290 research outputs found
High-resolution imaging of ultracold fermions in microscopically tailored optical potentials
We report on the local probing and preparation of an ultracold Fermi gas on
the length scale of one micrometer, i.e. of the order of the Fermi wavelength.
The essential tool of our experimental setup is a pair of identical,
high-resolution microscope objectives. One of the microscope objectives allows
local imaging of the trapped Fermi gas of 6Li atoms with a maximum resolution
of 660 nm, while the other enables the generation of arbitrary optical dipole
potentials on the same length scale. Employing a 2D acousto-optical deflector,
we demonstrate the formation of several trapping geometries including a tightly
focussed single optical dipole trap, a 4x4-site two-dimensional optical lattice
and a 8-site ring lattice configuration. Furthermore, we show the ability to
load and detect a small number of atoms in these trapping potentials. A site
separation of down to one micrometer in combination with the low mass of 6Li
results in tunneling rates which are sufficiently large for the implementation
of Hubbard-models with the designed geometries.Comment: 15 pages, 6 figure
HEMOPOIETIC RESPONSE TO LOW DOSE-RATES OF IONIZING RADIATION SHOWS STEM CELL TOLERANCE AND ADAPTATION
Chronic exposure of mammals to low dose-rates of ionizing radiation affects proliferating cell systems as a function of both dose-rate and the total dose accumulated. The lower the dose-rate the higher needs to be the total dose for a deterministic effect, i.e., tissue reaction to appear. Stem cells provide for proliferating, maturing and functional cells. Stem cells usually are particularly radiosensitive and damage to them may propagate to cause failure of functional cells. The paper revisits 1) medical histories with emphasis on the hemopoietic system of the victims of ten accidental chronic radiation exposures, 2) published hematological findings of long-term chronically gamma-irradiated rodents, and 3) such findings in dogs chronically exposed in large life-span studies. The data are consistent with the hypothesis that hemopoietic stem and early progenitor cells have the capacity to tolerate and adapt to being repetitively hit by energy deposition events. The data are compatible with the “injured stem cell hypothesis”, stating that radiation–injured stem cells, depending on dose-rate, may continue to deliver clones of functional cells that maintain homeostasis of hemopoiesis throughout life. Further studies perhaps on separated hemopoietic stem cells may unravel the molecular-biology mechanisms causing radiation tolerance and adaptation
Mathematical modeling of cell population dynamics in the colonic crypt and in colorectal cancer
Colorectal cancer is initiated in colonic crypts. A succession of genetic mutations or epigenetic changes can lead to homeostasis in the crypt being overcome, and subsequent unbounded growth. We consider the dynamics of a single colorectal crypt by using a compartmental approach [Tomlinson IPM, Bodmer WF (1995) Proc Natl Acad Sci USA 92: 11130-11134], which accounts for populations of stem cells, differential cells, and transit cells. That original model made the simplifying assumptions that each cell popuation divides synchronously, but we relax these assumptions by adopting an age-structured approach that models asynchronous cell division, and by using a continuum model. We discuss two mechanims that could regulate the growth of cell numbers and maintain the equilibrium that is normally observed in the crypt. The first will always maintain an equilibrium for all parameter values, whereas the second can allow unbounded proliferation if the net per capita growth rates are large enough. Results show that an increase in cell renewal, which is equivalent to a failure of programmed cell death or of differentiation, can lead to the growth of cancers. The second model can be used to explain the long lag phases in tumor growth, during which news, higher equilibria are reached, before unlimited growth in cell number ensues
Conduction of Ultracold Fermions Through a Mesoscopic Channel
In a mesoscopic conductor electric resistance is detected even if the device
is defect-free. We engineer and study a cold-atom analog of a mesoscopic
conductor. It consists of a narrow channel connecting two macroscopic
reservoirs of fermions that can be switched from ballistic to diffusive. We
induce a current through the channel and find ohmic conduction, even for a
ballistic channel. An analysis of in-situ density distributions shows that in
the ballistic case the chemical potential drop occurs at the entrance and exit
of the channel, revealing the presence of contact resistance. In contrast, a
diffusive channel with disorder displays a chemical potential drop spread over
the whole channel. Our approach opens the way towards quantum simulation of
mesoscopic devices with quantum gases
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Responses of Cell Renewal Systems to Long-term Low-Level Radiation Exposure: A Feasibility Study Applying Advanced Molecular Biology Techniques on Available Histological and Cytological Material of Exposed Animals and Men
First results of this feasibility study showed that evaluation of the stored material of the chronically irradiated dogs with modern molecular biological techniques proved to be successful and extremely promising. Therefore an in deep analysis of at least part of the huge amount of remaining material is of outmost interest. The methods applied in this feasibility study were pathological evaluation with different staining methods, protein analysis by means of immunohistochemistry, strand break analysis with the TdT-assay, DNA- and RNA-analysis as well as genomic examination by gene array. Overall more than 50% of the investigated material could be used. In particular the results of an increased stimulation of the immune system within the dogs of the 3mSv group as both compared to the control and higher dose groups gives implications for the in depth study of the cellular events occurring in context with low dose radiation. Based on the