The principles and methods of thermopower and electrical conductivity measurements at high temperatures (100 – 1000 K) are reviewed. These two properties define the so-called power factor of thermoelect ric materials. Moreover, in combination with thermal conductivity they give the efficiency of thermoelectric conversion. In spite of a principal obtained by different groups and hinders a realistic estimate of the potential thermoelectric efficiency of new materials. The lack of a commonly accepted reference material for thermopower exaggerates the problem. Therefore, it is very important to have a clear understanding of the capabilities and limitations of the measuring methods and set-ups. The review article deals with the definitions of the thermoelectric parameters and principles of their experimental determination. The metrological characteristics of the state-of-the-art experimental set-ups for high temperature measurements are analyzed. simplicity of the measurement methods of these properties, their practical realization is rather complicated, especially at high temperatures. This leads to large uncertainties in determination of the properties, complicates comparison of the results

Subject of study. A vector model for conversion of electromagnetic radiation in optical systems is considered, taking into account the influence of birefringence, as well as partially coherent illumination. Model. The proposed model is based on the representation of the complex amplitude of the monochromatic field through thesuperposition of basic plane waves. Transmitted light image with partially coherent illumination is performed by the sourceintegration method. Main results. The results of simulation for the point spread function are demonstrating the level of the birefringence influence on the image quality. In the presence of the wave aberration about 0.098 of the wavelength, the wave energy loss in the center of the Airy disk with an average birefringence of 4 nm/cm was 8%, and at 16 nm/cm it reached 30%. The calculation of the point spread function for a real sample of fluorite is given. The central peak of the PSF without birefringence was 0.722, with regard to birefringence it was equal to 0.701. Practical significance. The findings can be used in the development of photolithographic lenses, as well as for the manufacturing of any other optical systems that require consideration of the polarization properties of the materials. 

Subject of study. The paper deals with light quality improvement of multi–chip RGB light-emitting diodes (LEDs) and luminaries on their basis. In particular, we have studied the issues of the edge effect reducing, which is non–uniformity of color when observing the source of light under different angles as well as non-uniformity of color distribution on the illuminated surface. Methods. Experimental study of the edge effect has been performed, namely, the analysis of the halo at the periphery of the illuminated area and the non–uniformity of area at the surface of the screen illuminated with RGB LEDs with and without light concentrators. Modeling of illumination distribution at various distances from the source for the system containing four RGB LEDs with reflectors by ZEMAX software has been carried out. Assessment of the uniformity for light distribution via calculating the chromaticity coordinates has been performed. Main results. The possibility of modeling application at the stage of a luminary design is shown on the example of RGB LEDs for assessing the efficiency of light flux usage and colorimetric parameters. Suggested method simplifies significantly the design of luminaries and reduces associated costs. Practical relevance. The findings can be used in the design of luminaries based on RGB LEDs, including the ones with secondary optics elements.

The use of oxy-fuel combustion processes is of large interest for several industrial fields applications since it offers the advantages of low NOx emissions in combination with high combustion temperatures even without additional preheating. For optimization of such processеs a detailed understanding based on precise experimental data is necessary. So far there is still a lack of precise experimental data achieved with high spatial and temporal resolution from industrial relevant turbulent oxy-fuel combustion processes. Beside species concentration information the gas phase temperature is of utmost importance for an improved understanding of the basic chemical reactions and the pollutant formation. The coherent anti-Stokes Raman spectroscopy (CARS) technique is a very well suited laser based tool for a non-intrusive investigation of such turbulent high temperature combustion processes. In this work we analysed an industrial 400 kW oxy-fuel burner with the help of O2 based vibrational CARS system which is integrated in an industrial relevant test furnace. The burner is fed with pure oxygen and natural gas at an equivalence ratio of =0.9. At one downstream position temporal and spatial resolved temperatures were measured along a 600 mm line. Additional air sucked in from the environment seems to influence the gas phase temperature significantly.

