Multidirectional In Vivo Characterization of Skin Using Wiener Nonlinear Stochastic System Identification Techniques

A triaxial force-sensitive microrobot was developed to dynamically perturb skin in multiple deformation modes, in vivo. Wiener static nonlinear identification was used to extract the linear dynamics and static nonlinearity of the force–displacement behavior of skin. Stochastic input forces were applied to the volar forearm and thenar eminence of the hand, producing probe tip perturbations in indentation and tangential extension. Wiener static nonlinear approaches reproduced the resulting displacements with variances accounted for (VAF) ranging 94–97%, indicating a good fit to the data. These approaches provided VAF improvements of 0.1–3.4% over linear models. Thenar eminence stiffness measures were approximately twice those measured on the forearm. Damping was shown to be significantly higher on the palm, whereas the perturbed mass typically was lower. Coefficients of variation (CVs) for nonlinear parameters were assessed within and across individuals. Individual CVs ranged from 2% to 11% for indentation and from 2% to 19% for extension. Stochastic perturbations with incrementally increasing mean amplitudes were applied to the same test areas. Differences between full-scale and incremental reduced-scale perturbations were investigated. Different incremental preloading schemes were investigated. However, no significant difference in parameters was found between different incremental preloading schemes. Incremental schemes provided depth-dependent estimates of stiffness and damping, ranging from 300 N/m and 2 Ns/m, respectively, at the surface to 5 kN/m and 50 Ns/m at greater depths. The device and techniques used in this research have potential applications in areas, such as evaluating skincare products, assessing skin hydration, or analyzing wound healing.Foundation for Research, Science & Technology (N.Z.) (Grants UOA21647.001 and NERF 9077/3608892)Tertiary Education Commission of New Zealand (Medical Technologies Centre of Research Excellence (MedTech CoRE)

Bounds on Lorentz and CPT Violation from the Earth-Ionosphere Cavity

Electromagnetic resonant cavities form the basis of many tests of Lorentz invariance involving photons. The effects of some forms of Lorentz violation scale with cavity size. We investigate possible signals of violations in the naturally occurring resonances formed in the Earth-ionosphere cavity. Comparison with observed resonances places the first terrestrial constraints on coefficients associated with dimension-three Lorentz-violating operators at the level of 10^{-20} GeV.Comment: 8 pages REVTe

Single-color pyrometry of individual incandescent multiwalled carbon nanotubes

Objects that are small compared to their thermal photon wavelengths violate the assumptions underlying optical pyrometry and can show unusual coherence effects. To investigate this regime we measure the absolute light intensity from individual, incandescent multiwalled carbon nanotubes. The nanotube filaments' physical dimensions and composition are determined using transmission electron microscopy and their emissivities are calculated in terms of bulk conductivities. A single-color pyrometric analysis then returns a temperature value for each wavelength, polarization, and applied bias measured. Compared to the more common multiwavelength analysis, single-color pyrometry supports a more consistent and complete picture of the carbon nanotube lamps, one that describes their emissivity, optical conductivity, and thermal conductivity in the range 1600-2400 K.Comment: 8 pages, 5 figure

Psychometric validation of the Muscle Dysmorphic Disorder Inventory (MDDI) among U.S. transgender men

Muscle dysmorphia (MD) is characterized by a pervasive belief or fear of insufficient muscularity and an elevated drive for muscularity, representing the pathological and extreme pursuit of muscularity. Psychometric properties of one of the most widely used measures of MD symptoms—the Muscle Dysmorphic Disorder Inventory (MDDI)—have yet to be evaluated in transgender men despite emerging evidence suggesting differential risk for MD symptoms in this population. In this study, we assessed the psychometric properties of the MDDI in a sample of 330 transgender men ages 18–67 years who participated in a large-scale national longitudinal cohort study of sexual and gender minority adults in the U.S. Using a two-step, split-sample approach, an initial exploratory factor analysis supported a three-factor structure and a subsequent confirmatory factor analysis of a re-specified three-factor model demonstrated good overall fit (χ2/df = 1.84, CFI =0.94, TLI =0.92, RMSEA =0.07 [90% CI =0.05,.09], SRMR =0.08). Moreover, results supported the internal consistency and convergent validity of the MDDI subscales in transgender men. Findings inform the use of the MDDI among transgender men and provide a foundation to support further work on the MDDI and MD symptoms among gender minority populations