Broadband terahertz generation by optical rectification of ultrashort multiterawatt laser pulses near the beam breakup threshold.

We identify the physical factors that limit the terahertz (THz) yield of an optical rectification (OR) of ultrashort multiterawatt laser pulses in large-area quadratically nonlinear crystals. We show that the THz yield tends to slow its growth as a function of the laser driver energy, saturate, and eventually decrease as the laser beam picks up a spatiotemporal phase due to the intensity-dependent refraction of the OR crystal. We demonstrate that, with a careful management of the driver intensity aimed at keeping the nonlinear length larger than the coherence length, OR-based broadband THz generation in large-area lithium niobate (LN) crystals is energy-scalable, enabling an OR of multiterawatt laser pulses, yielding ∼10µJ/cm2 of THz output energy per unit crystal area. With a 27-fs, 10-TW, 800-nm Ti:sapphire laser output used as a driver for OR in large-area LN crystals, this approach is shown to provide a THz output with a pulse energy above 10 µJ and a bandwidth extending well beyond 6 THz, supporting single-cycle THz waveforms.

[Physiotherapy in early rehabilitation of patients with bone sarcomas after arthroplasty of large bones and joints]. / Fizioterapiya pri rannei reabilitatsii bol'nykh s kostnymi sarkomami posle endoprotezirovaniya krupnykh kostei i sustavov.

ACTUALITY: The modern method of treating patients with tumor lesions of the bones is the replacement of large bones and joints with the inclusion of reconstructive plastic component. The main functional postoperative disorders of this method (limitation of mobility in the operated joint, pain, muscle hypotrophy and edema of the operated limb) obstruct the ability of patients to return to a full life, which makes their early rehabilitation extremely urgent. Orthopedics uses a number of physical factors for this. The literature presents data on the absence of negative effects of low-frequency electro- and magnetotherapy in the treatment of late complications of oncopedic surgery on a number of bone sarcomas, which allowed them to be included in early rehabilitation for the first time. AIM OF STUDY: Development of a complex of early rehabilitation of patients with bone tumors after arthroplasty of large bones and joints and evaluation of its effectiveness. MATERIALS AND METHODS: A prospective, open, nonrandomized, controlled study included 36 patients aged 19-67 years (Me 42 years old) with primary malignant and metastatic bone tumors who underwent endoprosthesis replacement of large bones and joints with the inclusion of reconstructive plastic component (plastic by displaced muscles, synthetic mesh) and received local low-frequency magnetotherapy, low-intensity infrared laser radiation, electroneuromyostimulation and therapeutic exercises. Physiotherapy began from the first day after the operation and lasted for 10 days. To assess the functional result, the international MSTS scale was used. RESULTS: The combined use of the reconstructive plastic component during radical surgery and physiotherapy made it possible to obtain good functional result at 63,9% of patients, satisfactory functional results in 36.1% of patients according to the MSTS scale at the time of discharge. The function of the saved limb in 10 patients after distal femoral resection with knee replacement was 80% of normal function, in 7 patients after proximal tibia resection - 72%; in 13 patients after proximal resection of the femur with hip replacement - 59%; in 5 patients after proximal resection of the humerus with endoprosthetics of the shoulder joint - 61.3%; and in 1 patient after proximal resection of the ulna with endoprosthetics of the elbow joint - 70%. CONCLUSION: The multidisciplinary approach to the early rehabilitation of patients with bone tumors made it possible to achieve functional results in a short time, reduce the time spent by patients in the surgical department without increasing the number of postoperative complications. Based on the preliminary obtained results, it is necessary to continue the study on a larger number of patients and with a longer follow-up period.

Selective gas transfer through binary polymeric systems based on block-copolymers.