The spontaneous Raman scattering technique is an excellent tool for a quantitative analysis of multi-species gas mixtures. It is a noninvasive optical method for species identification and gas phase concentration measurement of all Raman active molecules, since the intensity of the species specific Raman signal is linearly dependent on the concentration. Applying a continuous wave (CW) laser it typically takes a few seconds to capture a gas phase Raman spectrum at room temperature. Nevertheless in contrast to these advantages the weak Raman signal intensity is a major drawback. Thus, it is still challenging to detect gas phase Raman spectra in alow-pressure regime with a temporal resolution of only a few 100 ms. In this work a fully functional gas phase Raman system for measurements in the low-pressure regime (p ≥ 980 hPa (absolute)) is presented. It overcomes the drawback of a weak Raman signal by using a multipass cavity. A description of the sensor setup and of the multipass arrangement will be presented. Moreover the complete functionality of the sensor system will be demonstrated by measurements at an anesthesia simulator under clinical relevant conditions and in comparison to a conventional gas monitor.

Modified phase-generated carrier homodyne demodulation technique for fiber-optic sensors is presented. Nowadays phase-generated carrier homodyne demodulation technique is one of the most widespread. One of its drawbacks is the temperature dependence of the output signal because of the modulator scale factor temperature dependence. In order to compensate this dependence an automatic adjustment of the phase modulation depth is necessary. To achieve the result, additional harmonics analysis is used with the help of the Bessel functions. For this purpose the known demodulation scheme is added with the branch, where interferometric signal is multiplied by the third harmonic of the modulation signal. The deviation of optimal ratio of odd harmonics is used as a feedback signal for adjusting the modulation depth. Unwanted emissions arise in the feedback signal, when the third harmonic possesses a value close to zero. To eliminate unwanted emission in the feedback signal, the principle scheme is added with one more branch, where interferometric signal is multiplied by the forth harmonic of the modulation signal. The deviation of optimal ratio of even harmonics is used as a feedback signal alternately with the deviation of optimal ratio of odd harmonics. A mathematical model of the algorithm is designed using the MATLAB package. Results of modeling have confirmed that suggested method gives the possibility for an automatic adjustment of the phase modulation depth and makes it possible to compensate temperature dependence for the modulator scale factor and output signal magnitude.

The paper deals with findings for the energy reflection coefficient distribution of anti- reflection coating along the surface of optical elements with a very small radius (2-12 mm). The factors influencing the magnitude of the surface area of the optical element, in which the energy reflection coefficient is constant, were detected. The main principles for theoretical models that describe the spectral characteristics of the multilayer interference coatings were used to achieve these objectives. The relative size of the enlightenment area is defined as the ratio of the radius for the optical element surface, where the reflection is less than a certain value, to its radius (ρ/r). The result of research is the following: this size is constant for a different value of the curvature radius for the optical element made of the same material. Its value is determined by the refractive index of material (nm), from which the optical element was made, and the design of antireflection coatings. For single-layer coatings this value is ρ/r = 0.5 when nm = 1.51; and ρ/r = 0.73 when nm = 1.75; for two-layer coatings ρ/r = 0.35 when nm = 1.51 and ρ/r = 0.41 when nm = 1.75. It is shown that with increasing of the material refractive index for the substrate size, the area of minimum reflection coefficient is increased. The paper considers a single-layer, two-layer, three-layer and five-layer structures of antireflection coatings. The findings give the possibility to conclude that equal thickness coverings formed on the optical element surface with a small radius make no equal reflection from the entire surface, and distribution of the layer thickness needs to be looked for, providing a uniform radiation reflection at all points of the spherical surface.

The paper deals with the scheme for the study of the Bragg wavelength shift dependence on the applied tensile force. Samples of fiber Bragg gratings with different coatings have been studied: the restored acrylate coating, the heatshrinkable fusion splice protection sleeve without metal rod, the heat-shrinkable fusion splice protection sleeve with a metal rod, the metal capillary, polyvinylchloride tube. For different coatings of diffractive structure, dependences of wavelength shift for the Bragg grating resonance have been obtained on the tensile strength applied to the ends of an optical fiber. It was determined that the studied FBG coatings give the possibility to reduce the mechanical impact on the Bragg wavelength shift for 1.1-15 times as compared to an uncoated waveguide. The most effective version of coated fiber Bragg grating is the heatshrinkable fusion splice protection sleeve with a metal rod. When the force (equal to 6 N) is applied to the 100 mm optical fiber area with the inscribed diffractive structure, the Bragg wavelength shift is 7.5 nm for the unprotected sample and 0.5 nm for the one coated with the heat-shrinkable fusion splice protection sleeve.

