Search

Advanced photoinjectors, which are critical to many next generation accelerators, open the door to new ways of material probing, both as injectors for free electron lasers and for ultra-fast electron diffraction. For these applications, the nonuniformity of the electric field near the cathode caused by surface roughness can be the dominant source of beam emittance. Therefore, improving the photocathode roughness while maintaining quantum efficiency is essential to the improvement of beam brightness. In this paper, we report the demonstration of a bi-alkali antimonide photocathode with an order of magnitude improved roughness by sputter deposition from a K2CsSb sputter target, using in situ and operando X-ray characterizations. We found that a surface roughness of 0.5 nm for a sputtered photocathode with a final thickness of 42 nm can be achieved while still yielding a quantum efficiency of 3.3% at 530 nm wavelength.

Reduction of roughness to the nm level is critical of achieving the ultimate performance from photocathodes used in high gradient fields. The thrust of this paper is to explore the evolution of roughness during sequential growth, and to show that deposition of multilayer structures consisting of very thin reacted layers results in an nm level smooth photocathode. Synchrotron x-ray methods were applied to study the multi-step growth process of a high efficiency K2CsSb photocathode. A transition point of the Sb film grown on Si was observed at the film thickness of ∼40 Å with the substrate temperature at 100 °C and the growth rate at 0.1 Å s-1. The final K2CsSb photocathode exhibits a thickness of around five times that of the total deposited Sb film regardless of how the Sb film was grown. The film surface roughening process occurs first at the step when K diffuses into the crystalline Sb. The photocathode obtained from the multi-step growth exhibits roughness in an order of magnitude lower than the normal sequential process. X-ray diffraction measurements show that the material goes through two structural changes of the crystalline phase during formation, from crystalline Sb to K3Sb and finally to K2CsSb.

Nano-roughness is one of the major factors degrading the emittance of electron beams that can be generated by high efficiency photocathodes, such as the thermally reacted alkali antimonide thin films. In this paper, we demonstrate a co-deposition based method for producing alkali antimonide cathodes that produce near atomic smoothness with high reproducibility. We calculate the effect of the surface roughness on the emittance and show that such smooth cathode surfaces are essential for operation of alkali antimonide cathodes in high field, low emittance radio frequency electron guns and to obtain ultracold electrons for ultrafast electron diffraction applications.

Granular flow problems characterized by large deformations are widespread in various applications, including coastal and geotechnical engineering. The paper deals with the application of a rigid‐perfectly plastic two‐phase model extended by the Drucker–Prager yield criterion to simulate granular media with a finite volume flow solver (FV). The model refers to the combination of a Bingham fluid and an Eulerian strain measure to assess the failure region of granular dam slides. A monolithic volume‐of‐fluid (VoF) method is used to distinguish between the air and granular phases, both governed by the incompressible Navier–Stokes equations. The numerical framework enables modeling of large displacements and arbitrary shapes for large‐scale applications. The displayed validation and verification focuses on the rigid‐perfectly plastic material model for noncohesive and cohesive materials with varying angles of repose. Results indicate a good agreement of the predicted soil surface and strain results with experimental and numerical data. [ABSTRACT FROM AUTHOR]

Background Objectives Patients and Methods Results Conclusions Permanent tattooing is the invasive introduction of tattoo ink (pigments) into the dermis. The ink and aftercare cosmetics applied on pre‐damaged skin may contain skin sensitisers.To identify patient characteristics and the pattern of sensitisation in tattooed patients patch tested within the Information Network of Departments of Dermatology (IVDK).Comparative analysis of patient characteristics and reaction frequencies to baseline series allergens in 1648 consecutive patients with and 8045 consecutive patients without permanent tattoos. Non‐overlapping 95%‐confidence intervals were considered as significant.Having permanent tattoos was related with female sex, age <40 years, tobacco smoking, atopic dermatitis, (occupational) hand dermatitis and being employed in particular occupational groups (e.g., healthcare workers, mechanics, hairdressers). Sensitisation to nickel was increased in tattooed patients and associated with female sex (OR 4.23 [95%‐CI, 3.48–5.18]), age ≥40 years (OR 1.26 [95%‐CI, 1.08–1.49]), tobacco smoking (OR 1.19 [95%‐CI, 1.01–1.40]) and having permanent tattoos (OR 1.27 [95%‐CI, 1.05–1.53]).The association between nickel sensitisation and permanent tattoos is probably confounded by past reactions to pierced costume jewellery. Socio‐economic factors most probably contribute to the connection between tattoos, tobacco smoking, occupational or hand dermatitis, and being employed in particular occupational groups. [ABSTRACT FROM AUTHOR]

Bi-alkali antimonide photocathodes are one of the best known sources of electrons for high current and/or high bunch charge applications like Energy Recovery Linacs or Free Electron Lasers. Despite their high quantum efficiency in visible light and low intrinsic emittance, the surface roughness of these photocathodes prohibits their use as low emittance cathodes in high accelerating gradient superconducting and normal conducting radio frequency photoguns and limits the minimum possible intrinsic emittance near the threshold. Also, the growth process for these materials is largely based on recipes obtained by trial and error and is very unreliable. In this paper, using X-ray diffraction, we investigate the different structural and chemical changes that take place during the growth process of the bi-alkali antimonide material K2CsSb. Our measurements give us a deeper understanding of the growth process of alkali-antimonide photocathodes allowing us to optimize it with the goal of minimizing the surface roughness to preserve the intrinsic emittance at high electric fields and increasing its reproducibility.

