We present a study of subcritical shocks in a highly collisional laboratory plasma with a dynamically significant magnetic field. Shocks were produced by placing cylindrical obstacles into the supermagnetosonic ($M_{{\rm MS}} \sim 1.9$) outflow from an inverse wire array z-pinch at the MAGPIE pulsed power facility ($n_{e} \sim 8.5 \times 10^{17}\,{\rm cm}^{-3}$, $v \sim 45\,{\rm km}\,{\rm s}^{-1}$). We demonstrate the existence of subcritical shocks in this regime and find that secondary stagnation shocks form in the downstream which we infer from interferometry and optical Thomson scattering measurements are hydrodynamic in nature. The subcritical shock width is found to be approximately equal to the resistive diffusion length and we demonstrate the absence of a jump in hydrodynamic parameters. Temperature measurements by collective optical Thomson scattering showed little temperature change across the subcritical shock (${<}10\,\%$ of the ion kinetic energy) which is consistent with a balance between adiabatic and Ohmic heating and radiative cooling. We demonstrate the absence of subcritical shocks when the obstacle diameter is less than the resistive diffusion length due to decoupling of the magnetic field from the plasma. These findings are supported by magnetohydrodynamic simulations using the Gorgon and AstroBEAR codes and discrepancies between the simulations and experiment are discussed.

In this review paper, different landing strategies of diverse species of animal flyers and gliders, both extinct and extant, are analysed. These methods vary depending on the animal group and the sensory system used by the animal to detect its landing site. In almost all species the use of delayed stall during the landing manoeuvre was observed. Sometimes wing flapping was used to aid in deceleration. With respect to guidance and navigation, most insect, bird and mammal gliders use their vision to guide them to landing via optical flow or motion parallax. Bats, which are nocturnal creatures, rely on their auditory system as they use echolocation to find their nesting site. Some butterfly and moth species guide themselves to landing using their olfactory sense as they follow pheromone trails. The information presented here can be used as a source of information for novel bio-inspired unmanned aircraft design.

In this review paper, several take-off techniques of different species of animal flyers and gliders, both extinct and extant, are analysed. The methods they use vary according to animal group and size. Smaller animals, such as insects, rely on the use of transient aerodynamic techniques or the use of stored elastic energy. Medium-size flyers such as birds, bats, and other mammal gliders initiate flight by a jump which involves leg and wing movement coordination. The largest animals to fly, the extinct pterosaurs, are believed to have used a combination of aerodynamic and mechanic techniques in order to become airborne. The information presented here can be used as a resource for novel biomimetic unmanned aircraft design.

The interaction of short (1−2 ps) laser pulses with solid targets at irradiances of over 1016 Wcm−2, in the presence of a substantial prepulse has been investigated. High absorption of laser energy is found even at high angles of incidence, with evidence for a resonance absorption peak being found for S, P, and circular polarizations. It is considered that this may be a result of refraction and beam filamentation, which causes loss of distinct polarization. Measurements of hard X-ray emission (∼ 100 keV) confirm a resonance absorption type peak at 45−50°, again for all three cases. Typically, 5−15% of the incident light is back-reflected by stimulated Brillouin scatter, with spatially resolved spectra showing evidence of beam hot-spots at high intensity. The possibility that filamentation and refraction of the beam can explain the lack of polarization dependence in the absorption and hard X-ray emission data is discussed.

The work performance of two teams of four donkeys (heavy, 680 kg and light, 460 kg) and one pair of Jersey crossbred oxen (646 kg) was compared when they ploughed 4 hi day on four types of soil (clay, redsoil, sandy soil and sandy clay) using two types of plough, a conventional ox plough (40 kg) and a lighter prototype, the ‘Walco’ plough (32 kg) on an experimental farm. Work parameters were also measured with farmers’ cattle and donkey teams ploughing on f arms in Matobo and Nkayi districts. Working speed, power and effective field capacity (ETC) were higher for the ox-team (1·03 m/s, 920 W and 14·5 h/ha for the conventional plough and 0·99 m/s, 745 W and 13·9 h/hafor the Walco plough) and the heavier donkey team (0·87 m/s, 689 W and 14·2 h/hafor the conventional plough and 0·87 m/s, 787 W and 17·3 h/hafor the Walco plough) than for the lighter donkey team (0·59 m/s, 461 W and 22·1 h/hafor the conventional plough and 0·64 m/s, 445 W and 23·4 h/hafor the Walco plough). Expressed as a proportion of live weight or metabolic live weight there were no significant differences in draught forces exerted between teams but power output per unit live weight was greater in the ox-team than in the light donkey team but similar to that in the heavy donkey team. The Walco plough required a lower force (742 N) to operate than the conventional plough (816 N) but apart from this did not have any marked advantages over the conventional plough. On-farm, team sizes of donkeys varied from three to seven animals (team weight 340 kg to 1007 kg) and cattle team sizes from two to four animals (team weights 558 to 1709 kg). Regardless of team number, the heavier teams tended to out-perform the lighter teams (speed range 0·63 to 1·08 m/s, power 395 to 1136 W, EFC 9·1 to 25 h/ha)) with one exception, a well trained team of two oxen (team weight 879 kg, speed 1·02 m/s, power 775 W, EFC 9·1 h/ha). Donkeys tended to plough at a slower pace than oxen, with a lower power output, although when weight differences between teams were equalized (four heavy donkeys compared with two oxen), then there was little to chose between the species. Results suggested that teams of three or more donkeys can effectively be used for ploughing on the soils tested. The results highlighted the importance that team live weight and training/experience have in determining work performance.

