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In this study, cauda epididymal sperm were collected from Amur leopard cats with various causes of death as well as Tsushima leopard cats that underwent castration surgery, and sperm quality was compared with that in domestic cats. A sufficient number of sperm similar to those in domestic cats could be collected from the cauda epididymis of Amur leopard cats. However, in old leopard cats, no or very few cauda epididymal sperm were recovered, although there were no differences in sperm motility and sperm abnormality. There were no significant differences in sperm quality immediately after collection and after freezing-thawing of cauda epididymal sperm compared with corresponding estimates in domestic cats.

Kanagawa Institute of Technology, 会議名: 言語資源活用ワークショップ2020, 開催地: オンライン, 会期: 2020年9月8日−9日, 主催: 国立国語研究所 コーパス開発センター, 電子図鑑等において柔軟な植物検索を可能とするため、日本語の自由形式による植物の特性記述から、コンピュータで処理しやすいJSON形式テキストを自動生成することを試みた。まず、それらの自由形式テキストに係り受け解析を施した。次に、葉と花と果実についてそれぞれ事前に設定した数種類のタグに対して、そのバリュー（値）を係り受け解析結果の木構造をたどりながら設定できる方式を考案した。さらに、自動生成されたJSONを、植物を表す（JAVAの）オブジェクトのストリームに変換して、マップやフィルタ処理を施すことにより、多様な検索を効率的に実行できることを示した。

Equine and human chorionic gonadotropins were administered to two female Amur leopard cats to induce estrus and ovulation during non-breeding season. Fresh semen collected from male cats was surgically inseminated into the uterine horn of the females. In one animal, two fetal sacs without heartbeats were observed on abdominal ultrasonography 31 days after insemination, which indicated that embryo death had occurred. In the other animal, fetal heartbeats were detected in two fetal sacs 29 days after insemination, which confirmed as pregnancy. This animal delivered two newborns 68 days after insemination; the one of the kittens was assumed to be stillbirth, and the other grew normally. In this study, we successfully obtained a kitten from an Amur leopard cat by artificial breeding for the first time in Japan.

Pangolins are ant specialists which are under intense threat from the illegal wildlife trade. Nutrition has notoriously been their downfall in captivity and is still an issue in regards to rescue and rehabilitation. We analyzed the nutrient content of diets used by institutions that are successfully keeping Asian pangolins and to assess the variety of the ingredients and nutrients, compared these with the nutritional requirements of potential nutritional model species. We performed intake studies at five institutions and also had data from three other institutions. We also analyzed five different wild food items to use as a proxy of wild diet. We observed two categories of captive diets: those mostly or completely composed of insects and those high in commercial feeds or animal meat. Nutrient values were broad and there was no clear rule. The non-protein energy to protein energy ratio of the diets were much higher than the wild food items, more so for those which receive less insects. The average contribution of carbohydrate, fat and protein energy were also further away from the wild samples the less insects they contained. The previously suggested nutritional model for pangolins is the domestic dog which is supported by our relatively large nutrient ranges of apparently successful diets, however due to their highly carnivorous nature; the upper most nutrient intake data are not consistent with this and favor the feline nutrient recommendations. We are unable to render a conclusion of what model is more appropriate based on our data collected.

A repeated bathymetric survey reveals seafloor displacement between before and after geodynamic events. We evaluated the less-known spatial resolution and estimation error of the seafloor displacement observation from a vessel-based multi-narrow beam bathymetric survey. In this evaluation, bathymetric data from vessel-based and near-seafloor high-resolution autonomous underwater vehicle (AUV)-based surveys in the same area were used. Simulated vessel-based bathymetric “before and after” data of the seafloor displacement were made using AUV-based bathymetric data. The displacement was verified by comparing these simulated data using the analysis conditions that no locational errors of beam sounding points exist, a footprint effect is uniform, depth accuracy is constant in the analysis area, and there are no depth offset between two data. As a result, we found that the smallest vertical seafloor displacement that can be detected occurs when the horizontal extent of the deformation is larger than several times the size of the footprint (area of the narrow sounding beam projected onto the seafloor) of the used vessel’s multi-narrow beam echo sounder, and in the situation that the amplitude of the depth difference is greater than the accuracy of the vessel-based depth measurement (standard deviation of measuring error). When local slopes of the bathymetry are gentler than those of the artificial variation appeared in the depth differences between two data, the horizontal seafloor displacement seems to be difficult to resolve accurately. The local slope of the artificial depth variation is derived from the wavelength and the amplitude which are equivalent to ~1–3 times of the footprint size and the accuracy of the depth measurement, respectively.

