V. M. Aniskin

Sand‐dwellers in rocky habitats: a new species of Gerbillus (Mammalia: Rodentia) from Mali

The genus Gerbillus (Mammalia: Rodentia) is characterized by an important morphological homogeneity associated with an extensive karyotypic diversity. Here we describe a new species of Gerbillus from the Inner Delta of the Niger River in Mali, on the basis of morphological and chromosomal data. This new species seems to be morphologically very similar to G. campestris, another bare-footed species known from northern Africa. Nevertheless, it can be distinguished from the latter species by a different molar pattern and a specific karyotype. The three specimens on which this description is based were caught in a rocky outcrop, and behavioural observations in captivity suggest an adaptation to life in rocky habitats. This finding is unusual as rodents of the genus Gerbillus are generally sand-dwellers. Moreover, this new species enriches the gerbil community of this Sahelian region, in which at least nine species of the genus can be found. Finally, this description highlights the importance of chromosomal studies for the characterization of biological diversity in tropical rodents, where morphological sibling species are numerous.

A new sibling species of Taterillus (Muridae, Gerbillinae) from West Africa

Summary Modern systematics can now rely on powerful discriminating techniques, such as cytogenetics. As a result, a growing number of sibling species has been described in a variety of taxa. Among mammals, this is particularly true in rodents. Here, we describe a new species of Taterillus (Rodentia, Gerbillinae), namely Taterillus tranieri sp. n. based on specimens from Mali and Mauritania. Neither external and cranial morphology nor morphometrics taking size and shape into account could lead to a satisfying diagnosis of this species relative to the four West African species known in this genus. Conversely, this new species could be characterized by a very specific karyotype (with 2N=14/15, the lowest diploid number in gerbilline rodents, NFa=22–24) differing from that of its closest relative Taterillus petteri (2N=18/19, NFa=28) by two tandem translocations accompanied by 2 centromere activations/desactivations, one non reciprocal translocation, and three pericentric inversions. In addition to providing non-ambiguous arguments in favour of the description of this taxon as a new biological species, these chromosomal results confirm the complex karyotypic evolution of Taterillus . Furthermore, this study illustrates how cytogenetics can contribute to the description of sibling species and hence to biodiversity. These cryptic taxa also constitute valuable support for evolutionary studies, especially concerning speciation processes. They also represent important issues in applied research such as in conservation biology or pest species control. The routine use of cytogenetics for species characterization will undoubtedly constitute a powerful diagnostic tool in these contexts.

Effect of nozzle size on supersonic microjet length

The gasdynamic structure of supersonic underexpanded nitrogen microjets emitted from supersonic nozzles with diameters of 10–340 μm has been studied. Data on the mean wave-structure cell length in the initial region and the length of the supersonic region have been obtained. The relative length of the supersonic region significantly increases when the nozzle diameter is reduced below about 20 μm. The results of measurements are compared to available published data for gas macro- and microjets.

Stability of a subsonic gas microjet

The stability of and the laminar-turbulent transition in a plane subsonic helium microjet flowing out into the atmosphere is studied experimentally. The microjet experiences both natural perturbations and controlled periodic acoustic effects. The averaged and instantaneous flow fields are visualized using the Schlieren method and particle tracking method. The pulsation parameters of the mass flow rate are measured, and data for nonlinear interaction between the perturbations at the laminar-turbulent transition in the microstructure are obtained by bispectral analysis.

Experimental determination of the friction factor coefficient in microchannels

Experimental data used to determine the friction factor in microchannels are presented. Glass microchannels with a circular cross section, diameters of 34.5, 33.6, and 24.5 μm, and different lengths are studied in the experiments. Pure deionized degassed water is used as a working fluid. The range of the Reynolds numbers is 13 ⩽ Re ⩽ 330. A method of two channels is used to calculate the friction factor. The results obtained are in good agreement with theoretical predictions for the case of a developed laminar flow in circular channels, but the use of the method of two channels has some constraints.

Relaminarization in supersonic microjets at low Reynolds numbers

Results of measuring the length of the supersonic portion of the air jets that flow out of axisymmetric sonic nozzles 10.4 μm-1 mm in diameter are presented. The measurements are carried out in a range of degree of jet noncalculation of 1–30 and in a wide Reynolds number range, including the laminar and turbulent flow modes. It is shown that the Reynolds number calculated from the nozzle diameter and the outlet parameters of gas is the parameter that governs jet flow. It is found that, for a laminar jet mixing layer, the length of the supersonic portion sharply increases. When the jet mixing layer becomes turbulent, the length of the supersonic portion decreases. The effect of increasing the length of the supersonic portion after its decrease due to the turbulization of flow in a jet and a growth in the Reynolds number is first discovered.