Evaluation of several versions of phenomenological theory of gas permeability in selective polymeric membranes is presented, along with the appropriate experimental methods for verification of these versions. The main focus is on a description of stationary mass transfer across membranes (films) containing dispersion inclusions of various shapes of one polymer in a matrix of another. Considering heterogeneous media as a membrane material, it was assumed that diffusion and sorption properties of inclusions are different from those of the dispersing medium. The problem of choosing optimal shape of inclusions is evaluated from the point of view of targeted permeability and selectivity of a membrane with respect to gases. To confirm this theoretical approach, the experimental results of the studies of diffusion (permeability) of permanent gases in polymeric membranes of different structures were used. The target gases included noble gases, hydrogen, nitrogen, oxygen, CO2, and methane. The target polymers included glassy polyvinyltrimethylsilane (PVTMS, T(gl)=155-180 °C), rubberlike polydimethylsiloxane (PDMS, T(gl)=-120 °C), and two-phase block-copolymers based on these materials within a wide range of composition, including the region of phase inversion. In addition, available experimental literature data on gas permeation parameters for polyarylat-polysiloxane, polysulfon-polysiloxane, and polycarbonate-polysiloxane block-copolymers are utilized. In order to describe the stationary gas permeability for two-phase systems (from diluted dispersion of one polymer in another to concentrated dispersion and complete phase inversion) the empiric approaches based on modified Maxwell equations are offered. The requirements for two-phase systems with high permeability and selectivity parameters for gas separation are identified. The permeability parameters are predicted for C1-C4 hydrocarbons in block-copolymers based on PDMS dispersion in PVTMS, phase inversion, and PVTMS dispersion in PDMS. Thus, the perspectives of designing heterogeneous membranes based on block-copolymers with predetermined molecular-selective properties are demonstrated.

Polymeric membrane materials: new aspects of empirical approaches to prediction of gas permeability parameters in relation to permanent gases, linear lower hydrocarbons and some toxic gases.

Membrane gas separation technologies (air separation, hydrogen recovery from dehydrogenation processes, etc.) use traditionally the glassy polymer membranes with dominating permeability of "small" gas molecules. For this purposes the membranes based on the low free volume glassy polymers (e.g., polysulfone, tetrabromopolycarbonate and polyimides) are used. On the other hand, an application of membrane methods for VOCs and some toxic gas recovery from air, separation of the lower hydrocarbons containing mixtures (in petrochemistry and oil refining) needs the membranes with preferable penetration of components with relatively larger molecular sizes. In general, this kind of permeability is characterized for rubbers and for the high free volume glassy polymers. Data files accumulated (more than 1500 polymeric materials) represent the region of parameters "inside" of these "boundaries." Two main approaches to the prediction of gas permeability of polymers are considered in this paper: (1) the statistical treatment of published transport parameters of polymers and (2) the prediction using model of ≪diffusion jump≫ with consideration of the key properties of the diffusing molecule and polymeric matrix. In the frames of (1) the paper presents N-dimensional methods of the gas permeability estimation of polymers using the correlations "selectivity/permeability." It is found that the optimal accuracy of prediction is provided at n=4. In the frames of the solution-diffusion mechanism (2) the key properties include the effective molecular cross-section of penetrating species to be responsible for molecular transportation in polymeric matrix and the well known force constant (ε/k)(eff i) of {6-12} potential for gas-gas interaction. Set of corrected effective molecular cross-section of penetrant including noble gases (He, Ne, Ar, Kr, Xe), permanent gases (H(2), O(2), N(2), CO), ballast and toxic gases (CO(2), NO(,) NO(2), SO(2), H(2)S) and linear lower hydrocarbons (CH(4), C(2)H(6), C(3)H(8), C(4)H(10), C(2)H(4), C(3)H(6), C(4)H(8) - 1, C(2)H(2), C(3)H(4)-m (methylacetylene) and C(3)H(4)-a (allen) is determined by using two above mentioned approaches. All of this allows calculating preliminary the permeability parameters of above mentioned gases for most part of known polymers based on limited experimental data. The new correlations suggested demonstrate that the available free volume of polymeric matrix plays an important role in providing of rate and selectivity of gas diffusion for glassy-like polymers; the rate and selectivity of gas diffusion in rubbers is affected mainly by cohesion energy density (CED) the both polymer parameters being calculated by traditional additive group contributions technique. Results of present study are demonstrated by calculation of expected permeability parameters in relation to lower hydrocarbons and some toxic gases for polynorbornene based polymers, PIM and PTMSP outlining potential of practical application for new membrane polymers.