We collected semen from a male Amur leopard cat using the transrectal electroejaculation method and investigated the semen qualities for about four years. In addition, the influence of the season on the spermatogenic function of the Amur leopard cat was investigated with regard to the semen qualities, testicular volume and serum testosterone level. As a result, we could collect semen with good sperm qualities that would be useable for artificial insemination. Some seasonality was noted in the testicular volume and serum testosterone level. We clarified that the semen qualities were favorable before and during the female breeding season compared with those after the breeding season.

Seismic reflection data around the Iheya North Knoll hydrothermal field provide insights into geological structures that control subseafloor hydrothermal fluid flow in the sediment-covered continental backarc basin of the mid-Okinawa Trough. We identified the seismic expression of widespread porous volcaniclastic pumiceous deposits and intrusions as a result of silicic arc volcanism. The porous and permeable volcanic deposits are distributed in an area extending updip from the thick succession of the deep trough to the seafloor at the hydrothermal field. Their regional structure focuses the flow of hydrothermal fluids derived from the surrounding trough-fill sediments and directs them to the vents of the hydrothermal field. The high concentrations of CH4 and NH4 in the fluids of the hydrothermal field are likely derived from the interaction of migrating fluids with trough-fill sediments.

Autonomousunderwatervehicles(AUVs)presenttheimportantadvantageofbeingabletoapproachtheseafloor more closely than surface vessel surveys can. To collect bathymetric data, bottom material information, and sub-surface images, multibeam echosounder, sidescan sonar (SSS) and subbottom profiler (SBP) equipment mounted on an AUV are powerful tools. The 3000m class AUV URASHIMA was developed by the Japan Agency for Marine-Earth Science and Technology(JAMSTEC). After finishingthe engineering developmentand examinationphase of a fuel-cell systemused for the vehicle's power supply system, a renovated lithium-ion battery power system was installed in URASHIMA. The AUV wasredeployedfromitspriorengineeringtaskstoscientificuse.Variousscientificinstrumentswereloadedonthevehicle,and experimental dives for science-oriented missions conducted from 2006. During the experimental cruise of 2007, high- resolutionacousticimageswereobtainedbySSSandSBPontheURASHIMAaroundthenorthernKumanoBasinoffJapan's Kii Peninsula. The map of backscatter intensity data revealed many debris objects, and SBP images revealed the subsurface structurearoundthenorth-easternendofourstudyarea.Thesefeaturessuggestastructurerelatedtotheformationofthelatest submarinefan.However,astrongreflectionlayerexistsbelow~20msbelowtheseafloorinthesouth-westernarea,whichwe interpret as a denudation feature, now covered with younger surface sediments. We continue to improve the vehicle's performance, and expect that many fruitful results will be obtained using URASHIMA.

We investigate frictional-drag reduction with electrolytic microbubbles based on image measurement of a turbulent flow in a water channel at Re = 4800 (based on the half channel height). Microbubbles with a diameter ranging 30–200 μm can reduce frictional drag by as much as 30% relative to single-phase flow even at low void fractions (α ≈ 3 × 10−4); however, drag reduction is only effective within a limited downstream distance from an electrode array. Arrangement of the optical system allows us to measure the bubble-production rate by water electrolysis from images near the wall and to trace the motion of bubbles. We also measure velocity fields using particle-tracking velocimetry based on a shallow depth-of-field approach by segregating tracer particles from microbubbles. Vertically oscillating microbubbles likely represent interaction with vortical structures near the wall, and bubbles approaching the wall appear to induce negative streamwise velocity relative to the surrounding fluid. We relate the wall friction with the double integral of the Reynolds-stress profile and show that its variation due to microbubbles decreases the drag on the wall. Microbubbles tend to coalesce downstream resulting in a fewer bubbles but with greater size; accordingly, the oscillatory motion diminishes, and the frictional drag rather increases.