A study of bend-induced losses in a silica-based single-mode microstructured fiber with a core diameter ranging from 20 to 35 microns and increased relative air content in the holey cladding has been conducted. With the use of the equivalent step-index profile method in approximation of waveguide parameters of microstructured fiber (normalized frequency and normalized transverse attenuation constant) the effect of bending on the spectral position of the fundamentalmode short-wavelength leakage boundary has been analyzed. Upon measurement of spectral characteristics of attenuation in the considered fibers good accordance of numerical and experimental data has been found out. It is shown that increase of the air content in the holey cladding leads to expansion of the mentioned boundary to lower wavelengths for the value from 150 to 800 nm depending on the core size and bending conditions. A single-transverse-mode propagation is achieved on fiber length of 5-10 meters due to a substantial difference in losses of fundamental and higher-order guided modes attained by bending. Optical losses in all studied samples are less than 10 dB/km at the wavelength λ = 1550 nm. The results of the study can be applied in the design of high-power laser systems having such basic requirements as a relatively large mode spot and high beam quality.

  Subject of research. Control system of a four-mass object (twin telescope) with dual motor drive is considered. Method. The reducing ability of an object model to the third order is used for simplification of control system. The synthesis of a discrete controller algorithm is completed based on the reduced model of the object. Characteristics of the system which consists of four-mass object with dual motor drive and obtained regulator are investigated. Control synthesis based on the modified design method of an optimal control with guaranteed degree of stability is used. Reduced-order observer is used in the control system since only one parameter of the plant can be measured — angular velocity of one lumped inertia. System robustness is verified by changing the nominal parameters of the plant in 10% range. Main results. In case of using a single motor drive a regulator can be built only on the basis of the model of object slow motions. System performance (bandwidth) should be enough low not to excite elastic vibrations. Control rate then is limited by the lowest resonating frequency of the plant. Numerical simulation reveals that transition time of the system with single motor drive significantly exceeds transition time of the system with dual motor drive. Both systems maintain the properties of robustness with changing parameter Practical relevance. The results can be used in the control systems design of the complex electromechanical mechanisms with elastic couplings such as telescope main drive axis.

Subject of study. Findings for the surface structure of conductive and semi-insulating substrates 6H-SiC(0001) and epitaxial graphene layers grown on them are presented. Materials and methods. We used two types of silicon carbide substrates of 6H polytype as a substrate: conductive (with resistivity less than 103 Ohm·cm), and semi-insulating (with resistivity greater than 105 Ohm·cm). Synthesis of graphene layers on substrates was carried out by thermal decomposition of SiC surface at the temperature of 1350ºC for 20 minutes in a vacuum sublimation epitaxy setup. Registration of high-energy electron diffraction (RHEED) patterns for reflection was carried out using two devices: electronograph EMR-102 at an accelerating voltage of 75 kV and electron diffractometer, built into the unit MBE Compact 21T (Riber France), at an accelerating voltage of 30 kV. Main results. The oriented growth of graphene is observed on the conductive substrate. Both oriented and disordered kinds of graphene grow on the semi-insulating substrate due to the partially formation of the polycrystalline component in the multilayered graphene film which in turn is caused by the lower perfection structure of the semi-insulating substrate surface as compared to the conductive one. Practical significance. Proposed findings will help to understand the quality dependence of the grown graphene film on the structure of the used silicon carbide substrate.

The present paper discusses development and implementation of the cross-platform application with a graphical user interface for estimation of the particle volume fraction distribution function and fitting specific surface area to this distribution pattern. SAXSEV implements the method of statistical regularization for ill-posed mathematical tasks being solved with the use of Numpy, Scipy and MathPlotlib libraries. The main features of this software application are the ability to adjust the arguments grid of the desired function and the ability to select the optimal value of the regularization parameter. This parameter is selected by several specific and one common criteria. The software application consists of modules written in Python3. The modules are combined by common interface based on Tkinter library. Current version SAXSEV 2.1 was tested on the basis of Windows XP / Vista / 7/8, Ubuntu 14.1. SAXSEV 2.1 was used successfully at effectiveness study of statistical regularization method for analyzing dispersed system by SAXS, at research of the powder consisting from nanoparticles and composite materials with nanoparticles inclusion.

