Antiferromagnetic Domain Wall Engineering in Chromium Films

We have engineered an antiferromagnetic domain wall by utilizing a magnetic frustration effect of a thin iron cap layer deposited on a chromium film. Through lithography and wet etching we selectively remove areas of the Fe cap layer to form a patterned ferromagnetic mask over the Cr film. Removing the Fe locally removes magnetic frustration in user-defined regions of the Cr film. We present x-ray microdiffraction microscopy results confirming the formation of a 90{\deg} spin-density wave propagation domain wall in Cr. This domain wall nucleates at the boundary defined by our Fe mask.Comment: submitted to AP

Task oriented Bayesian inference in interval timing: People use their prior reproduction experience to calibrate time reproduction

The estimation of duration has been shown to follow Bayesian inference, where people use their prior belief to calibrate the estimation. This explains timing biases such as the range bias where a duration is reproduced as longer when previously encountered durations were longer than shorter. However, it is unclear whether prior belief is based on previously perceived or reproduced durations. In 4 experiments, we show that the range bias occurs between short and long reproduction ranges but not between short and long perception ranges. Further analyses also show that the prior is updated by the most recent reproduced (but not perceived) duration. Together these results support a task-oriented Bayesian inference account of time reproduction, where people use the perceived duration and their past reproduction experience to make an inference about how much time to reproduce

A Tight Karp-Lipton Collapse Result in Bounded Arithmetic

Cook and Krajíček [9] have obtained the following Karp-Lipton result in bounded arithmetic: if the theory proves , then collapses to , and this collapse is provable in . Here we show the converse implication, thus answering an open question from [9]. We obtain this result by formalizing in a hard/easy argument of Buhrman, Chang, and Fortnow [3]. In addition, we continue the investigation of propositional proof systems using advice, initiated by Cook and Krajíček [9]. In particular, we obtain several optimal and even p-optimal proof systems using advice. We further show that these p-optimal systems are equivalent to natural extensions of Frege systems

Cyclic cosmology from Lagrange-multiplier modified gravity

We investigate cyclic and singularity-free evolutions in a universe governed by Lagrange-multiplier modified gravity, either in scalar-field cosmology, as well as in $f(R)$ one. In the scalar case, cyclicity can be induced by a suitably reconstructed simple potential, and the matter content of the universe can be successfully incorporated. In the case of $f(R)$-gravity, cyclicity can be induced by a suitable reconstructed second function $f_2(R)$ of a very simple form, however the matter evolution cannot be analytically handled. Furthermore, we study the evolution of cosmological perturbations for the two scenarios. For the scalar case the system possesses no wavelike modes due to a dust-like sound speed, while for the $f(R)$ case there exist an oscillation mode of perturbations which indicates a dynamical degree of freedom. Both scenarios allow for stable parameter spaces of cosmological perturbations through the bouncing point.Comment: 8 pages, 3 figures, references added, accepted for publicatio

Energetics in Condensate Star and Wormholes

It is known that the total gravitational energy in localized sources having static spherical symmetry and satisfying energy conditions is negative (attractive gravity). A natural query is how the gravitational energy behaves under circumstances where energy conditions are violated. To answer this, the known expression for the gravitational energy is suitably modified to account for situations like the ones occurring in wormhole spacetime. It is then exemplified that in many cases the modified expression yields desirable answers. The implications are discussed.Comment: 16 pages, 1 figure, references added, To appear in PR

Duality invariance and cosmological dynamics

A duality transformation that interrelates expanding and contracting cosmological models is shown to single out a duality invariant, interacting two-component description of any irrotational, geodesic and shearfree cosmic medium with vanishing three curvature scalar. We apply this feature to a system of matter and radiation, to a mixture of dark matter and dark energy, to minimal and conformal scalar fields, and to an enlarged Chaplygin gas model of the cosmic substratum. We extend the concept of duality transformations to cosmological perturbations and demonstrate the invariance of adiabatic pressure perturbations under these transformations.Comment: 14 pages, Discussion enlarged, accepted for publication in IJMP

Red and orange laser operation of Pr:KYF4 pumped by a Nd:YAG/LBO laser at 469.1nm and a InGaN laser diode at 444nm

We report the basic luminescence properties and the continuous-wave (CW) laser operation of a Pr3+-doped KYF4 single crystal in the Red and Orange spectral regions by using a new pumping scheme. The pump source is an especially developed, compact, slightly tunable and intra-cavity frequency-doubled diode-pumped Nd:YAG laser delivering a CW output power up to about 1.4 W around 469.1 nm. At this pump wavelength, red and orange laser emissions are obtained at about 642.3 and 605.5 nm, with maximum output powers of 11.3 and 1 mW and associated slope efficiencies of 9.3% and 3.4%, with respect to absorbed pump powers, respectively. For comparison, the Pr:KYF4 crystal is also pumped by a InGaN blue laser diode operating around 444 nm. In this case, the same red and orange lasers are obtained, but with maximum output powers of 7.8 and 2 mW and the associated slope efficiencies of 7 and 5.8%, respectively. Wavelength tuning for the two lasers is demonstrated by slightly tilting the crystal. Orange laser operation and laser wavelength tuning are reported for the first time