient in dimension $d\ge 3$. We also prove that the Green function has some finite moments and we characterize the finite moments. Our result is more general and applies for example to finitely generated symmetric transient Cayley graphs. In terms of reinforced random walks it implies that directed edge reinforced random walks are transient for $d\ge 3$.Comment: New version published at PTRF with an analytic proof of lemma

Comparison between measured and predicted turbulence frequency spectra in ITG and TEM regimes

The observation of distinct peaks in tokamak core reflectometry measurements - named quasi-coherent-modes (QCMs) - are identified as a signature of Trapped-Electron-Mode (TEM) turbulence [H. Arnichand et al. 2016 Plasma Phys. Control. Fusion 58 014037]. This phenomenon is investigated with detailed linear and nonlinear gyrokinetic simulations using the \gene code. A Tore-Supra density scan is studied, which traverses through a Linear (LOC) to Saturated (SOC) Ohmic Confinement transition. The LOC and SOC phases are both simulated separately. In the LOC phase, where QCMs are observed, TEMs are robustly predicted unstable in linear studies. In the later SOC phase, where QCMs are no longer observed, ITG modes are identified. In nonlinear simulations, in the ITG (SOC) phase, a broadband spectrum is seen. In the TEM (LOC) phase, a clear emergence of a peak at the TEM frequencies is seen. This is due to reduced nonlinear frequency broadening of the underlying linear modes in the TEM regime compared with the ITG regime. A synthetic diagnostic of the nonlinearly simulated frequency spectra reproduces the features observed in the reflectometry measurements. These results support the identification of core QCMs as an experimental marker for TEM turbulenc

Trends in Availability and Prices of Subsidized ACT over the First Year of the AMFm: Evidence from Remote Regions of Tanzania

Background: The Affordable Medicines Facility for malaria (AMFm) is a pilot supra-national subsidy program that aims to increase access and affordability of artemisinin combination therapy (ACT) in public sector clinics and private retail shops. It is unclear to what extent the AMFm model will translate into wide scale availability and price reductions in ACT, particularly for rural, remote areas where disparities in access to medicines often exist. This study is the first to rigorously examine the availability and price of subsidized ACT during the first year of the AMFm, measured through retail audits in remote regions of Tanzania. Methods: Periodic retail audits of Accredited Drug Dispensing Outlets (ADDOs) were conducted in two remote regions of Tanzania (Mtwara and Rukwa). Temporal and spatial variation in ACT availability and pricing were explored. A composite measure of ADDO remoteness, using variables, such as distance to suppliers and towns, altitude and population density, was used to explore whether ACT availability and price vary systematically with remoteness. Results: Between February 2011 and January 2012, the fraction of ADDOs stocking AMFm-ACT increased from 25% to 88% in Mtwara and from 3% to 62% in Rukwa. Availability was widespread, though diffusion throughout the region was achieved more quickly in Mtwara. No significant relationship was found between ACT availability and remoteness. Adult doses of AMFm-ACT were much more widely available than any other age/weight band. Average prices fell from 1529 TZS (1.03 USD) to 1272 TZS (0.81 USD) over the study period, with prices in Rukwa higher than Mtwara. The government recommended retail price for AMFm- ACT is 1,000 TZS ($0.64 USD). The median retail ACT price in the final round of data collection was 1,000 TZS. Conclusions: The AMFm led to large increases in availability of low priced ACT in Tanzania, with no significant variation in availability based on remoteness. Availability did remain lower and prices remained higher in Rukwa, which is a more remote region overall. Low availability of child and adolescent ACT doses could be due in part to lower quantities of non-adult packs imported into Tanzania. Future research will explore whether increased availability and affordability persists and whether it translates into higher ACT use in Tanzania

Discriminating the trapped electron modes contribution in density fluctuation spectra

Quasi-coherent (QC) modes have been reported for more than 10 years in reflectometry fluctuations spectra in the core region of fusion plasmas. They have characteristics in-between coherent and broadband fluctuations as they oscillate at a marked frequency but have a wide spectrum. This work presents further evidences of the link recently established between QC modes and the trapped electron modes (TEM) instabilities (Arnichand et al 2014 Nucl. Fusion 54 123017). In electron cyclotron resonance heated discharges of Tore Supra, an enhancement of QC modes amplitude is observed in a region where TEM cause impurity transport and turbulence. In JET Ohmic plasmas, QC modes disappear during density ramp-up and current ramp-down. This is reminiscent of Tore Supra and TEXTOR observations during transitions from the linear Ohmic confinement (LOC) to the saturated Ohmic confinement (SOC) regimes. Evidencing TEM activity then becomes experimentally possible via analysis of fluctuation spectra.EURATOM 63305

