1,547 research outputs found
Inductive queries for a drug designing robot scientist
It is increasingly clear that machine learning algorithms need to be integrated in an iterative scientific discovery loop, in which data is queried repeatedly by means of inductive queries and where the computer provides guidance to the experiments that are being performed. In this chapter, we summarise several key challenges in achieving this integration of machine learning and data mining algorithms in methods for the discovery of Quantitative Structure Activity Relationships (QSARs). We introduce the concept of a robot scientist, in which all steps of the discovery process are automated; we discuss the representation of molecular data such that knowledge discovery tools can analyse it, and we discuss the adaptation of machine learning and data mining algorithms to guide QSAR experiments
Up Quark Masses from Down Quark Masses
The quark and charged lepton masses and the angles and phase of the CKM
mixing matrix are nicely reproduced in a model which assumes SU(3)xSU(3)
flavour symmetry broken by the v.e.v.'s of fields in its bi-fundamental
representation. The relations among the quark mass eigenvalues, m_u/m_c \approx
m_c/m_t \approx m^2_d/m^2_s \approx m^2_s/m^2_b \approx
\Lambda^2_{GUT}/M^2_{Pl}, follow from the broken flavour symmetry. Large
tan(beta) is required which also provides the best fits to data for the
obtained textures. Lepton-quark grandunification with a field that breaks both
SU(5) and the flavour group correctly extends the predictions to the charged
lepton masses. The seesaw extension of the model to the neutrino sector
predicts a Majorana mass matrix quadratically hierarchical as compared to the
neutrino Dirac mass matrix, naturally yielding large mixings and low mass
hierarchy for neutrinos.Comment: 11 pages, 1 figure. Published version: model improved, references
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Short-range correlations in two-nucleon knockout reactions
A theory of short-range correlations in two-nucleon removal due to elastic
breakup (diffraction dissociation) on a light target is developed. Fingerprints
of these correlations will appear in momentum distributions of back-to-back
emission of the nucleon pair. Expressions for the momentum distributions are
derived and calculations for reactions involving stable and unstable nuclear
species are performed. The signature of short-range correlations in other
reaction processes is also studied.Comment: Nuclear Physics A, in pres
Quantum computation with two-level trapped cold ions beyond Lamb-Dicke limit
We propose a simple scheme for implementing quantum logic gates with a string
of two-level trapped cold ions outside the Lamb-Dicke limit. Two internal
states of each ion are used as one computational qubit (CQ) and the collective
vibration of ions acts as the information bus, i.e., bus qubit (BQ). Using the
quantum dynamics for the laser-ion interaction as described by a generalized
Jaynes-Cummings model, we show that quantum entanglement between any one CQ and
the BQ can be coherently manipulated by applying classical laser beams. As a
result, universal quantum gates, i.e. the one-qubit rotation and two-qubit
controlled gates, can be implemented exactly. The required experimental
parameters for the implementation, including the Lamb-Dicke (LD) parameter and
the durations of the applied laser pulses, are derived. Neither the LD
approximation for the laser-ion interaction nor the auxiliary atomic level is
needed in the present scheme.Comment: 12 pages, no figures, to appear in Phys. Rev.
Adiabatic creation of entangled states by a bichromatic field designed from the topology of the dressed eigenenergies
Preparation of entangled pairs of coupled two-state systems driven by a
bichromatic external field is studied. We use a system of two coupled spin-1/2
that can be translated into a three-state ladder model whose intermediate state
represents the entangled state. We show that this entangled state can be
prepared in a robust way with appropriate fields. Their frequencies and
envelopes are derived from the topological properties of the model.Comment: 10 pages, 9 figure
Cluster Masses Accounting for Structure along the Line of Sight
Weak gravitational lensing of background galaxies by foreground clusters
offers an excellent opportunity to measure cluster masses directly without
using gas as a probe. One source of noise which seems difficult to avoid is
large scale structure along the line of sight. Here I show that, by using
standard map-making techniques, one can minimize the deleterious effects of
this noise. The resulting uncertainties on cluster masses are significantly
smaller than when large scale structure is not properly accounted for, although
still larger than if it was absent altogether.Comment: 5 pages, 5 figure
Deployable Helical Antennas for CubeSats
This paper explores the behavior of a self-deploying helical pantograph antenna for CubeSats. The helical pantograph concept is described along with concepts for attachment to the satellite bus. Finite element folding simulations of a pantograph consisting of eight helices are presented and compared to compaction force experiments done on a prototype antenna. Reflection coefficient test are also presented, demonstrating the operating frequency range of the prototype antenna. The helical pantograph is shown to be a promising alternative to current small satellite antenna solutions
Effort-reward imbalance and burnout among humanitarian aid workers
Objectives: This study examined stress-related working conditions – defined in terms of effort-reward imbalance (ERI) – and its association with burnout among a large, international sample of humanitarian aid workers.
Methods: Descriptive statistics were applied on crosssectional survey data (N=1,980) to profile ERI and burnout and Pearson’s χ 2 tests used to characterize associated socio- and occupational-demographic factors. Associations between ERI and burnout were established using binary logistic regression to generate odds ratios and 95% confidence intervals adjusted for potential confounding variables.
Results: For high emotional exhaustion, the prevalence rate was 36% for women and 27% for men; high depersonalisation, 9% and 10%; and low personal achievement, 47% and 31%. Intermediate and high ERI was associated with significantly increased odds of high emotional exhaustion, with mixed findings for depersonalisation and personal achievement.
Conclusions: The ERI model was supported as a useful framework for investigating occupational correlates of burnout
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