A bremsstrahlung gamma-ray source based on stable ionization injection of electrons into a laser wakefield accelerator

Laser wakefield acceleration permits the generation of ultra-short, high-brightness relativistic electron beams on a millimeter scale. While those features are of interest for many applications, the source remains constraint by the poor stability of the electron injection process. Here we present results on injection and acceleration of electrons in pure nitrogen and argon. We observe stable, continuous ionization-induced injection of electrons into the wakefield for laser powers exceeding a threshold of 7 TW. The beam charge scales approximately linear with the laser energy and is limited by beam loading. For 40 TW laser pulses we measure a maximum charge of almost 1 nC per shot, originating mostly from electrons of less than 10 MeV energy. The relatively low energy, the high charge and its stability make this source well-suited for applications such as non-destructive testing. Hence, we demonstrate the production of energetic radiation via bremsstrahlung conversion at 1 Hz repetition rate. In accordance with Geant4 Monte-Carlo simulations, we measure a gamma-ray source size of less than 100 microns for a 0.5 mm tantalum converter placed at 2 mm from the accelerator exit. Furthermore we present radiographs of image quality indicators

Study of Two-Photon absorption in Organic Materials by thermal lensing and nonlinear transmission measurements

Experimental investigations of two-photon absorption (TPA) cross-section using nonlinear transmission (NLT) and a new pump-probe mode-mismatched thermal lens (TL) scheme, in the picosecond regime are reported. Both methods are used in a prospect of comparison. Values of the TPA coefficient and cross-section in perylenediimide derivatives (PDI) at 532 nm and 1064 nm wavelengths are given

What unleashes innovations in the Legumes and Cereals farming Systems in the drylands: A gendered perspective

Agricultural and natural resource management innovations have often been introduced, promoted and adopted among local communities / farmers. However, how the innovation process is perceived by men and women, the relationships involved, the distribution of benefits and the differing capacities of women and men to take advantage of the new opportunities in agriculture are not always carefully thought-out. This study examined both community and individual men and women's experiences with agricultural innovations and practices and how these interactions support or hinder the achievement of agricultural innovations across various contexts. By providing robust empirical evidence on the relationship between gender norms, agency and agricultural innovation, the study revealed that sociocultural structures and household dynamics chiefly shapes how individuals negotiate for space, freedom, resources and the capacities needed to innovate

Persistence of magnetic field driven by relativistic electrons in a plasma

The onset and evolution of magnetic fields in laboratory and astrophysical plasmas is determined by several mechanisms, including instabilities, dynamo effects and ultra-high energy particle flows through gas, plasma and interstellar-media. These processes are relevant over a wide range of conditions, from cosmic ray acceleration and gamma ray bursts to nuclear fusion in stars. The disparate temporal and spatial scales where each operates can be reconciled by scaling parameters that enable to recreate astrophysical conditions in the laboratory. Here we unveil a new mechanism by which the flow of ultra-energetic particles can strongly magnetize the boundary between the plasma and the non-ionized gas to magnetic fields up to 10-100 Tesla (micro Tesla in astrophysical conditions). The physics is observed from the first time-resolved large scale magnetic field measurements obtained in a laser wakefield accelerator. Particle-in-cell simulations capturing the global plasma and field dynamics over the full plasma length confirm the experimental measurements. These results open new paths for the exploration and modelling of ultra high energy particle driven magnetic field generation in the laboratory

Hodgkin Lymphoma at the Paediatric Oncology Unit of Gabriel Touré Teaching Hospital, Bamako, Mali: 5-Year Experience

Introduction. The aim of this retrospective, unicentric study over 5 years is to describe the epidemiologic, pathologic, clinic and therapeutic aspects of children treated for Hodgkin lymphoma in our paediatric oncology unit. Patients and Methods. From January 2005 to December 2009, all children under 18 years of age, with Hodgkin lymphoma were included in this study. The treatment protocol was the GFAOP (Groupe Franco—Africain d'Oncologie Pédiatrique) Hodgkin lymphoma treatment protocol. Results. During the study period, 217 cancer cases were diagnosed in our centre. Of these cases, 7 were Hodgkin Lymphoma (LH) (0.04%). The mean age was 11.7 years. The sex-ratio was 6/1. 4% (5/7) of patients were stage IIB and 28.6% (2/7) stage IIIB of Ann-Arbor classification. There were 3 cases (42.8%) of sclero-nodular subtype, 2 cases (28.6%) of lymphocyte-rich classical HL subtype, 1 case (14.3%) of mixed cellularity and 1 case (14.3%) of lymphocyte depleted subtype. With a median followup of 37 months, 5 patients (71.4%) are alive, and 2 patients (28.6%) died. Conclusion. Broader multicentric studies are needed for more accurate data on this malignancy