Trends in availability and prices of subsidized ACT over the first year of the AMFm: evidence from remote regions of Tanzania

Abstract Background The Affordable Medicines Facility for malaria (AMFm) is a pilot supra-national subsidy program that aims to increase access and affordability of artemisinin combination therapy (ACT) in public sector clinics and private retail shops. It is unclear to what extent the AMFm model will translate into wide scale availability and price reductions in ACT, particularly for rural, remote areas where disparities in access to medicines often exist. This study is the first to rigorously examine the availability and price of subsidized ACT during the first year of the AMFm, measured through retail audits in remote regions of Tanzania. Methods Periodic retail audits of Accredited Drug Dispensing Outlets (ADDOs) were conducted in two remote regions of Tanzania (Mtwara and Rukwa). Temporal and spatial variation in ACT availability and pricing were explored. A composite measure of ADDO remoteness, using variables, such as distance to suppliers and towns, altitude and population density, was used to explore whether ACT availability and price vary systematically with remoteness. Results Between February 2011 and January 2012, the fraction of ADDOs stocking AMFm-ACT increased from 25% to 88% in Mtwara and from 3% to 62% in Rukwa. Availability was widespread, though diffusion throughout the region was achieved more quickly in Mtwara. No significant relationship was found between ACT availability and remoteness. Adult doses of AMFm-ACT were much more widely available than any other age/weight band. Average prices fell from 1529 TZS (1.03 USD) to 1272 TZS (0.81 USD) over the study period, with prices in Rukwa higher than Mtwara. The government recommended retail price for AMFm- ACT is 1,000 TZS ($0.64 USD). The median retail ACT price in the final round of data collection was 1,000 TZS. Conclusions The AMFm led to large increases in availability of low priced ACT in Tanzania, with no significant variation in availability based on remoteness. Availability did remain lower and prices remained higher in Rukwa, which is a more remote region overall. Low availability of child and adolescent ACT doses could be due in part to lower quantities of non-adult packs imported into Tanzania. Future research will explore whether increased availability and affordability persists and whether it translates into higher ACT use in Tanzania.http://deepblue.lib.umich.edu/bitstream/2027.42/112716/1/12936_2012_Article_2494.pd

Do Price Subsidies on Artemisinin Combination Therapy for Malaria Increase Household Use?: Evidence from a Repeated Cross-Sectional Study in Remote Regions of Tanzania

Background: The Affordable Medicines Facility-malaria (AMFm) is a pilot program that uses price subsidies to increase access to Artemisinin Combination Therapies (ACTs), currently the most effective malaria treatment. Recent evidence suggests that availability and affordability of ACTs in retail sector drug shops (where many people treat malaria) has increased under the AMFm, but it is unclear whether household level ACT use has increased. Methods and Findings: Household surveys were conducted in two remote regions of Tanzania (Mtwara and Rukwa) in three waves: March 2011, December 2011 and March 2012, corresponding to 3, 13 and 16 months into the AMFm implementation respectively. Information about suspected malaria episodes including treatment location and medications taken was collected. Respondents were also asked about antimalarial preferences and perceptions about the availability of these medications. Significant increases in ACT use, preference and perceived availability were found between Rounds 1 and 3 though not for all measures between Rounds 1 and 2. ACT use among suspected malaria episodes was 51.1% in March 2011 and increased by 10.9 percentage points by Round 3 (p = .017). The greatest increase was among retail sector patients, where ACT use increased from 31% in Round 1 to 49% in Round 2 (p = .037) and to 61% (p<.0001) by Round 3. The fraction of suspected malaria episodes treated in the retail sector increased from 30.2% in Round 1 to 46.7% in Round 3 (p = .0009), mostly due to a decrease in patients who sought no treatment at all. No significant changes in public sector treatment seeking were found. Conclusions: The AMFm has led to significant increases in ACT use for suspected malaria, especially in the retail sector. No evidence is found supporting the concerns that the AMFm would crowd out public sector treatment or neglect patients in remote areas and from low SES groups