5,334 research outputs found
Modeling meander morphodynamics over self-formed heterogeneous floodplains
This work addresses the signatures embedded in the planform geometry of meandering rivers consequent to the formation of floodplain heterogeneities as the river bends migrate. Two geomorphic features are specifically considered: scroll bars produced by lateral accretion of point bars at convex banks and oxbow lake fills consequent to neck cutoffs. The sedimentary architecture of these geomorphic units depends on the type and amount of sediment, and controls bank erodibility as the river impinges on them, favoring or contrasting the river migration. The geometry of numerically generated planforms obtained for different scenarios of floodplain heterogeneity is compared to that of natural meandering paths. Half meander metrics and spatial distribution of channel curvatures are used to disclose the complexity embedded in meandering geometry. Fourier Analysis, Principal Component Analysis, Singular Spectrum Analysis and Multivariate Singular Spectrum Analysis are used to emphasize the subtle but crucial differences which may emerge between apparently similar configurations. A closer similarity between observed and simulated planforms is attained when fully coupling flow and sediment dynamics (fully-coupled models) and when considering self-formed heterogeneities that are less erodible than the surrounding floodplain
Closed-cycle, low-vibration 4 K cryostat for ion traps and other applications
In-vacuo cryogenic environments are ideal for applications requiring both low
temperatures and extremely low particle densities. This enables reaching long
storage and coherence times for example in ion traps, essential requirements
for experiments with highly charged ions, quantum computation, and optical
clocks. We have developed a novel cryostat continuously refrigerated with a
pulse-tube cryocooler and providing the lowest vibration level reported for
such a closed-cycle system with 1 W cooling power for a <5 K experiment. A
decoupling system suppresses vibrations from the cryocooler by three orders of
magnitude down to a level of 10 nm peak amplitudes in the horizontal plane.
Heat loads of about 40 W (at 45 K) and 1 W (at 4 K) are transferred from an
experimental chamber, mounted on an optical table, to the cryocooler through a
vacuum-insulated massive 120 kg inertial copper pendulum. The 1.4 m long
pendulum allows installation of the cryocooler in a separate, acoustically
isolated machine room. In the laser laboratory, we measured the residual
vibrations using an interferometric setup. The positioning of the 4 K elements
is reproduced to better than a few micrometer after a full thermal cycle to
room temperature. Extreme high vacuum on the mbar level is achieved.
In collaboration with the Max-Planck-Intitut f\"ur Kernphysik (MPIK), such a
setup is now in operation at the Physikalisch-Technische Bundesanstalt (PTB)
for a next-generation optical clock experiment using highly charged ions
A Method to Improve the Early Stages of the Robotic Process Automation Lifecycle
The robotic automation of processes is of much interest to
organizations. A common use case is to automate the repetitive manual
tasks (or processes) that are currently done by back-office staff
through some information system (IS). The lifecycle of any Robotic Process
Automation (RPA) project starts with the analysis of the process
to automate. This is a very time-consuming phase, which in practical
settings often relies on the study of process documentation. Such documentation
is typically incomplete or inaccurate, e.g., some documented
cases never occur, occurring cases are not documented, or documented
cases differ from reality. To deploy robots in a production environment
that are designed on such a shaky basis entails a high risk. This paper
describes and evaluates a new proposal for the early stages of an RPA
project: the analysis of a process and its subsequent design. The idea is to
leverage the knowledge of back-office staff, which starts by monitoring
them in a non-invasive manner. This is done through a screen-mousekey-
logger, i.e., a sequence of images, mouse actions, and key actions
are stored along with their timestamps. The log which is obtained in
this way is transformed into a UI log through image-analysis techniques
(e.g., fingerprinting or OCR) and then transformed into a process model
by the use of process discovery algorithms. We evaluated this method for
two real-life, industrial cases. The evaluation shows clear and substantial
benefits in terms of accuracy and speed. This paper presents the method,
along with a number of limitations that need to be addressed such that
it can be applied in wider contexts.Ministerio de Economía y Competitividad TIN2016-76956-C3-2-
Coherent states for the hydrogen atom
We construct wave packets for the hydrogen atom labelled by the classical
action-angle variables with the following properties. i) The time evolution is
exactly given by classical evolution of the angle variables. (The angle
variable corresponding to the position on the orbit is now non-compact and we
do not get exactly the same state after one period. However the gross features
do not change. In particular the wave packet remains peaked around the labels.)
