Dynamic susceptibility of soft ferrogels. Effect of interparticle interaction.

We present the results of theoretical analysis of the dynamic susceptibility of soft elastic-viscous ferrogels with embedded single-domain ferromagnetic particles chaotically distributed in the host medium. The magnetic anisotropy of the particle is supposed to be strong. The effect of magnetic interparticle interaction is a focus of our attention. A differential equation for the statistically averaged (measured) magnetic moment of the particle is derived. Our analysis shows that in the case of a weak applied field, the interparticle interaction increases the composite magnetization and decreases the rate of its remagnetization.

A kinetic model for magnetostriction of a ferrogel with physical networking.

Kinetics of magnetostriction of ferrogel with physical networking based on natural polysaccharide guar gum with embedded strontium hexaferrite magnetic particles were studied in the uniform magnetic field 420 mT. An ellipsoidal sample was elongated by 37% along the applied field and contracted by 15% in the transverse direction, while its volume was kept constant. The characteristic time of magnetostriction was 440 s. Dynamic mechanical analysis in an oscillatory mode showed that the deformation of ferrogel is mostly elastic rather than viscous. Its storage modulus was almost constant in a frequency range of 0.1-100 Hz and by at least an order of magnitude larger than the loss modulus. Meanwhile, a developed theoretical model based on the elasto-viscous behaviour of the ferrogel failed to estimate correctly the experimental value of its magnetostriction. Calculated values of the elongation of ferrogel in the field were several orders of magnitude lower than those observed in the experiment for the ferrogel with physical networking. Consistency between the experiment and the theory was achieved using the alternative consideration based on the deformation of a liquid droplet of ferrofluid. The applicability of such an approach was discussed concerning structural relaxation properties of the ferrogel with physical networking. This article is part of the theme issue 'Transport phenomena in complex systems (part 1)'.

Kinetics of field-induced phase separation of a magnetic colloid under rotating magnetic fields.

This paper is focused on the experimental and theoretical study of the phase separation of a magnetic nanoparticle suspension under rotating magnetic fields in a frequency range, 5 Hz ≤ ν ≤ 25 Hz, relevant for several biomedical applications. The phase separation is manifested through the appearance of needle-like dense particle aggregates synchronously rotating with the field. Their size progressively increases with time due to the absorption of individual nanoparticles (aggregate growth) and coalescence with neighboring aggregates. The aggregate growth is enhanced by the convection of nanoparticles toward rotating aggregates. The maximal aggregate length, Lmax ∝ ν-2, is limited by fragmentation arising as a result of their collisions. Experimentally, the aggregate growth and coalescence occur at a similar timescale, ∼1 min, weakly dependent on the field frequency. The proposed theoretical model provides a semi-quantitative agreement with the experiments on the average aggregate size, aggregation timescale, and size distribution function without any adjustable parameter.

Effect of particle concentration on the microstructural and macromechanical properties of biocompatible magnetic hydrogels.

We analyze the effect of nanoparticle concentration on the physical properties of magnetic hydrogels consisting of polymer networks of the human fibrin biopolymer with embedded magnetic particles, swollen by a water-based solution. We prepared these magnetic hydrogels by polymerization of mixtures consisting mainly of human plasma and magnetic nanoparticles with OH- functionalization. Microscopic observations revealed that magnetic hydrogels presented some cluster-like knots that were connected by several fibrin threads. By contrast, nonmagnetic hydrogels presented a homogeneous net-like structure with only individual connections between pairs of fibers. The rheological analysis demonstrated that the rigidity modulus, as well as the viscoelastic moduli, increased quadratically with nanoparticle content following a square-like function. Furthermore, we found that time for gel point was shorter in the presence of magnetic nanoparticles. Thus, we can conclude that nanoparticles favor the cross-linking process, serving as nucleation sites for the attachment of the fibrin polymer. Attraction between the positive groups of the fibrinogen, from which the fibrin is polymerized, and the negative OH- groups of the magnetic particle surface qualitatively justifies the positive role of the nanoparticles in the enhancement of the mechanical properties of the magnetic hydrogels. Indeed, we developed a theoretical model that semiquantitatively explains the experimental results by assuming the indirect attraction of the fibrinogen through the attached nanoparticles. Due to this attraction the monomers condense into nuclei of the dense phase and by the end of the polymerization process the nuclei (knots) of the dense phase cross-link the fibrin threads, which enhances their mechanical properties.

