3,630 research outputs found
Measuring Channel Planform Change From Image Time Series: A Generalizable, Spatially Distributed, Probabilistic Method for Quantifying Uncertainty
Abstract
Channels change in response to natural or anthropogenic fluctuations in streamflow and/or sediment supply and measurements of channel change are critical to many river management applications. Whereas repeated field surveys are costly and timeâconsuming, remote sensing can be used to detect channel change at multiple temporal and spatial scales. Repeat images have been widely used to measure longâterm channel change, but these measurements are only significant if the magnitude of change exceeds the uncertainty. Existing methods for characterizing uncertainty have two important limitations. First, while the use of a spatially variable image coâregistration error avoids the assumption that errors are spatially uniform, this type of error, as originally formulated, can only be applied to linear channel adjustments, which provide less information on channel change than polygons of erosion and deposition. Second, previous methods use a levelâofâdetection (LoD) threshold to remove nonâsignificant measurements, which is problematic because real changes that occurred but were smaller than the LoD threshold would be removed. In this study, we present a new method of quantifying uncertainty associated with channel change based on probabilistic, spatially varying estimates of coâregistration error and digitization uncertainty that obviates a LoD threshold. The spatially distributed probabilistic (SDP) method can be applied to both linear channel adjustments and polygons of erosion and deposition, making this the first uncertainty method generalizable to all metrics of channel change. Using a case study from the Yampa River, Colorado, we show that the SDP method reduced the magnitude of uncertainty and enabled us to detect smaller channel changes as significant. Additionally, the distributional information provided by the SDP method allowed us to report the magnitude of channel change with an appropriate level of confidence in cases where a simple LoD approach yielded an indeterminate result
Next-Generation Sequencing-Based Detection of Germline Copy Number Variations in <i>BRCA1/BRCA2</i>:Validation of a One-Step Diagnostic Workflow
The long-lived queen : reproduction and longevity in female eusocial Damaraland mole-rats (Fukomys damarensis)
The inverse relationship between reproduction and
lifespan is one of the main concepts of life history
theory. This association has been observed in most
taxa, although exceptions have been found in which
a breeding female outlives her non-reproductive
cohorts. This relationship is well known in social
insects, and it has recently come to light that reproductive
females of certain social mole-rat species also
exhibit extended lifespans relative to non-breeders.
We analysed markârecapture data over 13 years in
12 colonies of Damaraland mole-rats (Fukomys
damarensis) to assess if colony queens lived longer
than non-reproductive adult females. Queens were
recaptured up to 8.5 years after initial capture (X =
6.2 years); significantly longer than non-reproductive
females (X = 1.3 years), suggesting that a colony
queen lives longer than her non-reproductive subordinates.
This difference may be attributed to both
physiological and social factors which may relax
reproductive costs in queens.C.M.S. acknowledges funding from the University of
Pretoria, J.U.M.J. acknowledges funding from the
University of Cape Town and N.C.B. acknowledges
funding from the University of Pretoria and the National
Research Foundation.http://africanzoology.journals.ac.za/am2013ab201
Reproduction is associated with a tissue-dependent reduction of oxidative stress in eusocial female Damaraland mole-rats (Fukomys damarensis)
Oxidative stress has been implicated as both a physiological cost of reproduction and a driving force on an animalâs lifespan.
Since increased reproductive effort is generally linked with a reduction in survival, it has been proposed that oxidative stress
may influence this relationship. Support for this hypothesis is inconsistent, but this may, in part, be due to the type of
tissues that have been analyzed. In Damaraland mole-rats the sole reproducing female in the colony is also the longest
lived. Therefore, if oxidative stress does impact the trade-off between reproduction and survival in general, this species may
possess some form of enhanced defense. We assessed this relationship by comparing markers of oxidative damage
(malondialdehyde, MDA; protein carbonyls, PC) and antioxidants (total antioxidant capacity, TAC; superoxide dismutase,
SOD) in various tissues including plasma, erythrocytes, heart, liver, kidney and skeletal muscle between wild-caught
reproductive and non-reproductive female Damaraland mole-rats. Reproductive females exhibited significantly lower levels
of PC across all tissues, and lower levels of MDA in heart, kidney and liver relative to non-reproductive females. Levels of TAC
and SOD did not differ significantly according to reproductive state. The reduction in oxidative damage in breeding females
may be attributable to the unusual social structure of this species, as similar relationships have been observed between
reproductive and non-reproductive eusocial insects.A DST-NRF SARChI research chair for Behavioural Ecology and Physiology to NCB and a University of Pretoria
postdoctoral fellowship to CMS.http://www.plosone.orgam201
Pharmacological Inhibition of Epac1 Averts Ferroptosis Cell Death by Preserving Mitochondrial Integrity
Exchange proteins directly activated by cAMP (Epac) proteins are implicated in a wide range of cellular functions including oxidative stress and cell survival. Mitochondrial-dependent oxidative stress has been associated with progressive neuronal death underlying the pathology of many neurodegenerative diseases. The role of Epac modulation in neuronal cells in relation to cell survival and death, as well as its potential effect on mitochondrial function, is not well established. In immortalized hippocampal (HT-22) neuronal cells, we examined mitochondria function in the presence of various Epac pharmacological modulators in response to oxidative stress due to ferroptosis. Our study revealed that selective pharmacological modulation of Epac1 or Epac2 isoforms, exerted differential effects in erastin-induced ferroptosis conditions in HT-22 cells. Epac1 inhibition prevented cell death and loss of mitochondrial integrity induced by ferroptosis, while Epac2 inhibition had limited effects. Our data suggest Epac1 as a plausible therapeutic target for preventing ferroptosis cell death associated with neurodegenerative diseases
