The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is necessary to understand the source and acceleration of cosmic rays in the Milky Way. This ...work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with 2
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years of data recorded by the DArk Matter Particle Explorer (DAMPE). This is the first time that an experiment directly measures the cosmic ray protons up to ~100 TeV with high statistics. The measured spectrum confirms the spectral hardening at ~300 GeV found by previous experiments and reveals a softening at ~13.6 TeV, with the spectral index changing from ~2.60 to ~2.85. Our result suggests the existence of a new spectral feature of cosmic rays at energies lower than the so-called knee and sheds new light on the origin of Galactic cosmic rays.
The force exerted by photons is of fundamental importance in light-matter interactions. For example, in free space, optical tweezers have been widely used to manipulate atoms and microscale ...dielectric particles. This optical force is expected to be greatly enhanced in integrated photonic circuits in which light is highly concentrated at the nanoscale. Harnessing the optical force on a semiconductor chip will allow solid state devices, such as electromechanical systems, to operate under new physical principles. Indeed, recent experiments have elucidated the radiation forces of light in high-finesse optical microcavities, but the large footprint of these devices ultimately prevents scaling down to nanoscale dimensions. Recent theoretical work has predicted that a transverse optical force can be generated and used directly for electromechanical actuation without the need for a high-finesse cavity. However, on-chip exploitation of this force has been a significant challenge, primarily owing to the lack of efficient nanoscale mechanical transducers in the photonics domain. Here we report the direct detection and exploitation of transverse optical forces in an integrated silicon photonic circuit through an embedded nanomechanical resonator. The nanomechanical device, a free-standing waveguide, is driven by the optical force and read out through evanescent coupling of the guided light to the dielectric substrate. This new optical force enables all-optical operation of nanomechanical systems on a CMOS (complementary metal-oxide-semiconductor)-compatible platform, with substantial bandwidth and design flexibility compared to conventional electrical-based schemes.
ABSTRACT
SN 2018hti is a Type I superluminous supernova (SLSN I) with an absolute g-band magnitude of −22.2 at maximum brightness, discovered by the Asteroid Terrestrial-impact Last Alert System in a ...metal-poor galaxy at a redshift of 0.0612. We present extensive photometric and spectroscopic observations of this supernova, covering the phases from ∼−35 d to more than +340 d from the r-band maximum. Combining our BVgri-band photometry with Swift UVOT optical/ultraviolet photometry, we calculated the peak luminosity as ∼3.5 × 1044 erg s−1. Modelling the observed light curve reveals that the luminosity evolution of SN 2018hti can be produced by an ejecta mass of 5.8 M⊙ and a magnetar with a magnetic field of B = 1.8 × 1013 G having an initial spin period of P0 = 1.8 ms. Based on such a magnetar-powered scenario and a larger sample, a correlation between the spin of the magnetar and the kinetic energy of the ejecta can be inferred for most SLSNe I, suggesting a self-consistent scenario. Like for other SLSNe I, the host galaxy of SN 2018hti is found to be relatively faint (Mg = −17.75 mag) and of low metallicity (Z = 0.3 Z⊙), with a star formation rate of 0.3 M⊙ yr−1. According to simulation results of single-star evolution, SN 2018hti could originate from a massive, metal-poor star with a zero-age main sequence (ZAMS) mass of 25–40 M⊙, or from a less massive rotating star with MZAMS ≈ 16–25 M⊙. For the case of a binary system, its progenitor could also be a star with $M_\mathrm{ZAMS} \gtrsim 25\, \mathrm{ M}_\odot$.
Scanning probe microscopies (SPM) and cantilever-based sensors generally use low-frequency mechanical devices of microscale dimensions or larger. Almost universally, off-chip methods are used to ...sense displacement in these devices, but this approach is not suitable for nanoscale devices. Nanoscale mechanical sensors offer a greatly enhanced performance that is unattainable with microscale devices. Here we describe the fabrication and operation of self-sensing nanocantilevers with fundamental mechanical resonances up to very high frequencies (VHF). These devices use integrated electronic displacement transducers based on piezoresistive thin metal films, permitting straightforward and optimal nanodevice readout. This non-optical transduction enables applications requiring previously inaccessible sensitivity and bandwidth, such as fast SPM and VHF force sensing. Detection of 127 MHz cantilever vibrations is demonstrated with a thermomechanical-noise-limited displacement sensitivity of 39 fm Hz(-1/2). Our smallest devices, with dimensions approaching the mean free path at atmospheric pressure, maintain high resonance quality factors in ambient conditions. This enables chemisorption measurements in air at room temperature, with unprecedented mass resolution less than 1 attogram (10(-18) g).
State-of-the-art advances in nanoscale optomechanics allow light to be guided in free-standing waveguides or resonators. In closely spaced devices, the coupling between the guided lightwaves gives ...rise to an optical force known as the 'optical bonding force'. Indeed, attractive optical force has been observed in substrate coupled devices. According to recent theoretical predictions, the optical force should show bipolar behaviour depending on the relative phase between in-plane coupled lightwaves. So far, such an in-plane optical force has not been measured. Here, we experimentally demonstrate a bipolar optical force between planarly coupled nanophotonic waveguides. Both attractive and repulsive optical forces are obtained. The sign of the force can be switched reversibly by tuning the relative phase of the interacting lightwaves. This highly engineerable force of bipolar nature could be used as the operation principle for a new class of planar light force devices and circuits on a CMOS-compatible platform.
This study aimed to compare the therapeutic effects of single umbilical cord blood transplantation (UCBT) and unmanipulated haploidentical hematopoietic SCT (haplo-HSCT) in childhood hematologic ...malignances. We enrolled 410 consecutive children who received either single UCBT (n=37) or haplo-HSCT from a family donor (n=373) during the same time period. For each UCBT recipient, three recipients matched for year of HSCT, underlying diseases, disease status and the length of follow-up were randomly selected from the haplo-HSCT cohort. Hematopoietic recovery was significantly faster in haplo-HSCT recipients than in UCBT recipients. The incidence of chronic GVHD was significantly higher in haplo-HSCT recipients. The incidence of CMV-related interstitial pneumonia was higher in UCBT recipients. The haplo-HSCT recipients had better 1-year OS (73.0% vs 56.8%, P=0.048), lower 1-year non-relapse mortality (NRM, 18.0% vs 35.1%, P=0.026) and lower 2-year NRM rates (19.9% vs 35.1%, P=0.044). The relapse- and disease-free survival rates did not differ significantly between the groups. Our results showed that compared with UCBT, unmanipulated haplo-HSCT can improve the outcomes of children with hematologic malignances.
Nanoelectromechanical systems based on cantilevers have consistently set records for sensitivity in measurements of displacement, force and mass over the past decade. Continued progress will require ...the integration of efficient transduction on a chip so that nanoelectromechanical systems may be operated at higher speeds and sensitivities. Conventional electrical schemes have limited bandwidth, and although optical methods are fast, they are subject to the diffraction limit. Here, we demonstrate the integration of nanocantilevers on a silicon photonic platform with a non-interferometric transduction scheme that avoids the diffraction limit by making use of near-field effects in optomechanical interactions. The use of a non-interferometric method means that a coherent light source is not required, making the monolithic integration of optomechanical systems with on-chip light sources feasible. We further demonstrate optomechanical multiplexing of an array of ten nanocantilevers with a displacement sensitivity of 40 fm Hz(-1/2).
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