Two-stage kinetics of field-induced aggregation of medium-sized magnetic nanoparticles.

The present paper is focused on the theoretical and experimental study of the kinetics of field-induced aggregation of magnetic nanoparticles of a size range of 20-100 nm. Our results demonstrate that (a) in polydisperse suspensions, the largest particles could play a role of the centers of nucleation for smaller particles during the earliest heterogeneous nucleation stage; (b) an intermediate stage of the aggregate growth (due to diffusion and migration of individual nanoparticles towards the aggregates) is weakly influenced by the magnetic field strength, at least at high supersaturation;

[Method of preventive ultrasound diagnosis of venous thrombosis]. / Metod preventivnoi ul'trazvukovoi diagnostiki venoznykh trombozov.

AIM: The purpose of the study was to work out a method of preventive diagnosis of venous thromboses by means of ultrasonographic duplex scanning (USDS). PATIENTS AND METHODS: A total of 306 people were examined. Of these, 146 patients presented with acute venous thrombosis, 108 subjects suffered from varicose veins, and 52 were apparently healthy people composing the control group. All those enrolled into the study were examined by means of USDS, with the D-dimer level determined. RESULTS: The obtained findings made it possible to discover and duly describe an ultrasonographic phenomenon of the presence of echo-positive inclusions in the zone of valvular sinuses, which was called the phenomenon of spontaneous echo contrast (SEC). This was followed by working out a classification of this phenomenon, describing two degrees thereof. Degree 1 SEC reflects the fact that the area of valvular sinuses is the most thrombogenic zone. Degree 2 SEC is characterised as a pathological, being simultaneously pre-thrombotic, condition and may serve as one of the earliest predictors of the development of venous thrombosis. A close correlation was established between the degree 2 SEC phenomenon, the presence of venous thrombosis and the values of the D-dimer level (r=0.89, p<0.01). CONCLUSION: Ultrasonographic examination of valvular sinuses is a simple, readily available and reproducible method of screening and may thus be used for preventive diagnosis of acute venous thromboses. The findings of this study make it possible to form risk groups by the development of deep vein thrombosis, as well as to initiate timely measures on prevention of the pathology concerned.

Hysteresis of the magnetic properties of soft magnetic gels.

We present results of an experimental and theoretical study of the magnetic properties of soft magnetic gels consisting of micron-sized magnetizable particles embedded in a polymer matrix. Experiments demonstrate hysteretic dependences of composite magnetization on an applied magnetic field and non-monotonic, with maximum, dependence of the sample susceptibilities on the field. We propose a theoretical approach which describes the main physical features of these experimental results.

[Work of medical official and the Sisters of Charity during the Siege of Sevastopol in 1854-1855].

Work of medical officials and the Sisters of Charity during the Siege of Sevastopol in 1854-1855. The article is devoted to work of the medical officials and the Sisters of Charity during the Siege of Sevastopol in 1854-1855. At the present time on the territory of Sevastopol Naval Clinical Hospital accommodate a memorial complex dedicated to the memory of medical officials, worked in the besieged Sevastopol. Referring to the historical sources of the work of medical officials and the Sisters of Charity of Krestovozdvizheskaya community the authors emphasize the importance of and the need for the installation of the memorial complex.

Inverse magnetorheological fluids.

We report a new kind of field-responsive fluid consisting of suspensions of diamagnetic (DM) and ferromagnetic (FM) microparticles in ferrofluids. We designate them as inverse magnetorheological (IMR) fluids for analogy with inverse ferrofluids (IFFs). Observations on the particle self-assembly in IMR fluids upon magnetic field application showed that DM and FM microparticles were assembled into alternating chains oriented along the field direction. We explain such assembly on the basis of the dipolar interaction energy between particles. We also present results on the rheological properties of IMR fluids and, for comparison, those of IFFs and bidispersed magnetorheological (MR) fluids. Interestingly, we found that upon magnetic field application, the rheological properties of IMR fluids were enhanced with respect to bidispersed MR fluids with the same FM particle concentration, by an amount greater than the sum of the isolated contribution of DM particles. Furthermore, the field-induced yield stress was moderately increased when up to 30% of the total FM particle content was replaced with DM particles. Beyond this point, the dependence of the yield stress on the DM content was non-monotonic, as expected for FM concentrations decreasing to zero. We explain these synergistic results by two separate phenomena: the formation of exclusion areas for FM particles due to the perturbation of the magnetic field by DM particles and the dipole-dipole interaction between DM and FM particles, which enhances the field-induced structures. Based on the second phenomenon, we present a theoretical model for the yield stress that semi-quantitatively predicts the experimental results.