Although a theory of the climatology of tropical cyclone formation remains elusive, high-resolution climate models can now simulate many aspects of tropical cyclone climate.

The study investigated the use of patch testing with sodium tetrachloropalladate (Na2PdCl4) and palladium chloride (PdCl2) to detect palladium sensitization in patients. Results showed a higher proportion of positive reactions to Na2PdCl4 compared to PdCl2, with a significant number of clinically relevant reactions. The study suggests that Na2PdCl4 at 3% pet. is more suitable for detecting palladium sensitization due to its increased concentration of palladium and diagnostic performance. The findings align with previous studies indicating the higher sensitivity of Na2PdCl4 compared to PdCl2 in detecting palladium sensitization. [Extracted from the article]

Some of the long-term changes in weather and climate extremes across the US have occurred as expected in the warming climate, but the trends vary throughout the country and easily detected due to multiyear and decadal variations. The US National Climate Assessment has to address extremes, as these are changing and anthropogenic climate change has a role in altering the probabilities of some of the extreme events. Extreme events also drive changes in natural and human systems more than average climatic conditions. Four workshops have been held to provide technical input to the US National Climate Assessment writing team where leading scientists in the field worked jointly to determine how best to assess the state of the science in understanding the decadal- to century-scale variability and changes in various types of extreme events.

The article discusses the use of the Lifetech KONAR-MF VSD occluder, a percutaneous closure device, in the treatment of patients with ventricular septal defect (VSD). The study aimed to collect data on the device's performance during a 12-month follow-up period. The results showed a high success rate of VSD closure without complications, with only a small number of patients experiencing residual shunting. The study concluded that the KONAR-MF VSD occluder is an effective and safe option for patients with VSD. [Extracted from the article]

This article discusses the results of a study on the use of balloon angioplasty for the treatment of recurrent aortic coarctation in children under one year of age. The study found that balloon angioplasty was a safe procedure with good results, reducing the peak-to-peak gradient and increasing the diameter of the stenosis. Re-coarctation was more common in patients with concomitant malformations. Complications occurred in 15.2% of cases, and 42.4% of patients required further cardiac catheter interventions. Overall, the study concluded that early dilatation of recurrent aortic coarctation is a safe intervention with a high success rate. [Extracted from the article]

This article discusses the use of optical coherence tomography (OCT) as a diagnostic tool for early detection of cardiac allograft vasculopathy (CAV) in pediatric heart transplant patients. CAV is a major limitation to graft survival in the long-term after heart transplantation. The study reviewed the medical history and examination findings of 39 patients who underwent heart transplantation in childhood or adolescence. OCT was found to be a safe and valuable method for detecting regional intimal thickening at stages where coronary angiography may not show any abnormalities. Further investigation is needed to determine if earlier adjustment of immunosuppression can impact the course of CAV or graft survival. [Extracted from the article]

This article discusses the importance of prenatal diagnosis and hemodynamic risk stratification in fetuses with congenital heart defects (CHD). The study analyzed data from a 10-year period and included 1,210 newborns with CHD. The findings showed that a significant percentage of fetuses delivered at a cardiac center had a prenatal diagnosis that was consistent with the postnatal diagnosis. Emergency intervention was most commonly required in cases with a higher level of care assignment. The study concludes that fetuses with certain CHDs, such as HLHS with RAS or IAS, TGA with RAS or IAS, obstructed TAPVR, severe Ebstein's anomaly, or TOF/APV with hydrops, particularly benefit from delivery at a heart center. [Extracted from the article]

The European Union (EU) has implemented comprehensive regulations on tattoo and permanent make-up inks, but these regulations are not sufficient to protect European citizens. The regulations, known as the REACH restriction, do not prohibit sensitizing impurities that are not classified as hazardous. Additionally, some banned chemicals do not have adverse effects in tattoos, leading to the use of more toxic alternatives. The enforcement of the regulations is also challenging, as technology cannot detect all chemicals and some limits are technically unfeasible. Furthermore, the regulations do not cover microbial risks, leading to the use of potentially harmful preservatives. The authors suggest closer collaboration between legislators and experts to establish scientifically sound and enforceable limits, as well as the development of new approaches for minimum safety requirements for pigments in tattooing. Immediate and long-term efforts are needed to improve and protect the health of European people. [Extracted from the article]