897 research outputs found
The architecture of chicken chromosome territories changes during differentiation
BACKGROUND:
Between cell divisions the chromatin fiber of each chromosome is restricted to a subvolume of the interphase cell nucleus called chromosome territory. The internal organization of these chromosome territories is still largely unknown.
RESULTS:
We compared the large-scale chromatin structure of chromosome territories between several hematopoietic chicken cell types at various differentiation stages. Chromosome territories were labeled by fluorescence in situ hybridization in structurally preserved nuclei, recorded by confocal microscopy and evaluated visually and by quantitative image analysis. Chromosome territories in multipotent myeloid precursor cells appeared homogeneously stained and compact. The inactive lysozyme gene as well as the centromere of the lysozyme gene harboring chromosome located to the interior of the chromosome territory. In further differentiated cell types such as myeloblasts, macrophages and erythroblasts chromosome territories appeared increasingly diffuse, disaggregating to separable substructures. The lysozyme gene, which is gradually activated during the differentiation to activated macrophages, as well as the centromere were relocated increasingly to more external positions.
CONCLUSIONS:
Our results reveal a cell type specific constitution of chromosome territories. The data suggest that a repositioning of chromosomal loci during differentiation may be a consequence of general changes in chromosome territory morphology, not necessarily related to transcriptional changes
Formation of Nanopillar Arrays in Ultrathin Viscous Films: The Critical Role of Thermocapillary Stresses
Experiments by several groups during the past decade have shown that a molten
polymer nanofilm subject to a large transverse thermal gradient undergoes
spontaneous formation of periodic nanopillar arrays. The prevailing explanation
is that coherent reflections of acoustic phonons within the film cause a
periodic modulation of the radiation pressure which enhances pillar growth. By
exploring a deformational instability of particular relevance to nanofilms, we
demonstrate that thermocapillary forces play a crucial role in the formation
process. Analytic and numerical predictions show good agreement with the pillar
spacings obtained in experiment. Simulations of the interface equation further
determine the rate of pillar growth of importance to technological
applications.Comment: 5 pages, 4 figure
Asymmetric nanofluidic grating detector for differential refractive index measurement and biosensing.
Measuring small changes in refractive index can provide both sensitive and contactless information on molecule concentration or process conditions for a wide range of applications. However, refractive index measurements are easily perturbed by non-specific background signals, such as temperature changes or non-specific binding. Here, we present an optofluidic device for measuring refractive index with direct background subtraction within a single measurement. The device is comprised of two interdigitated arrays of nanofluidic channels designed to form an optical grating. Optical path differences between the two sets of channels can be measured directly via an intensity ratio within the diffraction pattern that forms when the grating is illuminated by a collimated laser beam. Our results show that no calibration or biasing is required if the unit cell of the grating is designed with an appropriate built-in asymmetry. In proof-of-concept experiments we attained a noise level equivalent to ∼10(-5) refractive index units (30 Hz sampling rate, 4 min measurement interval). Furthermore, we show that the accumulation of biomolecules on the surface of the nanochannels can be measured in real-time. Because of its simplicity and robustness, we expect that this inherently differential measurement concept will find many applications in ultra-low volume analytical systems, biosensors, and portable devices
Methods comparison for detecting trends in herbicide monitoring time-series in streams
An inadvertent consequence of pesticide use is aquatic pesticide pollution, which has prompted the implementation of mitigation measures in many countries. Water quality monitoring programs are an important tool to evaluate the efficacy of these mitigation measures. However, large interannual variability of pesticide losses makes it challenging to detect significant improvements in water quality and to attribute these improvements to the application of specific mitigation measures. Thus, there is a gap in the literature that informs researchers and authorities regarding the number of years of aquatic pesticide monitoring or the effect size (e.g., loss reduction) that is required to detect significant trends in water quality. Our research addresses this issue by combining two exceptional empirical data sets with modelling to explore the relationships between the achieved pesticide reduction levels due to mitigation measures and the length of the observation period for establishing statistically significant trends. Our study includes both a large (Rhine at Basel, ∼36,300 km2) and small catchment (Eschibach, 1.2 km2), which represent spatial scales at either end of the spectrum that would be realistic for monitoring programs designed to assess water quality. Our results highlight several requirements in a monitoring program to allow for trend detection. Firstly, sufficient baseline monitoring is required before implementing mitigation measures. Secondly, the availability of pesticide use data helps account for the interannual variability and temporal trends, but such data are usually lacking. Finally, the timing and magnitude of hydrological events relative to pesticide application can obscure the observable effects of mitigation measures (especially in small catchments). Our results indicate that a strong reduction (i.e., 70–90 %) is needed to detect a change within 10 years of monitoring data. The trade-off in applying a more sensitive method for change detection is that it may be more prone to false-positives. Our results suggest that it is important to consider the trade-off between the sensitivity of trend detection and the risk of false positives when selecting an appropriate method and that applying more than one method can provide more confidence in trend detection
Changes of macular pigment optical density in elderly eyes: a longitudinal analysis from the MARS study
Missing 2k_F Response for Composite Fermions in Phonon Drag
The response of composite Fermions to large wavevector scattering has been
studied through phonon drag measurements. While the response retains
qualitative features of the electron system at zero magnetic field, notable
discrepancies develop as the system is varied from a half-filled Landau level
by changing density or field. These deviations, which appear to be inconsistent
with the current picture of composite Fermions, are absent if half-filling is
maintained while changing density. There remains, however, a clear deviation
from the temperature dependence anticipated for 2k_F scattering.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. Let
Electrohydrodynamics within electrical double layer in a pressure-driven flow in presence of finite temperature gradients
A wide spectrum of electrokinetic studies is modelled as isothermal ones to
expedite analysis even when such conditions may be extremely difficult to
realize in practice. As a clear and novel departure from this trend, we address
the case of flow-induced electrohydrodynamics, commonly referred to as
streaming potential, in a situation where finite temperature gradients do
indeed exist. By way of analysing a model problem of flow through a narrow
parallel plate channel, we show that the temperature gradients have a
significant effect on the streaming potential, and, consequently, on the flow
itself. We incorporate thermoelectric effects in our model by a full-fledged
coupling among the electric potential, the ionic species distribution, the
fluid velocity and the local fluid temperature fields without resorting to ad
hoc simplifications. We expect this expository study to contribute towards more
sophisticated future inquiries into practical micro-/nano-fluidic applications
coupling thermal field focusing with electrokinetic effects.Comment: 13 pages, 5 figure
Recent highlights in nanoscale and mesoscale friction
Friction is the oldest branch of non-equilibrium condensed matter physics and, at the same time, the least established at the fundamental level. A full understanding and control of friction is increasingly recognized to involve all relevant size and time scales. We review here some recent advances on the research focusing of nano- and mesoscale tribology phenomena. These advances are currently pursued in a multifaceted approach starting from the fundamental atomic-scale friction and mechanical control of specific single-asperity combinations, e.g., nanoclusters on layered materials, then scaling up to the meso/microscale of extended, occasionally lubricated, interfaces and driven trapped optical systems, and eventually up to the macroscale. Currently, this "hot" research field is leading to new technological advances in the area of engineering and materials science
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