[Ultrasound elastography in assessing efficacy of treatment for lower limb varicose veins with a phlebotrophic drug containing a micronized purified flavonoid fraction].

UNLABELLED: Venous hypertension combined with other pathogenetic links of the development of chronic venous insufficiency creates conditions for activation of an inflammatory process. Chronization of inflammation leads to alterations in the histological structure of the vascular wall and perivasal tissues, which is reflected by changes in their physical properties (elasticity or compressibility), which may be studied by means of ultrasound elastography (USEG). OBJECTIVE: The study was aimed at exploring the possibility of using ultrasound elastography for monitoring efficacy of conservative treatment of varicose disease of lower extremities with an agent containing a micronized purified flavonoid fraction (MPFF). MATERIAL AND METHODS: we examined a total of 19 patients (38 limbs) presenting with varicose disease of clinical class C2 according to the CEAP classification. The standard ultrasound examination and USEG were carried out using the unit of expert-class "Toshiba" (Japan) with a multi-frequency linear transducer 5-12 Hz. We examined the great saphenous vein in the area of the femur and crus, its tributaries, and the small saphenous vein. All examinations were performed with the patient in the supine, prone and standing positions from the standard approaches in the second half of the day prior to treatment with a phlebotrophic agent containing MPFF (Detralex) and three months after taking the drug at a dose of 1,000 mg/day. RESULTS: at baseline, according to the findings of USEG the intact veins of the lower limbs had a homogeneous pattern of the elastogram in the perivasal area. The presence of varicose transformation was associated with an inhomogeneous elastographic picture. On the background of treatment with MPFF, all patients showed a positive clinical effect in the form of decreased intensity of manifestations of complaints or complete disappearance thereof. According to the findings of ultrasound examination, there was a tendency towards a decrease in the wall thickness and diameter of the examined veins. USEG demonstrated an increase in the perivasal zones of elastographic homogeneity of tissues. The USEG-revealed alterations were more pronounced in large-diameter vessels. On the background of treatment with Detralex there was a trend towards normalization of the elastographic pattern of the vessel as a whole. CONCLUSION: the obtained findings confirm feasibility of using the technique of ultrasound elastography for identification of objective markers of treatment response to MPFF in varicose disease.

[The organ-preserving surgical treatment of the splenic rupture after the blunt abdominal trauma].

The outcomes of 383 cases of heavy combined traumas (n=273) and isolated (n=110) closed injuries of the abdomen with spleen damage were analyzed. The overall mortality was 11.74% (n=45), whereas the mortality rate during the first day after admission was 7.83% (n=30). Removal of a spleen was executed at 228 patients. The spleen-preserving operation with ligation of splenic artery, was performed in 155 patients. The optimal level of the splenic artery ligation proved to be in its proximal and median parts. The postoperative CT-angiogarphy and Doppler US scanning together with the three-dimensional reconstruction confirmed that blood supply of the body and tail of the pancreas was satisfactory thanks to the natural collateral blood circulation. The dramatic decrease in lethality and of postoperative complication rates allows to consider spleen-preserving resections to be a good alternative to spleenectomy.

Nanowire implosion under laser amplified spontaneous emission pedestal irradiation.

