Hasil untuk "physics.app-ph"

B. Poole, S. Ohkuma

The spectral characteristics of dextran, labeled with fluorescein, depend upon pH. We have loaded the lysosomes of mouse peritoneal macrophages with this fluorescence probe and used it to measure the intralysosomal pH under various conditions. The pH of the medium has no effect on the intralysosomal pH. Weakly basic substances in the medium cause a concentration-dependent increase in the intralysosomal pH. However, the concentration of base necessary to produce a significant change in the intralysosomal pH varies over a wide range for different bases. The active form of the base is the neutral, unprotonated form. Although most of these weak bases cause an increase in the volume of the lysosomes, increase in lysosomal volume itself causes only a minor perturbation of the intralysosomal pH. This was demonstrated in cells whose lysosomes were loaded with sucrose, and in cells vacuolated as a demonstrated in cells whose lysosomes were loaded with sucrose, and in cells vacuolated as a consequence of exposure to concanavalin A. The results of these studies are interpreted in terms of energy-dependent lysosomal acidification and leakage of protons out of the lysosomes in the form of protonated weak bases.

A. Görg, W. Postel, S. Günther

J. Skehel, P. Bayley, E. Brown et al.

W. Busa, R. Nuccitelli

W. Moolenaar, R. Tsien, P. Saag et al.

B. S. Stein, B. S. Stein, S. D. Gowda et al.

I. H. Madshus

Benjamin Sims, David Sims, Sergey V. Baryshev et al.

We present the design and characterization of a dual-mode radiofrequency (rf) cavity, a novel electromagnetic structure with potential benefits such as compactness, efficiency, cost reduction and multifunctionality. The cavity was designed to balance the dual-mode structure considering several factors, such as mode frequencies, quality factor (Q-factor), and minimizing cross talk between couplers. We preformed various tests to verify that this cavity preformed as expected compared to simulated results. As exampled here, a combination of the the fundamental mode TM 010 and the TM 011 mode, tuned to a harmonic of the fundamental, was realized to linearize the off-crest electric field, thereby enabling concurrent bunching and acceleration of charged particle (e.g. electrons) beam in high power systems. The reduction in the number of cavities required to bunch and accelerate promises cost and space savings over conventional approaches. This research lays the foundation for further exploration of multi-mode cavity applications and optimization for specific use cases, with potential implications for a wide range of fields including quantum information platforms.

Dingxin Sun, Yi Chen, Xiaoning Liu et al.

The asymmetric transformation elasticity offers a promising method to control elastic waves. However, this method requires elastic materials that support asymmetric stresses, which is not objective within the Cauchy elasticity framework. Nevertheless, asymmetric stress tensor is a typical feature of micropolar continuum theory. Yet, possible connection between micropolar continuum theory and the asymmetric elasticity transformation has remained elusive. Here, we demonstrate that extremal micropolar media, which refer to micropolar media with easy deformation modes, can be used to design elastic cloaks following the asymmetric transformation method. A metamaterial model is proposed to achieve the required extremal micropolar parameters for cloaking. We further design a two-dimensional metamaterial cloak and verify its cloaking performance numerically. An excellent agreement between the metamaterial cloak simulation and an effective-medium calculation is obtained. This study unveils a novel strategy for controlling elastic waves through micropolar media and also sheds light on interesting properties of extremal micropolar materials.

