On preventing resonance condition in operation of rotary excavators

The article examines the causes of forced vibrations of the rotor. It was found that the increased tendency of rotary excavators to oscillate is caused by the frequency of scooping, which leads to self-oscillation. The frequencies of natural and forced rotor vibrations during the digging of different soils are determined depending on the speed of rotation of the working body and the depth of digging. The dynamic stability of the movement of the working body under the horizontal elastic pliability of the structure is investigated. The condition of occurrence of resonant phenomena during operation of a trench rotary excavator is determined. © 2020 IOP Publishing Ltd. All rights reserved

Nonlinear equation for curved stationary flames

A nonlinear equation describing curved stationary flames with arbitrary gas expansion $\theta = \rho_{{\rm fuel}}/\rho_{{\rm burnt}}$, subject to the Landau-Darrieus instability, is obtained in a closed form without an assumption of weak nonlinearity. It is proved that in the scope of the asymptotic expansion for $\theta \to 1,$ the new equation gives the true solution to the problem of stationary flame propagation with the accuracy of the sixth order in $\theta - 1.$ In particular, it reproduces the stationary version of the well-known Sivashinsky equation at the second order corresponding to the approximation of zero vorticity production. At higher orders, the new equation describes influence of the vorticity drift behind the flame front on the front structure. Its asymptotic expansion is carried out explicitly, and the resulting equation is solved analytically at the third order. For arbitrary values of $\theta,$ the highly nonlinear regime of fast flow burning is investigated, for which case a large flame velocity expansion of the nonlinear equation is proposed.Comment: 29 pages 4 figures LaTe

Risk of surgical site infection and efficacy of antibiotic prophylaxis: a cohort study of appendectomy patients in Thailand

BACKGROUND: No data currently exist about use of antibiotics to prevent surgical site infections (SSI) among patients undergoing appendectomy in Thailand. We therefore examined risk factors, use, and efficacy of prophylactic antibiotics for surgical site infection SSI among patients with uncomplicated open appendectomy. METHODS: From July 1, 2003 to June 30, 2004 we conducted a prospective cohort study in eight hospitals in Thailand. We used the National Nosocomial Infection Surveillance (NNIS) system criteria to identify SSI associated with appendectomy. We used logistic regression analysis to obtain relative risk estimates for predictors of SSI. RESULTS: Among 2139 appendectomy patients, we identified 26 SSIs, yielding a SSI rate of 1.2 infections/100 operations. Ninety-two percent of all patients (95% CI, 91.0–93.3) received antibiotic prophylaxis. Metronidazole and gentamicin were the two most common antibiotic agents, with a combined single dose administered in 39% of cases. In 54% of cases, antibiotic prophylaxis was administered for one day. We found that a prolonged duration of operation was significantly associated with an increased SSI risk. Antibiotic prophylaxis was significantly associated with a decreased risk of SSI regardless of whether the antibiotic was administered preoperatively or intraoperatively. Compared with no antibiotic prophylaxis, SSI relative risks for combined single-dose of metronidazole and gentamicin, one-day prophylaxis, and multiple-day antibiotic prophylaxis were 0.28 (0.09–0.90), 0.30 (0.11–0.88) and 0.32 (0.10–0.98), respectively. CONCLUSION: Single-dose combination of metronidazole and gentamicin seems sufficient to reduce SSIs in uncomplicated appendicitis patients despite whether the antibiotic was administered preoperatively or intraoperatively

A dressed bag model study of the final-state NΔN\Delta interaction in photoproduction processes off the deuteron

The impact of the short-range $N\Delta$ interaction on the pion photoproduction processes off the deuteron in the $\Delta$-resonance region is studied in the framework of recently proposed dressed-bag model. A common dressing procedure for bare three- and six-quark states is used to describe both the pion decay widths of baryon resonances and the effective $NN$ (or $N\Delta$) interaction at short ranges related to the inner dressed-bag states. It is shown that the effect of short-range $N\Delta$ interaction for the forward-angle $\pi^\mathrm{o}$ photoproduction off the deuteron cannot be neglected. The prospects for further development of the model to describe the short-range $NN$ (or $N\Delta$) correlations in the lightest nuclei are discussed

Parallel Evolution of Auditory Genes for Echolocation in Bats and Toothed Whales

The ability of bats and toothed whales to echolocate is a remarkable case of convergent evolution. Previous genetic studies have documented parallel evolution of nucleotide sequences in Prestin and KCNQ4, both of which are associated with voltage motility during the cochlear amplification of signals. Echolocation involves complex mechanisms. The most important factors include cochlear amplification, nerve transmission, and signal re-coding. Herein, we screen three genes that play different roles in this auditory system. Cadherin 23 (Cdh23) and its ligand, protocadherin 15 (Pcdh15), are essential for bundling motility in the sensory hair. Otoferlin (Otof) responds to nerve signal transmission in the auditory inner hair cell. Signals of parallel evolution occur in all three genes in the three groups of echolocators—two groups of bats (Yangochiroptera and Rhinolophoidea) plus the dolphin. Significant signals of positive selection also occur in Cdh23 in the Rhinolophoidea and dolphin, and Pcdh15 in Yangochiroptera. In addition, adult echolocating bats have higher levels of Otof expression in the auditory cortex than do their embryos and non-echolocation bats. Cdh23 and Pcdh15 encode the upper and lower parts of tip-links, and both genes show signals of convergent evolution and positive selection in echolocators, implying that they may co-evolve to optimize cochlear amplification. Convergent evolution and expression patterns of Otof suggest the potential role of nerve and brain in echolocation. Our synthesis of gene sequence and gene expression analyses reveals that positive selection, parallel evolution, and perhaps co-evolution and gene expression affect multiple hearing genes that play different roles in audition, including voltage and bundle motility in cochlear amplification, nerve transmission, and brain function