Instability waves in a laminar planar jet are extracted using hybrid unsteady-flow simulation combining particle tracking velocimetry (PTV) and direct numerical simulation (DNS). Unsteady velocity fields on a laser sheet in a water tunnel are measured with time-resolved PTV; subsequently, PTV velocity fields are rectified in a least squares sense so that the equation of continuity is satisfied, and they are transplanted to a two-dimensional incompressible Navier–Stokes solver by setting a multiple of the computational time step equal to the frame rate of the PTV system. As a result, the unsteady hybrid velocity field approaches that of the measured one over time, and we can simultaneously acquire the unsteady pressure field. The resultant set of flow quantities satisfies the governing equations, and their resolution is comparable to that of numerical simulation with the noise level much lower than the original PTV data. From hybrid unsteady velocity fields, we extract eigenfunctions using bi-orthogonal decomposition as a spatial problem for viscous instability. We also investigate stability/convergence characteristics of the hybrid simulation referring to linear stability analysis.

Hybrid unsteady-flow simulation combining particle tracking velocimetry (PTV) and direct numerical simulation (DNS) is introduced in the series of two papers. Particle velocities on a laser-light sheet acquired with time-resolved PTV in a water tunnel are supplied to two-dimensional DNS with time intervals corresponding to the frame rate of the PTV. Hybrid velocity fields then approach those representing the PTV data in the course of time, and the reconstructed velocity fields satisfy the governing equations with the resolution comparable to numerical simulation. In part 2, by extending the capabilities of the hybrid simulation to higher Reynolds numbers, we simulate flows past the NACA0012 airfoil over ranges of Reynolds numbers (Re ≤ 104) and angles of attack (−5° ≤ α ≤ 20°) and validate the proposed technique by comparing with experimental results in terms of the lift and drag coefficients. We also compare the results with unsteady Reynolds-averaged Navier–Stokes (URANS) simulation in two-dimensions and show the advantages of the hybrid simulation against two-dimensional URANS.

Our previous study showed that the frictional drag decreases with increasing void fraction at Re > 1300, while it increases at Re u '– v 'plane). Here, we focus on two specific Reynolds numbers (at Re ≈ 900 and ≈ 1410, which are close to the laminar-to-turbulent transition regime) and discuss bubble effects on sweep ( u ' > 0, v ' u ' v ' > 0) events as a function of the Reynolds number. We also illustrate velocity fluctuations in the vicinity of an individual bubble and a swarm of bubbles on the u '– v ' coordinates. The results show that a bubble swarm suppresses the velocity fluctuations at Re ≈ 1410.

To investigate the effect of microbubble injection into a turbulent boundary layer, we measure the velocity fields of gas–liquid two-phase flow in a horizontal water channel with a Particle Tracking Velocimetry (PTV) technique. In this study, we focus on a thin shear layer where the Reynolds shear stress is the highest. The effect of the shallow focal depth-of-field (DOF) in a lens system assists to improve the spatial resolution of the PTV results. Considering the distribution of luminous flux, we first enhance the illumination intensity to label the objects on images. With their assistance together with an image processing filter, we can then improve the in-depth resolution of tracer particles and determine their positions more accurately. We apply this shallow DOF-based PTV technique to measure the streamwise and spanwise velocity components and visualize the motion of bubbles relative to continuous phase in the near-wall region at three downstream positions. The result shows that the averaged velocity right downstream of the bubble injector clearly decreases due to microbubbles. The local instantaneous flow structure around bubbles shows no clear coherence because of highly turbulent background; however, the frequency spectrum analysis finds that the bubbles reduce the kinetic energy in a frequency range higher than the bubble passing frequency.

Backlight imaging tomography is used to experimentally investigate interfacial structures of gas–liquid two-phase flow in circular tubes. The tomography method is based on the attenuation of visible light that causes the inside of the liquid phases to be colored with dye. Increasing the number of light projections provides accurate phase distributions to be reconstructed by a linear backward projection scheme. After the reconstruction performance is examined with numerical simulations for several test cases, the method is applied to slug flows that have complicated 3D interfaces from turbulence. Interfacial structures are compared between straight and helical tubes to determine the effect of centrifugal acceleration. The result demonstrates that centrifugal acceleration provides a liquid-clinging layer on the inner wall against gravity while a high-speed collision of liquid with the top wall happens in a straight tube.

