Static Cylindrical Symmetric Solutions in the Einstein-Aether Theory

In this work we present all the possible solutions for a static cylindrical symmetric spacetime in the Einstein-Aether (EA) theory. As far as we know, this is the first work in the literature that considers cylindrically symmetric solutions in the theory of EA. One of these solutions is the generalization in EA theory of the Levi-Civita (LC) spacetime in General Relativity (GR) theory. We have shown that this generalized LC solution has unusual geodesic properties, depending on the parameter $c_{14}$ of the aether field. The circular geodesics are the same of the GR theory, no matter the values of $c_{14}$. However, the radial and $z$ direction geodesics are allowed only for certain values of $sigma$ and $c_{14}$. The $z$ direction geodesics are restricted to an interval of $sigma$ different from those predicted by the GR and the radial geodesics show that the motion is confined between the origin and a maximum radius. The latter is not affected by the aether field but the velocity and acceleration of the test particles are Besides, for $0leqsigma<1/2$, when the cylindrical symmetry is preserved, this spacetime is singular at the axis $r=0$, although for $sigma>1/2$ exists interval of $c_{14}$ where the spacetime is not singular, which is completely different from that one obtained with the GR theory, where the axis $r=0$ is always singular.

pi-GAN: Periodic Implicit Generative Adversarial Networks for 3D-Aware Image Synthesis

We have witnessed rapid progress on 3D-aware image synthesis, leveraging recent advances in generative visual models and neural rendering. Existing approaches however fall short in two ways: first, they may lack an underlying 3D representation or rely on view-inconsistent rendering, hence synthesizing images that are not multi-view consistent; second, they often depend upon representation network architectures that are not expressive enough, and their results thus lack in image quality. We propose a novel generative model, named Periodic Implicit Generative Adversarial Networks ($pi$-GAN or pi-GAN), for high-quality 3D-aware image synthesis. $pi$-GAN leverages neural representations with periodic activation functions and volumetric rendering to represent scenes as view-consistent 3D representations with fine detail. The proposed approach obtains state-of-the-art results for 3D-aware image synthesis with multiple real and synthetic datasets.

Detection of odor quality and ripening stage of Mangifera indica L. by graphdiyne nanosheet -- a DFT outlook

Using first-principles calculation, geometrical stability together with electronic properties of graphdiyne nanosheet (Gdn-NS) is investigated. The structural stability of Gdn-NS is established with the support of phonon band structure and cohesive energy. The main objective of the present study is to check the odor quality of Mangifera indica L. (mangoes) fruits during the various ripening stage with the influence of Gdn-NS material. In addition, the adsorption of various volatiles, namely ethyl butanoate, myrcene, (E,Z,Z)-1,3,4,8-undecatetraene and $gamma$-octalactone aromas on Gdn-NS is explored with the significant parameters including Bader charge transfer, energy gap, average energy gap changes and adsorption energy. The sensitivity of volatiles emitting from various ripening stages of mango on Gdn-NS were explored with the influence of density of states spectrum. The outcomes of the proposed work help us to check the ripening stage and odor quality of Mangifera indica L. by Gdn-NS material using density functional theory.

MetaSDF: Meta-learning Signed Distance Functions

Neural implicit shape representations are an emerging paradigm that offers many potential benefits over conventional discrete representations, including memory efficiency at a high spatial resolution. Generalizing across shapes with such neural implicit representations amounts to learning priors over the respective function space and enables geometry reconstruction from partial or noisy observations. Existing generalization methods rely on conditioning a neural network on a low-dimensional latent code that is either regressed by an encoder or jointly optimized in the auto-decoder framework. Here, we formalize learning of a shape space as a meta-learning problem and leverage gradient-based meta-learning algorithms to solve this task. We demonstrate that this approach performs on par with auto-decoder based approaches while being an order of magnitude faster at test-time inference. We further demonstrate that the proposed gradient-based method outperforms encoder-decoder based methods that leverage pooling-based set encoders.

Branching fractions for $P_{3/2}$ decays in Ba$^+$

Branching fractions for decays from the $P_{3/2}$ level in $^{138}$Ba$^+$ have been measured with a single laser-cooled ion. Decay probabilities to $S_{1/2}$, $D_{3/2}$ and $D_{5/2}$ are determined to be $0.741716(71)$, $0.028031(23)$ and $0.230253(61)$, respectively, which are an order of magnitude improvement over previous results. Our methodology only involves optical pumping and state detection, and is hence relatively free of systematic effects. Measurements are carried out in two different ways to check for consistency. Our analysis also includes a measurement of the $D_{5/2}$ lifetime, for which we obtain 30.14(40),s.