The paper deals with new concepts of biotesting method updating. Modern conductometric technologies and the analysis of microbial «growth curves» are used. The registration occurs in a real time mode for the set of parallel samples. Results are shown for comparison of the proposed impedance biotesting technique with standard cultural determination method for total amount of microorganismes in the tested samples. Results are presented for practical application of the proposed impedance biotesting technique to the analysis as inhibitory action of clorhexidine disinfectant on the vital activity of Escherichia coli, as milk ripening process at the presence of various microorganisms species and protein preparations. The impedance biotesting method, proposed in the present work, provides high level of its own data convergence with the data, being received as a result of application of standard cultural biotesting techniques. Thus, the proposed method has such advantages, as: an opportunity of the detailed information reception about dynamics change of magnitude of population and intensity of test microorganisms metabolism, significant reduction of the culture media amount used, as well as researcher's temporary and labor efforts while the analyses realization, and the growth of analysis objectivity.

Problem statement. Currently, the task of improving energy efficiency are addressed mainly through the creation of more efficient devices and appliances, the use of alternative energy sources, application of special additional equipment for power consumption control and other technological methods. All these solutions are quite expensive and often economically difficult to payback. At the same time, the issues of automated integrated analysis of existing data measuring equipment have been poorly known. But just these data contain all the necessary information for finding bottlenecks and failures in the equipment, leading to increased energy consumption. Methods. Methods of web services creation are considered for current state monitoring of electrical networks using CQELS for static and streaming data integration of smart meters. RDF data model is used as the main way of data representation. Results. The architecture of the energy monitoring system (Smart grid) based on semantic analysis of the streaming data is proposed. Ontology has been worked out, aimed at information domain model creation, which describes the measurement data and the possible situations for tracking by the system using semantic queries. An example of system operation is shown, and description of the visualization interfaces for streaming data and log of messages is given. Practical relevance. Industrial application of the proposed approach will give the possibility to achieve significant energy efficiency through integrated analysis of smart meters data based on existing infrastructure of test and measurement equipment. An additional effect lies in the ability to create flexible Smart grid monitoring system and visualization of their states by an ontological approach to the domain modeling.

The research results upon the application of the existing information transmission methods in polymodal info communication systems are presented herein. The analysis of the existing commutation ways and multiplexing schemes has revealed that modern means of telecommunication are capable of providing polymodal information delivery with the required quality to the customer correspondent terminal. Under these conditions substantial capacity resource consumption in the data transmission networks with a simultaneous static time multiplexing is required, however, it is easier to achieve the modality synchronization within that kind of an infrastructure. The data networks with a static time multiplexing demand employing more sophisticated supporting algorithms of the guaranteed data blocks delivery quality. However, due to the stochastic data blocks delays modality synchronizing during the off-line processing is more difficult to provide. Nowadays there are objective preconditions for a data networking realization which is invariable to the applied transmission technology. This capability is defined by a wide (person-to-person) application of the optical technologies in the transport infrastructure of the polymodal info communication systems. In case of the availability of the customer terminal and networking functioning matching mode it becomes possible to organize channels in the latter which can adaptively select the most effective networking technology according to the current volume allocation and modality types in the messages. 

The subject areas of the proposed research are monitoring facilities for protection of computer systems exposed to destructive attacks of accidental and malicious nature. The interval optimization model of test monitoring for the detection of hazardous states of security breach caused by destructive attacks is proposed. Optimization function is to maximize profit in case of requests servicing in conditions of uncertainty, and intensity variance of the destructive attacks including penalties when servicing of requests is in dangerous conditions. The vector task of system availability maximization and minimization of probabilities for its downtime and dangerous conditions is proposed to be reduced to the scalar optimization problem based on the criterion of profit maximization from information services (service of requests) that integrates these private criteria. Optimization variants are considered with the definition of the averaged periodic activities of monitoring and adapting of these periods to the changes in the intensity of destructive attacks. Adaptation efficiency of the monitoring frequency to changes in the activity of the destructive attacks is shown. The proposed solutions can find their application for optimization of test monitoring intervals to detect hazardous conditions of security breach that makes it possible to increase the system effectiveness, and specifically, to maximize the expected profit from information services.