Particle tracking velocimetry (PTV) is applied to flows around a Savonius turbine. The velocity vector field measured with PTV is utilized to estimate the pressure field around the turbine, as well as to evaluate the torque performance. The main objective of the work is the establishment of the pressure estimation scheme required to discuss the turbine performance. First, the PTV data are interpolated on a regular grid with a fourth-order ellipsoidal differential equation to generate velocity vectors satisfying the third-order spatio-temporal continuity both in time and space. Second, the phase-averaged velocity vector information with respect to the turbine angle is substituted into three different types of pressure-estimating equations, i.e. the Poisson equation, the Navier–Stokes equation and the sub-grid scale model of turbulence. The results obtained based on the Navier–Stokes equation are compared with those based on the Poisson equation, and have shown several merits in employing the Navier–Stokes-based method for the PTV measurement. The method is applied to a rotating turbine with the tip-speed ratio of 0.5 to find the relationship between torque behaviour and flow structure in a phase-averaged sense. We have found that a flow attached to the convex surface of the blades induces low-pressure regions to drive the turbine, namely, the lift force helps the turbine blades to rotate even when the drag force is insufficient. Secondary mechanisms of torque generation are also discussed.

Microbubble and air film methods are believed to be applicable to skin friction reduction in ships. Small bubbles are dispersed into the turbulent boundary layer in the former case, and wide air layers cover the wall surface in the latter case. Previous studies did not specifically address the intermediate case between the microbubble and air film conditions. This study is concerned with the possibility and mechanism of drag reduction using relatively large air bubbles compared to the boundary layer thickness in a horizontal turbulent channel flow. The relationship between local skin friction and the bubble’s interfacial structure is investigated by synchronizing the measurement of wall-shear stress with the image acquisition of bubbles. The bubble sizes range from 2 to 90 mm approximately. As a result, a negative correlation between the local skin friction and the local void fraction is confirmed by the time-resolved measurement. A new observation is the fact that the local skin friction decreases drastically in the rear part of individual large bubbles, and rapidly increases after the bubble’s rear interface passes. This characteristic underlies the bubble-size dependency of the average skin friction in the intermediate bubble size condition.

In February 2006, intensive seismic survey was carried out in Sagami Bay area, central Japan, during the KY06-01 cruise using R/V Kaiyo of JAMSTEC (Japan Agency for Marine-Earth Science and Technology). This cruise follows the pre- vious KY05-06 cruise survey, in which we conducted single-channel seismic survey in the same area. Used tools are a 18 channel streamer with two 355 in 3 GI guns, and a single-channel streamer with a cluster gun. We obtained 21 profiles with GI- guns in the eastern Sagami Bay, 20 profiles with GI-gun in the western Sagami Bay and 20 profiles with cluster gun near Hatsushima cold seep communities in the western Sagami Bay. Very clear acoustic images were captured with different fre- quencies on the same lines. We present here the seismic profiles obtained during the KY06-01 cruise.

Air–water two-phase flow in helically coiled tubes is investigated experimentally to elucidate the effects of centrifugal acceleration on the flow regime map and the spatial and the temporal flow structure distribution. Three kinds of test tubes with 20 mm inner diameters including a straight tube are used to compare the turbulent flow structure. Superficial velocities up to 6 m/s are tested so that the centrifugal Froude number covers a range from 0 to 3. The interfacial structure is photographed from two directions by a high-speed video system with synchronized measurement of local pressure fluctuations. The results reveal that the flow transition line alters due to centrifugal force acting on the liquid phase in the tube. In particular, the bubbly flow regime is narrowed significantly. The pressure fluctuation amplitude gets large relatively to the average pressure loss as void fraction increases. The frequency spectra of the pressure fluctuation have plural peaks in the case of strong curvature, implying that the periodicity of slugging two-phase flow is collapsed by an internal secondary flow activated inside the liquid phase. Moreover, under large Froude number conditions, the substantial velocity of the gas phase that biases to the inner side of the helical coil is slower than the total superficial velocity because the liquid flow is allowed to pass through the outer side and so resembles a radial stratified flow.

The pumping characteristics of an inscribed trochoid gear pump are investigated experimentally. The paper deals with viscosity-dominant conditions, i.e. low Reynolds number performances less than 5000 in order to develop a miniaturized pump. The test pump of 4 mm in the inner basic radius is designed for the experimentation. The volume flow rate and the pressure rise of the pump are measured using a test loop with two different liquids. Volumetric efficiency, dimensionless pressure rise, and pump's power efficiency are obtained as function of Reynolds number. The present results support the previous theoretical study, that is, the lower Reynolds number the higher performance the trochoid gear pump has. This implies an advantage toward miniaturization. On the other hand, the pump's power efficiency is obtained as only a few % because of significant increment of wear caused in six parts of gear clearance, which should be discussed as the next step of the research.

