Evolving turbulence and magnetic fields in galaxy clusters

We discuss, using simple analytical models and MHD simulations, the origin and parameters of turbulence and magnetic fields in galaxy clusters. Three physically distinct regimes can be identified in the evolution of cluster turbulence and magnetic fields. Firstly, the fluctuation dynamo will produce microgauss-strong, random magnetic fields during cluster formation and major mergers. Turbulent velocity of about 300 km/s can be maintained at scales 100-200 kpc. The magnetic field is intermittent, has a smaller scale of 20-30 kpc and average strength of 2 microgauss. Secondly, when major mergers end, turbulent speed and magnetic field undergo a power-law decay, decreasing in strength but increasing in scale by a factor of about two. Thirdly, smaller-mass subclusters and cluster galaxies produce turbulent wakes, with turbulent speeds and magnetic field strengths similar to those quoted above. The velocity scales are about 200 kpc and 10 kpc respectively, and the magnetic field scale is about 6 times smaller. Although these wakes may fill only a small fraction of the cluster volume, their area covering factor can be close to unity. So one can potentially reconcile observations that indicate the coexistence of turbulence with ordered filamentary gas structures, as in the Perseus cluster. Random Faraday rotation measure is estimated to be typically 100-200 rad/m^2, in agreement with observations. We predict detectable synchrotron polarization from cluster radio halos at wavelengths 3-6 cm, if observed at sufficiently high resolution (abridged).Comment: 20 pages, 9 figures, Replaced to match version accepted by MNRA

Worldwide Cutaneous Malignant Melanoma Incidences Analyzed by Sex, Age, and Skin Type Over Time (1955–2007): Is HPV Infection of Androgenic Hair Follicular Melanocytes a Risk Factor for Developing Melanoma Exclusively in People of European-Ancestry?

The cutaneous malignant melanoma (CMM) incidence has been increasing in an exponential manner in certain populations around the world for over 7 decades. To help illuminate the etiology, we performed worldwide temporal (1955–2007) CMM incidence analysis by sex, age (0–14, 15–29, 30–49, 50–69, 70–85+), and skin type on 6 continents using data from the International Agency for Research on Cancer. We observe an exponential increase in the CMM incidence over time and an increase of about 2 orders of magnitude between age groups 0–14 and 15–29 exclusively in European-ancestry populations around the world independent of skin type (I–III or III–IV). Other populations like the Chinese (III-IV) had much lower CMM incidences that either remained stable or temporally decreased but did not display a dramatic increase between the youngest age groups. The dramatic increase in the incidence between the youngest age groups found only in European-ancestry populations suggests one of the most important risk factors for CMM may be developing androgenic hair, the occurrence of which appears to correlate with the distribution of CMM over male and female body sites. Besides that potential new risk factor, the increasing CMM incidence with increasing age, known not to be from cumulative UV doses, may be associated with age-related changes to skin, i.e., thinning epidermis causing lower vitamin D3 levels, and hair, i.e., whitening from higher reactive oxygen species. The temporal exponential increasing CMM incidence in European-ancestry populations may be due to Human Papilloma Virus infection of follicular hair melanocytes, found in CMM biopsies

Worldwide Cutaneous Malignant Melanoma Incidences Analyzed by Sex, Age, and Skin Type Over Time (1955–2007): Is HPV Infection of Androgenic Hair Follicular Melanocytes a Risk Factor for Developing Melanoma Exclusively in People of European-Ancestry?

The cutaneous malignant melanoma (CMM) incidence has been increasing in an exponential manner in certain populations around the world for over 7 decades. To help illuminate the etiology, we performed worldwide temporal (1955–2007) CMM incidence analysis by sex, age (0–14, 15–29, 30–49, 50–69, 70–85+), and skin type on 6 continents using data from the International Agency for Research on Cancer. We observe an exponential increase in the CMM incidence over time and an increase of about 2 orders of magnitude between age groups 0–14 and 15–29 exclusively in European-ancestry populations around the world independent of skin type (I–III or III–IV). Other populations like the Chinese (III-IV) had much lower CMM incidences that either remained stable or temporally decreased but did not display a dramatic increase between the youngest age groups. The dramatic increase in the incidence between the youngest age groups found only in European-ancestry populations suggests one of the most important risk factors for CMM may be developing androgenic hair, the occurrence of which appears to correlate with the distribution of CMM over male and female body sites. Besides that potential new risk factor, the increasing CMM incidence with increasing age, known not to be from cumulative UV doses, may be associated with age-related changes to skin, i.e., thinning epidermis causing lower vitamin D3 levels, and hair, i.e., whitening from higher reactive oxygen species. The temporal exponential increasing CMM incidence in European-ancestry populations may be due to Human Papilloma Virus infection of follicular hair melanocytes, found in CMM biopsies

Cutaneous Malignant Melanoma Incidences Analyzed Worldwide by Skin Type over Advancing Age of Males and Females: Evidence Estrogen and Androgenic Hair are Risk Factors