Subject of research. The paper presents research and instructional tools for assessment of providing with the development strategy for information technologies in an organization. Method. The corresponding assessment model is developed which takes into consideration IT-processes equilibrium according to selected efficiency factors of information technologies application. Basic results. The model peculiarity resides in applying neuro-fuzzy approximators where the conclusion is drawn upon fuzzy logic, and membership functions are adjusted through the use of neural networks. For the adequacy testing of the suggested model, due diligence result analysis has been carried out for the IT-strategy executed in the “Navigator” group of companies at the stage of implementation and support of new technologies and production methods. Data visualization with a circle diagram is applied for the comparative evaluation of the analysis results. The chosen model adequacy is proved by the agreement between predictive assessments for IT-strategy performance targets derived by means of the fuzzy cognitive model over 12 months planning horizon and the real values of these targets upon the expiry of the given planning term.   Practical significance. The developed model application gives the possibility to solve the problem of sustainability assessment for the process of providing the required IT-strategy realization level based upon the fuzzy cognitive map analysis and to reveal IT-objectives changing tendencies for an organization over the stated planning interval.

The method is offered for planning radio networks by the cellular operator. The problem relevance is caused by the service providers effort to minimize costs for arrangement and content of necessary quantity of base stations with the support of the required signal/noise level within a coverage zone. The problem is solved in several stages by a rational choice of basing location points for retranslators. First of all, we carry out the terrain section analysis and a preliminary choice of a point set on it where the placement of base stations is potentially possible. As a rule, such problem is solved by means of specialized geoinformation systems. At the second stage we make calculation of a radio communication range, on condition that retranslators are located in the selected points. At the third stage we directly make selections of line items for basic stations on the ground of predesigns. The paper deals with stochastic approach for a rational choice of the line items. Feasibility of this approach is caused by a large number of the arbitrary uncontrollable factors influencing the signal/noise ratio in a reception point. In this case we consider the task of a line item optimum choice as an extremum problem where parameters of conditions are represented as random variables. Implementation of the method offered by the authors is illustrated on the example of a radio communication planning on an out-of-town region crossed by two highways. The input parameters in this example are: road section length, crossing coverage zones of retranslators, and concentration of subscribers on the higways. The target function and system of restrictions are formed accordingly to provide finding of subscribers within a coverage zone and to minimize intersections of coverage zones for adjacent retranslators. This technique application gives the possibility for receiving statistically optimum arrangement of base stations on the given terrain section that is confirmed by simulation modeling.

The paper describes the solution of the problem related to the specific admissible sets of variables in linear programming. We are discussing the feasible set which is the union of segments with multiplier parameter for some variable. The solution of this problem is performed in two stages: at the beginning the relaxed problem of linear optimization is solved (without additional restrictions to the variables), and then auxiliary nonlinear optimization problem is constructed on the basis of the obtained solution. Solution of the mentioned auxiliary problem is based on a specialized method of nonlinear optimization - Box method. The result is the algorithm proposed by the author for solving linear programming problems with additional restrictions to the variables with indication of the accuracy estimates. The solution of this problem has a high practical importance. Such restrictions to the variables in the linear programming problems occur often enough for production problems. Method application is shown on the example of an optimal plan finding for pattern cutting in the paper industry, when the task arises associated with the rounding of reels number for paper machines in terms of the found optimal paper cutting plan.

We consider the modeling problem for the human-operator functional activity. Productivity is selected as the main indicator of his function during the working shift. The problem is solved in the class of additive interval piecewise polynomial time views. Real labor productivity of human-operator is suggested to be formed by three interrelated processes: warming-up, tiredness and functionality restoration. Recreational interval for restoration during the first half of the working shift after cumulative tiredness over the first half-shift is considered by the authors as a system-related factor. The model takes into account: interval character of the human-operator individual properties. This gives the possibility to describe more fully and adequately the functional activity of the human-operator. Piecewise polynomial representation made it possible to describe adequately his performance, without complex approximation representations that accumulate errors of final grades for the human-operator performance. Obtained interval additive piecewise polynomial time operation model of human operator activity in the quasi-static environment has given the possibility to analyze and predict functional measures for performance management of human-operator functional activity in manufacturing static environment.

