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This article presents a demonstration of the improved performance of an X-ray free-electron laser (FEL) using the optical klystron mechanism and helical undulator configuration, in comparison with the common planar undulator configuration without optical klystron. The demonstration was carried out at Athos, the soft X-ray beamline of SwissFEL. Athos has variable-polarization undulators, and small magnetic chicanes placed between every two undulators to fully exploit the optical klystron. It was found that, for wavelengths of 1.24 nm and 3.10 nm, the required length to achieve FEL saturation is reduced by about 35% when using both the optical klystron and helical undulators, with each effect accounting for about half of the improvement. Moreover, it is shown that a helical undulator configuration provides a 20% to 50% higher pulse energy than planar undulators. This work represents an important step towards more compact and high-power FELs, rendering this key technology more efficient, affordable and accessible to the scientific community.

Abstract X-ray free-electron lasers (FELs) are state-of-the-art scientific tools capable to study matter on the scale of atomic processes. Since the initial operation of X-ray FELs more than a decade ago, several facilities with upgraded performance have been put in operation. Here we present the first lasing results of Athos, the soft X-ray FEL beamline of SwissFEL at the Paul Scherrer Institute in Switzerland. Athos features an undulator layout based on short APPLE-X modules providing full polarisation control, interleaved with small magnetic chicanes. This versatile configuration allows for many operational modes, giving control over many FEL properties. We show, for example, a 35% reduction of the required undulator length to achieve FEL saturation with respect to standard undulator configurations. We also demonstrate the generation of more powerful pulses than the ones obtained in typical undulators. Athos represents a fundamental step forward in the design of FEL facilities, creating opportunities in FEL-based sciences.

The emergence of SARS-CoV-2 in late 2019 initiated a global pandemic, which led to a need for effective therapeutics and diagnostic tools, including virus-specific antibodies. Here, we investigate different antigen preparations to produce SARS-CoV-2-specific and virus-neutralizing antibodies in chickens (n = 3/antigen) and rabbits (n = 2/antigen), exploring, in particular, egg yolk for large-scale production of immunoglobulin Y (IgY). Reactivity profiles of IgY preparations from chicken sera and yolk and rabbit sera were tested in parallel. We compared three types of antigens based on ancestral SARS-CoV-2: an inactivated whole-virus preparation, an S1 spike-protein subunit (S1 antigen) and a receptor-binding domain (RBD antigen, amino acids 319–519) coated on lumazine synthase (LS) particles using SpyCather/SpyTag technology. The RBD antigen proved to be the most efficient immunogen, and the resulting chicken IgY antibodies derived from serum or yolk, displayed strong reactivity with ELISA and indirect immunofluorescence and broad neutralizing activity against SARS-CoV-2 variants, including Omicron BA.1 and BA.5. Preliminary in vivo studies using RBD–lumazine synthase yolk preparations in a hamster model showed that local application was well tolerated and not harmful. However, despite the in vitro neutralizing capacity, this antibody preparation did not show protective effect. Further studies on galenic properties seem to be necessary. The RBD–lumazine antigen proved to be suitable for producing SARS-CoV-2 specific antibodies that can be applied to such therapeutic approaches and as reference reagents for SARS-CoV-2 diagnostics, including virus neutralization assays.

Little is known about the frequency of Zika virus (ZIKV) infections in Sudan. The aim of this study was to obtain data on the prevalence of ZIKV infections and the immunity of the population in the country. To this end, 198 sera obtained between December 2012 and January 2013 in different regions in Sudan were examined for neutralizing antibodies against ZIKV, dengue virus (DENV), and yellow fever virus (YFV). The sera were non-randomly selected. The neutralization titers were compared with each other and with the WHO 1st International Standard for anti-Asian lineage Zika virus antibody. Twenty-six sera neutralized ZIKV. One-third of these sera had higher neutralization titers against ZIKV than against DENV-2 and -3. Two sera showed higher neutralization titers than the WHO standard for ZIKV antibodies. These data suggest occasional ZIKV infections in Sudan. The low percentage of sera in this cohort that neutralized ZIKV indicates that, in the study period, the population was susceptible to ZIKV infection.

The aim of this study was to test the inactivation of viruses on germ carriers of different types of wood using a disinfectant in order to assess the biosafety of wood as a building material in animal husbandry. The laboratory disinfectant efficacy tests were based on German testing guidelines and current European standards. Five different types of wood germ carriers, i.e., spruce (Picea abies), pine (Pinus sylvestris), poplar (Populus sp.), beech (Fagus sylvatica) and Douglas fir (Pseudotsuga menziesii), were inoculated with enveloped or non-enveloped viruses and then treated with one of three different disinfectants. The results revealed that intact, fine-sawn timber with a low roughness depth can be effectively inactivated. Peracetic acid proved to be the most effective disinfectant across all tests. Regardless of the pathogen and the type of wood, a concentration of 0.1% of the pure substance at a temperature of 10 °C and an exposure time of one hour can be recommended. At a temperature of −10 °C, a concentration of 0.75% is recommended. The basic chemicals formic acid and glutaraldehyde demonstrated only limited effectiveness overall. The synergistic effects of various wood components on the inactivation of viruses offer potential for further investigation. Disinfectant tests should also be conclusively verified in field trials to ensure that the results from standardised laboratory tests can be transferred to real stable conditions.