Mingwei Xu, Ronghui Quan, Yunjia Yao

The Magnetic Sail is a space propulsion system that utilizes the interaction between solar wind particles and an artificial dipole magnetic field generated by a spacecraft's coil to produce thrust without the need for additional plasma or propellant. To reduce the size of the sail while improving the efficiency of capturing solar wind, a new type of rotating magnetic sail with an initial rotation speed is proposed. This study evaluates the thrust characteristics, attitude, and size design factors of a rotating magnetic sail using a 3-D single-component particle numerical simulation. The results show that an increase in rotational speed significantly increases the thrust of the rotating magnetic sail. The thrust is most significant when the magnetic moment of the sail is parallel to the direction of particle velocity. The study also found that the potential for the application of the rotating magnetic sail is greatest in orbits with high-density and low-speed space plasma environments. It suggests that a rotating magnetic sail with a magnetic moment (Mm) of 10^3-10^4 Am^2 operating at an altitude of 400 km in Low Earth Orbit (LEO) can achieve a similar thrust level to that of a rotating magnetic sail operating at 1 AU (astronomical unit) of 10^7-10^8 Am^2.

Marius Constantin Chirita Mihaila, Gabriel Lukas Szabo, Alexander Redl et al.

We present an efficient method to produce laser-triggered proton pulses well below 500 ps pulse width at keV energies. We use femtosecond photoelectron pulses emitted from a cathode to enable ultrafast electron-stimulated desorption of adsorbates on a stainless steel plate under ultrahigh vacuum conditions. While direct photoionization of atoms to form well-timed ion pulses can suffer from a laser-focus-limited large starting volume, in our method the two-dimensional starting plane of the ions is defined with nanometer precision at a solid surface. We clearly outline how the method could be used in the future to efficiently produce ion beam pulses in the (sub)picosecond range for pump-probe experiments with ions.

Antoine Demiquel, Vassos Achilleos, Georgios Theocharis et al.

In this paper, we study modulation instabilities (MI) in a one-dimensional chain configuration of a flexible mechanical metamaterial (flexMM). Using the lumped element approach, flexMMs can be modeled by a coupled system of discrete equations for the longitudinal displacements and rotations of the rigid mass units. In the long wavelength regime, and applying the multiple-scales method we derive an effective nonlinear Schrödinger equation for slowly varying envelope rotational waves. We are then able to establish a map of the occurrence of MI to the parameters of the metamaterials and the wavenumbers. We also highlight the key role of the rotation-displacement coupling between the two degrees of freedom in the manifestation of MI. All analytical findings are confirmed by numerical simulations of the full discrete and nonlinear lump problem. These results provide interesting design guidelines for nonlinear metamaterials offering either stability to high amplitude waves, or conversely being good candidates to observe instabilities.

S. Zhu, F. Crisa, M. Bal et al.

We present measurements and simulations of superconducting Nb co-planar waveguide resonators on sapphire substrate down to millikelvin temperature range with different readout powers. In the high temperature regime, we demonstrate that the Nb film residual surface resistance is comparable to that observed in the ultra-high quality, bulk Nb 3D superconducting radio frequency cavities while the resonator quality is dominated by the BCS thermally excited quasiparticles. At low temperature both the resonator quality factor and frequency can be well explained using the two-level system models. Through the energy participation ratio simulations, we find that the two-level system loss tangent is $\sim 10^{-2}$, which agrees quite well with similar studies performed on the Nb 3D cavities.

K. Ulbrich, V. Šubr

S. Angelos, Yingwei Yang, K. Patel et al.

Mohammad Saber Hashemi, Karl H. Kraus, Azadeh Sheidae

A tunable stiffness bone rod was designed, optimized, and 3D printed to address the common shortcomings of existing bone rods in the healing of long fractured bones. The common deficiencies of existing bone fixations are high stiffness, thereby negligible flexibility in deformation for best bone growth results, and stress-shielding effect. Our novel design framework provides the surgeons with ready-for-3D-printing patient-specific designs, optimized to have desired force-displacement response with a stopping mechanism for preventing further deformation under higher than usual loads such as falling. The framework is a design optimization based on the multi-objective genetic algorithm (GA) optimization to quantify the objectives, tunning the varied stiffness while minimizing the maximum Mises stress of the model to avoid plastic and permanent deformation of the bone rod. The optimum design computational framework of tunable stiffness material presented in this paper is not specific for a tibia bone rod. It can be used for any application where bilinear stiffness is desirable.

