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Institute
Vertebrate life depends on renal function to filter excess fluid and remove low-molecular-weight waste products. An essential component of the kidney filtration barrier is the slit diaphragm (SD), a specialized cell-cell junction between podocytes. Although the constituents of the SD are largely known, its molecular organization remains elusive. Here, we use super-resolution correlative light and electron microscopy to quantify a linear rate of reduction in albumin concentration across the filtration barrier. Next, we use cryo-electron tomography of vitreous lamellae from high-pressure frozen native glomeruli to analyze the molecular architecture of the SD. The resulting densities resemble a fishnet pattern. Fitting of Nephrin and Neph1, the main constituents of the SD, results in a complex interaction pattern with multiple contact sites between the molecules. Using molecular dynamics flexible fitting, we construct a blueprint of the SD, where we describe all interactions. Our architectural understanding of the SD reconciles previous findings and provides a mechanistic framework for the development of novel therapies to treat kidney dysfunction.
Vertebrate life depends on renal function to filter excess fluid and remove low-molecular-weight waste products. An essential component of the kidney filtration barrier is the slit diaphragm (SD), a specialized cell-cell junction between podocytes. Although the constituents of the SD are largely known, its molecular organization remains elusive. Here, we use super-resolution correlative light and electron microscopy to quantify a linear rate of reduction in albumin concentration across the filtration barrier under no-flow conditions. Next, we use cryo-electron tomography of vitreous lamellae from high-pressure frozen native glomeruli to analyze the molecular architecture of the SD. The resulting densities resemble a fishnet pattern. Fitting of Nephrin and Neph1, the main constituents of the SD, results in a complex interaction pattern with multiple contact sites between the molecules. Using molecular dynamics simulations, we construct a blueprint of the SD that explains its molecular architecture. Our architectural understanding of the SD reconciles previous findings and provides a mechanistic framework for the development of novel therapies to treat kidney dysfunction.
Supermassive black hole binaries (SMBHBs) are among the most powerful known sources of gravitational waves (GWs). Accordingly, these systems could dominate the stochastic gravitational wave background (GWB) in the micro- and millihertz frequency range. The time until the merger of two SMBHs in the nucleus of a galaxy can be shortened through dynamical friction due to the presence of dark matter (DM) spikes around the SMBHs. To calculate the orbital evolution of individual SMBHBs within the Newtonian approximation, the SMBHBpy code is developed. This work confirms that the GW signals from SMBHBs with DM spikes can be clearly distinguished from those without any matter. Making use of the upper limit on the characteristic strain of the GWB derived from the data of the Cassini spacecraft mission in 2001/2002, a lower limit on the matter density around SMBHBs is derived in this study. The result is subsequently compared with the theoretical density profiles for cold dark matter and self-interacting dark matter spikes.
Binary neutron star mergers represent unique observational phenomena because all four fundamental interactions play an important role at various stages of their evolution by leaving imprints in astronomical observables. This makes their accurate numerical modeling a challenging multiphysics problem that promises to increase our understanding of the high-energy astrophysics at play, thereby providing constraints for the underlying fundamental theories such as the gravitational interaction or the strong interaction of dense matter. For example, the first and so far only multi-messenger observation of the binary neutron star merger GW170817 resulted in numerous bounds on the parameters of isolated non-rotating neutron stars, e.g., their maximum mass or their distribution in radii, which can be directly used to constrain the equation of state of cold nuclear matter. While many of these results stem from the observation of the inspiral gravitational-wave signal, the postmerger phase of binary neutron star mergers encodes even more details about the extreme physics of hot and dense neutron star matter. In this Thesis we focus on the exploration of dissipative and shearing effects in binary neutron star mergers in order to identify novel approaches to constrain hot and dense neutron star matter.
The first effect is the well-motivated dissipation of energy due to the bulk viscosity which arises from violations of weak chemical equilibrium. We start by exploring the impact of bulk viscosity on black-hole accretion. This simplified problem gives us the opportunity to develop a test case for future codes taking into account the effects of dissipation in a fully general-relativistic setup and build intuition in the physics of relativistic dissipation. Next, we move on to isolated neutron stars and binary neutron star mergers by developing a robust implementation of bulk-viscous dissipation for numerical relativity simulations. We test our implementation by calculating the damping of eigenmodes of isolated neutron stars and the violent migration scenario. Finally, we present the first results on the impact of bulk viscosity on binary neutron star mergers. We identify a number of ways how bulk viscosity impacts the postmerger phase, out of which the suppression of gravitational-wave emission and dynamical mass ejection are the most notable ones.
In the last part of this Thesis we investigate how the shearing dynamics at the beginning of the merger affects the amplification of different initial magnetic-field topologies. We explore the hypothesis that magnetic fields which are located only in a small region near the stellar surface prior to merger lead to a weaker magnetic-field amplification. We show first evidence which confirms this hypothesis and discuss possible implications for constraining the physics of superconduction in cold neutron stars.