The aim of this study was to analyse the hygienic suitability of wood often used in animal husbandry. To this end, the inactivation of viruses (Enterovirus E as a surrogate for non-enveloped viruses and Newcastle disease virus as a surrogate for enveloped viruses) on germ carriers consisting of various types of wood was studied over an extended period to assess the biosafety of wood as an agricultural building material. The study was designed to assess the intrinsic biocidal activity of the wood itself, without the use of a disinfectant. The laboratory tests were based on German test guidelines and current European standards. Five different types of wood germ carriers, i.e., spruce (Picea abies), pine (Pinus sylvestris), poplar (Populus sp.), beech (Fagus sylvatica) and Douglas fir (Pseudotsuga menziesii), as well as stainless-steel carriers, were inoculated with enveloped and non-enveloped viruses and stored for up to four months, and the remaining infectivity of the viruses was continuously assessed. The results showed that intact, finely sawn timber with a low depth of roughness had an inactivating effect on the viruses up to 7.5 decadal logarithmic levels. For the non-enveloped virus, inactivation was fastest on Douglas fir wood, with the target reduction for effective inactivation (reduction by factor 4.0 log10) being achieved after two weeks, and for the enveloped virus on pine wood, it was already achieved from the day of drying. The hygienic effects of the wood carriers may be due to their hygroscopic properties and wood constituents. These effects offer potential for further investigation, including tests with other wood species rich in extractives.

N6-methyladenosine (m6A) is one of the most abundant modifications of cellular RNA, where it serves various functions. m6A methylation of many viral RNA species has also been described; however, little is known about the m6A epitranscriptome of haemorrhagic fever-causing viruses like Ebola virus (EBOV). Here, we analysed the importance of the methyltransferase METTL3 for the life cycle of this virus. We found that METTL3 interacts with the EBOV nucleoprotein and the transcriptional activator VP30 to support viral RNA synthesis, and that METTL3 is recruited into EBOV inclusions bodies, where viral RNA synthesis occurs. Analysis of the m6A methylation pattern of EBOV mRNAs showed that they are methylated by METTL3. Further studies revealed that METTL3 interaction with the viral nucleoprotein, as well as its importance for RNA synthesis and protein expression, is also observed for other haemorrhagic fever viruses such as Junín virus (JUNV) and Crimean-Congo haemorrhagic fever virus (CCHFV). The negative effects on viral RNA synthesis due to loss of m6A methylation are independent of innate immune sensing, as METTL3 knockout did not affect type I interferon induction in response to viral RNA synthesis or infection. Our results suggest a novel function for m6A that is conserved among diverse haemorrhagic fever-causing viruses (i.e. EBOV, JUNV and CCHFV), making METTL3 a promising target for broadly-acting antivirals.

We demonstrate the generation of coherent soft x-ray free-electron laser (FEL) pulses with a duration below 1 fs using nonlinear compression with a low-charge electron beam (10 pC). The approach is simple, and it does not require any special hardware, so it can be readily implemented at any x-ray FEL facility. We present temporal and spectral diagnostics confirming the production of single-spike sub-femtosecond pulses for photon energies of 642 and 1111 eV. Our work will be important for ultrafast FEL applications requiring soft x-rays.

The Paul Scherrer Institute is implementing laser-based seeding in the soft X-ray beamline (Athos) of its free-electron laser, SwissFEL, to enhance the temporal and spectral properties of the delivered photon pulses. This technique requires, among other components, two identical modulators for coupling the electron beam with an external laser with a wavelength range between 260 and 1600 nm. The design, magnetic measurements results, alignment, operation and also details of the novel and exotic magnetic configuration of the prototype are described.

Rustrela virus (RusV) was detected in the brains of 27 out of 29 domestic cats with ‘staggering disease’, but not of 29 control cats. This suggests RusV as the long-sought causative agent of ‘staggering disease’, which had been obscure for 50 years.

The intrinsic energy spread of electron beams needs to be measured to characterize and optimize high-brightness electron beam sources such as those driving x-ray free-electron lasers (FELs). We demonstrate the use of the optical klystron effect as a precise and high-resolution method to measure the electron beam energy spread. The optical klystron setup consists of undulator modules and magnetic chicanes placed between them. The energy spread is found by measuring the radiation power produced in the undulators as a function of the chicanes’ strengths. High resolution and simplicity are the advantages of this approach, in contrast to the standard method, which measures the longitudinal phase space of the electron beam with a transverse deflector. The demonstration was performed at Athos, the soft x-ray FEL beamline of SwissFEL, for which we measured energy spreads below 1 MeV at a central beam energy of 3.4 GeV. We have verified the consistency of the method for different parameters (radiation wavelengths, undulator polarization configurations, and electron bunch durations) and we have benchmarked it against the standard measurement approach using a transverse deflector. Our results confirm the optical klystron as a valid approach to measure the electron beam energy spread. The method can be especially useful to reconstruct low energy spread values, where the conventional approach may be resolution limited, such as in ultra high-brightness radiofrequency photoinjectors or plasma sources, or when transverse deflectors are not available.

