4,057 research outputs found
Machine learning -- based diffractive imaging with subwavelength resolution
Far-field characterization of small objects is severely constrained by the
diffraction limit. Existing tools achieving sub-diffraction resolution often
utilize point-by-point image reconstruction via scanning or labelling. Here, we
present a new imaging technique capable of fast and accurate characterization
of two-dimensional structures with at least wavelength/25 resolution, based on
a single far-field intensity measurement. Experimentally, we realized this
technique resolving the smallest-available to us 180-nm-scale features with
532-nm laser light. A comprehensive analysis of machine learning algorithms was
performed to gain insight into the learning process and to understand the flow
of subwavelength information through the system. Image parameterization,
suitable for diffractive configurations and highly tolerant to random noise was
developed. The proposed technique can be applied to new characterization tools
with high spatial resolution, fast data acquisition, and artificial
intelligence, such as high-speed nanoscale metrology and quality control, and
can be further developed to high-resolution spectroscop
Andreev Probe of Persistent Current States in Superconducting Quantum Circuits
Using the extraordinary sensitivity of Andreev interferometers to the
superconducting phase difference associated with currents, we measure the
persistent current quantum states in superconducting loops interrupted by
Josephson junctions. Straightforward electrical resistance measurements of the
interferometers give continuous read-out of the states, allowing us to
construct the energy spectrum of the quantum circuit. The probe is estimated to
be more precise and faster than previous methods, and can measure the local
phase difference in a wide range of superconducting circuits.Comment: Changes made in light of referees comments; to appear in PR
“Fix the system … the people who are in it are not the ones that are broken” A qualitative study exploring UK academic researchers’ views on support at work
Recent evidence suggests that it remains difficult for academic researchers to preserve global well-being when working in the UK higher education sector. Our study aimed to explore academic researchers' perspectives on how they feel their mental health and well-being could be better supported within the UK higher education system. Using a combination of semi-structured and narrative interviewing techniques, we gathered the perspectives of 26 researchers. Narrative and reflexive thematic analysis were then used on the data collected. Our findings highlight the need to tackle systemic issues such job insecurity and unrealistically high workloads, given the risk they can pose to researchers' mental health and well-being. Our findings also highlight the key influence of managers and supervisors in creating a supportive environment, and the importance of going beyond what support is offered. That is, it is vital to effectively promote any existing or emerging support systems, and to be proactive in offering this support. Given the diversity identified in researchers’ individual situations, it is important that support is flexible and takes into consideration individual requirements and preferences. Higher education authorities and institutions need to determine how they can foster a healthy, caring environment for researchers working in this sector going forwards
Detecting periodicity in experimental data using linear modeling techniques
Fourier spectral estimates and, to a lesser extent, the autocorrelation
function are the primary tools to detect periodicities in experimental data in
the physical and biological sciences. We propose a new method which is more
reliable than traditional techniques, and is able to make clear identification
of periodic behavior when traditional techniques do not. This technique is
based on an information theoretic reduction of linear (autoregressive) models
so that only the essential features of an autoregressive model are retained.
These models we call reduced autoregressive models (RARM). The essential
features of reduced autoregressive models include any periodicity present in
the data. We provide theoretical and numerical evidence from both experimental
and artificial data, to demonstrate that this technique will reliably detect
periodicities if and only if they are present in the data. There are strong
information theoretic arguments to support the statement that RARM detects
periodicities if they are present. Surrogate data techniques are used to ensure
the converse. Furthermore, our calculations demonstrate that RARM is more
robust, more accurate, and more sensitive, than traditional spectral
techniques.Comment: 10 pages (revtex) and 6 figures. To appear in Phys Rev E. Modified
styl
Giant Alcohol: A Worthy Opponent for the Children of the Band of Hope
From its foundation in 1847, the temperance organisation the Band of Hope addressed its young members as consumers, victims, and agents. In the first two roles they encountered the effects of drink of necessity, but in the third role they were encouraged to seek it out, attempting to influence individuals and wider society against 'Giant Alcohol'.
With an estimated membership of half the school-age population by the early twentieth century, well over three million, the Band of Hope also acted more directly to influence policy, and encouraged young people to consider issues of policy and politics. With its wide range of activities and material to educate, entertain and empower millions of children, and its radical view of the place of the child, the Band of Hope not only mobilised its child members to lobby for legal change, including prohibition, but took an active part in pointing out the cost of alcohol to society, particularly during the 14-18 war. The organisation began to decline post 1918, and this paper focuses on the address made to children by the Band of Hope in the late nineteenth and early twentieth centuries, at a time when its innovative view of children as able to understand and influence policy decisions reflected developments in the construction of childhood. This article draws on the archive of the British National Temperance League, over 50,000 items located in the Livesey Collection, University of Central Lancashire
Evidence-Based Interventions and Strategies for the Grand Challenges Approach: The Need for Judgement
What is the value of evidence-based interventions in addressing “Grand Challenges”?
Building upon the EPOS Grand Challenges work (Sakhrani et al., 2017), this paper explores
whether evidence-based approaches developed for management and policy are relevant to
addressing Grand Challenges. It discusses the criticisms of the Evidence-based Management
approach and argues that evidence is a necessary, but not sufficient input in the decisionmaking process of addressing Grand Challenges
Stochastic Faraday Rotation
Different ray paths through a turbulent plasma can produce stochastic Faraday
rotation leading to depolarization of any linearly polarized component. Simple
theory predicts that the average values of the Stokes parameters decay
according to , $\propto\exp(-\delta_l)$, with
$\delta_l\propto\lambda^4$. It is pointed out that a definitive test for such
depolarization is provided by the fact that remains constant while
decreases . The averages to which this
effect, called polarization covariance, should apply are discussed; it should
apply to spatial averages over a polarization map or temporal averages over a
data set, but not to beamwidth and bandwidth averages that are intrinsic to the
observation process. Observations of depolarization would provide statistical
information on fluctuations in the turbulent plasma along the line of sight,
specifically, the variance of the rotation measure. Other effects that can also
cause depolarization are discussed.Comment: 15 pages, Accepted for publication in Ap
Compact hyperbolic universe and singularities
Recently many people have discussed the possibility that the universe is
hyperbolic and was in an inflationary phase in the early stage. Under these
assumptions, it is shown that the universe cannot have compact hyperbolic
time-slices. Though the universal covering space of the universe has a past
Cauchy horizon and can be extended analytically beyond it, the extended region
has densely many points which correspond to singularities of the compact
universe. The result is essentially attributed to the ergodicity of the
geodesic flow on a compact negatively curved manifold. Validity of the result
is also discussed in the case of inhomogeneous universe. Relationship with the
strong cosmic censorship conjecture is also discussed.Comment: 8 pages with 7 figure
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