Inertial Effects on the Stress Generation of Active Fluids

Suspensions of self-propelled bodies generate a unique mechanical stress owing to their motility that impacts their large-scale collective behavior. For microswimmers suspended in a fluid with negligible particle inertia, we have shown that the virial `swim stress' is a useful quantity to understand the rheology and nonequilibrium behaviors of active soft matter systems. For larger self-propelled organisms like fish, it is unclear how particle inertia impacts their stress generation and collective movement. Here, we analyze the effects of finite particle inertia on the mechanical pressure (or stress) generated by a suspension of self-propelled bodies. We find that swimmers of all scales generate a unique `swim stress' and `Reynolds stress' that impacts their collective motion. We discover that particle inertia plays a similar role as confinement in overdamped active Brownian systems, where the reduced run length of the swimmers decreases the swim stress and affects the phase behavior. Although the swim and Reynolds stresses vary individually with the magnitude of particle inertia, the sum of the two contributions is independent of particle inertia. This points to an important concept when computing stresses in computer simulations of nonequilibrium systems---the Reynolds and the virial stresses must both be calculated to obtain the overall stress generated by a system

Range-Point Migration-Based Image Expansion Method Exploiting Fully Polarimetric Data for UWB Short-Range Radar

Ultrawideband radar with high-range resolution is a promising technology for use in short-range 3-D imaging applications, in which optical cameras are not applicable. One of the most efficient 3-D imaging methods is the range-point migration (RPM) method, which has a definite advantage for the synthetic aperture radar approach in terms of computational burden, high accuracy, and high spatial resolution. However, if an insufficient aperture size or angle is provided, these kinds of methods cannot reconstruct the whole target structure due to the absence of reflection signals from large part of target surface. To expand the 3-D image obtained by RPM, this paper proposes an image expansion method by incorporating the RPM feature and fully polarimetric data-based machine learning approach. Following ellipsoid-based scattering analysis and learning with a neural network, this method expresses the target image as an aggregation of parts of ellipsoids, which significantly expands the original image by the RPM method without sacrificing the reconstruction accuracy. The results of numerical simulation based on 3-D finite-difference time-domain analysis verify the effectiveness of our proposed method, in terms of image-expansion criteria

Fabrication of highly dense SiN4 ceramics without additives by high pressure sintering

Silicon nitride (Si3N4) is one of candidate materials for the engineering ceramics which is used at high temperatures. The mechanical strengths of hot pressed or sintered Si2N4 ceramics containing some amount of additives, however, are deteriorated at elevated temperatures. To improve the high temperature strength of Si3N4 ceramics, an attempt to consolidate Si3N4 without additives was made by high pressure sintering technique. Scanning electron micrographs of fracture surfaces of the sintered bodies showed the bodies had finely grained and fully self-bonded sintered bodies were 310N sq m at room temperature and 174N/sq m at 1200 C

Studies on the metabolism of connective tissue

A granuloma pouch was formed on the back of rats by the original method of SELYE. Seven days when granuloma tissue reached its maximum, 35S labeled ChS, 59Fe labeled ChS-Fe, labeled ferric ammoninum citrate and colloidal 198Au were injected into the pouch and their absorption and organ distribution examined and compared with the results in the case where 59Fe labeled ferric ammoninum citrate and colloidal 198Au were injected into the gluteal muscle. 1. When 35S labeled ChS was injected into the granuloma pouch, radioactivity of the organs per gram tissue was high in the kidney, liver, bone marrow and spleen, in descending order. The maximum activity was seen 12 to 24 hours after injection, which is slow compared to the results obtained by KISHIDA in intraperitoneal and oral administration. 2. The absorption of Ch S-Fe by pouch where the iron is enveloped by the large ChS molecule, is slower than that of ferric ammonium citrate, an inorganic compound. 3. The uptake of Fe from the blood by bone marrow is larger when the increase of blood Fe ion concentration is slow, rater than when the increase is rapid. 4. When conoidal 198Au is injected into the pouch and injected into the&#34; gluteal muscle, the 198Au is phargocytozed by the reticuloendothelial system organs, the liver showing the largest uptake among all organs. 5. In the intramuscular injection of colloidal 198Au and 59Fe labeled ferric ammonium citrate, radioactivity of pouch fluid is lower than that of blood. However, the difference between the two is less in the case of colloidal 198Au. 6. In the granuloma ponch, radioactivity of the abdominal wall proves to be greater than that of the dorsal wall.</p

