High mobility single and few-layer graphene sheets are in many ways attractive as nanoelectronic circuit hosts but lack energy gaps, which are essential to the operation of field-effect transistors. ...One of the methods used to create gaps in the spectrum of graphene systems is to form long period moiré patterns by aligning the graphene and hexagonal boron nitride (h-BN) substrate lattices. Here, we use planar tunneling devices with thin h-BN barriers to obtain direct and accurate tunneling spectroscopy measurements of the energy gaps in single-layer and bilayer graphene-h-BN superlattice structures at charge neutrality (first Dirac point) and at integer moiré band occupancies (second Dirac point, SDP) as a function of external electric and magnetic fields and the interface twist angle. In single-layer graphene, we find, in agreement with previous work, that gaps are formed at neutrality and at the hole-doped SDP, but not at the electron-doped SDP. Both primary and secondary gaps can be determined accurately by extrapolating Landau fan patterns to a zero magnetic field and are as large as ≈17 meV for devices in near-perfect alignment. For bilayer graphene, we find that gaps occur only at charge neutrality where they can be modified by an external electric field.
This study presents a fast precision measurement method that uses pattern recognition. First, a specific micro-structured surface was designed and manufactured, providing a unique pattern for ...recognition and matching. Second, a measurement system was proposed based on the algorithms of circle Hough transform (CHT), neural classifier (NC), template matching (TM) and sub-pixel interpolation (SI). Then, a series of experiments were carried out from three aspects: circle detection, length uncertainty, and measurement speed and range. The results showed the correct circle classification percentage was more than 96% and the CHT search accuracy was within a two-pixel level. The length uncertainty test demonstrated the method was able to achieve 90-nm length uncertainty, and a comparison of measurement speeds showed it helped to speed up measurements by a factor of 1000 compared to the original one.
•A fast precision measurement method that uses pattern recognition is presented.•A polar microstructure surface is manufactured to provide a unique pattern for recognition.•Unique feature circles are used to solve the problem of computational efficiency.•This method greatly reduces the strict requirements for the measurement components.
Atom based RF electric field sensing Fan, Haoquan; Kumar, Santosh; Sedlacek, Jonathon ...
Journal of physics. B, Atomic, molecular, and optical physics,
10/2015, Volume:
48, Issue:
20
Journal Article
Peer reviewed
Open access
Atom-based measurements of length, time, gravity, inertial forces and electromagnetic fields are receiving increasing attention. Atoms possess properties that suggest clear advantages as self ...calibrating platforms for measurements of these quantities. In this review, we describe work on a new method for measuring radio frequency (RF) electric fields based on quantum interference using either Cs or Rb atoms contained in a dielectric vapor cell. Using a bright resonance prepared within an electromagnetically induced transparency window it is possible to achieve high sensitivities, <1 V cm−1 Hz−1/2, and detect small RF electric fields V cm−1 with a modest setup. Some of the limitations of the sensitivity are addressed in the review. The method can be used to image RF electric fields and can be adapted to measure the vector electric field amplitude. Extensions of Rydberg atom-based electrometry for frequencies up to the terahertz regime are described.
This paper addresses a simple question: how small can one make a gravitational source mass and still detect its gravitational coupling to a nearby test mass? We describe an experimental scheme based ...on micromechanical sensing to observe gravity between milligram-scale source masses, thereby improving the current smallest source mass values by three orders of magnitude and possibly even more. We also discuss the implications of such measurements both for improved precision measurements of Newton's constant and for a new generation of experiments at the interface between quantum physics and gravity.
•A high precision optical sensor for coal dust concentration measurement is developed.•A new design was adopted for the intrinsic safety circuit and optical structure.•The developed sensor has higher ...accuracy and more stable performance.•A more accurate method for measuring coal dust concentrations was provided.
A higher precision optical sensor for coal dust concentration measurement was developed in this study, in order to overcome the deficiencies of current coal mine dust detection (such as their low precision and poor stability). Based on Mie scattering theory, the effects of the dust particle size, refractive index, and scattering angle on the distribution of the scattered light intensity were examined by using numerical simulations in MATLAB and MiePlot. Accordingly, the scattering structure was determined, and the mathematical model of the sensor was established. Then the sensor was developed after the selection and assembly of optimal devices through redesigning the circuit and control system independently and optimizing the optical structure. After calibration, the mean measured error of the developed sensor was 3.884%, 3.546%, and 3.037% in the short-term test. The relative errors in long-term detection increased to some extent, but still remained between 4% and 5%. It is firmly indicated that the developed sensor can reliably measure the dust concentration and exhibits excellent stability. This study provides a more accurate method for measuring and monitoring dust concentrations in coal mines.
Abstract
JUNO is a multi-purpose neutrino observatory under construction in the south of China. This publication presents new sensitivity estimates for the measurement of the
,
,
, and
oscillation ...parameters using reactor antineutrinos, which is one of the primary physics goals of the experiment. The sensitivities are obtained using the best knowledge available to date on the location and overburden of the experimental site, the nuclear reactors in the surrounding area and beyond, the detector response uncertainties, and the reactor antineutrino spectral shape constraints expected from the TAO satellite detector. It is found that the
and
oscillation parameters will be determined to 0.5% precision or better in six years of data collection. In the same period, the
parameter will be determined to about
% precision for each mass ordering hypothesis. The new precision represents approximately an order of magnitude improvement over existing constraints for these three parameters.
In this paper, a new non-contact method for measuring the cone angle of axicon lens based on vortex interference is presented. We use an improved Mach–Zehnder interferometer to make the vortex beam ...interfere with the cone wave. The peak curve of interference pattern is consistent with the Archimedean spiral, and the cone angle of axicon lens can be figured out with the spiral coefficient. The simulation analyzed influences of the tilt-angle error and the alignment error on measuring accuracy. In actual measuring, the structure of our device can be built within 100 mm*100 mm. The experimental results show that this method can realize an accuracy of 0.0030°. Compared to other methods, this method has advantages of high precision, compact structure and simple operation.
•The principle of this measurement has never been proposed.•It has high precision and simple operation.•It is an alternative to the contact measurement, which can eliminate the surface damage.•The device has small dimension and compact structure.
Abstract
The Newtonian gravitational constant G, which is one of the most important fundamental physical constants in nature, plays a significant role in the fields of theoretical physics, ...geophysics, astrophysics and astronomy. Although G was the first physical constant to be introduced in the history of science, it is considered to be one of the most difficult to measure accurately so far. Over the past two decades, eleven precision measurements of the gravitational constant have been performed, and the latest recommended value for G published by the Committee on Data for Science and Technology (CODATA) is (6.674 08 ± 0.000 31) × 10−11 m3 kg−1 s−2 with a relative uncertainty of 47 parts per million. This uncertainty is the smallest compared with previous CODATA recommended values of G; however, it remains a relatively large uncertainty among other fundamental physical constants. In this paper we briefly review the history of the G measurement, and introduce eleven values of G adopted in CODATA 2014 after 2000 and our latest two values published in 2018 using two independent methods.
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