We continue previous investigations of the (inhomogeneous) phase structure of the Gross-Neveu model in a noninteger number of spatial dimensions (1≤d<3) in the limit of an infinite number of fermion species (N→∞) at (non)zero chemical potential μ. In this work, we extend the analysis from zero to nonzero temperature T.
The phase diagram of the Gross-Neveu model in 1≤d<3 spatial dimensions is well known under the assumption of spatially homogeneous condensation with both a symmetry broken and a symmetric phase present for all spatial dimensions. In d=1 one additionally finds an inhomogeneous phase, where the order parameter, the condensate, is varying in space. Similarly, phases of spatially varying condensates are also found in the Gross-Neveu model in d=2 and d=3, as long as the theory is not fully renormalized, i.e., in the presence of a regulator. For d=2, one observes that the inhomogeneous phase vanishes, when the regulator is properly removed (which is not possible for d=3 without introducing additional parameters).
In the present work, we use the stability analysis of the symmetric phase to study the presence (for 1≤d<2) and absence (for 2≤d<3) of these inhomogeneous phases and the related moat regimes in the fully renormalized Gross-Neveu model in the μ,T-plane. We also discuss the relation between "the number of spatial dimensions" and "studying the model with a finite regulator" as well as the possible consequences for the limit d→3.
Inhomogeneous condensation in the Gross-Neveu model in noninteger spatial dimensions 1 ≤ d < 3
(2023)
The Gross-Neveu model in the N→∞ limit in d=1 spatial dimensions exhibits a chiral inhomogeneous phase (IP), where the chiral condensate has a spatial dependence that spontaneously breaks translational invariance and the Z2 chiral symmetry. This phase is absent in d=2, while in d=3 its existence and extent strongly depends on the regularization and the value of the finite regulator. This work connects these three results smoothly by extending the analysis to noninteger spatial dimensions 1≤d<3, where the model is fully renormalizable. To this end, we adapt the stability analysis, which probes the stability of the homogeneous ground state under inhomogeneous perturbations, to noninteger spatial dimensions. We find that the IP is present for all d<2 and vanishes exactly at d=2. Moreover, we find no instability toward an IP for 2≤d<3, which suggests that the IP in d=3 is solely generated by the presence of a regulator.
We show the absence of an instability of homogeneous (chiral) condensates against spatially inhomogeneous perturbations for various (2+1)-dimensional four-fermion and Yukawa models. All models are studied at nonzero baryon chemical potential, while some of them are also subjected to chiral and isospin chemical potential. The considered theories contain up to 16 Lorentz-(pseudo)scalar fermionic interaction channels. We prove the stability of homogeneous condensates by analyzing the bosonic two-point function, which can be expressed in a purely analytical form at zero temperature. Our analysis is presented in a general manner for all of the different discussed models. We argue that the absence of an inhomogeneous chiral phase (where the chiral condensate is spatially nonuniform) follows from this lack of instability. Furthermore, the existence of a moat regime, where the bosonic wave-function renormalization is negative, in these models is ruled out.
A synchrotron is a particular type of cyclic particle accelerator and the first accelerator concept to enable the construction of large-scale facilities [10], such as the largest particle accelerator in the world, the 27-kilometre-circumference Large Hadron Collider (LHC) by CERN near Geneva, Switzerland, the European Synchrotron Radiation Facility (ESRF) in Grenoble, France for the synchrotron radiation, the superconducting, heavy ion synchrotron SIS100 under construction for the FAIR facility at GSI, Darmstadt, Germany and so on. Unlike a cyclotron, which can accelerate particles starting at low kinetic energy, a synchrotron needs a pre-acceleration facility to accelerate particles to an appropriate initial value before synchrotron injection. A pre-acceleration can be realized by a chain of other accelerator structures like a linac, a microtron in case of electrons, for example, Proton and ion injectors Linac 4 and Linac 3 for the LHC, UNLAC as the injector for the SIS18 in GSI and in future the SIS18 as injector for the SIS100. The linac is a commonly used injector for the ion synchrotron and consists of some key components. The three main parts of a linac are: An ion source creating the particles, a buncher system or an RFQ followed by the main drift tube accelerator DTL. In order to meet the energy and the beam current requirement of a synchrotron injector linac, its cost is a remarkable percentage of the total facility costs.
However, the normal conducting linac operation at cryogenic temperatures can be a promising solution in improving the efficiency and reducing the costs of a linac. Synchrotron injectors operate at very low duty factor with beam pulse lengths in 1 micros to 100 micros range, as most of the time is needed to perform the synchrotron cycle. Superconducting linacs are not convenient, as they cannot efficiently operate at low duty factor and high beam currents.
