Phonons in random alloys: the itinerant coherent-potential approximation

We present the itinerant coherent-potential approximation(ICPA), an analytic, translationally invariant and tractable form of augmented-space-based, multiple-scattering theory in a single-site approximation for harmonic phonons in realistic random binary alloys with mass and force-constant disorder. We provide expressions for quantities needed for comparison with experimental structure factors such as partial and average spectral functions and derive the sum rules associated with them. Numerical results are presented for Ni_{55} Pd_{45} and Ni_{50} Pt_{50} alloys which serve as test cases, the former for weak force-constant disorder and the latter for strong. We present results on dispersion curves and disorder-induced widths. Direct comparisons with the single-site coherent potential approximation(CPA) and experiment are made which provide insight into the physics of force-constant changes in random alloys. The CPA accounts well for the weak force-constant disorder case but fails for strong force-constant disorder where the ICPA succeeds.Comment: 19 pages, 12 eps figures, uses RevTex

Knowledge, perceived stigma, and care-seeking experiences for sexually transmitted infections: a qualitative study from the perspective of public clinic attendees in Rio de Janeiro, Brazil

BACKGROUND: An estimated 12 million sexually transmitted infections (STIs) are documented in Brazil per year. Given the scope of this public health challenge and the importance of prompt treatment and follow-up counseling to reduce future STI/HIV-related risk behavior, we sought to qualitatively explore STI clinic experiences among individuals diagnosed with STIs via public clinics in Rio de Janeiro, Brazil. The study focused on eliciting the perspective of clinic users with regard to those factors influencing their STI care-seeking decisions and the health education and counseling which they received during their clinic visit. METHODS: Thirty semi-structured interviews were conducted with heterosexual men and women and men who have sex with men presenting with STIs at two public clinics. Content analysis was conducted by coding transcripts of audio-taped interviews for key domains of interest and comparing and synthesizing code output across participants and sub-groups. Thematic narratives were then developed per each of the study sub-groups. RESULTS: Salient themes that emerged from participant narratives included the importance of low STI-related knowledge and high perceived stigma, both STI-related and other types of social stigma, on STI care-seeking delays. However, there are indications in the data that the level of STI-related knowledge and the amount and types of stigma experienced vary across the study sub-groups suggesting the need for further research on the significance and program relevance of these potential differences. Interview findings also suggest that such barriers to care seeking are not adequately addressed through ongoing health education and counseling efforts at public STI clinics and in turn critical opportunities for STI/HIV prevention are currently being missed. CONCLUSION: Information, communication and education regarding early recognition and prompt care-seeking for STIs should be developed, with consideration given to the possibility of tailoring messages tailored to specific sub-groups. To promote prompt treatment-seeking, interventions must also address both STI-specific and other forms of social stigma which may limit access to care. Efforts to further assess and respond to barriers related to the delivery of quality health education and counseling within the context of public STI clinics are also needed