The brightness of x-ray sources has been increased one to ten billion times by x-ray free-electron lasers (XFELs) that generate high intensity coherent photon pulses at wavelengths from nanometers to ...less than one angstrom and a duration of a few to 100 femtoseconds. For the first time XFELs allow for experimental exploration of the structure and dynamics of atomic and molecular systems at the angstrom-femtosecond space and time scale, creating new opportunities for scientific research in physics, chemistry, biology, material science and high energy density physics. This paper reviews the history of this development, concentrating on the Linac Coherent Light Source (LCLS), the world's first hard x-ray XFEL. It also presents the physical principles on which XFELs are based, their present status and future developments, together with some recent experimental results in physics, chemistry and biology. LCLS success has spurred the worldwide construction of more XFELs; SACLA in Japan, XFEL and FLASH in Germany, Swiss FEL, Korean XFEL, Fermi in Italy. The characteristics of these other sources are also discussed.
X-ray free-electron lasers (x-ray FELs) give us for the first time the possibility to explore structures and dynamical processes of atomic and molecular systems at the angstrom-femtosecond space and ...time scales. They generate coherent photon pulses with time duration of a few to 100 fs, peak power of 10 to 100 GW, over a wavelength range extending from about 100 nm to less than 1 A. Using these novel and unique capabilities new scientific results are being obtained in atomic and molecular sciences, in areas of physics, chemistry, and biology. This paper reviews the physical principles, the theoretical models, and the numerical codes on which x-ray FELs are based, starting from a single electron spontaneous undulator radiation to the FEL collective instability of a high density electron beam, strongly enhancing the electromagnetic radiation field intensity and its coherence properties. A short review is presented of the main experimental properties of x-ray FELs, and the results are discussed of the most recent research to improve their longitudinal coherence properties, increase the peak power, and generate multicolor spectra.
The fundamental coherent radiation emission processes from a bunched charged particles beam are outlined. In contrast to spontaneous emission of radiation from a random electron beam that is ...proportional to the number of particles, a prebunched electron beam can emit spontaneously coherent radiation proportional to the number of particles-squared, through the process of (spontaneous) superradiance (SP-SR) (in the sense of Dicke's). The coherent SP-SR emission of a bunched electron beam can be even further enhanced by a process of stimulated superradiance in the presence of a seed-injected radiation field. In this review, these coherent radiation emission processes for both single bunch and periodically bunched beams are considered in a model of radiation mode expansion. The general model of coherent spontaneous emission is extended to the nonlinear regime, particularly for undulator (wiggler) interaction: tapering-enhanced stimulated-superradiant amplification (TESSA). Processes of SP-SR and TESSA take place in tapered wiggler seed-injected free-electron lasers (FELs). In such FELs, operating in the x-ray regime, these processes are convoluted with other effects. However these fundamental emission concepts are useful guidelines for the strategy of wiggler tapering efficiency and power enhancement. Based on this model, previous theories and experiments are reviewed on coherent radiation sources based on SP-SR (coherent undulator radiation, synchrotron radiation, Smith-Purcell radiation, etc.), in the THz regime and on-going works on tapered wiggler efficiency-enhancement concepts in all optical frequency regimes up to x rays.
The aim of this prospective study was to determine the prevalence and characteristics of acid gastro-oesophageal reflux (GER) in patients with idiopathic pulmonary fibrosis (IPF). Sixty-five ...consecutive patients with well-defined IPF were subjected to 24-h pH monitoring and oesophageal manometry. A total of 133 consecutive patients with intractable asthma and symptoms of GER were used as comparisons. The prevalence of abnormal acid GER in IPF patients was 87%, with 76% and 63% demonstrating abnormal distal and proximal oesophageal acid exposures, respectively. Abnormal acid GER was significantly more common in IPF patients than asthma patients. Only 47% of IPF patients experienced classic GER symptoms. Despite treatment with standard doses of proton pump inhibitors (PPIs), 12 out of 19 patients receiving PPIs during the 24-h pH monitoring had abnormal oesophageal acid exposures by pH probe. There was no correlation between IPF severity and acid GER severity. In conclusion, abnormal acid gastro-oesophageal reflux is highly prevalent, but often clinically occult in patients with idiopathic pulmonary fibrosis. Standard doses of proton pump inhibitors may not suppress the acid gastro-oesophageal reflux in this population. Therefore, further studies are needed to determine if acid abnormal gastro-oesophageal reflux represents an important risk factor for idiopathic pulmonary fibrosis development or progression, and if optimal suppression of acid gastro-oesophageal reflux slows the progression of idiopathic pulmonary fibrosis and/or decreases episodic exacerbations of idiopathic pulmonary fibrosis.
Purpose
To identify the attributable mortality of central line associated blood stream infections (CLABSI) through meta-analysis.
Methods
Meta-analysis of case control and cohort studies, matched and ...unmatched, that reported on mortality of patients with and without CLABSI was performed. MEDLINE, CENTRAL, CINAHL were searched. Non-interventional studies of all languages that reported mortality in patients with CLABSI were included. Data were extracted on patient population, study setting, design, diagnostic criteria for CLABSI, and mortality. Results from studies comparing mortality due to CLABSI were pooled using a random effects model with assessment of heterogeneity. Heterogeneity of studies was assessed with an
I
2
statistic and a funnel plot was generated to assess for publication bias.