Alterations of slow and fast rod ERG signals in patients with molecularly confirmed Stargardt disease type 1 (STGD1)

purpose. To investigate the slow and fast rod signals of the scotopic 15-Hz flicker ERG in patients with molecularly confirmed Stargardt disease type I (STGD1). There is evidence that these slow and the fast rod ERG signals can be attributed to the rod bipolar–AII cell pathway and the rod–cone coupling pathway, respectively. methods. Twenty-seven patients with STGD1 with mutations in both alleles of the ABCA4 gene were included. Scotopic ERG response amplitudes and phases to flicker intensities ranging from −3.37 to −0.57 log scotopic troland · sec (log scot td · sec) were measured at a flicker frequency of 15 Hz. In addition, scotopic standard ERGs were obtained. Twenty-two normal subjects served as controls. results. The amplitudes of both the slow and fast rod ERG signals were significantly reduced in the STGD1 group. The phases of the slow rod signals lagged significantly, whereas those of the fast rod signals did not. The standard scotopic ERG did not reveal significant alterations. conclusions. The results provide evidence that a defective ABCA4 transporter can functionally affect both the rod bipolar–AII cell pathway and the rod–cone coupling pathway. In STGD1, the scotopic 15-Hz flicker ERG may reveal subtle abnormalities at different sites within the rod system that remain undetected by standard ERG techniques

Barriers to the uptake of community-based curative child health services in Ethiopia

Background Uptake of services to treat newborns and children has been persistently low in Ethiopia, despite being provided free-of-charge by Health Extension Workers (HEWs). In order to increase the uptake of these services, the Optimizing the Health Extension Project was designed to be implemented in four regions in Ethiopia. This study was carried out to identify barriers to the uptake of these services and potential solutions to inform the project. Methods Qualitative data were collected in October and November 2015 in 15 purposely selected districts in four regions. We conducted 90 focus group discussions and 60 in-depth interviews reaching a total of 664 participants. Thematic analysis was used to identify key barriers and potential solutions. Results Five demand-side barriers to utilization of health services were identified. Misconceptions about illness causation, compounded with preference for traditional healers has affected service uptake. Limited awareness of the availability of free curative services for children at health posts; along with the prevailing perception that HEWs were providing preventive services only had constrained uptake. Geographic challenge that made access to the health post difficult was the other barrier. Four supply-side barriers were identified. Health post closure and drug stock-out led to inconsistent availability of services. Limited confidence and skill among HEWs and under-resourced physical facilities affected the service delivery. Study participants suggested demand creation solutions such as increasing community awareness on curative service availability and educating them on childhood illness causation. Maintaining consistent supplies and ensuring service availability; along with regular support to build HEWs’ confidence were the suggested supply-side solutions. Creating community feedback mechanisms was suggested as a way of addressing community concerns on the health services. Conclusion This study explored nine demand- and supply-side barriers that decreased the uptake of community-based services. It indicated the importance of increasing awareness of new services and addressing prevailing barriers that deprioritize health services. At the same time, supply-side barriers would have to be tackled by strengthening the health system to uphold newly introduced services and harness sustainable impact

Uptake of plasmodium falciparum gametocytes during mosquito bloodmeal by direct and membrane feeding

