1,286 research outputs found
From the countryside to the cities: a comparative historical analysis of rural-urban migration in Russia and in the Soviet Union during the industrialization drive
Der vorliegende Beitrag untersucht die Voraussetzungen und Umstände in der UdSSR der 30er Jahre, die zu der bisher wohl schnellsten Verstädterung in der Weltgeschichte geführt haben. In der Periode von 1926 bis 1939 zogen ungefähr 19 bis 23 Millionen Landbewohner in die Städte (Zensusdaten). Der Autor fragt nach den 'pull'-Faktoren für diese Entwicklung: Löhne, Unabhängigkeit, Lebensstil oder etwas anderes? Eine mögliche Antwort geben die Zensusdaten des Jahres 1918. Das neu installierte Paßwesen mit der Meldepflicht erlaubte es der kommunistischen Regierung, die für die forcierte Industrialisierung erforderliche Migration politisch zu steuern. (pmb)'The author investigates the prerequisites and circumstances of the most rapid urbanization in world history which took place in the USSR during the 1930s. The work is based on mass statistic sources, for instance, a cencus of 1918. The author of the paper was one who actively participated in processing the original data of that cencus. What were primary 'pull' factors in the cities: salaries, independency, new style of living or something else? Some possibilities for answering these questions exist on the basis of the 1918 cencus data. The courses of passport system in the USSR and the courses of 'propiska' (a stamp in one's passport which indicates a person's residence) are analysed. The reason for this was an attempt of the Soviet government to stop uncontrolled migration.' (author's abstract
Complications of Resection Arthroplasty in Two-Stage Revision for the Treatment of Periprosthetic Hip Joint Infection
Little data is available regarding complications associated with resection arthroplasty in the treatment of hip periprosthetic joint infection (PJI). We assessed complications during and after two-stage revision using resection arthroplasty. In this retrospective study, 93 patients undergoing resection arthroplasty for hip PJI were included. Patients were assigned to a prosthesis-free interval of ≤10 weeks (group 1; 49 patients) or >10 weeks (group 2; 44 patients). The complication rates between groups were compared using the chi-squared test. The revision-free and infection-free survival was estimated using a Kaplan-Meier survival analysis. Seventy-one patients (76%) experienced at least one local complication (overall 146 complications). Common complications were blood loss during reimplantation (n = 25) or during explantation (n = 23), persistent infection (n = 16), leg length discrepancy (n = 13) and reinfection (n = 9). Patients in group 1 experienced less complications after reimplantation (p = 0.012). With increasing severity of acetabular bone defects, higher incidence of complications (p = 0.008), periprosthetic bone fractures (p = 0.05) and blood loss (p = 0.039) was observed. The infection-free survival rate at 24 months was 93.9% in group 1 and 85.9% in group 2. The indication for resection arthroplasty needs to be evaluated carefully, considering the high rate of complications and reduced mobility, particularly if longer prosthesis-free intervals are used
Backaction in metasurface etalons
We consider the response of etalons created by a combination of a
conventional mirror and a metasurface, composed of a periodic lattice of metal
scatterers with a resonant response. This geometry has been used previously for
perfect absorption, in so-called Salisbury screens, and for hybridization of
localized plasmons with Fabry-Perot resonances. The particular aspect we
address is if one can assume an environment-independent reflectivity for the
metasurface when calculating the reflectivity of the composite system, as in a
standard Fabry-Perot analysis, or whether the fact that the metasurface
interacts with its own mirror image renormalizes its response. Using lattice
sum theory, we take into account all possible retarded dipole-dipole
interactions of scatterers in the metasurface amongst each other, and through
the mirror. We show that while a layer-by-layer Fabry-Perot formalism captures
the main qualitative features of metasurface etalons, in fact the mirror
modifies both the polarizability and reflectivity of the metasurface in a
fashion that is akin to Drexhage's modification of the radiative properties of
a single dipole.Comment: 10 pages, 5 figure
Dynamical mean-field theory of indirect magnetic exchange
To analyze the physical properties arising from indirect magnetic exchange
between several magnetic adatoms and between complex magnetic nanostructures on
metallic surfaces, the real-space extension of dynamical mean-field theory
(R-DMFT) appears attractive as it can be applied to systems of almost arbitrary
geometry and complexity. While R-DMFT describes the Kondo effect of a single
adatom exactly, indirect magnetic (RKKY) exchange is taken into account on an
approximate level only. Here, we consider a simplified model system consisting
of two magnetic Hubbard sites ("adatoms") hybridizing with a non-interacting
tight-binding chain ("substrate surface"). This two-impurity Anderson model
incorporates the competition between the Kondo effect and indirect exchange but
is amenable to an exact numerical solution via the density-matrix
renormalization group (DMRG). The particle-hole symmetric model at half-filling
and zero temperature is used to benchmark R-DMFT results for the magnetic
coupling between the two adatoms and for the magnetic properties induced in the
substrate. In particular, the dependence of the local adatom and the nonlocal
adatom-adatom static susceptibilities as well as the magnetic response of the
substrate on the distance between the adatoms and on the strength of their
coupling with the substrate is studied. We find both, excellent agreement with
the DMRG data even on subtle details of the competition between RKKY exchange
and the Kondo effect but also complete failure of the R-DMFT, depending on the
parameter regime considered. R-DMFT calculations are performed using the
Lanczos method as impurity solver. With the real-space extension of the
two-site DMFT, we also benchmark a simplified R-DMFT variant.Comment: 14 pages, 8 figure
Linear viscoelastic properties of the vertex model for epithelial tissues
Epithelial tissues act as barriers and, therefore, must repair themselves,
respond to environmental changes and grow without compromising their integrity.
Consequently, they exhibit complex viscoelastic rheological behavior where
constituent cells actively tune their mechanical properties to change the
overall response of the tissue, e.g., from solid-like to fluid-like. Mesoscopic
mechanical properties of epithelia are commonly modeled with the vertex model.
While previous studies have predominantly focused on the rheological properties
of the vertex model at long time scales, we systematically studied the full
dynamic range by applying small oscillatory shear and bulk deformations in both
solid-like and fluid-like phases for regular hexagonal and disordered cell
configurations. We found that the shear and bulk responses in the fluid and
solid phases can be described by standard spring-dashpot viscoelastic models.
Furthermore, the solid-fluid transition can be tuned by applying
pre-deformation to the system. Our study provides insights into the mechanisms
by which epithelia can regulate their rich rheological behavior.Comment: 24 pages, 10 figures + Supplemental Information (12 pages, 12
figures
Quenching and Propagation of Combustion Without Ignition Temperature Cutoff
We study a reaction-diffusion equation in the cylinder , with combustion-type reaction term without
ignition temperature cutoff, and in the presence of a periodic flow. We show
that if the reaction function decays as a power of larger than three as
and the initial datum is small, then the flame is extinguished -- the
solution quenches. If, on the other hand, the power of decay is smaller than
three or initial datum is large, then quenching does not happen, and the
burning region spreads linearly in time. This extends results of
Aronson-Weinberger for the no-flow case. We also consider shear flows with
large amplitude and show that if the reaction power-law decay is larger than
three and the flow has only small plateaux (connected domains where it is
constant), then any compactly supported initial datum is quenched when the flow
amplitude is large enough (which is not true if the power is smaller than three
or in the presence of a large plateau). This extends results of
Constantin-Kiselev-Ryzhik for combustion with ignition temperature cutoff. Our
work carries over to the case , when
the critical power is , as well as to certain non-periodic flows
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