5,692 research outputs found
Induction methods used in low temperature physics
A study has been made of induction bridges used in low temperature physics.\ud
\ud
In Part 1 the design of a mutual inductance bridge of the Hartshorn type is discussed. This design is based on a critical analysis of impurity effects of the different parts of the Hartshorn bridge. With this equipment frequencies up to 0.5 MHz can be used. Two methods have been developed to examine the secondary signal. In one of these use has been made of AD conversion techniques. In the other one, the secondary signal, produced by a superconducting sample, which is generally distorted, is analysed by using a Fourier expansion.\ud
\ud
In Part 2 equipment is described which enables us to measure the phase and amplitude of the harmonics of the output signal of the bridge. For synchronous detection a reference signal of the same frequency of the harmonic of interest is required. This reference signal is generated from the input signal of the bridge by means of a digital frequency multiplier with programmable multiplication factor N.\ud
\ud
In Part 3 some experimental results, showing the possibilities of the equipment, on some superconductors are presented
Designs of magnetic atom-trap lattices for quantum simulation experiments
We have designed and realized magnetic trapping geometries for ultracold
atoms based on permanent magnetic films. Magnetic chip based experiments give a
high level of control over trap barriers and geometric boundaries in a compact
experimental setup. These structures can be used to study quantum spin physics
in a wide range of energies and length scales. By introducing defects into a
triangular lattice, kagome and hexagonal lattice structures can be created.
Rectangular lattices and (quasi-)one-dimensional structures such as ladders and
diamond chain trapping potentials have also been created. Quantum spin models
can be studied in all these geometries with Rydberg atoms, which allow for
controlled interactions over several micrometers. We also present some
nonperiodic geometries where the length scales of the traps are varied over a
wide range. These tapered structures offer another way to transport large
numbers of atoms adiabatically into subwavelength traps and back.Comment: 9 pages, 10 figure
Surface-micromachined Ta–Si–N beams for use in micromechanics
Realization and characterization of free-standing surface-microstructures based on Ta-Si-N films are presented. Due to their significant physical and chemical properties, such ternary films are promising candidates for application in microelectromechanical devices
Youth care in time of COVID-19: Experiences of professionals and adolescent clients with telehealth
Measures aimed at preventing the COVID-19 virus from spreading restricted all aspects of public life, including possibilities for meeting in-person. Youth care professionals were forced to turn to telehealth tools, such as video calling and e-health methods, to be able to continue support and treatment of children, adolescents, caregivers, and families. This study consists of two qualitative interview studies on the experiences with and transition to telehealth during COVID-19: (1) interviews with youth care professionals (N = 20), and (2) interviews with adolescents who used mental health care support (N = 14). We specifically asked participants about five themes which were selected based on pre-COVID literature on telehealth: (1) tools (i.e., which programs are being used), (2) privacy, (3) methods (i.e., what was the same and what was different compared to in-person sessions), (4) relationship/therapeutic alliance, and (5) effectiveness (i.e., what was their impression of effectiveness of telehealth). The majority of professionals reported that they had very little to no experience with telehealth prior to the pandemic. Both professionals and adolescent clients mentioned benefits and limitations of telehealth. On several themes professionals and adolescent clients mentioned similar barriers in the transition to telehealth during COVID such as limitations of the available hard- and software (theme 1: tools); forced changes in the content and methods of the sessions (theme 3: methods); and difficulties with non-verbal communication (theme 4: alliance). However, whereas most professionals expressed the intention to keep using several aspects of telehealth after restrictions due to COVID are lifted, most adolescent clients expressed they see telehealth as a temporary solution and prefer meeting professionals in person. Their experiences and the barriers and enabling aspects they mentioned may provide important insights in the acceptability and usability of telehealth for youth care organizations, youth care professionals, researchers and higher educational training programs
Measuring very negative water potentials with polymer tensiometers: principles, performance and applications
In recent years, a polymer tensiometer (POT) was developed and tested to directly measure matric potentials in dry soils. By extending the measurement range to wilting point (a 20-fold increase compared to conventional, water-filled tensiometers), a myriad of previously unapproachable research questions are now open to experimental exploration. Furthermore, the instrument may well allow the development of more water-efficient irrigation strategies by recording water potential rather than soil water content. The principle of the sensor is to fill it with a polymer solution instead of water, thereby building up osmotic pressure inside the sensor. A high-quality ceramic allows the exchange of water with the soil while retaining the polymer. The ceramic has pores sufficiently small to remain saturated even under very negative matric potentials. Installing the sensor in an unsaturated soil causes the high pressure of the polymer solution to drop as the water potentials in the soil and in the POT equilibrate. As long as the pressure inside the polymer chamber remains sufficiently large to prevent cavitation, the sensor will function properly. If the osmotic potential in the polymer chamber can produce a pressure of approximately 2.0 MPa when the sensor is placed in water, proper readings down to wilting point are secured. Various tests in disturbed soil, including an experiment with root water uptake, demonstrate the operation and performance of the new polymer tensiometer and illustrate how processes such as root water uptake can be studied in more detail than before. The paper discusses the available data and explores the long term perspectives offered by the instrument
Space Saving by Dynamic Algebraization
Dynamic programming is widely used for exact computations based on tree
decompositions of graphs. However, the space complexity is usually exponential
in the treewidth. We study the problem of designing efficient dynamic
programming algorithm based on tree decompositions in polynomial space. We show
how to construct a tree decomposition and extend the algebraic techniques of
Lokshtanov and Nederlof such that the dynamic programming algorithm runs in
time , where is the maximum number of vertices in the union of
bags on the root to leaf paths on a given tree decomposition, which is a
parameter closely related to the tree-depth of a graph. We apply our algorithm
to the problem of counting perfect matchings on grids and show that it
outperforms other polynomial-space solutions. We also apply the algorithm to
other set covering and partitioning problems.Comment: 14 pages, 1 figur
Probing the magnetic moment of FePt micromagnets prepared by Focused Ion Beam milling
We investigate the degradation of the magnetic moment of a 300 nm thick FePt
film induced by Focused Ion Beam (FIB) milling. A rod is milled out of a film by a FIB process and is attached
to a cantilever by electron beam induced deposition. Its magnetic moment is
determined by frequency-shift cantilever magnetometry. We find that the
magnetic moment of the rod is , which implies that 70% of the magnetic moment is preserved
during the FIB milling process. This result has important implications for atom
trapping and magnetic resonance force microscopy (MRFM), that are addressed in
this paper.Comment: 4 pages, 4 figure
A comparative study of deconvolution techniques for quantum-gas microscope images
Quantum-gas microscopes are used to study ultracold atoms in optical lattices
at the single particle level. In these system atoms are localised on lattice
sites with separations close to or below the diffraction limit. To determine
the lattice occupation with high fidelity, a deconvolution of the images is
often required. We compare three different techniques, a local iterative
deconvolution algorithm, Wiener deconvolution and the Lucy-Richardson
algorithm, using simulated microscope images. We investigate how the
reconstruction fidelity scales with varying signal-to-noise ratio, lattice
filling fraction, varying fluorescence levels per atom, and imaging resolution.
The results of this study identify the limits of singe-atom detection and
provide quantitative fidelities which are applicable for different atomic
species and quantum-gas microscope setups
- …