Summary: La Crosse virus, responsible for pediatric encephalitis in the United States, and Schmallenberg virus, a highly teratogenic veterinary virus in Europe, belong to the large Orthobunyavirus genus of zoonotic arthropod-borne pathogens distributed worldwide. Viruses in this under-studied genus cause CNS infections or fever with debilitating arthralgia/myalgia syndromes, with no effective treatment. The main surface antigen, glycoprotein Gc (∼1,000 residues), has a variable N-terminal half (GcS) targeted by the patients’ antibody response and a conserved C-terminal moiety (GcF) responsible for membrane fusion during cell entry. Here, we report the X-ray structure of post-fusion La Crosse and Schmallenberg virus GcF, revealing the molecular determinants for hairpin formation and trimerization required to drive membrane fusion. We further experimentally confirm the role of residues in the fusion loops and in a vestigial endoplasmic reticulum (ER) translocation sequence at the GcS-GcF junction. The resulting knowledge provides essential molecular underpinnings for future development of potential therapeutic treatments and vaccines.

Viral disinfection is important for medical facilities, the food industry, and the veterinary field, especially in terms of controlling virus outbreaks. Therefore, standardized methods and activity levels are available for these areas. Usually, disinfectants used in these areas are characterized by their activity against test organisms (i.e., viruses, bacteria, and/or yeasts). This activity is usually determined using a suspension test in which the test organism is incubated with the respective disinfectant in solution to assess its bactericidal, yeasticidal, or virucidal activity. In addition, carrier methods that more closely reflect real-world applications have been developed, in which microorganisms are applied to the surface of a carrier (e.g., stainless steel frosted glass, or polyvinyl chloride (PVC)) and then dried. However, to date, no standardized methods have become available for addressing genetically modified vectors or disinfection-resistant oncolytic viruses such as the H1-parvovirus. Particularly, such non-enveloped viruses, which are highly resistant to disinfectants, are not taken into account in European standards. This article proposes a new activity claim known as “virucidal activity PLUS”, summarizes the available methods for evaluating the virucidal activity of chemical disinfectants against genetically modified organisms (GMOs) using current European standards, including the activity against highly resistant parvoviridae such as the adeno-associated virus (AAV), and provides guidance on the selection of disinfectants for pharmaceutical manufacturers, laboratories, and clinical users.

The first generation of S-band injectors for free-electron lasers has illustrated high reliability and performance by driving the latest generation of high brightness machines. However, the ultimate electron beam brightness of these devices is limited by the electric field that they can achieve on the cathode. With the aim of a higher beam brightness at SwissFEL, this paper presents the design of a C-band traveling-wave (TW) radio-frequency photogun that aims to offer the possibility to move to a cathode gradient up to 200 MV/m. This increased gradient comes from the ability to operate with rf pulse lengths approximately an order of magnitude shorter than the current state-of-the-art room-temperature S-band standing-wave rf photoguns. With this high cathode gradient, this novel gun is able to produce an electron bunch whose 5D beam brightness is 5 times greater than the current SwissFEL photogun. Furthermore, the low power dissipation within the photogun, resulting from the short rf pulse length and TW philosophy, opens up the opportunity for rf pulse repetition rates up to 1 kHz.

Serial femtosecond crystallography (SFX) at X-ray free-electron lasers (XFELs) enables essentially radiation-damage-free macromolecular structure determination using microcrystals that are too small for synchrotron studies. However, SFX experiments often require large amounts of sample in order to collect highly redundant data where some of the many stochastic errors can be averaged out to determine accurate structure-factor amplitudes. In this work, the capability of the Swiss X-ray free-electron laser (SwissFEL) was used to generate large-bandwidth X-ray pulses [Δλ/λ = 2.2% full width at half-maximum (FWHM)], which were applied in SFX with the aim of improving the partiality of Bragg spots and thus decreasing sample consumption while maintaining the data quality. Sensitive data-quality indicators such as anomalous signal from native thaumatin micro-crystals and de novo phasing results were used to quantify the benefits of using pink X-ray pulses to obtain accurate structure-factor amplitudes. Compared with data measured using the same setup but using X-ray pulses with typical quasi-monochromatic XFEL bandwidth (Δλ/λ = 0.17% FWHM), up to fourfold reduction in the number of indexed diffraction patterns required to obtain similar data quality was achieved. This novel approach, pink-beam SFX, facilitates the yet underutilized de novo structure determination of challenging proteins at XFELs, thereby opening the door to more scientific breakthroughs.