Tommaso Ghigna, Mario Zannoni, Michael Jones et al.

Radio, millimetre and sub-millimetre astronomy experiments as well as remote sensing applications often require castable absorbers with well known electromagnetic properties to design and realize calibration targets. In this context, we fabricated and characterized two samples using different ratios of two easily commercially available materials: epoxy (Stycast 2850FT) and magnetite ($\mathrm{Fe_{3}O_{4}}$) powder. We performed transmission and reflection measurements from 7 GHz up to 170 GHz with a VNA equipped with a series of standard horn antennas. Using an empirical model we analysed the data to extract complex permittivity and permeability from transmission data; then we used reflection data to validate the results. In this paper we present the sample fabrication procedure, analysis method, parameter extraction pipeline, and results for two samples with different epoxy-powder mass ratios.

Jixing Zhang, Lixia Xu, Guodong Bian et al.

Diamond nitrogen-vacancy (NV) center magnetometry has recently received considerable interest from researchers in the fields of applied physics and sensors. The purpose of this review is to analyze the principle, sensitivity, technical development potential, and application prospect of the diamond NV center magnetometry. This review briefly introduces the physical characteristics of NV centers, summarizes basic principles of the NV center magnetometer, analyzes the theoretical sensitivity, and discusses the impact of technical noise on the NV center magnetometer. Furthermore, the most critical technologies that affect the performance of the NV center magnetometer are described: diamond sample preparation, microwave manipulation, fluorescence collection, and laser excitation. The theoretical and technical crucial problems, potential solutions and research technical route are discussed. In addition, this review discusses the influence of technical noise under the conventional technical conditions and the actual sensitivity which is determined by the theoretical sensitivity and the technical noise. It is envisaged that the sensitivity that can be achieved through an optimized design is in the order of 10 fT/Hz^1/2. Finally, the roadmap of applications of the diamond NV center magnetometer are presented.

Robert Zimmermann, Michael Seidling, Peter Hommelhoff

We report guiding and manipulation of charged particle beams by means of electrostatic optics based on a principle similar to the electrodynamic Paul trap. We use hundreds of electrodes fabricated on planar substrates and supplied with static voltages to create a ponderomotive potential for charged particles in motion. Shape and strength of the potential can be locally tailored by the electrodes' layout and the applied voltages, enabling the control of charged particle beams within precisely engineered effective potentials. We demonstrate guiding of electrons and ions for a large range of energies (from 20 to 5000 eV) and masses (5E-4 to 131 atomic mass units) as well as electron beam splitting as a proof-of-concept for more complex beam manipulation. Simultaneous confinement of charged particles with different masses is possible, as well as guiding of electrons with energies in the keV regime, and the creation of highly customizable potential landscapes, which is all hard to impossible with conventional electrodynamic Paul traps.

Conal E. Murray

A strategy aimed at decreasing dielectric loss in coplanar waveguides (CPW) and qubits involves the creation of trenches in the underlying substrate within the gaps of the overlying metallization. Participation of contamination layers residing on surfaces and interfaces in these designs can be reduced due to the change in the effective dielectric properties between the groundplane and conductor metallization. Although finite element method approaches have been previously applied to quantify this decrease, an analytical method is presented that can uniquely address geometries possessing small to intermediate substrate trench depths. Conformal mapping techniques produce transformed CPW and qubit geometries without substrate trenching but a non-uniform contamination layer thickness. By parametrizing this variation, one can calculate surface participation through the use of a two-dimensional, analytical approximation that properly captures singularities in the electric field intensity near the metallization corners and edges. Examples demonstrate two regimes with respect to substrate trench depth that capture an initial increase in substrate-to-air surface participation due to the trench sidewalls and an overall decrease in surface participation due to the reduction in the effective dielectric constant, and are compared to experimental measurements to extract loss tangents on this surface.