Regular and Mach (irregular) reflection of an oblique shock wave from the wall is considered. Criteria for the transition from regular to irregular reflection are described: von Neumann criterion and the criterion for fixed Mach configuration. Specific incident shock wave intensities corresponding to the two criteria for the transition from regular to irregular reflection were plotted. The area of ambiguity solutions was demonstrated in which both regular and Mach reflection is not prohibited by the conditions of dynamic compatibility. Areas in which the transition from one type of reflection to another is possible only by a shock wave were described, as well as areas of a possible smooth transition. Dependence of the magnitude of this abrupt change in reflected discontinuity intensity from the intensity of the incident shock wave was plotted. Intensity dependences of the reflected discontinuity from the intensity of the shock wave incident on the wall for all types of reflections were shown.

The subject of study. We examined the interaction of counterpropagating shock waves. The necessity of counterpropagating shock waves studying occurs at designing of high Mach number modern internal compression air intakes, Ramjets with  subsonic and supersonic combustion, in asymmetrical supersonic nozzles and in some other cases. In a sense, this problem is a generalization of the case of an oblique shock reflection from the wall or from the plane of symmetry. With the renewed vigor, the interest to this problem emerged at the end of the 90s. This was due to the start of the programs for flight study at hypersonic speeds. The first experiments performed with air intakes, which realized the interaction of counterpropagating shock waves have shown that the change in flow velocity is accompanied by abrupt alteration of shock-wave structure, the occurrence of nonstationary and oscillatory phenomena. With an increase of flow velocity these phenomena undesirable for aircraft structure became more marked. The reason is that there are two fundamentally different modes of interaction of counterpropagating shock waves: a four-wave regular and a five-wave irregular. The transition from one mode to another can be nonstationary abrupt or gradual, it can also be accompanied by hysteresis. Main results. Criteria for the transition from regular reflection of counterpropagating shock waves to irregular are described: the criterion of von Neumann and the stationary Mach configuration criterion. We described areas in which the transition from one reflection type to another is possible only in abrupt way, as well as areas of possible gradual transition. Intensity dependences of the reflected shock waves from the intensity of interacting counterpropagating shocks were given. Qualitative pictures of shock-wave structures arising from the interaction of counterpropagating shock waves were shown. Calculation results of the intensity of outgoing gas-dynamic discontinuities, the intensities corresponding to the transition from regular to irregular interference were described. Numerical calculations of the shock-wave structure transformation in the conditions of hysteresis were performed. The results were compared with the experiments carried out by hydraulic analogy method. Practical significance. Results of the work complement well the theory of stationary gas-dynamic discontinuities interference and can be used at designing of perspective images of supersonic and hypersonic aircraft.

We propose methods for compact representation of priority matrix with high dimensionality, which is used to describe priority queueing disciplines of demands in systems with nonhomogeneous load. This considerably decreases dimensionality of the priority matrix in comparison with original values in case that the number of classes of demands, entering the system, is large. Two methods for compact representation of priority matrix are considered: for canonical and non-canonical original matrix. It is shown that there is one-to-one correspondence between priority matrix and its compact representation. Mathematical expressions are derived for forward and backward recalculation of elements of original priority matrix into its compact representation. Rules governing the construction of correct matrixes are given for canonical and noncanonical priority matrixes.

Cadmium sulfide quantum dots are perspective materials in optics, medicine, biology and optoelectronics. Fluorophosphate glasses, doped with cadmium sulfide quantum dots, were examined in the paper. Heat treatment led to the formation of quantum dots with diameters equal to 2.8 nm, 3.0 nm and 3.8 nm. In view of such changes in the quantum dots size the fundamental absorption edge shift and the luminescence band are being displaced to the long wavelengths. Luminescence lifetime has been found to be dependent on the registration wavelength in the range from 450 to 700 nm. Obtained fluorophosphate glasses with CdS quantum dots can find their application as fluorescent materials with intensive luminescence band and long excited-state natural lifetime.

The paper deals with the findings of negative anastigmatic lenses at the final position of an object. The negative lenses are considered with refraction index n=1.7849 (type of glass is TF12) and thickness d=5 mm, working with paraxial magnifications β=1,1x;1,3x;1,5x with account of the distances from the first lens surface to the object S1=9; 25 mm and the size of the object y=15 mm. Dependences of negative lens forms from the position of anastigmatic pupils and from radii of meridional caustics which are convenient for understanding aberrational properties of anastigmatic lenses. The findings give the possibility to synthesize wide-angle lenses with the corrected aberrations of image curvature and meridional coma without geometrical vignetting of wide sloping bunches.