We demonstrate the generation of widely tunable two-color x-ray free-electron laser (FEL) pulses at SwissFEL. In a split-undulator configuration, each color is produced in a different undulator section, and a chicane between the two sections allows for a variable time separation between the two pulses of up to 500 fs. We show an unprecedented photon energy ratio between the two colors of about three (350 and 915 eV), with each individual pulse having a peak power of a few gigawatts and a duration down to the femtosecond level. Moreover, we demonstrate the reduction of the required undulator length via the optical klystron mechanism and the time-resolved diagnostics of the FEL pulses utilizing the same beam setup as for the pulse generation. The unique combination of widely tunable energy and time separation of the two-color pulse pair offers opportunities to study ultrafast x-ray-induced energy transfer and relaxation processes in physics, chemistry, and biology.

Abstract Background Newcastle disease is a devastating disease in poultry caused by virulent Newcastle disease virus (NDV), a paramyxovirus endemic in many regions of the world despite intensive vaccination. Phylogenetic analyses reveal ongoing evolution of the predominant circulating genotype 2.VII, and the relevance of potential antigenic drift is under discussion. To investigate variation within neutralization-sensitive epitopes within the protein responsible for receptor binding, i.e. the Hemagglutinin-Neuraminidase (HN) spike protein, we were interested in establishing genotype-specific monoclonal antibodies (MAbs). Methods An HN-enriched fraction of a gradient-purified NDV genotype 2.VII was prepared and successfully employed to induce antibodies in BalbC mice that recognize conformationally intact sites reactive by haemagglutination inhibition (HI). For subsequent screening of mouse hybridoma cultures, an NDV-ELISA was established that utilizes Concanavalin A (ConA-ELISA) coupled glycoproteins proven to present conformation-dependent epitopes. Results Six out of nine selected MAbs were able to block receptor binding as demonstrated by HI activity. One MAb recognized an epitope only present in the homologue virus, while four other MAbs showed weak reactivity to selected other genotypes. On the other hand, one broadly cross-reacting MAb reacted with all genotypes tested and resembled the reactivity profile of genotype-specific polyclonal antibody preparations that point to minor antigenic differences between tested NDV genotpyes. Conclusions These results point to the concurrent presence of variable and conserved epitopes within the HN molecule of NDV. The described protocol should help to generate MAbs against a variety of NDV strains and to enable in depth analysis of the antigenic profiles of different genotypes.

Summary: Biobanking infrastructures, which are crucial for responding early to new viral outbreaks, share pathogen genetic resources in an affordable, safe, and impartial manner and can provide expertise to address access and benefit-sharing issues. The European Virus Archive has had a crucial role in the global response to the COVID-19 pandemic by distributing EU-subsidised (free of charge) viral resources to users worldwide, providing non-monetary benefit sharing, implementing access and benefit-sharing compliance, and raising access and benefit-sharing awareness among members and users. All currently available SARS-CoV-2 material in the European Virus Archive catalogue, including variants of concern, are not access and benefit-sharing cases per se, but multilateral benefit-sharing has nevertheless occurred. We propose and discuss how a multilateral system enabling access and benefit-sharing from pathogen genetic resources, based on the European Virus Archive operational model, could help bridge the discrepancies between the current bilateral legal framework for pathogen genetic resources and actual pandemic response practices.

SwissFEL has a unique capability, among the normal conducting linac-based light sources, to simultaneously serve two separate undulator lines (Aramis and Athos) up to the machine repetition rate of 100 Hz using the double bunch operation mode. It increases twice the experiments throughput of the facility with modest additional investment. Two electron bunches spaced 28 ns apart are extracted from the cathode by two laser pulses with individually controlled repetition rates. The bunches are accelerated up to about 3 GeV in the main linac using the same rf macropulse. After separation, one bunch serves the Athos soft x-ray beamline and the other is further accelerated to serve the hard x-ray beamline – Aramis. A fast and high-stability beam kicker separates the two bunches without disturbing the electron beam and consequently the x-ray lasing. The timing and control system sets hybrid machine modes utilizing independent operation of the two undulator lines with individually programmed repetition rates. Beam diagnostics and feedback systems have to operate with two closely spaced bunches where the two beams share the same machine path. The low-level rf system manipulates the rf amplitude and phase within a fraction of the rf macropulse to provide decoupling of the acceleration parameters of the first and the second bunch. This manuscript presents measurements that show that the bunch separation does not degrade FEL lasing stability.

We present high-resolution measurements of the electron beam energy spread at the SwissFEL injector as a function of the electron bunch charge, the optics, and the longitudinal dispersion of the lattice. The measured values are in general an order of magnitude higher than what is predicted by standard simulation codes. The measured dependences indicate that the energy spread blowup is caused primarily by intrabeam scattering and microbunching instabilities, effects not covered in the conventional modeling of radio-frequency injectors. We present further a numerical model that qualitatively reproduces the experimental data and an approach to mitigate the energy spread deterioration. The work underlines the importance of considering the energy spread in the optimization and design of high-brightness electron beam sources and the need to develop new models to adequately understand and simulate the observed physics effects.

