Peptide hydrogels from twisted ribbon aggregates

We have studied the rheology of an aqueous solution phase formed in the model peptide system A10K (A=alanine, K=lysine), where the short hydrophobic peptides self-assemble into twisted ribbon structures consisting of laminated beta-sheets. The ribbons are crystalline in 2 dimensions, therefore rigid, and they are weakly charged. The average ribbon lengths, \u3cL \u3e≈ 60 nm, corresponding to an aspect ratio, L/d≈10. With increasing concentration a transition from a viscous liquid into a gel-like solid occurs around a volume fraction f ≈ 0.02, that we identify as the overlap concentration f*. Coinciding with the overlap concentration is also a phase transition, from the low concentration isotropic liquid phase to a nematic phase. This concentration is significantly lower than what is predicted for hard rods by Onsager theory for this given aspect ratio. We attribute this to the ribbon charge and long range electrostatic interactions, stabilizing the nematic phase. In this nematic phase, the storage modulus G’ increases strongly with increasing Please click Additional Files below to see the full abstract

Kathetergestützte Aortenklappenimplantation: Was müssen Anästhesisten wissen?

Zusammenfassung: Der chirurgische Aortenklappenersatz gilt als Goldstandard in der Therapie der hochgradigen Aortenklappenstenose. Die veränderte Demografie konfrontiert die behandelnden medizinischen Fachdisziplinen jedoch mit einem zunehmend höheren Risikoprofil der Patienten; dies machte die Entwicklung neuer weniger invasiver Behandlungsalternativen in der operativen Therapie der Aortenklappenstenose erforderlich. Dieser Entwicklungsprozess führte über die Minithorakotomie hin zur kathetergestützten Aortenklappenimplantation ("transcatheter aortic valve implantation", TAVI). Die TAVI ist ein neues therapeutisches Verfahren zur Behandlung von Patienten mit hochgradiger Aortenklappenstenose und hohem perioperativen Morbiditäts- sowie Mortalitätsrisiko für einen konventionellen Aortenklappenersatz. Da die TAVI am schlagenden Herzen ohne Sternotomie und Herz-Lungen-Maschine durchgeführt werden kann, eignet sich dieses Verfahren insbesondere für den älteren, multimorbiden und/oder kardial voroperierten Patienten. Die ersten Ergebnisse großer prospektiver Multizenterstudien unterstreichen den Stellenwert der TAVI in der modernen Behandlung von Hochrisikopatienten mit symptomatischer Aortenklappenstenose. Die TAVI erfordert vom Anästhesisten neben dem Verständnis des chirurgischen Ablaufs die genaue Kenntnis des perioperativen anästhesiologischen Managements und der möglichen Komplikationen des Verfahren

Heating and Trapping of Electrons in ECRIS from Scratch to Afterglow

Plasmas in Electron Cyclotron Resonance Ion Sources (ECRIS) are collisionless and can therefore be simulated by just following the motion of electrons in the confining static magnetic and oscillating microwave (MW) electric field of ECRIS. With a powerful algorithm the three-dimensional trajectories of 104 ECR-heated and confined electrons are calculated in a standard ECRIS with a deep minimum of |B| and a new ECRIS with a very flat minimum of |B|. The spatial electron (plasma) densities and electron energy densities deduced from these trajectories yield new and surprising insight in the performance of ECRIS. With computer animation we plan to present: The energy increase of certain electrons on extremely stable trajectories, the power dependence of the electron energy density up to the X-ray collapse, the time dependent build up of the electron density and energy density distributions, and the time evolution of these electron distributions under afterglow conditions

Saturable discrete vector solitons in one-dimensional photonic lattices

Localized vectorial modes, with equal frequencies and mutually orthogonal polarizations, are investigated both analytically and experimentally in a one-dimensional photonic lattice with saturable nonlinearity. It is shown that these modes may span over many lattice elements and that energy transfer among the two components is both phase and intensity dependent. The transverse electrically polarized mode exhibits a single-hump structure and spreads in cascades in saturation, while the transverse magnetically polarized mode exhibits splitting into a two-hump structure. Experimentally such discrete vector solitons are observed in lithium niobate lattices for both coherent and mutually incoherent excitations.Comment: 4 pages, 5 figures (reduced for arXiv

Extending PT symmetry from Heisenberg algebra to E2 algebra

The E2 algebra has three elements, J, u, and v, which satisfy the commutation relations [u,J]=iv, [v,J]=-iu, [u,v]=0. We can construct the Hamiltonian H=J^2+gu, where g is a real parameter, from these elements. This Hamiltonian is Hermitian and consequently it has real eigenvalues. However, we can also construct the PT-symmetric and non-Hermitian Hamiltonian H=J^2+igu, where again g is real. As in the case of PT-symmetric Hamiltonians constructed from the elements x and p of the Heisenberg algebra, there are two regions in parameter space for this PT-symmetric Hamiltonian, a region of unbroken PT symmetry in which all the eigenvalues are real and a region of broken PT symmetry in which some of the eigenvalues are complex. The two regions are separated by a critical value of g.Comment: 8 pages, 7 figure

