Quantum critical phenomena in a compressible displacive ferroelectric.

The dielectric and magnetic polarizations of quantum paraelectrics and paramagnetic materials have in many cases been found to initially increase with increasing thermal disorder and hence, exhibit peaks as a function of temperature. A quantitative description of these examples of "order-by-disorder" phenomena has remained elusive in nearly ferromagnetic metals and in dielectrics on the border of displacive ferroelectric transitions. Here, we present an experimental study of the evolution of the dielectric susceptibility peak as a function of pressure in the nearly ferroelectric material, strontium titanate, which reveals that the peak position collapses toward absolute zero as the ferroelectric quantum critical point is approached. We show that this behavior can be described in detail without the use of adjustable parameters in terms of the Larkin-Khmelnitskii-Shneerson-Rechester (LKSR) theory, first introduced nearly 50 y ago, of the hybridization of polar and acoustic modes in quantum paraelectrics, in contrast to alternative models that have been proposed. Our study allows us to construct a detailed temperature-pressure phase diagram of a material on the border of a ferroelectric quantum critical point comprising ferroelectric, quantum critical paraelectric, and hybridized polar-acoustic regimes. Furthermore, at the lowest temperatures, below the susceptibility maximum, we observe a regime characterized by a linear temperature dependence of the inverse susceptibility that differs sharply from the quartic temperature dependence predicted by the LKSR theory. We find that this non-LKSR low-temperature regime cannot be accounted for in terms of any detailed model reported in the literature, and its interpretation poses an empirical and conceptual challenge.

Oral antibiotic use and risk of colorectal cancer in the United Kingdom, 1989-2012: a matched case-control study.

BACKGROUND: Microbiome dysbiosis predisposes to colorectal cancer (CRC), but a population-based study of oral antibiotic exposure and risk patterns is lacking. OBJECTIVE: To assess the association between oral antibiotic use and CRC risk. DESIGN: A matched case-control study (incident CRC cases and up to five matched controls) was performed using the Clinical Practice Research Datalink from 1989 to 2012. RESULTS: 28 980 CRC cases and 137 077 controls were identified. Oral antibiotic use was associated with CRC risk, but effects differed by anatomical location. Antibiotic use increased the risk of colon cancer in a dose-dependent fashion (ptrend <0.001). The risk was observed after minimal use, and was greatest in the proximal colon and with antibiotics with anti-anaerobic activity. In contrast, an inverse association was detected between antibiotic use and rectal cancers (ptrend=0.003), particularly with length of antibiotic exposure >60 days (adjusted OR (aOR), 0.85, 95% CI 0.79 to 0.93) as compared with no antibiotic exposure. Penicillins, particularly ampicillin/amoxicillin increased the risk of colon cancer (aOR=1.09 (1.05 to 1.13)), whereas tetracyclines reduced the risk of rectal cancer (aOR=0.90 (0.84 to 0.97)). Significant interactions were detected between antibiotic use and tumour location (colon vs rectum, pinteraction<0.001; proximal colon versus distal colon, pinteraction=0.019). The antibiotic-cancer association was found for antibiotic exposure occurring >10 years before diagnosis (aOR=1.17 (1.06 to 1.31)). CONCLUSION: Oral antibiotic use is associated with an increased risk of colon cancer but a reduced risk of rectal cancer. This effect heterogeneity may suggest differences in gut microbiota and carcinogenesis mechanisms along the lower intestinal tract.

Author Correction: Temperature Chaos, Memory Effect, and Domain Fluctuations in the Spiral Antiferromagnet Dy.

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Temperature Chaos, Memory Effect, and Domain Fluctuations in the Spiral Antiferromagnet Dy.