findings of this study a further evaluation and statistically analysis of more material can help to identify promising biomarkers for low dose radiation. A systematic evaluation of a correlation of dose rates and strand breaks within the dog tissue might moreover help to explain mechanisms of tolerance to IR. One central problem is that most sequences for dog specific primers are not known yet. The discovery of the dog genome is still under progress. In this study the isolation of RNA within the dog tissue was successful. But up to now there are no gene arrays or gene chips commercially available, tested and adapted for canine tissue. The uncritical use of untested genomic test systems for canine tissue seems to be ineffective at the moment, time consuming and ineffective. Next steps in the investigation of genomic changes after IR within the stored dog tissue should be limited to quantitative RT-PCR of tested primer sequences for the dog. A collaboration with institutions working in the field of the discovery of the dog genome could have synergistic effects
Comparison of established and emerging biodosimetry assays
Rapid biodosimetry tools are required to assist with triage in the case of a large-scale radiation incident. Here, we aimed to determine the dose-assessment accuracy of the well-established dicentric chromosome assay (DCA) and cytokinesis-block micronucleus assay (CBMN) in comparison to the emerging γ-H2AX foci and gene expression assays for triage mode biodosimetry and radiation injury assessment. Coded blood samples exposed to 10 X-ray doses (240 kVp, 1 Gy/min) of up to 6.4 Gy were sent to participants for dose estimation. Report times were documented for each laboratory and assay. The mean absolute difference (MAD) of estimated doses relative to the true doses was calculated. We also merged doses into binary dose categories of clinical relevance and examined accuracy, sensitivity and specificity of the assays. Dose estimates were reported by the first laboratories within 0.3-0.4 days of receipt of samples for the γ-H2AX and gene expression assays compared to 2.4 and 4 days for the DCA and CBMN assays, respectively. Irrespective of the assay we found a 2.5-4-fold variation of interlaboratory accuracy per assay and lowest MAD values for the DCA assay (0.16 Gy) followed by CBMN (0.34 Gy), gene expression (0.34 Gy) and γ-H2AX (0.45 Gy) foci assay. Binary categories of dose estimates could be discriminated with equal efficiency for all assays, but at doses ≥1.5 Gy a 10% decrease in efficiency was observed for the foci assay, which was still comparable to the CBMN assay. In conclusion, the DCA has been confirmed as the gold standard biodosimetry method, but in situations where speed and throughput are more important than ultimate accuracy, the emerging rapid molecular assays have the potential to become useful triage tools
Acute radiation syndrome caused by accidental radiation exposure - therapeutic principles
Fortunately radiation accidents are infrequent occurrences, but since they have the potential of large scale events like the nuclear accidents of Chernobyl and Fukushima, preparatory planning of the medical management of radiation accident victims is very important. Radiation accidents can result in different types of radiation exposure for which the diagnostic and therapeutic measures, as well as the outcomes, differ. The clinical course of acute radiation syndrome depends on the absorbed radiation dose and its distribution. Multi-organ-involvement and multi-organ-failure need be taken into account. The most vulnerable organ system to radiation exposure is the hematopoietic system. In addition to hematopoietic syndrome, radiation induced damage to the skin plays an important role in diagnostics and the treatment of radiation accident victims. The most important therapeutic principles with special reference to hematopoietic syndrome and cutaneous radiation syndrome are reviewed
Emergence of Anti-Cancer Drug Resistance: Exploring the Importance of the Microenvironmental Niche via a Spatial Model
Practically, all chemotherapeutic agents lead to drug resistance. Clinically,
it is a challenge to determine whether resistance arises prior to, or as a
result of, cancer therapy. Further, a number of different intracellular and
microenvironmental factors have been correlated with the emergence of drug
resistance. With the goal of better understanding drug resistance and its
connection with the tumor microenvironment, we have developed a hybrid
discrete-continuous mathematical model. In this model, cancer cells described
through a particle-spring approach respond to dynamically changing oxygen and
DNA damaging drug concentrations described through partial differential
equations. We thoroughly explored the behavior of our self-calibrated model
under the following common conditions: a fixed layout of the vasculature, an
identical initial configuration of cancer cells, the same mechanism of drug
action, and one mechanism of cellular response to the drug. We considered one
set of simulations in which drug resistance existed prior to the start of
treatment, and another set in which drug resistance is acquired in response to
treatment. This allows us to compare how both kinds of resistance influence the
spatial and temporal dynamics of the developing tumor, and its clonal
diversity. We show that both pre-existing and acquired resistance can give rise
to three biologically distinct parameter regimes: successful tumor eradication,
reduced effectiveness of drug during the course of treatment (resistance), and
complete treatment failure
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Temperature controls phenology in continuously flowering Protea species of subtropical Africa
PREMISE OF THE STUDY: Herbarium specimens are increasingly used as records of plant flowering
phenology. However, most herbarium-based
studies on plant phenology focus on taxa
from temperate regions. Here, we explore flowering phenologic responses to climate in the
subtropical plant genus Protea (Proteaceae), an iconic group of plants that flower year-round
and are endemic to subtropical Africa.