Nanowire array targets exhibit high optical absorption when interacting with short, intense laser pulses. This leads to an increased yield in the production of accelerated particles for a variety of applications. However, these interactions are sensitive to the laser prepulse and could be significantly affected. Here, we show that an array of aligned nanowires is imploded when irradiated by an Amplified Spontaneous Emission pedestal of a [Formula: see text] laser with an intensity on the order of [Formula: see text]. Using radiation hydrodynamics simulations, we demonstrate that the electron density profile is radially compressed at the tip by the rocket-like propulsion of the ablated plasma. The mass density compression increases up to [Formula: see text] when a more dense nanowire array is used. This is due to the ablation pressure from the neighboring nanowires. These findings offer valuable information for selecting an appropriate target design for experiments aimed at enhancing production of accelerated particles.

Increased throughput of proteomics analysis by multiplexing high-resolution tandem mass spectra.

High-resolution and high-accuracy Fourier transform mass spectrometry (FTMS) is becoming increasingly attractive due to its specificity. However, the speed of tandem FTMS analysis severely limits the competitive advantage of this approach relative to faster low-resolution quadrupole ion trap MS/MS instruments. Here we demonstrate an entirely FTMS-based analysis method with a 2.5-3.0-fold greater throughput than a conventional FT MS/MS approach. The method consists of accumulating together the MS/MS fragments ions from multiple precursors, with subsequent high-resolution analysis of the mixture. Following acquisition, the multiplexed spectrum is deconvoluted into individual MS/MS spectra which are then combined into a single concatenated file and submitted for peptide identification to a search engine. The method is tested both in silico using a database of MS/MS spectra as well as in situ using a modified LTQ Orbitrap mass spectrometer. The performance of the method in the experiment was consistent with theoretical expectations.

[Sonoelastography in differential diagnosis of thyroid nodes].

The study was aimed to assess the diagnostic possibilities of the new method of sonoelastography. 68 patients with different thyroid nodes were studied. Sonoelastography increased the sensitivity of the routine ultrasound investigation from 89 to 94.8%, the specificity from the 83 to 93%, and the accuracy of the method from 76 to 89%. The method assignes the information of the structural changes of the thyroid, unavailable by the routine ultrasound investigation.

Investigating epidemiologic trends and the geographic distribution of patients with anal squamous cell carcinoma throughout Canada.

Background: Anal cancer is a rare disease, constituting 0.5% of new cancer cases in the United States. The most common subtype is squamous cell carcinoma (scc). Studies in several developed nations have reported on an increasing incidence of anal cancer in recent decades, and various risk factors pertaining to the pathogenesis of the disease have been identified, including infection with the human papillomavirus, tobacco use, and immunosuppression. The epidemiology and distribution of anal scc throughout Canada remain poorly understood, however. Methods: Using 3 population-based cancer registries, a retrospective analysis of demographic data across Canada for 1992-2010 was performed. The incidence and mortality for anal scc was examined at the levels of provinces, cities, and the forward sortation area (FSA) component (first 3 characters) of postal codes. Results: During 1992-2010, 3720 individuals were diagnosed with anal scc in Canada; 64% were women. The overall national incidence rate was 6.3 cases per million population per year, with an average age at diagnosis of 60.4 years. The incidence increased over time, with significantly higher incidence rates documented in British Columbia and Nova Scotia (9.3 cases per million population each). Closer examination revealed clustering of cases in various urban centres and self-identified lgbtq communities in Toronto, Montreal, and Vancouver. Discussion: This study provides, for the first time, a comprehensive analysis of the burden of anal scc in Canada, identifying susceptible populations and shedding light onto novel avenues of research to lower the incidence of anal cancer throughout the country.

Epidemiology of adult and pediatric Burkitt lymphoma in Canada: sequelae of the HIV epidemic.

Background: Although the pathogenesis and epidemiology of endemic Burkitt lymphoma (bl) have been extensively studied, the epidemiologic landscape of sporadic and immunodeficiency-associated bl in North America remains poorly understood. Methods: We used 3 distinct population-based cancer registries to retrospectively study bl incidence and mortality in Canada. Data for patient sex; age at the time of diagnosis; and reporting province, city, and forward sortation area (fsa, the first three characters of a postal code) were analyzed. Results: During 1992-2010, 1420 patients with bl in Canada were identified (incidence rate: 2.40 cases per million patient-years), of which 71.1% were male patients. Mean age at diagnosis was 55.5 ± 20.8 years. A bimodal incidence by age distribution was seen in both sexes, with pediatric- and adult-onset peaks. An analysis based on fsas identified select communities with statistically higher rates of adult bl. Several of those fsas were located within the 3 major metropolitan areas (Montreal, Vancouver, Toronto) and within self-identified lgbtq communities. The fsas with a higher socioeconomic status score were associated with lower rates of bl. Conclusions: Current results highlight the geographic and historic pattern of bl in Canada. The human immunodeficiency virus remains an important risk factor for adult bl.

