Helical Buckling in Filopodia

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PT-symmetry breaking and maximal chirality in a nonuniform PT-symmetric ring

We study the properties of an N-site tight-binding ring with parity and time-reversal (PT) symmetric, Hermitian, site-dependent tunneling and a pair of non-Hermitian, PT-symmetric, loss and gain impurities $\pm i\gamma$. The properties of such lattices with open boundary conditions have been intensely explored over the past two years. We numerically investigate the PT-symmetric phase in a ring with a position-dependent tunneling function $t_\alpha(k)=[k(N-k)]^{\alpha/2}$ that, in an open lattice, leads to a strengthened PT-symmetric phase, and study the evolution of the PT-symmetric phase from the open chain to a ring. We show that, generally, periodic boundary conditions weaken the PT-symmetric phase, although for experimentally relevant lattice sizes $N \sim 50$, it remains easily accessible. We show that the chirality, quantified by the (magnitude of the) average transverse momentum of a wave packet, shows a maximum at the PT-symmetric threshold. Our results show that although the wavepacket intensity increases monotonically across the PT-breaking threshold, the average momentum decays monotonically on both sides of the threshold.Comment: 11 pages, 5 figures, preprin

PT-Symmetric Electronics

We show both theoretically and experimentally that a pair of inductively coupled active LRC circuits (dimer), one with amplification and another with an equivalent amount of attenuation, display all the features which characterize a wide class of non-Hermitian systems which commute with the joint parity-time PT operator: typical normal modes, temporal evolution, and scattering processes. Utilizing a Liouvilian formulation, we can define an underlying PT-symmetric Hamiltonian, which provides important insight for understanding the behavior of the system. When the PT-dimer is coupled to transmission lines, the resulting scattering signal reveals novel features which reflect the PT-symmetry of the scattering target. Specifically we show that the device can show two different behaviors simultaneously, an amplifier or an absorber, depending on the direction and phase relation of the interrogating waves. Having an exact theory, and due to its relative experimental simplicity, PT-symmetric electronics offers new insights into the properties of PT-symmetric systems which are at the forefront of the research in mathematical physics and related fields.Comment: 17 pages, 7 figure

An exactly solvable quantum-lattice model with a tunable degree of nonlocality

An array of N subsequent Laguerre polynomials is interpreted as an eigenvector of a non-Hermitian tridiagonal Hamiltonian $H$ with real spectrum or, better said, of an exactly solvable N-site-lattice cryptohermitian Hamiltonian whose spectrum is known as equal to the set of zeros of the N-th Laguerre polynomial. The two key problems (viz., the one of the ambiguity and the one of the closed-form construction of all of the eligible inner products which make $H$ Hermitian in the respective {\em ad hoc} Hilbert spaces) are discussed. Then, for illustration, the first four simplest, $k-$parametric definitions of inner products with $k=0,k=1,k=2$ and $k=3$ are explicitly displayed. In mathematical terms these alternative inner products may be perceived as alternative Hermitian conjugations of the initial N-plet of Laguerre polynomials. In physical terms the parameter $k$ may be interpreted as a measure of the "smearing of the lattice coordinates" in the model.Comment: 35 p

Skin microbiota analysis in patients with anorexia nervosa and healthy-weight controls reveals microbial indicators of healthy weight and associations with the antimicrobial peptide psoriasin