トロコイドギヤポンプは，トロコイド曲線を持つ内外２つのギヤで流体を封入する複数の密閉室が回転することで，流体を輸送するポンプである．このポンプでは密閉室の位置と形状が回転に伴って時間的に変化し複雑な流動を持つ．特にギヤのクリヤランス部を通る流れがポンプの性能を支配するため，トロコイドギヤポンプの可視化装置を設計・製作し，密閉室内の流動をRe＝300～10000の範囲で可視化した．可視化のトレーサ粒子としては，微小平板形状のカリロスコープ粒子(公称サイズ：30μｍｘ6μｍｘ0.07μｍ)を用いた．可視化された時系列画像を位相統計することで，密閉室内の流動構造のレイノルズ数依存性，容積効率依存性が明らかとなった．具体的には、Re＝1600～2000において流れが乱流遷移すること，この乱流化の主要因がギヤのクリアランス部から上流側に向けて逆流する噴流であることなどが見いだされた．

The helically coiled tube of heat exchanger is used for the evaporator of prototype fast breeder reactor “Monju”. This paper aims at the grasp of two-phase flow phenomena of forced convective boiling of water inside helical coiled tube, especially focusing on oscillation phenomena of dryout point. A glass-made helically coiled tube was used to observe the inside water boiling behavior flowing upward, which was heated by high temperature oil outside the tube. This oil was also circulated through a glass made tank to provide the heat source for water evaporation. The criterion for oscillation of dryout point was found to be a function of inlet liquid velocity and hot oil temperature. The observation results suggest the mechanism of dryout point oscillation mainly consists of intensive nucleate boiling near the dryout point and evaporation of thin liquid film flowing along the helical tube. In addition, the oscillation characteristics were experimentally confirmed. As inlet liquid velocity increases, oscillation amplitude also increases but oscillation cycle does not change so much. As hot oil temperature increases, oscillation amplitude and cycle gradually decreases.

In bubbly two-phase flow, the gas phase and liquid phase have different flow fields. The relative velocity of the two phases depends on the motion characteristic of the bubbles. The mathematical expression for the motion of a small bubble at low Reynolds number is already established. Using the equation, the liquid velocity along the trajectory of the bubble is calculated inversely using the motion equation. Whole field liquid flow structure is also estimated using a spatial and/or temporal interpolation method. This paper proposes an algorithm for estimating the liquid phase flow field from measurement data on bubble motion. In order to verify this principle, Taylor–Green vortex flow and Karman vortex shedding from a square cylinder have been chosen. The results reveal that by combining the inverse analysis and PTV with the spatio-temporal post-processing algorithm one can reconstruct well the carrier phase flow of the gas–liquid two-phase flow.

Air–water two-phase flow in a helically coiled tube is investigated using backlight imaging tomography to elucidate the effect of centrifugal acceleration on phase distribution and interfacial structure. Superficial velocities up to 6 m s−1 in 20 mm diameter tube are tested. We focused on a slug flow regime in which centrifugal acceleration dominates the flow. The interfacial structure is visualized in six directions using a set of originally designed mirror-mounted water jackets. A temporal expansion image is made from line-sampled images and is used to reconstruct phase distribution through a linear backward projection algorithm. The present topography measurement showed various new features of gas–liquid two-phase flow in a helically coiled tube, such as a wall-covering effect in the case of high superficial velocity.

An image analysis method for measuring bubble velocity fields at high bubble number density is proposed. It is based on computing the cross correlation of bubble images with multiple spatial resolutions, i.e. a recursive cross correlation technique. Comparing several PTV and PIV schemes, it is confirmed that the recursive cross correlation leads to the best measurement results because of the robustness with respect to optical and dynamic characteristics of bubbles. The method is applied successfully to the measurement of bubble motion in bubble plumes accompanying a strong unsteadiness over a wide frequency range. The results reveal that the high frequency fluctuations of bubble velocities grow in the shear layer and near the top surface, while low frequency fluctuations dominate in the middle part of the tank. The characteristic frequency divides the frequency spectrum of the bubble fluctuation intensity into two regions: where there are turbulent behaviors and where there are macroscopic convection patterns in the bubble plumes.

Skin frictional drag of bubbly two-phase mixture in a horizontal turbulent channel is investigated experimentally using a shear stress sensor and a high-speed video camera. We choose non micro bubbles having a size of 1 to 10 mm intentionally to confirm that the drag reduction still works with relatively large bubbles to the channel height. The measurement results have shown that the drag reduction realized in case of a void fraction higher than a critical value that depends on liquid flow velocity. Also, significant bubble size dependence was found in the region near bubble injector. A synchronized measurement of local shear stress and interfacial structure has newly shown that the instantaneous friction factor decreased in rear part of individual bubble.