ii) Resolution of identity using this overcomplete set involves exactly the
classical phase space measure. iii) Semi-classical limit is related to
Bohr-Sommerfield quantization. iv) They are almost minimum uncertainty wave
packets in position and momentum.Comment: 9 pages, 2 figures, minor change in language and journal reference
adde
The Dynamics of a Meandering River
We present a statistical model of a meandering river on an alluvial plane
which is motivated by the physical non-linear dynamics of the river channel
migration and by describing heterogeneity of the terrain by noise. We study the
dynamics analytically and numerically. The motion of the river channel is
unstable and we show that by inclusion of the formation of ox-bow lakes, the
system may be stabilised. We then calculate the steady state and show that it
is in agreement with simulations and measurements of field data.Comment: Revtex, 12 pages, 2 postscript figure
Coarse grained description of the protein folding
We consider two- and three-dimensional lattice models of proteins which were
characterized previously. We coarse grain their folding dynamics by reducing it
to transitions between effective states. We consider two methods of selection
of the effective states. The first method is based on the steepest descent
mapping of states to underlying local energy minima and the other involves an
additional projection to maximally compact conformations. Both methods generate
connectivity patterns that allow to distinguish between the good and bad
folders. Connectivity graphs corresponding to the folding funnel have few loops
and are thus tree-like. The Arrhenius law for the median folding time of a
16-monomer sequence is established and the corresponding barrier is related to
easily identifiable kinetic trap states.Comment: REVTeX, 9 pages, 15 EPS figures, to appear in Phys. Rev.
Pediatric Trauma and Trauma Team Activation in a Swiss Pediatric Emergency Department: An Observational Cohort Study.
BACKGROUND
Trauma is one of the most common causes of death in childhood, but data on severely injured Swiss children are absent from existing national registries. Our aim was to analyze trauma activations and the profiles of critically injured children at a tertiary, non-academic Swiss pediatric emergency department (PED). In the absence of a national pediatric trauma database, this information may help to guide the design of infrastructure, processes within organizations, training, and policies.
METHODS
A retrospective analysis of pediatric trauma patients in a prospective resuscitation database over a 2-year period. Critically injured trauma patients under the age of 16 years were included. Patients were described with established triage and injury severity scales. Statistical evaluation included logistic regression analysis.
RESULTS
A total of 82 patients matched one or more of the study inclusion criteria. The most frequent age group was 12-15 years, and 27% were female. Trauma team activation (TTA) occurred with 49 patients (59.8%). Falls were the most frequent mechanism of injury, both overall and for major trauma. Road-traffic-related injuries had the highest relative risk of major trauma. In the multivariate analysis, patients receiving medicalized transport were more likely to trigger a TTA, but there was no association between TTA and age, gender, or Injury Severity Score (ISS). Nineteen patients (23.2%) sustained major trauma with an ISS > 15. Injuries of Abbreviated Injury Scale severity 3 or greater were most frequent to the head, followed by abdomen, chest, and extremities. The overall mortality rate in the cohort was 2.4%.
CONCLUSIONS
Major trauma presentations only comprise a small proportion of the total patient load in the PED, and trauma team activation does not correlate with injury severity. Low exposure to high-acuity patients highlights the importance of deliberate learning and simulation for all professionals in the PED. Our findings indicate that high priority should be given to training in the management of severely injured children in the PED. The leading major trauma mechanisms were preventable, which should prompt further efforts in injury prevention
Geometry of River Networks II: Distributions of Component Size and Number
The structure of a river network may be seen as a discrete set of nested
sub-networks built out of individual stream segments. These network components
are assigned an integral stream order via a hierarchical and discrete ordering
method. Exponential relationships, known as Horton's laws, between stream order
and ensemble-averaged quantities pertaining to network components are observed.
We extend these observations to incorporate fluctuations and all higher moments
by developing functional relationships between distributions. The relationships
determined are drawn from a combination of theoretical analysis, analysis of
real river networks including the Mississippi, Amazon and Nile, and numerical
simulations on a model of directed, random networks. Underlying distributions
of stream segment lengths are identified as exponential. Combinations of these
distributions form single-humped distributions with exponential tails, the sums
of which are in turn shown to give power law distributions of stream lengths.
Distributions of basin area and stream segment frequency are also addressed.
The calculations identify a single length-scale as a measure of size
fluctuations in network components. This article is the second in a series of
three addressing the geometry of river networks.Comment: 16 pages, 13 figures, 4 tables, Revtex4, submitted to PR
Algorithmic Ground-state Cooling of Weakly-Coupled Oscillators using Quantum Logic
Most ions lack the fast, cycling transitions that are necessary for direct laser cooling. In most cases, they can still be cooled sympathetically through their Coulomb interaction with a second, coolable ion species confined in the same potential. If the charge-to-mass ratios of the two ion types are too mismatched, the cooling of certain motional degrees of freedom becomes difficult. This limits both the achievable fidelity of quantum gates and the spectroscopic accuracy. Here we introduce a novel algorithmic cooling protocol for transferring phonons from poorly- to efficiently-cooled modes. We demonstrate it experimentally by simultaneously bringing two motional modes of a Be-Ar mixed Coulomb crystal close to their zero-point energies, despite the weak coupling between the ions. We reach the lowest temperature reported for a highly charged ion, with a residual temperature of only in each of the two modes, corresponding to a residual mean motional phonon number of . Combined with the lowest observed electric field noise in a radiofrequency ion trap, these values enable an optical clock based on a highly charged ion with fractional systematic uncertainty below the level. Our scheme is also applicable to (anti-)protons, molecular ions, macroscopic charged particles, and other highly charged ion species, enabling reliable preparation of their motional quantum ground states in traps
- …