METHODS: We present a novel, circular sliding window approach to investigate phenological
patterns developed for species with year-round
flowering. We employ our method to evaluate
the extent to which site-to-
site
and year-to-
year
variation in temperature and precipitation
affect flowering dates using a database of 1727 herbarium records of 25 Protea species.
We also explore phylogenetic conservatism in flowering phenology.
RESULTS: We show that herbarium data combined with our sliding window approach
successfully captured independently reported flowering phenology patterns (r = 0.93).
Both warmer sites and warmer years were associated with earlier flowering of 3–5 days/°C,
whereas precipitation variation had no significant effect on flowering phenology. Although
species vary widely in phenological responsiveness, responses are phylogenetically
conserved, with closely related species tending to shift flowering similarly with increasing
temperature.
DISCUSSION: Our results point to climate-responsive
phenology for this important plant
genus and indicate that the subtropical, aseasonally flowering genus Protea has temperature-driven
flowering responses that are remarkably similar to those of better-studied
northern
temperate plant species, suggesting a generality across biomes that has not been described
elsewhere.APPENDIX S1. Specimen collection frequency across day of flowering
year (DOFY), a normalized version of the Julian day of year.
Red vertical dashed lines correspond to January 1.APPENDIX S2. Comparison of species peak flowering season
(in Julian days) recorded from herbarium specimen records
versus the literature (Rebelo, 2001). Rebelo (2001) reports both
a “long” season of increased flowering activity and a narrower
“short” season of maximal flowering activity for each species, the
centers of which are shown here relative to the peak flowering
date we calculated from herbarium data as described in the text.
Although the y-axis
ranges from 0–365, the x-axis
has a slightly
broader range—given the circular nature of the calendar year, a
given Julian date can take multiple values (e.g., 10 = 375), and the
value that best communicates alignment with the field guide data
set is shown.APPENDIX S3. Parameters used to characterize phenologic responsiveness
to climate in Protea species, estimated from the mixed
effects model.APPENDIX S4. Changes in flowering times of Protea species across
South Africa in relation to anomalies in temperature. Statistical
analysis based on mixed effects model using both spatial temperature
variation (A) and temporal climate (year-to-
year
temperature
variation) (B) as predictors, with species as random effect. Negative
slopes indicate advancement of flowering with warming. Lines indicate
fitted slopes for individual Protea species. Points indicate input
specimen data, and have been truncated for visualization at the extremes
of the y-axis
range.APPENDIX S5. Species-specific
statistics generated by the sliding
window phenology analysis and the mixed effects model (MEM)
climate analysis for each of the 25 Protea species.APPENDIX S6. Relationship between the aseasonality of species’
annual flowering phenology cycles (aseasonality index) and their
estimated phenological responses to temperature variation across
space and time (coefficients from the linear mixed effects model).
Dashed lines show linear regressions with 95% confidence intervals
shaded.APPENDIX S7. Tests of phylogenetic signal in different dimensions
of Protea flowering.Texas A&M
University–Corpus Christi, a National Science Foundation Graduate
Research Fellowship and the National Science Foundation Postdoctoral Research Fellowship in Biology.http://www.wileyonlinelibrary.com/journal/AppsPlantSciam2020Plant Production and Soil Scienc
Quantum flutter of supersonic particles in one-dimensional quantum liquids
The non-equilibrium dynamics of strongly correlated many-body systems
exhibits some of the most puzzling phenomena and challenging problems in
condensed matter physics. Here we report on essentially exact results on the
time evolution of an impurity injected at a finite velocity into a
one-dimensional quantum liquid. We provide the first quantitative study of the
formation of the correlation hole around a particle in a strongly coupled
many-body quantum system, and find that the resulting correlated state does not
come to a complete stop but reaches a steady state which propagates at a finite
velocity. We also uncover a novel physical phenomenon when the impurity is
injected at supersonic velocities: the correlation hole undergoes long-lived
coherent oscillations around the impurity, an effect we call quantum flutter.
We provide a detailed understanding and an intuitive physical picture of these
intriguing discoveries, and propose an experimental setup where this physics
can be realized and probed directly.Comment: 13 pages, 9 figure
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