Plasmodium falciparum remains one of the leading causes of child mortality, and nearly half of the world’s population is at risk of contracting malaria. While pathogenesis results from replication of asexual forms in human red blood cells, it is the sexually differentiated forms, gametocytes, which are responsible for the spread of the disease. For transmission to succeed, both mature male and female gametocytes must be taken up by a female Anopheles mosquito during its blood meal for subsequent differentiation into gametes and mating inside the mosquito gut. Observed circulating numbers of gametocytes in the human host are often surprisingly low. A pre-fertilization behavior, such as skin sequestration, has been hypothesized to explain the efficiency of human-to-mosquito transmission but has not been sufficiently tested due to a lack of appropriate tools. In this study, we describe the optimization of a qPCR tool that enables the relative quantification of gametocytes within very small input samples. Such a tool allows for the quantification of gametocytes in different compartments of the host and the vector that could potentially unravel mechanisms that enable highly efficient malaria transmission. We demonstrate the use of our gametocyte quantification method in mosquito blood meals from both direct skin feeding on Plasmodium gametocyte carriers and standard membrane feeding assay. Relative gametocyte abundance was not different between mosquitoes fed through a membrane or directly on the skin suggesting that there is no systematic enrichment of gametocytes picked up in the skin

Profile of humoral and cellular immune responses to single doses of BNT162b2 or ChAdOx1 nCoV-19 vaccines in residents and staff within residential care homes (VIVALDI): an observational study

BACKGROUND: Residents of long-term care facilities (LTCFs) have been prioritised for COVID-19 vaccination because of the high COVID-19 mortality in this population. Several countries have implemented an extended interval of up to 12 weeks between the first and second vaccine doses to increase population coverage of single-dose vaccination. We aimed to assess the magnitude and quality of adaptive immune responses following a single dose of COVID-19 vaccine in LTCF residents and staff. METHODS: From the LTCFs participating in the ongoing VIVALDI study (ISRCTN14447421), staff and residents who had received a first dose of COVID-19 vaccine (BNT162b2 [tozinameran] or ChAdOx1 nCoV-19), had pre-vaccination and post-vaccination blood samples (collected between Dec 11, 2020, and Feb 16, 2021), and could be linked to a pseudoidentifier in the COVID-19 Data Store were included in our cohort. Past infection with SARS-CoV-2 was defined on the basis of nucleocapsid-specific IgG antibodies being detected through a semiquantitative immunoassay, and participants who tested positive on this assay after but not before vaccination were excluded from the study. Processed blood samples were assessed for spike-specific immune responses, including spike-specific IgG antibody titres, T-cell responses to spike protein peptide mixes, and inhibition of ACE2 binding by spike protein from four variants of SARS-CoV-2 (the original strain as well as the B.1.1.7, B.1.351, and P.1 variants). Responses before and after vaccination were compared on the basis of age, previous infection status, role (staff or resident), and time since vaccination. FINDINGS: Our cohort comprised 124 participants from 14 LTCFs: 89 (72%) staff (median age 48 years [IQR 35·5–56]) and 35 (28%) residents (87 years [77–90]). Blood samples were collected a median 40 days (IQR 25–47; range 6–52) after vaccination. 30 (24%) participants (18 [20%] staff and 12 [34%] residents) had serological evidence of previous SARS-CoV-2 infection. All participants with previous infection had high antibody titres following vaccination that were independent of age (rs=0·076, p=0·70). In participants without evidence of previous infection, titres were negatively correlated with age (rs=–0·434, p<0·0001) and were 8·2-times lower in residents than in staff. This effect appeared to result from a kinetic delay antibody generation in older infection-naive participants, with the negative age correlation disappearing only in samples taken more than 42 days post-vaccination (rs=–0·207, p=0·20; n=40), in contrast to samples taken after 0–21 days (rs=–0·774, p=0·0043; n=12) or 22–42 days (rs=–0·437, p=0·0034; n=43). Spike-specific cellular responses were similar between older and younger participants. In infection-naive participants, antibody inhibition of ACE2 binding by spike protein from the original SARS-CoV-2 strain was negatively correlated with age (rs=–0·439, p<0·0001), and was significantly lower against spike protein from the B.1.351 variant (median inhibition 31% [14–100], p=0·010) and the P.1 variant (23% [14–97], p<0·0001) than against the original strain (58% [27–100]). By contrast, a single dose of vaccine resulted in around 100% inhibition of the spike–ACE2 interaction against all variants in people with a history of infection. INTERPRETATION: History of SARS-CoV-2 infection impacts the magnitude and quality of antibody response after a single dose of COVID-19 vaccine in LTCF residents. Residents who are infection-naive have delayed antibody responses to the first dose of vaccine and should be considered for an early second dose where possible. FUNDING: UK Government Department of Health and Social Care