Spherically Symmetric Analytic Solutions and Naked Singularities in Einstein-Aether Theory

In the present work we analyze all the possible spherically symmetric exterior vacuum solutions allowed by the Einstein-Aether theory with static aether. We show that there are four classes of solutions corresponding to different values of a combination of the free parameters, $c_{14}=c_1+c_4$, which are: $ 0 < c_{14}<2$, $c_{14} < 0$, $c_{14}=2$ and $c_{14}=0$. We present explicit analytical solutions for $c_{14}=3/2, 16/9, 48/25, -16, 2$ and $0$. The first case has some pathological behavior, while the rest have all singularities at $r=0$ and are asymptotically flat spacetimes. For the solutions $c_{14}=16/9, 48/25, mathrm{, and ,}, -16$ we show that there exist no horizons, neither Killing nor universal horizon, thus we have naked singularities. Finally, the solution for $c_{14}=2$ has a metric component as an arbitrary function of radial coordinate, when it is chosen to be the same as in the Schwarzschild case, we have a physical singularity at finite radius, besides the one at $r=0$. This characteristic is completely different from General Relativity.

Existence of New Singularities in Einstein-Aether Theory

How do the global properties of a Lorentzian manifold change when endowed with a vector field? This interesting question is tackled in this paper within the framework of Einstein-Aether (EA) theory which has the most general diffeomorphism-invariant action involving a spacetime metric and a vector field. After classifying all the possible nine vacuum solutions with and without cosmological constant in Friedmann-Lema{^{i}}tre-Robertson-Walker (FLRW) cosmology, we show that there exist three singular solutions in the EA theory which are not singular in the General Relativity (GR), all of them for $k=-1$, and another singular solution for $k=1$ in EA theory which does not exist in GR. This result is cross-verified by showing the focusing of timelike geodesics using the Raychaudhuri equation. These new singular solutions show that GR and EA theories can be completely different, even for the FLRW solutions when we go beyond flat geometry ($k=0$). In fact, they have different global structures. In the case where $Lambda=0$ ($k=pm 1$) the vector field defining the preferred direction is the unique source of the curvature.

In-situ monitoring of room temperature reactions of lanthanides with nitrogen and hydrogen at low pressures

The dissociative chemisorption of molecular nitrogen on clean lanthanide surfaces at ambient temperature and low pressure is explored. In-situ conductance measurements track the conversion from the lanthanide metals to the insulating lanthanide nitrides. A small partial pressure of oxygen ($sim 10^{-8}$ mbar) is shown to inhibit the nitridation of lanthanides at $10^{-4}$ mbar of N$_2$. The rate of nitridation as a function of nitrogen pressure is measured at low pressure for a series of lanthanide elements, gadolinium, terbium, dysprosium, ytterbium and praseodymium. Exposure of the lanthanide surfaces to both N$_2$ and H$_2$ results in the formation of NH$_3$.

Magic wavelength of the $^{138}$Ba$^+$ $6s;{}^2S_{1/2}-5d;{}^2D_{5/2}$ clock transition

The zero crossing of the dynamic differential scalar polarizability of the $S_{1/2}-D_{5/2}$ clock transition in $^{138}$Ba$^+$ has been determined to be $459.1614(28),$THz. Together with previously determined matrix elements and branching ratios, this tightly constrains the dynamic differential scalar polarizability of the clock transition over a large wavelength range ($gtrsim 700,$nm). In particular it allows an estimate of the blackbody radiation shift of the clock transition at room temperature.

Silicene nanosheet to discriminate the quality of pear fruit based on volatiles adsorption --- a DFT application

We report the interaction between the silicene nanosheet (Si-NS) and volatile organic compounds (VOCs) released from the pear fruit (Pyrus communis) in ripened and over-ripened stages using density functional theory (DFT) technique. The geometric stability of Si-NS is studied from the phonon band structure. Further, the electronic property of Si-NS is studied from the energy band gap structure, and the energy gap is found to be 0.46 eV, which exhibits semiconductor property. The outcomes infer that the adsorption of volatiles released from the pear fruit on silicene nanosheet is in the following order hexyl acetate $rightarrow$ butyl acetate $rightarrow$ butyl butyrate in the ripened stage whereas in the over-ripened stage the adsorption sequence is noticed to be acetic acid $rightarrow$ ethyl acetate $rightarrow$ 1-butanol. The adsorption property of pear fruit volatiles on silicene nanosheet is documented with the adsorption energy, average energy gap changes, and Bader charge transfer. Moreover, the adsorption of VOCs on silicene nanosheet is also explored using the energy band structure, electron density along with the adsorption sites and density of states (DOS) spectrum. Besides, the findings reveal that the silicene nanosheet can be used to discriminate the quality of pear fruit.