The spiral antiferromagnetic phase of polycrystalline dysprosium between 140 K and the Néel temperature at 178 K and its domain wall (DW) dynamics were investigated using high-resolution ultrasonic spectroscopy. Two kinetic processes of quasi-static DW motion occur under non-isothermal and isothermal conditions. A "fast" process is proportional to the rate of the temperature change and results in a new category of anelastic phenomena: magnetic transient ultrasonic internal friction (IF). This IF, related to fast moving magnetic DWs, decays rapidly after interruptions of cooling/heating cycles. A second, "slow" kinetic process is seen as logarithmic IF relaxation under isothermal conditions. This second process is glass-like and results in memory and temperature chaos effects. Low-frequency thermal fluctuations of DWs, previously detected by X-ray photon correlation spectroscopy, are related to critical fluctuations with Brownian motion-like dynamics of DWs.

Group-theoretical analysis of structural instability, vacancy ordering and magnetic transitions in the system troilite (FeS)-pyrrhotite (Fe1-xS).

A group-theoretical framework to describe vacancy ordering and magnetism in the Fe1-xS system is developed. This framework is used to determine the sequence of crystal structures consistent with the observed magnetic structures of troilite (FeS), and to determine the crystallographic nature of the low-temperature Besnus transition in Fe0.875S. It is concluded that the Besnus transition is a magnetically driven transition characterized by the rotation of the moments out of the crystallographic plane to which they are confined above the transition, accompanied by small atomic displacements that lower the symmetry from monoclinic to triclinic at low temperatures. Based on the phase diagram, magnetically driven phase transitions at low temperatures are predicted in all the commensurate superstructures of pyrrhotite. Based on the phase diagram, magnetically driven spin reorientations at low temperatures are predicted in all the commensurate superstructures of pyrrhotite. The exact nature of the spin rotation is determined by the symmetry of the vacancy-ordered state and based on this spin-flop transitions in 3C and 5C pyrrhotite and a continuous rotation akin to that seen in 4C pyrrhotite are predicted. A Besnus-type transition is also possible in 6C pyrrhotite. Furthermore, it is clarified that 3C and 4C pyrrhotite carry a ferrimagnetic moment whereas 5C and 6C are antiferromagnetic.

Closing the Gap in Antiretroviral Initiation and Viral Suppression: Time Trends and Racial Disparities.

BACKGROUND: In the current antiretroviral (ART) era, the evolution of HIV guidelines and emergence of new ART agents might be expected to impact the times to ART initiation and HIV virologic suppression. We sought to determine if times to AI and virologic suppression decreased and if disparities exist by age, race/ethnicity, and HIV risk. METHODS: We performed a retrospective cohort study of data from 12 sites of the HIV Research Network, a consortium of US clinics caring for HIV-infected patients. HIV-infected adults (≥18 year old) newly presenting for care between 2003 and 2013 were included in this study. Times to AI and virologic suppression were defined as time from enrollment to AI and HIV RNA <400 copies per milliliter, respectively. We conducted time-to-event analyses using competing risk regression in the HIV Research Network cohort from 2003 to 2012 in 2-year intervals, with follow-up through 2013. RESULTS: Among 15,272 participants, 76.9% were male, 48.4% black, and 10.9% were injection drug use with median age of 38 years (interquartile range: 29-46 years). The adjusted subdistribution hazards ratios (SHRs) for AI and virologic suppression each increased for years 2007-2008 [SHR 1.23 (1.16-1.30), and SHR 1.25 (1.17-1.34), respectively], 2009-2010 [1.55 (1.46-1.64), and 1.54 (1.43-1.65), respectively], and 2011-2012 [1.94 (1.83-2.07), and 1.73 (1.61-1.86), respectively] compared with 2003-2004. Blacks had a lower probability of AI than whites and Hispanics. CONCLUSIONS: Since 2007, times from enrollment to AI and virologic suppression have decreased significantly compared with 2003-2004, but persisting disparities should be addressed.

Increase in CD4 count among new enrollees in HIV care in the modern antiretroviral therapy era.