We previously analyzed cutaneous malignant melanoma (CMM) incidences worldwide by sex, age, and Fitzpatrick skin type over time (1955-2007) and found only European-ancestry populations have exponential increasing incidences and about a 2-log increase in the risk between the youngest age groups (0-14 and 15-29 yr). We proposed the increasing incidence over time may be from the spread of Human Papilloma Virus (HPV) found in CMM biopsies, and that the 2-log incidence increase between the youngest age groups might be from developing androgenic hair. The increasing incidence with age may be from white hairs transmitting UV radiation to follicular melanocytes. Here we analyzed CMM incidences over the advancing age of males and females of every skin type (I-VI) worldwide. We found only European-ancestry females have a linear increase in their CMM risk while males of all races have a power function increase in their risk with advancing age. We propose the gradual loss of HPV-infected androgenic follicles with advancing age of only European-ancestry females during and after menopause significantly reduces their CMM risk compared to all males who do not have significant estrogen loss and consequent loss of androgenic hair with advancing age. All other races have females with significantly lower amounts of androgenic body hair so that its loss with advancing age is not significant. These results combined with those in the literature and our previous findings showing CMM has been increasing over time, suggests estrogen synergizes HPV infection of androgenic follicular melanocytes significantly increasing the risk for getting CMM

Effect of oxygen concentration on the structural and magnetic properties of LaRh1/2Mn1/2O3 thin films

Epitaxial LaRh1/2Mn1/2O3 thin films have been grown on (001)-oriented LaAlO3 and SrTiO3 substrates using pulsed laser deposition. The optimized thin film samples are semiconducting and ferromagnetic with a Curie temperature close to 100 K, a coercive field of 1200 Oe, and a saturation magnetization of 1.7muB per formula unit. The surface texture, structural, electrical, and magnetic properties of the LaRh1/2Mn1/2O3 films was examined as a function of the oxygen concentration during deposition. While an elevated oxygen concentration yields thin films with optimal magnetic properties, slightly lower oxygen concentrations result in films with improved texture and crystallinity

Cutaneous Malignant Melanoma Incidences Analyzed Worldwide by Sex, Age, and Skin Type over Personal Ultraviolet-B Dose Shows No Role for Sunburn but Implies One for Vitamin D\u3csub\u3e3\u3c/sub\u3e

Because the incidence of cutaneous malignant melanoma (CMM) was reported to increase with increasing terrestrial UVR (290–400 nm) doses in the US back in 1975 and a recent publication showed no association exists with UVR exposure at all, we set out to fully elucidate the role of UVR in CMM. To achieve this goal, we analyzed the CMM incidences over latitude and estimated the average personal UVR dose in the US and numerous countries (\u3e 50) on 5 continents around the world. Using data from the International Agency for Research on Cancer in 2005, we performed worldwide analysis of CMM over UVR dose by sex, age group (0–14, 15–29, 30–49, 50–69, 70–85+) and Fitzpatrick skin types I-VI. Surprisingly, increasing UVR doses, which represent erythemally-weighted doses comprised primarily of UVB (290–315 nm) radiation, did not significantly correlate with increasing CMM incidence for people with any skin type anywhere in the world. Paradoxically, we found significant correlations between increasing CMM and decreasing UVB dose in Europeans with skin types I-IV. Both Europeans and Americans in some age groups have significant increasing CMM incidences with decreasing UVB dose, which shows UVB is not the main driver in CMM and suggests a possible role for lower cutaneous vitamin D3 levels and UVA (315–400 nm) radiation. CMM may be initiated or promoted by UVA radiation because people are exposed to it indoors through windows and outdoors through some sunscreen formulations. Thus, our findings may explain why some broad-spectrum sunscreen formulations do not protect against getting CM

Dielectric and polarization experiments in high loss dielectrics: a word of caution

The recent quest for improved functional materials like high permittivity dielectrics and/or multiferroics has triggered an intense wave of research. Many materials have been checked for their dielectric permittivity or their polarization state. In this report, we call for caution when samples are simultaneously displaying insulating behavior and defect-related conductivity. Many oxides containing mixed valent cations or oxygen vacancies fall in this category. In such cases, most of standard experiments may result in effective high dielectric permittivity which cannot be related to ferroelectric polarization. Here we list few examples of possible discrepancies between measured parameters and their expected microscopic origin

Penetration depth of low-coherence enhanced backscattered light in sub-diffusion regime

The mechanisms of photon propagation in random media in the diffusive multiple scattering regime have been previously studied using diffusion approximation. However, similar understanding in the low-order (sub-diffusion) scattering regime is not complete due to difficulties in tracking photons that undergo very few scatterings events. Recent developments in low-coherence enhanced backscattering (LEBS) overcome these difficulties and enable probing photons that travel very short distances and undergo only a few scattering events. In LEBS, enhanced backscattering is observed under illumination with spatial coherence length L_sc less than the scattering mean free path l_s. In order to understand the mechanisms of photon propagation in LEBS in the subdiffusion regime, it is imperative to develop analytical and numerical models that describe the statistical properties of photon trajectories. Here we derive the probability distribution of penetration depth of LEBS photons and report Monte Carlo numerical simulations to support our analytical results. Our results demonstrate that, surprisingly, the transport of photons that undergo low-order scattering events has only weak dependence on the optical properties of the medium (l_s and anisotropy factor g) and strong dependence on the spatial coherence length of illumination, L_sc, relative to those in the diffusion regime. More importantly, these low order scattering photons typically penetrate less than l_s into the medium due to low spatial coherence length of illumination and their penetration depth is proportional to the one-third power of the coherence volume (i.e. [l_s \pi L_sc^2 ]^1/3).Comment: 32 pages(including 7 figures), modified version to appear in Phys. Rev.