Multiple scattering of ultrasound in weakly inhomogeneous media: application to human soft tissues

Waves scattered by a weakly inhomogeneous random medium contain a predominant single scattering contribution as well as a multiple scattering contribution which is usually neglected, especially for imaging purposes. A method based on random matrix theory is proposed to separate the single and multiple scattering contributions. The experimental set up uses an array of sources/receivers placed in front of the medium. The impulse responses between every couple of transducers are measured and form a matrix. Single-scattering contributions are shown to exhibit a deterministic coherence along the antidiagonals of the array response matrix, whatever the distribution of inhomogeneities. This property is taken advantage of to discriminate single from multiple-scattered waves. This allows one to evaluate the absorption losses and the scattering losses separately, by comparing the multiple scattering intensity with a radiative transfer model. Moreover, the relative contribution of multiple scattering in the backscattered wave can be estimated, which serves as a validity test for the Born approximation. Experimental results are presented with ultrasonic waves in the MHz range, on a synthetic sample (agar-gelatine gel) as well as on breast tissues. Interestingly, the multiple scattering contribution is found to be far from negligible in the breast around 4.3 MHz.Comment: 35 pages, 11 figures, final version, contains the appendix of the original articl

Organizational stressors associated with job stress and burnout in correctional officers: a systematic review.

BackgroundIn adult correctional facilities, correctional officers (COs) are responsible for the safety and security of the facility in addition to aiding in offender rehabilitation and preventing recidivism. COs experience higher rates of job stress and burnout that stem from organizational stressors, leading to negative outcomes for not only the CO but the organization as well. Effective interventions could aim at targeting organizational stressors in order to reduce these negative outcomes as well as COs' job stress and burnout. This paper fills a gap in the organizational stress literature among COs by systematically reviewing the relationship between organizational stressors and CO stress and burnout in adult correctional facilities. In doing so, the present review identifies areas that organizational interventions can target in order to reduce CO job stress and burnout.MethodsA systematic search of the literature was conducted using Medline, PsycINFO, Criminal Justice Abstracts, and Sociological Abstracts. All retrieved articles were independently screened based on criteria developed a priori. All included articles underwent quality assessment. Organizational stressors were categorized according to Cooper and Marshall's (1976) model of job stress.ResultsThe systematic review yielded 8 studies that met all inclusion and quality assessment criteria. The five categories of organizational stressors among correctional officers are: stressors intrinsic to the job, role in the organization, rewards at work, supervisory relationships at work and the organizational structure and climate. The organizational structure and climate was demonstrated to have the most consistent relationship with CO job stress and burnout.ConclusionsThe results of this review indicate that the organizational structure and climate of correctional institutions has the most consistent relationship with COs' job stress and burnout. Limitations of the studies reviewed include the cross-sectional design and the use of varying measures for organizational stressors. The results of this review indicate that interventions should aim to improve the organizational structure and climate of the correctional facility by improving communication between management and COs

Physician-based availability of psychotherapy in Ontario : a population-based retrospective cohort study

BACKGROUND: Psychotherapy is recommended as a first-line treatment for the management of common psychiatric disorders. The objective of this study was to evaluate the availability of publicly funded psychotherapy provided by physicians in Ontario by describing primary care physicians (PCPs) and psychiatrists whose practices focus on psychotherapy and comparing them to PCPs and psychiatrists whose practices do not. METHODS: This was a population-based retrospective cohort study. We included all PCPs and psychiatrists in Ontario who submitted at least 1 billing claim to the Ontario Health Insurance Plan between Apr. 1, 2015, and Mar. 31, 2016, and categorized them as psychotherapists if at least 50% of their outpatient billings were related to the provision of psychotherapy. We measured practice characteristics such as total number of patients and new patients, and average visit frequency for 4 physician categories: PCP nonpsychotherapists, PCP psychotherapists, psychiatrist nonpsychotherapists and psychiatrist psychotherapists. We also measured access to care for people with urgent need for mental health services. RESULTS: Of 12 772 PCPs, 404 (3.2%) were PCP psychotherapists; of 2150 psychiatrists, 586 (27.3%) were psychotherapists. Primary care physician nonpsychotherapists had the highest number of patients and number of new patients, followed by psychiatrist nonpsychotherapists, PCP psychotherapists and psychiatrist psychotherapists. Primary care physician nonpsychotherapists had the lowest average annual number of visits per patient, whereas both types of psychotherapists had a much greater number of visits per patient. Primary care physician and psychiatrist nonpsychotherapists saw about 25% of patients with urgent needs for mental health services, whereas PCP and psychiatrist psychotherapists saw 1%-3% of these patients. INTERPRETATION: Physicians who provide publicly funded psychotherapy in Ontario see a small number of patients, and they see few of those with urgent need for mental health services. Our findings suggest that improving access to psychotherapy will require the development of alternative strategies

Dye molecules in electrolytes: new approach for suppression of dye-desorption in dye-sensitized solar cells

The widespread commercialization of dye-sensitized solar cells remains limited because of the poor long-term stability. We report on the influence of dye-molecules added in liquid electrolyte on long-term stability of dye-sensitized solar cells. Dye-desorption from the TiO2 surface during long-term cycling is one of the decisive factors that degrade photocurrent densities of devices which in turn determine the efficiencies of the devices. For the first time, desorption of dye from the TiO2 surface could be suppressed by controlling thermodynamic equilibrium; by addition of dye molecules in the electrolyte. The dye molecules in the electrolyte can suppress the driving forces for the adsorbed dye molecules to be desorbed from TiO2 nanoparticles. As a result, highly enhanced device stabilities were achieved due to the reduction of dye-desorption although there was a little decrease in the initial efficiencies.open4