Orthobunyaviruses (OBVs) cause severe disease in humans and farm animals, but the molecular basis for infection is not fully understood. Here, the authors present crystal structures of free and antibody-bound OBV envelope glycoproteins and show that their domains enable efficient immunization in a mouse model.

Rift Valley fever virus (RVFV) is a zoonotic arbovirus that causes severe disease in humans and ruminants. The infection is characterized by abortions in pregnant animals, high mortality in neonates as well as febrile illness in humans that develop in 1% of cases encephalitis or hemorrhagic fever. There is presently no specific antiviral treatment for RVFV infection available. In this study, two monoclonal antibodies (mAbs), raised against glycoprotein Gn, were applied in a therapeutic study. Treatment of RVFV infected mice with neutralizing mAb Gn3 alone at two different time points (30 minutes before or 30 minutes after virus challenge) showed only moderate efficacy of about 58.3% survival in both applications. However, a combination therapy together with non-neutralizing mAb Gn32 demonstrated complete protection (100% survival) when applied 30 minutes after the lethal challenge dose. The increase of mAb efficacy is probably based on cooperative neutralization effects. These data suggest that a combination therapy with mAbs Gn3 and Gn32 could be an effective treatment option against RVFV infection.

X-ray free-electron lasers (XFELs), with pulse durations of a few tens of femtoseconds or shorter, are cutting-edge instruments capable of observing structure and dynamics at the atomic scale. Temporal diagnostics are challenging but of fundamental importance for XFEL performance and experiments. In this paper, we demonstrate a method to characterize on a single-shot basis the temporal profile of both the electron beam and the XFEL radiation with femtosecond resolution. The approach consists in streaking the electron beam after the undulator using the wakefields of a corrugated structure. Its merits are arrival time stability and cost-effectiveness. Our method allows access to self-synchronized femtosecond diagnostics to any XFEL facility at low cost.

We report on the generation of one- and two-color attosecond hard x-ray pulses at SwissFEL by appropriately tailoring the nonlinear compression of the electron beam. For achieving very short [about 300 attoseconds (as)] and stable single-color pulses, we minimize the collective effects of the longitudinal space-charge forces by strongly compressing the electron beam right before the undulator, utilizing the energy collimator chicane as a third compression stage. For achieving two-color short pulses, we exploit enhanced space-charge forces splitting the beam into two energy components.

The energy spread of the electron beam is a critical parameter in x-ray free-electron lasers (XFELs) and needs to be optimized for best performance. The uncorrelated energy spread of the electrons can be a few keV or less in XFEL injectors, thus very challenging to measure. The standard method to characterize the electron beam energy spread, consisting in streaking the beam with a transverse deflector and measuring the time-resolved beam size of the electrons in a dispersive location for a single electron beam energy, has a typical resolution of several keV. To overcome this limitation we introduce a novel method to measure the beam size at a dispersive location for different beam energies so that it is possible to disentangle the beam size contributions related to the energy spread, the intrinsic beam size and the monitor resolution. As a consequence, the energy spread can be characterized with a much higher precision and resolution than in the standard approach. We also suggest to perform measurements for different deflection amplitudes so that the energy spread induced by the transverse deflector can be subtracted properly. The scheme does not require any additional hardware and thus can be readily applied in any standard XFEL facility. Numerical simulations and experimental results at SwissFEL confirm the validity of our method. Our calculations show that the approach can be used to significantly overcome the resolution of the standard approach and measure energy spreads well below 1 keV. As an example we present energy spreads of few keV measured at the SwissFEL injector.

A broadband energy-chirped hard X-ray pulse has been demonstrated at the SwissFEL (free electron laser) with up to 4% bandwidth. We consider the characteristic parameters for analyzing the time dependence of stationary protein diffraction with energy-chirped pulses. Depending on crystal mosaic spread, convergence, and recordable resolution, individual reflections are expected to spend at least ≈ 50 attoseconds and up to ≈ 8 femtoseconds in reflecting condition. Using parameters for a chirped XFEL pulse obtained from simulations of 4% bandwidth conditions, ray-tracing simulations have been carried out to demonstrate the temporal streaking across individual reflections and resolution ranges for protein crystal diffraction. Simulations performed at a higher chirp (10%) emphasize the importance of chirp magnitude that would allow increased observation statistics for the temporal separation of individual reflections for merging and structure determination. Finally, we consider the fundamental limitation for obtaining time-dependent observations using chirped pulse diffraction. We consider the maximum theoretical time resolution achievable to be on the order of 50–200 as from the instantaneous bandwidth of the chirped SASE pulse. We then assess the ability to propagate ultrafast optical pulses for pump-probe cross-correlation under characteristic conditions of material dispersion; in this regard, the limiting factors for time resolution scale with crystal thickness. Crystals that are below a few microns in size will be necessary for subfemtosecond time resolution.