Formation of Complex and Unstable Chromosomal Translocations in Yeast
Genome instability, associated with chromosome breakage syndromes and most human
cancers, is still poorly understood. In the yeast Saccharomyces
cerevisiae, numerous genes with roles in the preservation of genome
integrity have been identified. DNA-damage-checkpoint-deficient yeast cells that
lack Sgs1, a RecQ-like DNA helicase related to the human
Bloom's-syndrome-associated helicase BLM, show an increased rate of
genome instability, and we have previously shown that they accumulate recurring
chromosomal translocations between three similar genes, CAN1,
LYP1 and ALP1. Here, the chromosomal
location, copy number and sequence similarity of the translocation targets
ALP1 and LYP1 were altered to gain insight
into the formation of complex translocations. Among 844 clones with chromosomal
rearrangements, 93 with various types of simple and complex translocations
involving CAN1, LYP1 and ALP1
were identified. Breakpoint sequencing and mapping showed that the formation of
complex translocation types is strictly dependent on the location of the
initiating DNA break and revealed that complex translocations arise via a
combination of interchromosomal translocation and template-switching, as well as
from unstable dicentric intermediates. Template-switching occurred between
sequences on the same chromosome, but was inhibited if the genes were
transferred to different chromosomes. Unstable dicentric translocations
continuously gave rise to clones with multiple translocations in various
combinations, reminiscent of intratumor heterogeneity in human cancers. Base
substitutions and evidence of DNA slippage near rearrangement breakpoints
revealed that translocation formation can be accompanied by point mutations, and
their presence in different translocation types within the same clone provides
evidence that some of the different translocation types are derived from each
other rather than being formed de novo. These findings provide
insight into eukaryotic genome instability, especially the formation of
translocations and the sources of intraclonal heterogeneity, both of which are
often associated with human cancers
Towards better air quality using the plume chasing method : validation studies of real driving NOx emission measurements of vehicles
The reliability of Plume Chasing as a Remote Emission Measurement Technique in detecting NOx emissions is investigated. It allows, for example, to identify high-NOx-emitting vehicles with high precision. During a 5-day study of the CARES project, controlled Plume Chasing measurements of different types of vehicles were performed on a test track. The test track experiments included 21 different sessions with different driving properties and different test vehicles representative for a common vehicle fleet. During the experiments, the emission control systems were activated and deactivated in a blind comparison experiment. The Plume Chasing method showed excellent correlation with the averaged reference SEMS NOx data. The main cause for deviations was found to be situations when emissions are significantly influenced by plumes from high emitting vehicles driving ahead
Emission ratio determination from road vehicles using a range of remote emission sensing techniques
The development of remote emission sensing techniques such as plume chasing and point sampling has progressed significantly and is providing new insight into vehicle emissions behaviour. However, the analysis of remote emission sensing data can be highly challenging and there is currently no standardised method available. In this study we present a single data processing approach to quantify vehicle exhaust emissions measured using a range of remote emission sensing techniques. The method uses rolling regression calculated over short time intervals to derive the characteristics of diluting plumes. We apply the method to high time-resolution plume chasing and point sampling data to quantify gaseous exhaust emission ratios from individual vehicles. Data from a series of vehicle emission characterisation experiments conducted under controlled conditions is used to demonstrate the potential of this approach. First, the method is validated through comparison with on-board emission measurements. Second, the ability of this approach to detect changes in NOx / CO2 ratios associated with aftertreatment system tampering and different engine operating conditions is shown. Third, the flexibility of the approach is demonstrated by varying the pollutants used as regression variables and quantifying the NO2 / NOx ratios for different vehicle types. A higher proportion of total NOx is emitted as NO2 when the selective catalytic reduction system of the measured heavy duty truck is tampered. In addition, the applicability of this approach to urban environments is illustrated using mobile measurements conducted in Milan, Italy in 2021. Emissions from local combustion sources are distinguished from a complex urban background and the spatiotemporal variability in emissions is shown. The mean NOx / CO2 ratio of 1.61 ppb/ppm is considered representative of the local vehicle fleet. It is envisaged that this approach can be used to quantify emissions from a range of mobile and stationary fuel combustion sources, including non-road vehicles, ships, trains, boilers and incinerators
To observe or not to observe peers when learning physical examination skills; That is the question
Background: Learning physical examination skills is an essential element of medical education. Teaching strategies include practicing the skills either alone or in-group. It is unclear whether students benefit more from training these skills individually or in a group, as the latter allows them to observing their peers. The present study, conducted in a naturalistic setting, investigated the effects of peer observation on mastering psychomotor skills necessary for physical examination. Methods. The study included 185 2§ssup§nd§esup§-year medical students, participating in a regular head-to-toe physical examination learning activity. Students were assigned either to a single-student condition (n = 65), in which participants practiced alone with a patient instructor, or to a multiple-student condition (n = 120), in which participants practiced in triads under patient instructor supervision. The students subsequently carried out a complete examination that was videotaped and subsequently evaluated. Student's performance was used as a measure of learning. Results: Students in the multiple-student condition learned more than those who practiced alone (8
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