Condensation phase transitions in ferrofluids.

Experiments show that under suitable conditions magnetic particles in ferrofluids and other polar suspensions undergo condensation phase transitions and form dense liquidlike or solidlike phases. The problem of fundamental features and scenarios of the phase transitions is one of the central problems of the physics of these systems. This work deals with the theoretical study of scenarios of condensation phase transitions in ferrofluids, consisting of identical magnetic particles. Our results show that, unlike the classical condensation phase transitions, the appearance of the linear chains precedes the magnetic particle bulk condensation. The effect of the chains on the diagrams of the equilibrium phase transitions is studied.

Theoretical study of the magnetization dynamics of nondilute ferrofluids.

The paper is devoted to the theoretical investigation of the magnetodipolar interparticle interaction effect on magnetization dynamics in moderately concentrated ferrofluids. We consider a homogenous (without particle aggregates) ferrofluid consisting of identical spherical particles and employ a rigid dipole model, where the magnetic moment of a particle is fixed with respect to the particle itself. In particular, for the magnetization relaxation after the external field is instantly switched off, we show that the magnetodipolar interaction leads to the increase of the initial magnetization relaxation time. For the complex ac susceptibility chi(omega)=chi'(omega)+ ichi''(omega) we find that this interaction leads to an overall increase of chi''(omega) and shifts the chi''(omega) peak towards lower frequencies. Comparing results obtained with our analytical approach (second order virial expansion) to numerical simulation data (Langevin dynamics method), we demonstrate that the employed virial expansion approximation gives a good qualitative description of the ferrofluid magnetization dynamics and provides a satisfactory quantitative agreement with numerical simulations for the dc magnetization relaxation, up to the particle volume fraction phi approximately 10% , and for the ac susceptibility, up to phi approximately 5%.

Magnetic hyperthermia in a system of immobilized magnetically interacting particles.

This paper deals with the theoretical study of magnetic hyperthermia, induced by a system of immobilized single-domain ferro- (ferri-) magnetic particles under the action of an oscillating magnetic field. It is supposed that the particles are randomly distributed in a host medium. The effect of magnetic interparticle interaction on the intensity of the heat production is the focus of our attention. The results show that interparticle interaction enhances the thermal effect.

Incidence and mortality trends and geographic patterns of follicular lymphoma in Canada.

Background: Follicular lymphoma (fl) is the most common indolent lymphoma and the 2nd most common non-Hodgkin lymphoma, accounting for 10%-20% of all lymphomas in the Western world. Epidemiologic and geographic trends of fl in Canada have not been investigated. Our study's objective was to analyze incidence and mortality rates and the geographic distribution of fl patients in Canada for 1992-2010. Methods: Demographic and geographic patient data for fl cases were obtained using the Canadian Cancer Registry, the Registre québécois du cancer, and the Canadian Vital Statistics database. Incidence and mortality rates and 95% confidence intervals were calculated per year and per geographic area. Rates were plotted using linear regression models to assess trends over time. Overall data were mapped using Microsoft Excel mapping software (Redmond, WA, U.S.A.) to identify case clusters across Canada. Results: Approximately 22,625 patients were diagnosed with fl during 1992-2010. The age-standardized incidence rate of this malignancy in Canada was 38.3 cases per million individuals per year. Geographic analysis demonstrated that a number of Maritime provinces and Manitoba had the highest incidence rates, and that the provinces of Nova Scotia and Quebec had the highest mortality rates in the nation. Regional data demonstrated clustering of fl within cities or regions with high herbicide use, primary mining, and a strong manufacturing presence. Conclusions: Our study provides a comprehensive overview of the fl burden and its geographic distribution in Canada. Regional clustering of this disease in concentrated industrial zones strongly suggests that multiple environmental factors might play a crucial role in the development of this lymphoma.