An orbital window into the ancient Sun's mass

Models of the Sun's long-term evolution suggest that its luminosity was substantially reduced 2-4 billion years ago, which is inconsistent with substantial evidence for warm and wet conditions in the geological records of both ancient Earth and Mars. Typical solutions to this so-called "faint young Sun paradox" consider changes in the atmospheric composition of Earth and Mars, and while attractive, geological verification of these ideas is generally lacking-particularly for Mars. One possible underexplored solution to the faint young Sun paradox is that the Sun has simply lost a few percent of its mass during its lifetime. If correct, this would slow, or potentially even offset the increase in luminosity expected from a constant-mass model. However, this hypothesis is challenging to test. Here, we propose a novel observational proxy of the Sun's ancient mass that may be readily measured from accumulation patterns in sedimentary rocks on Earth and Mars. We show that the orbital parameters of the Solar system planets undergo quasi-cyclic oscillations at a frequency, given by secular mode g_2-g_5, that scales approximately linearly with the Sun's mass. Thus by examining the cadence of sediment accumulation in ancient basins, it is possible distinguish between the cases of a constant mass Sun and a more massive ancient Sun to a precision of greater than about 1 per cent. This approach provides an avenue toward verification, or of falsification, of the massive early Sun hypothesis.Comment: 7 pages, 4 Figures. Accepted to The Astrophysical Journal Letter

The use of charge -charge correlation in impedance measurements: A test of the EPET method

It is well known that biological tissues possess impedance properties that might be useful in medical diagnostics and treatment. Electrical Impedance Tomography (EIT) images internal electrical properties by using numerical methods to solve Laplace\u27s differential equation. The indirect reconstruction method (IRM), a common method in application, predicts internal electrical property distribution by iteratively computing a forward and inverse solution. This approach reduces the non-linear Laplace\u27s equation into a poorly conditioned series of linear equations, which are solved simultaneously. This method suffers from high computational effort and is susceptible to prediction errors that stem from measurement noise.;As an alternative to Laplace\u27s differential equation, this research applies the quasi-static approximation, Dirichlet boundary conditions and a rectangular shaped domain (with corresponding Green\u27s function for Cartesian coordinates) to solve the integral form of Poisson\u27s equation (Green\u27s 2nd identity). The result is the charge-charge correlation method (CCCM), a well-conditioned relationship between static charge build-up at internal structures and induced domain boundary charge build-up (which corresponds to measured boundary current). The CCCM is applied in a reconstruction technique called Electrical Property Enhanced Tomography (EPET). While related to the existing impedance imaging methods, EPET does not attempt to create the image with the electrical data but rather adds electrical property information to an existing conventional imaging modality (CT or MI) and, in fact, requires the data from the other modality to locate the position of internal structures in the object. Predicted electrical properties are then superimposed over the a priori structural image to yield the electrical property distribution.;To test the feasibility of the CCCM, experiments using agar media placed in a saline bath were performed. The position, size and conductivity of the agar were varied and the CCCM applied to predict the conductivities from external boundary current measurements. Predicted conductivities yielded relative errors less than 10%, results that are equal to or better than the IRM. Additionally, CCCM was able to compute these results with a 104 improvement in speed over the IRM

Traversing the Highwire from Pop to Optical

A visual neuroscientist comments on the art of Roy Lichtenstein, as viewed in a recent exhibition at the San Francisco Museum of Modern Ar