Integrated Detector Control and Calibration Processing at the European XFEL

The European X-ray Free Electron Laser is a high-intensity X-ray light source currently being constructed in the area of Hamburg, that will provide spatially coherent X-rays in the energy range between $0.25\,\mathrm{keV}$ and $25\,\mathrm{keV}$. The machine will deliver $10\,\mathrm{trains/s}$, consisting of up to $2700\,\mathrm{pulses}$, with a $4.5\,\mathrm{MHz}$ repetition rate. The LPD, DSSC and AGIPD detectors are being developed to provide high dynamic-range Mpixel imaging capabilities at the mentioned repetition rates. A consequence of these detector characteristics is that they generate raw data volumes of up to $15\,\mathrm{Gbyte/s}$. In addition the detector's on-sensor memory-cell and multi-/non-linear gain architectures pose unique challenges in data correction and calibration, requiring online access to operating conditions and control settings. We present how these challenges are addressed within XFEL's control and analysis framework Karabo, which integrates access to hardware conditions, acquisition settings (also using macros) and distributed computing. Implementation of control and calibration software is mainly in Python, using self-optimizing (py) CUDA code, numpy and iPython parallels to achieve near-real time performance for calibration application.Comment: Proceeding ICALEPS 201

From the Feynman-Schwinger representation to the non-perturbative relativistic bound state interaction

We write the 4-point Green function in QCD in the Feynman-Schwinger representation and show that all the dynamical information are contained in the Wilson loop average. We work out the QED case in order to obtain the usual Bethe-Salpeter kernel. Finally we discuss the QCD case in the non-perturbative regime giving some insight in the nature of the interaction kernel.Comment: 25 pages, RevTex, 3 figures included, typos corrected, to appear in Phys. Rev. D 5

Host genetic factors determining COVID-19 susceptibility and severity.

The COVID-19 pandemic caused by the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) poses an unprecedented challenge to humanity. SARS-CoV-2 infections range from asymptomatic to severe courses of COVID-19 with acute respiratory distress syndrome (ARDS), multiorgan involvement and death. Risk factors for disease severity include older age, male sex, increased BMI and pre-existing comorbidities. Ethnicity is also relevant to COVID-19 susceptibility and severity. Host genetic predisposition to COVID-19 is now increasingly recognized and whole genome and candidate gene association studies regarding COVID-19 susceptibility have been performed. Several common and rare variants in genes related to inflammation or immune responses have been identified. We summarize research on COVID-19 host genetics and compile genetic variants associated with susceptibility to COVID-19 and disease severity. We discuss candidate genes that should be investigated further to understand such associations and provide insights relevant to pathogenesis, risk classification, therapy response, precision medicine, and drug repurposing

CPT-symmetric discrete square well

A new version of an elementary PT-symmetric square well quantum model is proposed in which a certain Hermiticity-violating end-point interaction leaves the spectrum real in a large domain of couplings $\lambda\in (-1,1)$. Within this interval we employ the usual coupling-independent operator P of parity and construct, in a systematic Runge-Kutta discrete approximation, a coupling-dependent operator of charge C which enables us to classify our P-asymmetric model as CPT-symmetric or, equivalently, hiddenly Hermitian alias cryptohermitian.Comment: 12 pp., presented to conference PHHQP IX (http://www.math.zju.edu.cn/wjd/

Spawning rings of exceptional points out of Dirac cones

The Dirac cone underlies many unique electronic properties of graphene and topological insulators, and its band structure--two conical bands touching at a single point--has also been realized for photons in waveguide arrays, atoms in optical lattices, and through accidental degeneracy. Deformations of the Dirac cone often reveal intriguing properties; an example is the quantum Hall effect, where a constant magnetic field breaks the Dirac cone into isolated Landau levels. A seemingly unrelated phenomenon is the exceptional point, also known as the parity-time symmetry breaking point, where two resonances coincide in both their positions and widths. Exceptional points lead to counter-intuitive phenomena such as loss-induced transparency, unidirectional transmission or reflection, and lasers with reversed pump dependence or single-mode operation. These two fields of research are in fact connected: here we discover the ability of a Dirac cone to evolve into a ring of exceptional points, which we call an "exceptional ring." We experimentally demonstrate this concept in a photonic crystal slab. Angle-resolved reflection measurements of the photonic crystal slab reveal that the peaks of reflectivity follow the conical band structure of a Dirac cone from accidental degeneracy, whereas the complex eigenvalues of the system are deformed into a two-dimensional flat band enclosed by an exceptional ring. This deformation arises from the dissimilar radiation rates of dipole and quadrupole resonances, which play a role analogous to the loss and gain in parity-time symmetric systems. Our results indicate that the radiation that exists in any open system can fundamentally alter its physical properties in ways previously expected only in the presence of material loss and gain