Year 1 of the ZTF high-cadence Galactic plane survey Kupfer, Thomas; Prince, Thomas A.; van Roestel, Jan ...
Monthly notices of the Royal Astronomical Society,
07/2021, Letnik:
505, Številka:
1
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We present the goals, strategy, and first results of the high-cadence Galactic plane survey using the Zwicky Transient Facility (ZTF). The goal of the survey is to unveil the Galactic population of ...short-period variable stars, including short-period binaries, and stellar pulsators with periods less than a few hours. Between 2018 June and 2019 January, we observed 64 ZTF fields resulting in 2990 deg 2 of high stellar density in the ZTF- r band along the Galactic plane. Each field was observed continuously for 1.5 to 6 h with a cadence of 40 sec. Most fields have between 200 and 400 observations obtained over 2–3 continuous nights. As part of this survey, we extract a total of ≈230 million individual objects with at least 80 epochs obtained during the high-cadence Galactic plane survey reaching an average depth of ZTF– r ≈ 20.5 mag. For four selected fields with 2–10 million individual objects per field, we calculate different variability statistics and find that ≈1–2 per cent of the objects are astrophysically variable over the observed period. We present a progress report on recent discoveries, including a new class of compact pulsators, the first members of a new class of Roche lobe filling hot subdwarf binaries as well as new ultracompact double white dwarfs and flaring stars. Finally, we present a sample of 12 new single-mode hot subdwarf B-star pulsators with pulsation amplitudes between ZTF– r = 20–76 mmag and pulsation periods between P = 5.8–16 min with a strong cluster of systems with periods ≈6 min. All of the data have now been released in either ZTF Data Release 3 or Data Release 4.
The fundamental properties of light derive from its constituent particles--massless quanta (photons) that do not interact with one another. However, it has long been known that the realization of ...coherent interactions between individual photons, akin to those associated with conventional massive particles, could enable a wide variety of novel scientific and engineering applications. Here we demonstrate a quantum nonlinear medium inside which individual photons travel as massive particles with strong mutual attraction, such that the propagation of photon pairs is dominated by a two-photon bound state. We achieve this through dispersive coupling of light to strongly interacting atoms in highly excited Rydberg states. We measure the dynamical evolution of the two-photon wavefunction using time-resolved quantum state tomography, and demonstrate a conditional phase shift exceeding one radian, resulting in polarization-entangled photon pairs. Particular applications of this technique include all-optical switching, deterministic photonic quantum logic and the generation of strongly correlated states of light.
This study examines how the historical state conditions long-run development, using Vietnam as a laboratory. Northern Vietnam (Dai Viet) was ruled by a strong, centralized state in which the village ...was the fundamental administrative unit. Southern Vietnam was a peripheral tributary of the Khmer (Cambodian) Empire, which followed a patron-client model with more informal, personalized power relations and no village intermediation. Using a regression discontinuity design, the study shows that areas exposed to Dai Viet administrative institutions for a longer period prior to French colonization have experienced better economic outcomes over the past 150 years. Rich historical data document that in Dai Viet villages, citizens have been better able to organize for public goods and redistribution through civil society and local government. We argue that institutionalized village governance crowded in local cooperation and that these norms persisted long after the original institutions disappeared.
This essay critically evaluates the analytic literature concerned with causal connections between Islam and economic performance. It focuses on works since 1997, when this literature was last ...surveyed comprehensively. Among the findings are the following: Ramadan fasting by pregnant women harms prenatal development; Islamic charities mainly benefit the middle class; Islam affects educational outcomes less through Islamic schooling than through structural factors that handicap learning as a whole; Islamic finance has a negligible effect on Muslim financial behavior; and low generalized trust depresses Muslim trade. The last feature reflects the Muslim world’s delay in transitioning from personal to impersonal exchange. The delay resulted from the persistent simplicity of the private enterprises formed under Islamic law. Weak property rights reinforced the private sector’s stagnation by driving capital from commerce to rigid waqfs. Waqfs limited economic development through their inflexibility and democratization by keeping civil society embryonic. Parts of the Muslim world conquered by Arab armies are especially undemocratic, which suggests that early Islamic institutions were particularly critical to the persistence of authoritarian patterns of governance. States have contributed to the persistence of authoritarianism by treating Islam as an instrument of governance. As the world started to industrialize, non- Muslim subjects of Muslim-governed states pulled ahead of their Muslim neighbors, partly by exercising the choice of law they enjoyed under Islamic law in favor of a Western legal system.
This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:
To assess the effects of acupuncture for treating OAB in adults; and summarise the principal findings of ...relevant economic evaluations.
High-harmonic generation by focusing a femtosecond laser onto a gas is a well-known method of producing coherent extreme-ultraviolet (EUV) light. This nonlinear conversion process requires high pulse ...intensities, greater than 1013 W cm-2, which are not directly attainable using only the output power of a femtosecond oscillator. Chirped-pulse amplification enables the pulse intensity to exceed this threshold by incorporating several regenerative and/or multi-pass amplifier cavities in tandem. Intracavity pulse amplification (designed not to reduce the pulse repetition rate) also requires a long cavity. Here we demonstrate a method of high-harmonic generation that requires no extra cavities. This is achieved by exploiting the local field enhancement induced by resonant plasmons within a metallic nanostructure consisting of bow-tie-shaped gold elements on a sapphire substrate. In our experiment, the output beam emitted from a modest femtosecond oscillator (100-kW peak power, 1.3-nJ pulse energy and 10-fs pulse duration) is directly focused onto the nanostructure with a pulse intensity of only 1011 W cm-2. The enhancement factor exceeds 20 dB, which is sufficient to produce EUV wavelengths down to 47 nm by injection with an argon gas jet. The method could form the basis for constructing laptop-sized EUV light sources for advanced lithography and high-resolution imaging applications.