Anorexia nervosa (AN), a psychiatric condition defined by low body weight for age and height, is associated with numerous dermatological conditions. Yet, clinical observations report that patients with AN do not suffer from infectious skin diseases like those associated with primary malnutrition. Cell-mediated immunity appears to be amplified in AN; however, this proinflammatory state does not sufficiently explain the lower incidence of infections. Antimicrobial peptides (AMPs) are important components of the innate immune system protecting from pathogens and shaping the microbiota. In Drosophila melanogaster starvation precedes increased AMP gene expression. Here, we analyzed skin microbiota in patients with AN and age-matched, healthy-weight controls and investigated the influence of weight gain on microbial community structure. We then correlated features of the skin microbial community with psoriasin and RNase 7, two highly abundant AMPs in human skin, to clarify whether an association between AMPs and skin microbiota exists and whether such a relationship might contribute to the resistance to cutaneous infections observed in AN. We find significant statistical correlations between Shannon diversity and the highly abundant skin AMP psoriasin and bacterial load, respectively. Moreover, we reveal psoriasin significantly associates with Abiotrophia, an indicator for the healthy-weight control group. Additionally, we observe a significant correlation between an individual’s body mass index and Lactobacillus, a microbial indicator of health. Future investigation may help clarify physiological mechanisms that link nutritional intake with skin physiology

Radical cation salts of TTF donors with XF6 (X = Re,Ta) anions

Electrocrystallization of the dianionic Re(IV)F6 species with different organic π electron donors was carried out. Depending on the first oxidation potential of the TTF derivatives this crystallization technique gave rise to various radical cations salts involving Re(IV) or Re(V) anions. With tetramethyltetrathiafulvalene (TMTTF) the (TMTTF)2Re(IV)F6  salt was obtained. However, with tetramethyltetraselenafulvalene (TMTSF) we obtained very small needles of the (TMTSeF)2Re(V)F6 system, analogue to the so called “Bechgaard salts” [1]. We present some characteristics of this new metallic phase. We compare to the diamagnetic (TMTSeF)2Ta(V)F6 obtained by the same strategy using TBATaF6 prepared according to the Browstein’s method [2] and explore electrocrystallization of the tantalum based anions [3], [4]. References: [1] K. Bechgaard, C.S. Jacobsen, K. Mortensen, H.J. Pedersen, N. Thorup, Solid State Commun. 1980, 33, 1119-1125. [2] S. Brownstein, Inorg. Chem. 1973, 12, N°3, 584-589. [3] C. Lenoir, K. Boubekeur, P. Batail, E. Canadell, P. Auban, O. Traetteberg, D. Jérome, Synth. Met. 1991, 42, 1939-1942. [4] F. Iwase, K. Sugiura, K. Furukawa, T. Nakamura, J. Phys. Soc. Jpn. 2009, 78, N°10, 104717:1-104717:7

Cognitive Change during the Life Course and Leukocyte Telomere Length in Late Middle-Aged Men

AbstractImportance: Cognitive skills are known to decline through the lifespan with large individual differences. The molecular mechanisms for this decline are incompletely understood. Although leukocyte telomere length provides an index of cellular age that predicts the incidence of age-related diseases, it is unclear whether there is an association between cognitive decline and leukocyte telomere length. Objective: To examine the association between changes in cognitive function during adult life and leukocyte telomere length after adjusting for confounding factors such as education, mental health and life style. Design, setting and participants: Two groups of men with negative (n=97) and positive (n=93) change in cognitive performance were selected from a birth cohort of 1985 Danish men born in 1953. Cognitive performance of each individual was assessed at age ~20 and ~56 years. Leukocyte telomere length at age ~58 was measured using qPCR. Linear regression models were used to investigate the association between cognitive function and leukocyte telomere length. Results: Men with negative change in cognitive performance during adult life had significantly shorter mean leukocyte telomere length than men with positive change in cognitive performance (unadjusted difference β= - 0.09, 95% CI -0.16 - -0.02, p= 0.02). This association remained significant after adjusting for smoking, alcohol consumption, leisure time activity, body mass index and cholesterol (adjusted difference β= -0.09, 95% CI -0.17 - -0.01, p= 0.02) but was nonsignificant after adjusting for smoking, alcohol consumption, leisure time activity, body mass index cholesterol, current cognitive function, depression and education (adjusted difference β= -0.07, 95% CI -0.16 - -0.01, p= 0.08). Conclusion and relevance: Preclinical cognitive changes may be associated with leukocyte telomere length