The frictional drag reduction provided with small bubbles is investigated experimentally using vertical concentric cylinders. The friction reduction ratio is measured using a torque meter mounted on the inner cylinder for a wide range in Reynolds number from wavy vortex flow (WVF) to turbulent Taylor vortex flow (TTV). The present data show around 36% drag reduction in the case of WVF regime at Re =600 and the reduction maintains until Re =4 000. The friction reduction ratioη defined by the unit void fraction obeyed in a linear relation with inverse values of Froude number, and reached up to 10 in the best case, that implies the highest sensitivity for the drag reduction. The bubble distribution measured in the gap showed a peak near the inner cylinder surface resulting in high local shear stress reduction.

Wall-sliding bubbly flow is experimentally investigated using a shallow focus imaging technique. The technique allows to capture the motion of tracer particles inside a thin layer from a wall. Adding digital image processing provides further fine spatial resolution up to 100 ratio of the length of the viewing area to the focused thickness. Bubble-bubble interaction, which is one of dominant phenomena in wall-sliding bubbles, is analyzed with using Particle Tracking Velocimetry applied to both phases. Transition of bubbles' pattern from vertically chained to horizontally clustered arrangement is discussed with the local liquid phase flow structure around individual bubble. The results reveal that the temporally high fluctuation velocity in the liquid phase generates during the transition, and the circulation of bubble-vicinity liquid induces rapid transition of the arrangement.

This paper concerns with flow visualization and image measurement of bubbly flows around various shapes of cylinders. A coaxial confined double rectangular chamber is constructed in order to provide a wide two-dimensional uniform bubble distribution upstream of the obstacle. The experiment shows that a wide two-phase convection is induced around the obstacle, though such an effect is not observed in research on the single-phase flow around objects. The spatial scale of the two-phase convection depends sensitively on the shape of the obstacle. Dense arrangement of cylinders is also investigated to find the interaction among the convection. The measurement results of void fraction, bubble velocity and liquid phase flow, which are obtained by image processing including particle tracking velocimetry (PTV), explore the detailed mechanism of generating the convection.Copyright © 2003 by ASME

Bubble-driven flow around circular cylinders in a narrow channel is experimentally investigated by means of image processing. The cylinders are settled in the channel with three kinds of arrangement pattern to clarify the difference of the internal two-phase flow structure. Thinning algorithm is applied to the detection of all the bubbles in order to measure the bubble motion in locally high void fraction. Size and spatial distribution of the bubbles are also obtained with the image analysis to discuss the bubble's coalescence/fragmentation due to the collision with the cylinders. The results imply that the rising velocity of the bubble is governed not only by bouncing on the cylinders but also by the liquid phase flow pattern that is sensitively dependent on the gas flow rate and the cylinders' arrangement pattern.

The pumping characteristics and the internal flow structure of an inscribed trochoid gear pump are investigated by means of three-dimensional numerical simulation. Cartesian grid system is employed to calculate the fluid flow while the boundary conditions on rigidly rotating gear surface is expressed with Lagrangian markers. The results reveal that the flow rate and the pressure rise obtained by the pump become the highest at Re=10 when the clearance between the two gears is considered. At lower Re numbers, the shear stress transfer on the gear surface fluctuates significantly resulting into lower performance. For higher Re numbers, backward induced jet flow through the clearance makes the internal flow complicated due to non-uniform centrifugal acceleration.

The method of direct measurement of vorticity (DMV) is used for extracting vorticity directly from digital particle images. It is the analogue of cross-correlation in particle image velocimetry (PIV) evaluation. There are two main purposes behind the present study: one is to compare the implementation of DMV with PIV in order to clarify the characteristics of the DMV technique; the other is to investigate the influence of the experimental parameters such as particle image size, the size of the sample pattern and the particle density on the precision of DMV. The investigation is performed by applying the DMV method to two kinds of pairs of synthetic digital particle recordings, which respectively represent a solid rotational and a parallel shearing flow. The statistical uncertainty errors are obtained by varying a single parameter at a time. The DMV method shows good measurement results for the stronger rotational flow. Limitations of the DMV technique with regard to the measurable intensity of the shear flow are discussed. The optimum experimental parameters for both flows are given.