Ebola virus (EBOV) causes severe outbreaks of viral hemorrhagic fever in humans. While virus-host interactions are promising targets for antivirals, there is only limited knowledge regarding the interactions of EBOV with cellular host factors. Recently, we performed a genome-wide siRNA screen that identified the nuclear RNA export factor 1 (NXF1) as an important host factor for the EBOV life cycle. NXF1 is a major component of the nuclear mRNA export pathway that is usurped by many viruses whose life cycles include nuclear stages. However, the role of NXF1 in the life cycle of EBOV, a virus replicating in cytoplasmic inclusion bodies, remains unknown. In order to better understand the role of NXF1 in the EBOV life cycle, we performed a combination of co-immunoprecipitation and double immunofluorescence assays to characterize the interactions of NXF1 with viral proteins and RNAs. Additionally, using siRNA-mediated knockdown of NXF1 together with functional assays, we analyzed the role of NXF1 in individual aspects of the virus life cycle. With this approach we identified the EBOV nucleoprotein (NP) as a viral interaction partner of NXF1. Further studies revealed that NP interacts with the RNA-binding domain of NXF1 and competes with RNA for this interaction. Co-localization studies showed that RNA binding-deficient, but not wildtype NXF1, accumulates in NP-derived inclusion bodies, and knockdown experiments demonstrated that NXF1 is necessary for viral protein expression, but not for viral RNA synthesis. Finally, our results showed that NXF1 interacts with viral mRNAs, but not with viral genomic RNAs. Based on these results we suggest a model whereby NXF1 is recruited into inclusion bodies to promote the export of viral mRNA:NXF1 complexes from these sites. This would represent a novel function for NXF1 in the life cycle of cytoplasmically replicating viruses, and may provide a basis for new therapeutic approaches against EBOV, and possibly other emerging viruses.

Hendra virus (HeV) and Nipah virus (NiV) belong to the genus Henipavirus in the family Paramyxoviridae. Henipavirus infections were first reported in the 1990's causing severe and often fatal outbreaks in domestic animals and humans in Southeast Asia and Australia. NiV infections were observed in humans in Bangladesh, India and in the first outbreak in Malaysia, where pigs were also infected. HeV infections occurred in horses in the North-Eastern regions of Australia, with singular transmission events to humans. Bats of the genus Pteropus have been identified as the reservoir hosts for henipaviruses. Molecular and serological indications for the presence of henipa-like viruses in African fruit bats, pigs and humans have been published recently. In our study, truncated forms of HeV and NiV attachment (G) proteins as well as the full-length NiV nucleocapsid (N) protein were expressed using different expression systems. Based on these recombinant proteins, Enzyme-linked Immunosorbent Assays (ELISA) were developed for the detection of HeV or NiV specific antibodies in porcine serum samples. We used the NiV N ELISA for initial serum screening considering the general reactivity against henipaviruses. The G protein based ELISAs enabled the differentiation between HeV and NiV infections, since as expected, the sera displayed higher reactivity with the respective homologous antigens. In the future, these assays will present valuable tools for serosurveillance of swine and possibly other livestock or wildlife species in affected areas. Such studies will help assessing the potential risk for human and animal health worldwide by elucidating the distribution of henipaviruses.

We present a novel and flexible method to generate two-color x-ray free-electron-laser (FEL) pulses with variable color separation and time delay using a double-slotted foil on a beam with a large energy chirp. The color separation and time delay between pulses can be set independently by tuning the separation between the slots and the longitudinal dispersion of a magnetic chicane. This method presents some advantages in comparison to previous proposals; it is compact, no large hardware component is needed, and no modifications of the machine settings in the FEL injector are required. Start-to-end numerical simulations for the SwissFEL case show the validity and tunability of our method and its application range: -60 to +80 fs time delay and 0 to 3% color separation between the two pulses for a central wavelength of 0.1 nm.

The diversity of virus-specific antibodies and of B cells among different individuals is unknown. Using single-cell cloning of antibody genes, we generated recombinant human monoclonal antibodies from influenza nucleoprotein-specific memory B cells in four adult humans with and without preceding influenza vaccination. We examined the diversity of the antibody repertoires and found that NP-specific B cells used numerous immunoglobulin genes. The heavy chains (HCs) originated from 26 and the kappa light chains (LCs) from 19 different germ line genes. Matching HC and LC chains gave rise to 43 genetically distinct antibodies that bound influenza NP. The median lengths of the CDR3 of the HC, kappa and lambda LC were 14, 9 and 11 amino acids, respectively. We identified changes at 13.6% of the amino acid positions in the V gene of the antibody heavy chain, at 8.4% in the kappa and at 10.6 % in the lambda V gene. We identified somatic insertions or deletions in 8.1% of the variable genes. We also found several small groups of clonal relatives that were highly diversified. Our findings demonstrate broadly diverse memory B cell repertoires for the influenza nucleoprotein. We found extensive variation within individuals with a high number of point mutations, insertions, and deletions, and extensive clonal diversification. Thus, structurally conserved proteins can elicit broadly diverse and highly mutated B-cell responses.