Positive electrodes for Li-ion and lithium batteries (also termed “cathodes”) have been under intense scrutiny since the advent of the Li-ion cell in 1991. This is especially true in the past decade. ...Early on, carbonaceous materials dominated the negative electrode and hence most of the possible improvements in the cell were anticipated at the positive terminal; on the other hand, major developments in negative electrode materials made in the last portion of the decade with the introduction of nanocomposite Sn/C/Co alloys and Si−C composites have demanded higher capacity positive electrodes to match. Much of this was driven by the consumer market for small portable electronic devices. More recently, there has been a growing interest in developing Li−sulfur and Li−air batteries that have the potential for vastly increased capacity and energy density, which is needed to power large-scale systems. These require even more complex assemblies at the positive electrode in order to achieve good properties. This review provides an overview of the major developments in the area of positive electrode materials in both Li-ion and Li batteries in the past decade, and particularly in the past few years. Highlighted are concepts in solid-state chemistry and nanostructured materials that conceptually have provided new opportunities for materials scientists for tailored design that can be extended to many different electrode materials.
Photonic Floquet topological insulators RECHTSMAN, Mikael C; ZEUNER, Julia M; PLOTNIK, Yonatan ...
Nature (London),
04/2013, Letnik:
496, Številka:
7444
Journal Article
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Topological insulators are a new phase of matter, with the striking property that conduction of electrons occurs only on their surfaces. In two dimensions, electrons on the surface of a topological ...insulator are not scattered despite defects and disorder, providing robustness akin to that of superconductors. Topological insulators are predicted to have wide-ranging applications in fault-tolerant quantum computing and spintronics. Substantial effort has been directed towards realizing topological insulators for electromagnetic waves. One-dimensional systems with topological edge states have been demonstrated, but these states are zero-dimensional and therefore exhibit no transport properties. Topological protection of microwaves has been observed using a mechanism similar to the quantum Hall effect, by placing a gyromagnetic photonic crystal in an external magnetic field. But because magnetic effects are very weak at optical frequencies, realizing photonic topological insulators with scatter-free edge states requires a fundamentally different mechanism-one that is free of magnetic fields. A number of proposals for photonic topological transport have been put forward recently. One suggested temporal modulation of a photonic crystal, thus breaking time-reversal symmetry and inducing one-way edge states. This is in the spirit of the proposed Floquet topological insulators, in which temporal variations in solid-state systems induce topological edge states. Here we propose and experimentally demonstrate a photonic topological insulator free of external fields and with scatter-free edge transport-a photonic lattice exhibiting topologically protected transport of visible light on the lattice edges. Our system is composed of an array of evanescently coupled helical waveguides arranged in a graphene-like honeycomb lattice. Paraxial diffraction of light is described by a Schrödinger equation where the propagation coordinate (z) acts as 'time'. Thus the helicity of the waveguides breaks z-reversal symmetry as proposed for Floquet topological insulators. This structure results in one-way edge states that are topologically protected from scattering.
The incorporation of energetic helium gaseous species into materials such as tungsten (W) imparts intrinsic surface fragility, yielding fuzzy tungsten. To enhance the robustness of the surface ...layers, aluminum oxide (AlO x ) was deposited by atomic layer deposition into the fuzzy W. The conformally deposited ceramic yields a new class of surface composites. Structural characterization of the fuzzy W–AlO x composites through nanoindentation testing indicated enhanced indentation modulus (E ind) and hardness (H ind) and was modeled through various rules of mixtures approaches. The distribution of AlO x in fuzzy W was explored and a systematic study of the extent of incorporation of the AlO x into the fuzzy W was carried out. The synthesized composites may be utilized for improved structural characteristics, e.g., in reducing crack initiation and fracture.
In this study, we successfully synthesized two-phase titanium oxide (TiO x ) heterogeneous nanoparticles (NPs) using an advanced sol–gel method, a significant stride in developing efficient, room ...temperature (RT) NO2 gas sensors. The prepared two-phase TiO x heterogeneous NPs exhibited exceptional sensitivity to low concentrations of NO2 gas at RT. The heightened gas response was attributed to a significant presence of oxygen vacancies, creating intermediate states within the two-phase heterostructures and thus narrowing the band gap. This facilitated electron transport from the valence band (VB) to the conduction band (CB), resulting in increased current at RT. The XPS analysis confirmed a substantial amount of chemisorbed oxygen O2(ads) – within the two-phase heterostructures, providing more chemisorption sites for nitrogen dioxide gas. This increase in chemisorption sites significantly improved the gas response. Furthermore, the introduction of zinc into the TiO x NPs reduced their band gap, enhancing the background resistance signal-to-noise ratio and increasing the response while maintaining remarkable stability. In summary, our work introduces a promising RT NO2 sensor based on two-phase TiO x heterogeneous NPs, holding great potential for applications in environmental monitoring and gas sensing technology. In future work, we aim to delve deeper into the capabilities of the sensor, exploring broader applications and refining its design for enhanced practicality in environmental monitoring.
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