An experimental study of the flow of subsonic flat mini and micro air jets

We have experimentally studied subsonic submerged air jets emitted from flat mini and micro nozzles with characteristic dimensions from 22 to 600 μm in a range of Reynolds numbers 70–2600. The point of laminar-turbulent transition (jet penetration range) was determined using the flow visualization technique. It is established that the penetration range of micro jets can reach 100–300 nozzle calibers. The Reynolds number for the transition to turbulence in flat mini and micro jets reaches high values (1000–2600), which are two to three orders of magnitude greater than the Reynolds numbers for the loss of stability (3–10). Available experimental data are summarized and generalized based on the Reynolds number determined for the jet penetration range.

Nano-Fabricated Hot-Tubes for Flow Measurements

New type of sensor for thermal anemometry – hot-tube sensor is presented. Some details on manufacture procedure and mechanical properties of sensors are given. Hot-tube response on pulse heating is checked. It is found that time constant of hot-tube is 80 times less that hot-wire one. Pulsations measurements in subsonic flow show that hot-tube does not require thermal inertia compensation for frequencies up to 20-40 kHz and that hot-tube has much better signal/noise ratio than hot-wire. I. Introduction HE fast-responsible flow microsensors with high spatial and temporal resolution are necessary for the solution of key challenges in aero-gas-dynamics. One of such unresolved problems is the problem of the laminarturbulent transition and description of turbulent flows. The measurement of the high-frequency oscillations of low amplitude at the early stage of the laminar-turbulent transition is an important task 1 . The only sensor fit to measure the disturbances in the high-speed flows is a hot-wire probe, its sensitive element being a thin metal wire or film. The time constant of these sensors normally lies within the range of 0.2 – 1 ms, and is limited, in the case of wire sensors, by the wire thermal capacity; and in the case of film sensors – by the heat exchange with the substrate 2,3,4,5,6 . As a result, the sensitivity of the hot-wire anemometers rapidly decreases at the frequencies above 1 kHz, and becomes insufficient to measure the high-frequency (higher than 100 kHz) pulsations, which are typical for the high-speed flows. A search for new methods of batch production of the anemometers sensors involving integral circuit technology is active in the world. Attempts are made to increase the sensitivity with the aid of suspended bridges or membranes 3-6, 7 . Recently 8 an original method of production of monocrystal semiconductor micro- and nano-tubes has been proposed and realized. The method is based on self-rolling of a thin heterofilms detached from the substrate under the action of inner mechanics stresses (Fig. 1). The diameter of the tubes formed in this way can be precisely controlled in the range of 100 µm -2 nm by a proper choice of thicknesses and compositions of the layers in the starting heterostructure. The proposed method has been successfully applied to a number of dielectrics, metals, and semiconductors 8,9, . The purpose of the present paper is to fabricate pilot models of the hot-tube sensors for thermal anemometers from hybrid Metal/GaAs/InGaAs heterofilms using self-scrolling heterostructure technology.

Karyotype of the rare Johnston’s genetGenetta johnstoni (Viverridae) and a reassessment of chromosomal characterization among congeneric species

We present herein new data on karyotypes of members of the genusGenetta. G- and C-banded chromosomes of the Johnston’s genetGenetta johnstoni Pocock, 1908 (2n = 50 / FNa = 92) are described for the first time, and compared with those ofG. genetta (2n = 54 / FNa = 92). In addition, the standard karyotype ofG. maculata (2n = 52 / FNa = 96) was studied. A reassessment of taxonomic attribution of previously published material allowed us to characterize (2n, FNa, and chromosome morphology) the karyotypes of three genets, previously unknown (G. pardina, G. letabae andG. tigrina). Our results show that despite a rather low interspecific variability in 2n and FNa, all the species of genets (exceptG. pardina andG. maculata) appear differentiated when chromosomal morphology is taken into account. Although chromosomal banding data are limited, confrontation of G-band karyotypes with preliminary molecular phylogenetic results reveals that karyotypic evolution within the genusGenetta might involve various rearrangements like Robertsonian and tandem translocations, pericentric inversions, and centromere fissions; thus providing at least for some taxa a solid postzygotic isolation. Finally, our study suggests that cytogenetic analyses might constitute a useful tool for questioning interspecific boundaries, especially within the taxonomically debated complex of large-spotted genets.

An experimental study of the structure of supersonic flat underexpanded microjets

We have experimentally studied the structure of supersonic flat underexpanded room-temperature air jets escaping from micro nozzles with characteristic heights from 47 to 175 μm and widths within 2410–3900 μm in a range of Reynolds numbers of 1280–9460. The dimensions of the first shock cell are established. The supersonic core length of supersonic flat underexpanded air jets has been determined for the first time. A flow regime with a large supersonic core length has been observed for air jets escaping from a 47-μm-high nozzle.