SCMR president's page

News from the Society for Cardiovascular Magnetic Resonanc

Single Muscle Fibre Contractile Function With Ageing

Ageing is accompanied by decrements in the size and function of skeletal muscle that compromise independence and quality of life in older adults. Developing therapeutic strategies to ameliorate these changes is critical but requires an in-depth mechanistic understanding of the underlying physiology. Over the past 25 years, studies on the contractile mechanics of isolated human muscle fibres have been instrumental in facilitating our understanding of the cellular mechanisms contributing to age-related skeletal muscle dysfunction. The purpose of this review is to characterize the changes that occur in single muscle fibre size and contractile function with ageing and identify key areas for future research. Surprisingly, most studies observe that the size and contractile function of fibres expressing slow myosin heavy chain (MHC) I are well-preserved with ageing. In contrast, there are profound age-related decrements in the size and contractile function of the fibres expressing the MHC II isoforms. Notably, lifelong aerobic exercise training is unable to prevent most of the decrements in fast fibre contractile function, which have been implicated as a primary mechanism for the age-related loss in whole-muscle power output. These findings reveal a critical need to investigate the effectiveness of other nutritional, pharmaceutical or exercise strategies, such as lifelong resistance training, to preserve fast fibre size and function with ageing. Moreover, integrating single fibre contractile mechanics with the molecular profile and other parameters important to contractile function (e.g. phosphorylation of regulatory proteins, innervation status, mitochondrial function, fibre economy) is necessary to comprehensively understand the ageing skeletal muscle phenotype

A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars

We present radial velocities, equivalent widths, model atmosphere parameters, and abundances or upper limits for 53 species of 48 elements derived from high resolution optical spectroscopy of 313 metal-poor stars. A majority of these stars were selected from the metal-poor candidates of the HK Survey of Beers, Preston, and Shectman. We derive detailed abundances for 61% of these stars for the first time. Spectra were obtained during a 10-year observing campaign using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coude Spectrograph on the Harlan J. Smith Telescope at McDonald Observatory, and the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. We perform a standard LTE abundance analysis using MARCS model atmospheres, and we apply line-by-line statistical corrections to minimize systematic abundance differences arising when different sets of lines are available for analysis. We identify several abundance correlations with effective temperature. A comparison with previous abundance analyses reveals significant differences in stellar parameters, which we investigate in detail. Our metallicities are, on average, lower by approx. 0.25 dex for red giants and approx. 0.04 dex for subgiants. Our sample contains 19 stars with [Fe/H] < -3.5, 84 stars with [Fe/H] < -3.0, and 210 stars with [Fe/H] < -2.5. Detailed abundances are presented here or elsewhere for 91% of the 209 stars with [Fe/H] < -2.5 as estimated from medium resolution spectroscopy by Beers, Preston, and Shectman. We will discuss the interpretation of these abundances in subsequent papers.Comment: Accepted for publication in the Astronomical Journal. 60 pages, 59 figures, 18 tables. Machine-readable versions of the long tables can be found in the ancillary data file

Prevalence of Mentoring on Clinical Versus Experimental Doctoral Programs: Survey Findings, Implications, and Recommendations

Previous research suggests that mentorships are quite important in the development of junior professionals in a range of fields, including psychology. Yet some evidence suggests that clinical doctoral students may be less frequently mentored by graduate faculty than other psychology doctoral students. Results of a survey of clinical and experimental psychology doctorates who earned the degree in four distinct time frames from 1945 to the present indicated that clinical PhDs (53%) were indeed less likely than experimental PhDs (69%) to be mentored. Potential explanations for this discrepancy include the nature of clinical training, diffusion in clinical training, and the advent of professional training models. The implications of less frequent mentoring for clinical doctorates are discussed, and several recommendations for addressing this phenomenon are offered

Phenotypic analysis of extracellular vesicles:a review on the applications of fluorescence

Extracellular vesicles (EVs) have numerous potential applications in the field of healthcare and diagnostics, and research into their biological functions is rapidly increasing. Mainly because of their small size and heterogeneity, there are significant challenges associated with their analysis and despite overt evidence of the potential of EVs in clinical diagnostic practice, guidelines for analytical procedures have not yet been properly established. Here, we present an overview of the main methods for studying the properties of EVs based on the principles of fluorescence. Setting aside the isolation, purification and physicochemical characterization strategies which answer questions about the size, surface charge and stability of EVs (reviewed elsewhere), we focus on available optical tools that enable the direct analysis of phenotype and mechanisms of interaction with tissues. In brief, the topics on which we elaborate range from the most popular approaches such as nanoparticle tracking analysis and flow cytometry, to less commonly used techniques such as fluorescence depolarization and microarrays as well as emerging areas such as fast fluorescence lifetime imaging microscopy (FLIM). We highlight that understanding the strengths and limitations of each method is essential for choosing the most appropriate combination of analytical tools. Finally, future directions of this rapidly developing area of medical diagnostics are discussed