The SwissFEL X-ray Free Electron Laser (XFEL) facility started construction at the Paul Scherrer Institute (Villigen, Switzerland) in 2013 and will be ready to accept its first users in 2018 on the Aramis hard X-ray branch. In the following sections we will summarize the various aspects of the project, including the design of the soft and hard X-ray branches of the accelerator, the results of SwissFEL performance simulations, details of the photon beamlines and experimental stations, and our first commissioning results.

We present a setup based on the optical klystron concept, consisting of two undulator modules separated by a magnetic chicane, that addresses two issues in free-electron-laser (FEL) facilities. On the one hand, it allows increasing the intrinsic energy spread of the beam at the source, which is useful to counteract the harmful microbunching instability. This represents an alternative method to the more conventional laser heater with the main advantage that no laser system is required. On the other hand, the setup can be used to reconstruct the initial beam energy spread, whose typical values in FEL injectors around 1 keV are very difficult to measure with standard procedures.

X-ray free-electron lasers (XFELs) are modern research tools in disciplines such as biology, material science, chemistry, and physics. Besides the standard operation that aims at minimizing the bandwidth of the produced XFEL radiation, there is a strong scientific demand to produce large-bandwidth XFEL pulses for several applications such as nanocrystallography, stimulated Raman spectroscopy, and multiwavelength anomalous diffraction. We present a self-consistent method that maximizes the XFEL pulse bandwidth by systematically maximizing the energy chirp of the electron beam at the undulator entrance. This is achieved by optimizing the compression scheme and the electron distribution at the source in an iterative back-and-forward tracking. Start-to-end numerical simulations show that a relative bandwidth of 3.25% full-width can be achieved for the hard x-ray pulses in the SwissFEL case.

The design of a photoinjector, in particular that of the electron source, is of central importance for free electron laser (FEL) machines where a high beam brightness is required. In comparison to standard designs, an rf traveling-wave photocathode gun can provide a more rigid beam with a higher brightness and a shorter pulse. This is illustrated by applying a specific optimization procedure to the SwissFEL photoinjector, for which a brightness improvement up to a factor 3 could be achieved together with a double gun output energy compared to the reference setup foreseeing a state-of-the-art S-band rf standing-wave gun. The higher brightness is mainly given by a (at least) double peak current at the exit of the gun which brings benefits for both the beam dynamics in the linac and the efficiency of the FEL process. The gun design foresees an innovative coaxial rf coupling at both ends of the structure which allows a solenoid with integrated bucking coil to be placed around the cathode in order to provide the necessary focusing right after emission.

X-ray free electron lasers (XFELs) are innovative research tools able to produce high-power and short radiation pulses for multiple scientific applications. We present a new method to produce XFEL radiation with much higher power and shorter pulse lengths than the ones obtained at standard XFEL facilities. This will enable new kinds of experiments in scientific fields such as nonlinear optics and bioimaging. The scheme is based on introducing a transverse tilt to the electron beam, thus limiting the fraction of the bunch able to produce XFEL radiation. In the first part of the undulator beam line only the tail of the electron bunch lases. Then, by properly delaying and correcting the trajectory of the electron beam between some undulator modules, all the electrons can contribute to the amplification of a very short XFEL pulse. Apart from being efficient, our method is flexible since by tuning the tilt amplitude one can obtain shorter or more energetic XFEL pulses. The scheme can readily be applied since, besides the standard components of an XFEL facility, it only needs small chicanes between certain undulator modules. We have confirmed the validity of our proposal with numerical simulations done for the SwissFEL case.

Free electron lasers in the X-ray regime require a good slice alignment along the electron bunch to achieve their best performance. A transverse beam slice shift reduces this alignment and spoils projected emittance and optics. Coherent synchrotron radiation specifically for over-compression and transverse wakefields are major contributors to this. In the case of the large-bandwidth operation, based on a strictly monotonic energy chirp of the bunch, the here introduced correction additionally enhances the spectral bandwidth of the FEL pulse. Well-defined leaking of dispersion at places with a strictly monotonic longitudinal phase space can compensate a beam tilt. This work presents a way to characterize the beam tilt as well as a method to correct for it within a linear accelerator with at least one high dispersive section with corrector magnets.