BACKGROUND: Earlier HIV diagnosis and engagement in care improve outcomes and is cost effective, as a result, in 2006, the Centers for Disease Control and Prevention (CDC) revised the HIV-screening guidelines. We sought to determine whether the CD4 count (CD4) at presentation, a surrogate for time to presentation, increased during the study period. Our a priori hypothesis was that the CD4 at presentation increased during the study period, particularly after the CDC guideline revision. METHODS: We performed a retrospective cohort study and analyzed data from the HIV Research Network, a consortium of 18 US clinics caring for HIV-infected patients. HIV-infected adults (≥18 years old) newly presenting for care between 2003 and 2011 were included in this study. Multivariable linear regression examined associations with CD4 at enrollment. Calendar year was modeled as a linear spline with a change in slope at 2008, allowing determination of the mean change in CD4 per year during 2003-2007 and 2008-2011. RESULTS: Over 13,543 newly presenting subjects enrolled from 2003 to 2011. Median CD4 at enrollment rose from 285 to 317 cells per cubic millimeter between 2003-2007 and 2008-2011 (P < 0.001). After adjusting for age, race/ethnicity, gender, HIV risk factor, and clinic site, the mean increase in the CD4 count at presentation per year was 13.3 cells per cubic millimeter per year (95% confidence interval 6.4 to 20.1 cells per cubic millimeter per year) greater during 2008-2011 than during 2003-2007. CONCLUSIONS: We demonstrate a small, but statistically significant, increase in CD4 at presentation after the CDC guideline revision. More efforts are needed to decrease time to presentation to HIV care.

Clostridium difficile in a HIV-infected cohort: incidence, risk factors, and clinical outcomes.

OBJECTIVE: Clostridium difficile is the most commonly reported infectious diarrhoea in HIV-infected patients in the United States. We set out to determine the incidence, risk factors and clinical presentation of C. difficile infections (CDIs) in a cohort of HIV-infected individuals. DESIGN: We performed a nested, case-control analysis with four non-CDI controls randomly selected for each case. METHODS: We assessed the incidence of CDI in the Johns Hopkins HIV Clinical Cohort between 1 July 2003 and 31 December 2010. Incident cases were defined as first positive C. difficile cytotoxin assay or PCR for toxin B gene. We used conditional logistic regression models to assess risk factors for CDI. We abstracted data on the clinical presentation and outcomes from case chart review. RESULTS: We identified 154 incident CDI cases for an incidence of 8.3 cases per 1000 patient years. No unique clinical features of HIV-associated CDI were identified. In multivariate analysis, risk of CDI was independently increased for CD4 cell count of 50 cells/µl or less [adjusted odds ratio (AOR) 20.7, 95% confidence interval (CI) 2.8-151.4], hospital onset CDI (AOR 26.7, 95% CI 3.1-231.2) and use of clindamycin (AOR 27.6, 95% CI 2.2-339.4), fluoroquinolones (AOR 4.5, 95% CI 1.2-17.5), macrolides (AOR 6.3, 95% CI 1.8-22.1), gastric acid suppressants (AOR 3.1, 95% CI 1.4-6.9) or immunosuppressive agents (AOR 6.8, 95% CI 1.2-39.6). CONCLUSION: The incidence of CDI in HIV-infected patients was twice that previously reported. Our data show that compromised cellular immunity, as defined by CD4 cell count of 50 cells/µl or less, is a risk factor for CDI. Clinicians should be aware of the increased CDI risk, particularly in those with severe CD4 cell count suppression.

IL-7 receptor deficient SCID with a unique intronic mutation and post-transplant autoimmunity due to chronic GVHD.

Severe combined immunodeficiency (SCID) may result from a variety of genetic defects that impair the development of T cells. Signaling mediated by the cytokine interleukin-7 is essential for the differentiation of T cells from lymphoid progenitors, and mutations of either the interleukin-7 receptor alpha chain (IL-7Ralpha) or its associated cytokine receptor chain, the common gamma chain (gammac), result in SCID. Here we report a case of SCID due to heterozygous mutations of the IL7R gene encoding IL-7Ralpha. A previously unrecognized mutation found within intron 3 created a new exon between exons 3 and 4 in the mRNA transcribed from this allele, producing a truncated, unstable mRNA. This mutation illustrates the necessity of evaluating both coding and non-coding regions of genes when searching for pathogenic mutations. Following hematopoietic stem cell transplantation of our patient, immune reconstitution was accompanied by two unusual complications, immune-mediated myositis and myasthenia gravis.