291 research outputs found
Group delay in THz spectroscopy with ultra-wideband log-spiral antennae
We report on the group delay observed in continuous-wave terahertz
spectroscopy based on photomixing with phase-sensitive homodyne detection. We
discuss the different contributions of the experimental setup to the phase
difference \Delta\phi(\nu) between transmitter arm and receiver arm. A simple
model based on three contributions yields a quantitative description of the
overall behavior of \Delta\phi(\nu). Firstly, the optical path-length
difference gives rise to a term linear in frequency. Secondly, the
ultra-wideband log-spiral antennae effectively radiate and receive in a
frequency-dependent active region, which in the most simple model is an annular
area with a circumference equal to the wavelength. The corresponding term
changes by roughly 6 pi between 100 GHz and 1 THz. The third contribution stems
from the photomixer impedance. In contrast, the derivative (d\Delta\phi / d\nu)
is dominated by the contribution of periodic modulations of \Delta\phi(\nu)
caused by standing waves, e.g., in the photomixers' Si lenses. Furthermore, we
discuss the Fourier-transformed spectra, which are equivalent to the waveform
in a time-domain experiment. In the time domain, the group delay introduced by
the log-spiral antennae gives rise to strongly chirped signals, in which low
frequencies are delayed. Correcting for the contributions of antennae and
photomixers yields sharp peaks or "pulses" and thus facilitates a
time-domain-like analysis of our continuous-wave data.Comment: 7 pages, 7 figure
Self-normalizing phase measurement in multimode terahertz spectroscopy based on photomixing of three lasers
Photomixing of two near-infrared lasers is well established for
continuous-wave terahertz spectroscopy. Photomixing of three lasers allows us
to measure at three terahertz frequencies simultaneously. Similar to Fourier
spectroscopy, the spectral information is contained in an nterferogram, which
is equivalent to the waveform in time-domain spectroscopy. We use one fixed
terahertz frequency \nu_ref to monitor temporal drifts of the setup, i.e., of
the optical path-length difference. The other two frequencies are scanned for
broadband high-resolution spectroscopy. The frequency dependence of the phase
is obtained with high accuracy by normalizing it to the data obtained at
\nu_ref, which eliminates drifts of the optical path-length difference. We
achieve an accuracy of about 1-2 microns or 10^{-8} of the optical path length.
This method is particularly suitable for applications in nonideal environmental
conditions outside of an air-conditioned laboratory.Comment: 5 pages, 5 figure
Current status of the IAG working group 4.3.7 on geodetic GNSS-R
Presentación realizada online en el Scientific Assembly of the International Association of Geodesy (2021) celebrado del 28 de junio al 2 de julio en Beijing
Evidence for a nuclear compartment of transcription and splicing located at chromosome domain boundaries
The nuclear topography of splicing snRNPs, mRNA transcripts and chromosome domains in various mammalian cell types are described. The visualization of splicing snRNPs, defined by the Sm antigen, and coiled bodies, revealed distinctly different distribution patterns in these cell types. Heat shock experiments confirmed that the distribution patterns also depend on physiological parameters. Using a combination of fluorescencein situ hybridization and immunodetection protocols, individual chromosome domains were visualized simultaneously with the Sm antigen or the transcript of an integrated human papilloma virus genome. Three-dimensional analysis of fluorescence-stained target regions was performed by confocal laser scanning microscopy. RNA transcripts and components of the splicing machinery were found to be generally excluded from the interior of the territories occupied by the individual chromosomes. Based on these findings we present a model for the functional compartmentalization of the cell nucleus. According to this model the space between chromosome domains, including the surface areas of these domains, defines a three-dimensional network-like compartment, termed the interchromosome domain (ICD) compartment, in which transcription and splicing of mRNA occurs
Maternal Lipids as Strong Determinants of Fetal Environment and Growth in Pregnancies With Gestational Diabetes Mellitus
OBJECTIVE—To determine the contribution of maternal glucose and lipids to intrauterine metabolic environment and fetal growth in pregnancies with gestational diabetes mellitus (GDM)
Limitations and pitfalls of using family letters to communicate genetic risk: a qualitative study with patients and healthcare professionals
European genetic testing guidelines recommend that healthcare professionals (HCPs) discuss the familial implications of any test with a patient and offer written material to help them share the information with family members. Giving patients these “family letters” to alert any relatives of their risk has become part of standard practice and has gone relatively unquestioned over the years. Communication with at-risk relatives will become an increasingly pressing issue as mainstream and routine practice incorporates broad genome tests and as the number of findings potentially relevant to relatives increases. This study therefore explores problems around the use of family letters to communicate about genetic risk. We conducted 16 focus groups with 80 HCPs, and 35 interviews with patients, recruited from across the UK. Data were analyzed thematically and we constructed four themes: 1) HCPs writing family letters: how to write them and why?, 2) Patients’ issues with handing out family letters, 3) Dissemination becomes an uncontrolled form of communication, and 4) When the relative has the letter, is the patient’s and HCP’s duty discharged? We conclude by suggesting alternative and supplementary methods of communication, for example through digital tools, and propose that in comparison to communication by family letter, direct contact by HCPs might be a more appropriate and successful option
How to use implantable loop recorders in clinical trials and hybrid therapy
Epidemiological studies show that atrial fibrillation (AF) is associated with a doubling of mortality, even after adjustment for confounders. AF can be asymptomatic, but this does not decrease the thromboembolic risk of the patient. Office ECGs, occasional 24-h Holter recordings and long-term ECG event recording might not be sensitive and accurate enough in patients with AF, especially in those with paroxysmal episodes. In one study, 7 days of continuous monitoring with event recorders detected paroxysmal AF in 20 of 65 patients with a previous negative 24-h Holter recording. Over the last decade, enormous improvements have been made in the technology of implantable devices, which can now store significant information regarding heart rhythm. The first subcutaneous implantable monitor (Reveal XT, Medtronic) was validated for continuous AF monitoring by the XPECT study. The dedicated AF detection algorithm uses irregularity and incoherence of R–R intervals to identify and classify patterns in ventricular conduction. Its sensitivity in identifying patients with AF is >96%. Numerous clinical data from continuous monitoring of AF have recently been published. The first applications of this technology have been in the field of surgical and catheter AF ablation. With regard to cryptogenic stroke, an international randomized trial is ongoing to compare standard care with standard care plus the implantable cardiac monitor for AF detection in patients discharged with the diagnosis of cryptogenic stroke: the Crystal AF trial. Continuous AF monitoring provides an optimal picture of daily AF burden, both symptomatic and asymptomatic. Implantable cardiac monitors have high sensitivity, enable better assessment of therapy success and may guide further AF therapy
Predictive genetic testing for motor neuron disease : time for a guideline?
Predictive (presymptomatic) testing refers to the situation where a person at risk of inheriting a specific condition requests a genetic test to clarify their status. This most commonly occurs in familial cancer, cardiac and neurodegenerative disorders. People seek predictive testing for a variety of reasons including to reduce uncertainty, enable financial planning or access reproductive medicine option
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