The emittance of the electron beam is crucial for Free-Electron Laser facilities: it has a strong influence on the lasing performance and on the total length of the accelerator. We present our procedure to measure and minimize the projected and slice emittance at the SwissFEL Injector Test Facility. The normalized slice emittance resolution achieved is about 3 nm and the longitudinal resolution is about 13 fs, with measurement errors estimated to be below 5%. After performing a full optimization we have obtained, for uncompressed beams, a slice emittance of about 200 nm for a beam charge of 200 pC, and a slice emittance of about 100 nm for 10 pC. These values are consistent with our simulations and are well below the requirements of the SwissFEL under construction at the Paul Scherrer Institute. At these bunch charges our measured slice emittances are, to our knowledge, the lowest reported so far for an electron linear accelerator.

In this paper we investigate and compare the properties of two narrow-bandwidth free-electron laser (FEL) schemes, one using self-seeding and the other high gain harmonic generation (HGHG). The two systems have been thoroughly studied analytically and numerically in the past. The aim of this work is to compare their performances when the FEL is driven by an electron beam with nonideal properties, thus including effects such as shot-to-shot energy fluctuations and nonlinear energy chirp. In both cases nonlinearities produce a bandwidth larger than the Fourier transform limited value. However, our analysis indicates that, for approximately the same output power levels, the self-seeding scheme is less affected than the HGHG scheme by quadratic energy chirps in the electron beam longitudinal phase space. This is confirmed by a specific numerical example corresponding to SPARX parameters where the electron beam was optimized to minimize the FEL gain length. The work has been carried out with the aid of the time dependent FEL codes GENESIS 1.3 (3D) and PERSEO (1D).

The physical effects of optical mode dispersion in the electron beam of a free-electron laser are investigated for modes that carry orbital angular momentum. The analysis is performed using a derived equivalence between two different formulations that describe the radiation fields in the linear regime.

Laser synthesis and processing of colloids (LSPC) is an established method for producing functional and durable nanomaterials and catalysts in virtually any liquid of choice. While the redox reactions during laser synthesis in water are fairly well understood, the corresponding reactions in organic liquids remain elusive, particularly because of the much greater complexity of carbon chemistry. To this end, this article first reviews the knowledge base of chemical reactions during LSPC and then deduces identifiable reaction pathways and mechanisms. This review also includes findings that are specific to the LSPC method variants laser ablation (LAL), fragmentation (LFL), melting (LML), and reduction (LRL) in organic liquids. A particular focus will be set on permanent gases, liquid hydrocarbons, and solid, carbonaceous species generated, including the formation of doped, compounded, and encapsulated nanoparticles. It will be shown how the choice of solvent, synthesis method, and laser parameters influence the nanostructure formation as well as the amount and chain length of the generated polyyne by-products. Finally, theoretical approaches to address the mechanisms of organic liquid decomposition and carbon shell formation are highlighted and discussed regarding current challenges and future perspectives of LSPC using organic liquids instead of water.

Abstract Surface hydroxyls (OH) are crucial for heterogeneous catalysis in water. However, they are commonly characterized at solid–gas interfaces (e.g., FTIR, XPS, TGA), which may not represent the surface in aqueous environments. Here, the surface OH of five catalytically relevant oxides (Al2O3, ZrO2, TiO2, Fe2O3, Co3O4) are quantified by substituting them with F− ions at pH 3–10, where the surface fluoride (F) density is evaluated by XPS using the geometry factor for spherical particles. These results show that the surface F density peaks at around pH 4 across all oxides, but decreases at more basic pH due to increased OH− competition. Generally, oxides more abundant in surface OH can also accommodate more surface F, establishing F− ions as effective probes. While terminal F are likely the preferential substitution product, bridging F also appear to form at lower pH levels. Furthermore, fluoride substitution is applied to a series of Co3O4 gradually enriched with defects using pulsed laser defect engineering in liquid (PUDEL). This approach reveals a linear correlation between laser processing and surface OH density, which aligns with a previously observed improvement in OER activity, and is supported by additional DFT calculations here. This work will stimulate further studies adopting fluoride substitution to better understand the relationship between surface chemistry and catalytic processes in aqueous environments.

Over the last decade, the CO2 reduction reaction (CO2RR) has been increasingly exploited for the synthesis of high‐value raw materials in gaseous or liquid form, although no examples of CO2 fixation in nanoparticle systems have been demonstrated. Herein, CO2 fixation into solid nanomaterials by laser synthesis and processing of gold colloids in water, traditionally considered a green approach leading to ligand‐free nanoparticles without the formation of by‐products, is reported. If carbon monoxide‐rich gold nanoparticles are observable even after synthesis in deionized water, the presence of CO2 derivatives in alkaline water environment leads to C2 and C3 coupling with the production of carboxylic acids as a typical CO2RR fingerprint. While laser processing of preformed gold colloids is selective for C2 coupling, both C2 and C3 coupling to lactic acid are observed during pulsed laser ablation of a gold target. In the latter case, it is demonstrated that it is possible to synthesize photoluminescent organometallic nanocomposites in the blue spectral region with a quantum yield of about 20% under adequate experimental conditions. In this research, new pathways are offered to be explored in energetics, photonics, catalysis, and synthesis at the nanoscale.