Novel polymorphisms and lack of mutations in the ACD gene in patients with ACTH resistance syndromes

Objective  ACTH resistance is a feature of several human syndromes with known genetic causes, including familial glucocorticoid deficiency (types 1 and 2) and triple A syndrome. However, many patients with ACTH resistance lack an identifiable genetic aetiology. The human homolog of the Acd gene, mutated in a mouse model of adrenal insufficiency, was sequenced in 25 patients with a clinical diagnosis of familial glucocorticoid deficiency or triple A syndrome. Design  A 3·4 kilobase genomic fragment containing the entire ACD gene was analysed for mutations in all 25 patients. Setting  Samples were obtained by three investigators from different institutions. Patients  The primary cohort consisted of 25 unrelated patients, primarily of European or Middle Eastern descent, with a clinical diagnosis of either familial glucocorticoid deficiency (FGD) or triple A syndrome. Patients lacked mutations in other genes known to cause ACTH resistance, including AAAS for patients diagnosed with triple A syndrome and MC2R and MRAP for patients diagnosed with familial glucocorticoid deficiency. Thirty-five additional patients with adrenal disease phenotypes were added to form an expanded cohort of 60 patients. Measurements  Identification of DNA sequence changes in the ACD gene in the primary cohort and analysis of putative ACD haplotypes in the expanded cohort. Results  No disease-causing mutations were found, but several novel single nucleotide polymorphisms (SNPs) and two putative haplotypes were identified. The overall frequency of SNPs in ACD is low compared to other gene families. Conclusions  No mutations were identified in ACD in this collection of patients with ACTH resistance phenotypes. However, the newly identified SNPs in ACD should be more closely examined for possible links to disease.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73948/1/j.1365-2265.2007.02855.x.pd

Human-centered specification exemplars for critical infrastructure environments.

Specification models of critical infrastructure focus on parts of a larger environment. However, to consider the security of critical infrastructure systems, we need approaches for modelling the sum of these parts; these include people and activities, as well as technology. This paper presents human-centered specification exemplars that capture the nuances associated with interactions between people, technology, and critical infrastructure environments. We describe requirements each exemplar needs to satisfy, and present preliminary results in developing and evaluating them

Aggregating Centrality Rankings: A Novel Approach to Detect Critical Infrastructure Vulnerabilities

Assessing critical infrastructure vulnerabilities is paramount to arrange efficient plans for their protection. Critical infrastructures are network-based systems hence, they are composed of nodes and edges. The literature shows that node criticality, which is the focus of this paper, can be addressed from different metric-based perspectives (e.g., degree, maximal flow, shortest path). However, each metric provides a specific insight while neglecting others. This paper attempts to overcome this pitfall through a methodology based on ranking aggregation. Specifically, we consider several numerical topological descriptors of the nodes’ importance (e.g., degree, betweenness, closeness, etc.) and we convert such descriptors into ratio matrices; then, we extend the Analytic Hierarchy Process problem to the case of multiple ratio matrices and we resort to a Logarithmic Least Squares formulation to identify an aggregated metric that represents a good tradeoff among the different topological descriptors. The procedure is validated considering the Central London Tube network as a case study

Effector diversification within compartments of the Leptosphaeria maculans genome affected by Repeat-Induced Point mutations

Fungi are of primary ecological, biotechnological and economic importance. Many fundamental biological processes that are shared by animals and fungi are studied in fungi due to their experimental tractability. Many fungi are pathogens or mutualists and are model systems to analyse effector genes and their mechanisms of diversification. In this study, we report the genome sequence of the phytopathogenic ascomycete Leptosphaeria maculans and characterize its repertoire of protein effectors. The L. maculans genome has an unusual bipartite structure with alternating distinct guanine and cytosine-equilibrated and adenine and thymine (AT)-rich blocks of homogenous nucleotide composition. The AT-rich blocks comprise one-third of the genome and contain effector genes and families of transposable elements, both of which are affected by repeat-induced point mutation, a fungal-specific genome defence mechanism. This genomic environment for effectors promotes rapid sequence diversification and underpins the evolutionary potential of the fungus to adapt rapidly to novel host-derived constraints

Influence of electrolyte co-additives on the performance of dye-sensitized solar cells

The presence of specific chemical additives in the redox electrolyte results in an efficient increase of the photovoltaic performance of dye-sensitized solar cells (DSCs). The most effective additives are 4-tert-butylpyridine (TBP), N-methylbenzimidazole (NMBI) and guanidinium thiocyanate (GuNCS) that are adsorbed onto the photoelectrode/electrolyte interface, thus shifting the semiconductor's conduction band edge and preventing recombination with triiodides. In a comparative work, we investigated in detail the action of TBP and NMBI additives in ionic liquid-based redox electrolytes with varying iodine concentrations, in order to extract the optimum additive/I2 ratio for each system. Different optimum additive/I2 ratios were determined for TBP and NMBI, despite the fact that both generally work in a similar way. Further addition of GuNCS in the optimized electrolytic media causes significant synergistic effects, the action of GuNCS being strongly influenced by the nature of the corresponding co-additive. Under the best operation conditions, power conversion efficiencies as high as 8% were obtained