Results
Eighteen studies were included with 1,976 CLABSI cases. Of the included studies, 17 took place in intensive care unit settings, most involved a mixed population of medical and surgical patients, and ten were matched using an illness severity index. Our findings show an odds ratio of in hospital death associated with CLABSI as 2.75 (CI 1.86–4.07) and 1.51 (CI 1.08–2.09) in the subgroup of the ten matched studies. Those studies where greater than 30 % of CLABSI were attributed to coagulase-negative
Staphylococcus
had an odds ratio of death of 1.64 (95 % CI 1.02–2.65) compared with 4.71 (95 % CI 1.54–14.39).
Conclusions
CLABSI is associated with a significantly increased risk of death supporting the use of extensive efforts to reduce these infections.
We propose a practical alternative to Eliashberg equations for the ab initio calculation of superconducting transition temperatures and gap functions. Within the recent density functional theory for ...superconductors, we develop an exchange-correlation functional that retains the accuracy of Migdal's approximation to the many-body electron-phonon self-energy, while having a simple analytic form. Our functional is based on a parametrization of the Eliashberg self-energy for a superconductor with a single Einstein frequency, and enables density functional calculations of experimental excitation gaps. By merging electronic structure methods and Eliashberg theory, the present approach sets a new standard in quality and computational feasibility for the prediction of superconducting properties.
In the field of beam physics, two frontier topics have taken center stage due to their potential to enable new approaches to discovery in a wide swath of science. These areas are: advanced, high ...gradient acceleration techniques, and x-ray free electron lasers (XFELs). Further, there is intense interest in the marriage of these two fields, with the goal of producing a very compact XFEL. In this context, recent advances in high gradient radio-frequency cryogenic copper structure research have opened the door to the use of surface electric fields between 250 and 500 MV m−1. Such an approach is foreseen to enable a new generation of photoinjectors with six-dimensional beam brightness beyond the current state-of-the-art by well over an order of magnitude. This advance is an essential ingredient enabling an ultra-compact XFEL (UC-XFEL). In addition, one may accelerate these bright beams to GeV scale in less than 10 m. Such an injector, when combined with inverse free electron laser-based bunching techniques can produce multi-kA beams with unprecedented beam quality, quantified by 50 nm-rad normalized emittances. The emittance, we note, is the effective area in transverse phase space (x, p x /m e c) or (y, p y /m e c) occupied by the beam distribution, and it is relevant to achievable beam sizes as well as setting a limit on FEL wavelength. These beams, when injected into innovative, short-period (1-10 mm) undulators uniquely enable UC-XFELs having footprints consistent with university-scale laboratories. We describe the architecture and predicted performance of this novel light source, which promises photon production per pulse of a few percent of existing XFEL sources. We review implementation issues including collective beam effects, compact x-ray optics systems, and other relevant technical challenges. To illustrate the potential of such a light source to fundamentally change the current paradigm of XFELs with their limited access, we examine possible applications in biology, chemistry, materials, atomic physics, industry, and medicine-including the imaging of virus particles-which may profit from this new model of performing XFEL science.
Cutaneous squamous cell carcinoma (cSCC) represents 20% of all skin cancers. Although primary cSCCs can be successfully treated with surgery, a subset of highly aggressive lesions may progress to ...advanced disease, representing a public healthcare problem with significant cancer‐related morbidity and mortality. A complex network of genes (TP53, CDKN2A, NOTCH1 and NOTCH2, EGFR and TERT) and molecular pathways (RAS/RAF/MEK/ERK and PI3K/AKT/mTOR) have been shown to play an important role in the pathogenesis of cSCC. The epigenetic regulation of TP53 and CDKN2A is an attractive therapeutic target for the treatment of cSCC, as well as NOTCH‐activating agents capable to restore its tumour‐suppressor function. EGFR inhibitors including both monoclonal antibodies (cetuximab and panitumumab) and tyrosine kinase inhibitors (erlotinib, gefitinib and dasatinib) have been used in clinical trials for the treatment of advanced cSCC, achieving only partial clinical benefit. Recently, an immune‐modulatory drug (cemiplimab) has been introduced for the treatment of advanced cSCC with good clinical results and a favourable safety profile, while other PD1/PD‐L1 inhibitors, either as monotherapy or in combination with targeted therapies, are currently under investigation. This review focuses on molecular findings involved in the pathogenesis of cSCC and their implications for the future development of new treatment strategies. In addition, current and ongoing treatments on targeted therapies and/or immunotherapy are illustrated.
Invariant measure for quantum trajectories Benoist, T.; Fraas, M.; Pautrat, Y. ...
Probability theory and related fields,
06/2019, Letnik:
174, Številka:
1-2
Journal Article
Recenzirano
Odprti dostop
We study a class of Markov chains that model the evolution of a quantum system subject to repeated measurements. Each Markov chain in this class is defined by a measure on the space of matrices, and ...is then given by a random product of correlated matrices taken from the support of the defining measure. We give natural conditions on this support that imply that the Markov chain admits a unique invariant probability measure. We moreover prove the geometric convergence towards this invariant measure in the Wasserstein metric. Standard techniques from the theory of products of random matrices cannot be applied under our assumptions, and new techniques are developed, such as maximum likelihood-type estimations.
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