Swim stress, motion, and deformation of active matter: effect of an external field

We analyze the stress, dispersion, and average swimming speed of self-propelled particles subjected to an external field that affects their orientation and speed. The swimming trajectory is governed by a competition between the orienting influence (i.e., taxis) associated with the external (e.g., magnetic, gravitational, thermal, nutrient concentration) field versus the effects that randomize the particle orientations (e.g., rotary Brownian motion and/or an intrinsic tumbling mechanism like the flagella of bacteria). The swimmers' motion is characterized by a mean drift velocity and an effective translational diffusivity that becomes anisotropic in the presence of the orienting field. Since the diffusivity yields information about the micromechanical stress, the anisotropy generated by the external field creates a normal stress difference in the recently developed “swim stress” tensor [Takatori, Yan, and Brady, Phys. Rev. Lett., 2014]. This property can be exploited in the design of soft, compressible materials in which their size, shape, and motion can be manipulated and tuned by loading the material with active swimmers. Since the swimmers exert different normal stresses in different directions, the material can compress/expand, elongate, and translate depending on the external field strength. Such an active system can be used as nano/micromechanical devices and motors. Analytical solutions are corroborated by Brownian dynamics simulations

Superfluid Behavior of Active Suspensions from Diffusive Stretching

The current understanding is that the non-Newtonian rheology of active matter suspensions is governed by fluid-mediated hydrodynamic interactions associated with active self-propulsion. Here we discover an additional contribution to the suspension shear stress that predicts both thickening and thinning behavior, even when there is no nematic ordering of the microswimmers with the imposed flow. A simple micromechanical model of active Brownian particles in homogeneous shear flow reveals the existence of off-diagonal shear components in the swim stress tensor, which are independent of hydrodynamic interactions and fluid disturbances. Theoretical predictions from our model are consistent with existing experimental measurements of the shear viscosity of active suspensions, but also suggest new behavior not predicted by conventional models

A theory for the phase behavior of mixtures of active particles

Systems at equilibrium like molecular or colloidal suspensions have a well-defined thermal energy k_BT that quantifies the particles' kinetic energy and gauges how “hot” or “cold” the system is. For systems far from equilibrium, such as active matter, it is unclear whether the concept of a “temperature” exists and whether self-propelled entities are capable of thermally equilibrating like passive Brownian suspensions. Here we develop a simple mechanical theory to study the phase behavior and “temperature” of a mixture of self-propelled particles. A mixture of active swimmers and passive Brownian particles is an ideal system for discovery of the temperature of active matter and the quantities that get shared upon particle collisions. We derive an explicit equation of state for the active/passive mixture to compute a phase diagram and to generalize thermodynamic concepts like the chemical potential and free energy for a mixture of nonequilibrium species. We find that different stability criteria predict in general different phase boundaries, facilitating considerations in simulations and experiments about which ensemble of variables are held fixed and varied

カンジダ特異的IgG(4)抗体と気管支喘息

Serum levels of Candida-specific IgG(4) antibodies were examined in 66 patients with bronchial asthma, relating to patient age and asthma severity. 1. The levels of Candida-specific IgG(4) antibodies were the highest in patients with 60+years of age, compared to the levels in cases with 0-39 and 40-59 years of age. 2. In cases with 40-59 years of age, the levels of Candida-specific IgG(4) were significantly higher in cases with long-term steroid therapy (severe intractable asthma) than in cases without steroid regimen. The results suggest that increased levels of Candida-specific IgG(4) were observed in relation to patient age and asthma severity.66例の気管支喘息症例を対象に，血清中カンジダ特異的lgG(4)抗体を測定し，その血中レベルと年齢および喘息の重症度との関連について検討を加えた。1．血清カンジダ特異的IgG(4)値は，0～39才，40～59才の年齢層にくらべ，60才以上の年齢層において高く，年齢によりその値が変動することが 示唆された。2．40～59才の年齢層では，血清カンジダ特異的IgG(4)は，ステロイド非使用例にくらべ，ステロイド依存性重症難治性喘息症例で有意の高値を示し，この年齢層では，カンジダ特異的IgG(4)抗体がその発症病態に関連している可能性が示唆された。以上，カンジダ特異的IgG(4)抗体の上昇は，高年齢層の症例（60才以上）では全般的に，また40～59才の年齢層で重症型喘息症例において観察されることが明らかにされた