The cryogenic operation of ion linacs is discussed and investigated at IAP in Frankfurt since around 2012 [1, 37]. The motivation was to develop very compact synchrotron injectors at reduced overall linac costs per MV of acceleration voltage. As the needed beam currents for new facilities are increasing as well, the new technology will also allow an efficient realization of higher injector linac energies, which is needed in that case. Operating normal conducting structures at cryogenic temperature exploits the significantly higher conductivity of copper at temperatures of liquid nitrogen and below. On the other hand, the anomalous skin effect reduces the gain in shunt impedance quite a bit[25, 31, 9]. Some intense studies and experiments were performed recently, which are encouraging with respect to increased field levels at linac operation temperatures between 30 K and 70 K [17, 24, 4, 23, 5, 8]. While these studies are motivated by applications in electron acceleration at GHz-frequencies, the aim of this paper is to find applications in the 100 to 700 MHz range, typical for proton and ion acceleration. At these frequencies, a higher impact in saving RF power is expected due to the larger skin depth, which is proportional to the frequency to the power of negative half with respect to the normal skin effect. On the other hand, it is assumed that the improvement in maximum surface field levels will be similar to what was demonstrated already for electron accelerator cavities. This should allow to find a good compromise between reduced RF power needs for achieving a given accelerator voltage and a reduced total linac length to save building costs.
A very important point is the temperature stability of the cavity surface during the RF pulse. This is of increasing importance the lower the operating temperature is chosen: the temperature dependence of the electric conductivity in copper gets rather strong below 80 K, as long as the RRR - value of the copper is adequate. It is very clear, that this technology is suited for low duty cycle operated cavities only - with RF pulse lengths below one millisecond. At longer pulses the cavity surface will be heated within the pulse to temperatures, where the conductivity advantage is reduced substantially. These conditions fit very well to synchrotron injectors or to pulsed beam power applications.
H – Mode structures of the IH – and of the CH – type are well-known to have rather small cavity diameters at a given operating frequency. Moreover, they can achieve effective acceleration voltage gains above 10 MV/m even at low beam energies, and already at room temperature operation[29]. With the new techniques of 3d – printing of stainless steel and copper components one can reduce cavity sizes even further – making the realization of complex cooling channels much easier.
Another topic are copper components in superconducting cavities – like power couplers. It is of great importance to know exactly the thermal losses at these surfaces, which can’t be cooled efficiently in an easy way.
In this work we study the 3+1-dimensional Nambu-Jona-Lasinio (NJL) model in the mean field-approximation. We carry out calculations using five different regularization schemes (two continuum and three lattice regularization schemes) with particular focus on inhomogeneous phases and condensates. The regularization schemes lead to drastically different inhomogeneous regions. We provide evidence that inhomogeneous condensates appear for all regularization schemes almost exclusively at values of the chemical potential and with wave numbers, which are of the order of or even larger than the corresponding regulators. This can be interpreted as indication that inhomogeneous phases in the 3+1-dimensional NJL model are rather artifacts of the regularization and not a consequence of the NJL Lagrangian and its symmetries.
In the last twenty years, a variety of unexpected resonances had been observed within the charmonium mass region. Although the existence of unconventional states has been predicted by the quantum chromodynamics (QCD), a quantum field theory describing the strong force, a clear evidence was missing. The Y(4260) is such an unexpected and supernummerary state, first observed at BaBar in 2005, and aroused great interest, because it couples much stronger to hidden charm decays (charm-anticharm states like J/Psi or h_c) instead of open charm decays (D meson pairs). This is unusual for states with masses above the D anti-D threshold. Furthermore, it decays into a charged exotic state Y(4260)->Z_c(3900)^+- pi^-+. The charge of the Z_c(3900)^+- is an indication that it comprises of two more quarks than the charm-anticharm pair, and could therefore be assumed to be a four-quark state. Due to these still not understood properties of these QCD-allowed states, they are referred to as exotic XYZ states to emphasize their particularity.
In 2017, the collaboration of the Beijing Spectrometer III (BESIII) investigated the production reaction of the Y(4260) resonance based on a high-luminosity data set. This significantly improved precision of the measurement of the cross-section sigma(e+e- -> J/Psi pi^+ pi^-) permitted a resolution into two resonances, the Y(4230) and the Y(4360). The Z_c(3900)^+- had been discovered by the BESIII collaboration in 2013, thus this experiment at the Beijing Electron-Positron Collider II (BEPCII) is a top-performing facililty to study exotic charmonium-like states.
In this work, an inclusive reconstruction of the strange hyperon Lambda in the charmonium mass region is performed to study possible decays of Y states in order to provide further insight into their nature. Finding more states or new decay channels may provide crucial hints to understand the strong interaction beyond nonperturbative approaches.
Three resonances are observed in the energy dependent cross-section: the first with a mass of (4222.01 +- 5.68) MeV and a width of (154.26 +- 28.16) MeV, the second with a mass of (4358.88 +- 4.97) MeV and a width of (49.58 +- 13.54) MeV and the third with a mass of (4416.41 +- 2.37) MeV and a width of (23.88 +- 7.18) MeV. These resonances, with a statistical significance Z > 5sigma, can be interpreted as the states Y(4230), Y(4360) and psi(4415).
Additionally, a proton momentum-dependent analysis strategy has been used in terms of the inclusiveness of the reconstruction and to address the momentum discrepancies between generic MC and measured data.