Sliding Screw-Nut Gearing

FIELD: machine building. SUBSTANCE: invention relates to gearings. Sliding screw — nut gearing comprises a screw with an external trapezoidal thread and a female nut with a similar internal thread. On side surfaces of the nut there are pockets connected through throttles to the oil supply channel from the pump. Diametrical surfaces of the nut are made with holes connected to the oil drain channel to the hydraulic tank. Gearing is equipped with an adjustable additional throttle connected to the oil drain channel and a gearbox-multiplier. Hydraulic pump is gear-type reversible, and screw is kinematically connected to its drive shaft through gearbox-multiplier. EFFECT: reduced wear of gearing. 1 cl, 1 dwg.Изобретение относится к области машиностроения, а более конкретно к передачам. Передача винт-гайка скольжения содержит винт с наружной трапецеидальной резьбой и охватывающую его гайку с аналогичной внутренней резьбой. На боковых поверхностях гайки выполнены карманы, соединенные через дроссели с каналом подачи масла от насоса. Диаметральные поверхности гайки выполнены с отверстиями, соединенными с каналом слива масла в гидробак. Передача снабжена регулируемым дополнительным дросселем, включенным в канал слива масла, и редуктором-мультипликатором. Гидронасос выполнен шестеренным реверсивным, а винт через редуктор-мультипликатор кинематически связан с его приводным валом. Достигается снижение износа передачи. 1 ил

Development of a New Design of the Working Body of a Rotary Excavator

The design of working body of rotary trench excavator is proposed, the peculiarity of which is that the load on the buckets will be distributed between three rows of buckets and will decrease for each bucket; the constructive scheme of the working body is designed; the continuous digging of the soil by the proposed of working body is designed.Предложена конструкция рабочего органа роторного траншейного экскаватора, особенностью которого является то, что нагрузка на ковши распределится между тремя рядами ковшей и уменьшится на каждый ковш; разработана конструктивная схема предлагаемого рабочего органа; спроектировано непрерывное копание грунта предложенным рабочим органом

Development of a Wheel Milling Machine for the Repair of Wheel Pairs of Locomotives and Wagons Without Rolling

The design of the wheel milling machine for repairing non-driven wheelsets without rolling out the bogie is proposed; the prefabricated shaped tool is designed, the feature of which is that it consists of two mirror- reflected shaped cutters, the torque transmission of which carried out by one drive; the transmission’s design consisting of an asynchronous motor and a worm drive with the possibility of lubrication is developed.Предложена конструкция колесофрезерного станка для ремонта приводных и неприводных колесных пар без выкатки тележки; спроектирован сборный фасонный инструмент, особенностью которого является то, что он состоит из двух зеркальных фасонных фрез, вращение которых происходит от одного привода; разработана конструкция привода главного движения, состоящего из асинхронного двигателя и червячной пары с принудительной смазкой последней

Rotary Excavator Working Body

Изобретение относится к области землеройной техники, а именно к роторным экскаваторам, предназначенным для разработки траншей под магистральные трубопроводы. Технический результат – повышение надежности рабочего органа. Рабочий орган роторного экскаватора состоит из ротора, выполненного в виде колеса диаметром D с приводом вращения, и ковшей, размещенных на колесе двумя параллельными кольцевыми рядами, каждый из которых содержит n ковшей, установленных с шагом πD/n. Причем ковши первого ряда относительно ковшей второго ряда расположены с окружным смещением. Рабочий органа снабжен дополнительным кольцевым рядом n ковшей, размещенным между первым и вторым рядами ковшей. Окружное смещение ковшей дополнительного ряда относительно ковшей первого ряда и ковшей второго ряда относительно ковшей дополнительного ряда выполнено равным πD/3n. Передние режущие лезвия ковшей выполнены с угловым наклоном относительно оси ротора. 3 ил.FIELD: excavation equipment. SUBSTANCE: invention relates to the field of excavation equipment, namely to rotary excavators intended for the development of tranches for main pipelines. A working body of a rotary excavator consists of a rotor made in the form of a wheel with a diameter D with a rotary drive and buckets placed on the wheel in two parallel annular rows, each of which contains n buckets installed with an interval of πD/n. Moreover, buckets of the first row are located with circular displacement relatively to buckets of the second row. The working body is equipped with an additional annular row of n buckets, placed between the first and the second rows of buckets. Circular displacement of buckets of the additional row relatively to buckets of the first row and buckets of the second row relatively to buckets of the additional row is equal to πD/3n. Front cutting blades of buckets are made with an angular tilt relatively to the axis of the rotor. EFFECT: increase in the reliability of a working body. 1 cl, 3 dwg