Three experiments were undertaken to assess the Zimbabwean donkey. In the first study, 191 male and 144 female working donkeys from Matopos, Nkayi and Matobo districts were weighed. Age, sex and coat colour were recorded and heart girth, umbilical girth, body length and height were measured. There were no differences (P > 0⋅05) in live weight, 142 and 141 kg, heart girth 115 and 115 cm, body length 89 and 90 cm and height 105 and 105 cm between males and females. This suggests that draught potential might be similar between the sexes. Heart girth was the best single predictor of live weight: live weight (kg) = heart girth (cm)2⋅83/4786 (R2 = 0⋅86). Donkeys were similar in size to others in Africa. In the second study, the voluntary dry-matter intake (DMI) of a poor quality hay was measured for 35 days in nine male (mean live weight 150 kg) and nine female donkeys (142 kg) allocated to one of three treatment groups: water available ad libitum, or given every 48 h, or every 72 h. There were significant differences in daily water (P < 0.001) and DMIs (P < 0.05): 8.5, 4.9 and 5.1l and 3.1, 2.8 and 2.7 kg for the three treatment groups, respectively. However even with restricted access to water, donkeys maintained a relatively high DMI. In the third experiment a 3 Х 3 Latin square was designed with three teams of four male donkeys each, either working (5 h/day) I no access to food (5 h/day); not working/no access to food (5 h/day) or not working/access to food 24 h/day, for 63 days. For working and non-working donkeys, there were no significant differences (P > 0.05) in DMI, DM apparent digestibility and mean retention time (MRT) of hay. Time of access to food did not influence DMI. The apparent lack of response was attributed primarily to the poor quality of the hay.

A partnership between California State University, Hayward and Ohlone College, Fremont, California resulted in a program to introduce undergraduate students to scanning electron microscopy (SEM) sample preparation procedures. Ten students enrolled in a biology major's course at the Ohlone Community College are selected each semester to participate in the program. In addition to these students, ten others from a Basic Skills Enhancement program for underrepresented students participate through a short course offered during the summer. The program, in effect for two years, resulted in the compilation of a laboratory manual describing basic sample preparation techniques that are appropriate for an outreach program. We select samples that are simple to prepare yet yield results that are germane to a biology student's curriculum. A selection of plants, pollen grains, bacteria, fungi, yeast, Drosophilia melanogaster, and various other invertebrates are typical samples that lend themselves to an outreach program that emphasizes biological concepts. Initially our program required the Ohlone College students to come to the Hayward campus to prepare their samples. External funding has allowed us to purchase sample preparation equipment for the community college.

A partnership has developed between the Microscope and Graphic Imaging Center (MAGIC) at California State University, Hayward and Ohlone Community College. The purpose of the collaboration is to develop a program to allow community college students to gain experience in preparing and viewing samples using scanning electron microscopy technology. The learning module involves students from the Ohlone College Biology Majors Program and student mentors from CSUH. An additional component is the introduction of under-represented students into a Biology Fellowship Program in which they also participate in the SEM learning module. Participants for these programs are selected on the basis of their interest and how this experience will benefit them as expressed in a one-page written essay. Ten students are selected to participate in the programs.

The objectives of the learning module are to: 1) learn specimen preparation techniques and develop skills in SEM technology; 2) gain hands-on experience and develop some laboratory skills necessary for effective use of a SEM in studying biological specimens; 3) share the experience gained with peers at their home institution.

Since the discovery of fading X-rays from Gamma-Ray Bursts (GRBs) with BeppoSAX (Piro et al. 1997, Costa et al. 1997), world-wide follow-up observations in optical band have achieved the fruitful results. The case of GRB 970228, there was an optical transient, coincides with the BeppoSAX position and faded (Paradijs et al. 1997, Sahu et al. 1997). These optical observations also confirmed the extended component, which was associated with the optical transient. The new transient are fading with a power-law function in time and the later observation of HST confirmed the extended emission is stable (Fruchter et al. 1997). This extended object seems to be a distant galaxy and strongly suggests to be the host.

It has become fashionable in educational circles to pay homage to what is described as ‘cultural activities’ in schools, particularly those schools in which the clientele is drawn from a culturally different community. Such an addition to the curriculum content of schools is a response to the concern that schools are somehow irrelevant to the needs of the client group. While the latter point may indeed be true, this paper argues that curriculum decisions in the area of ‘culture’ are deceptively simple.

We have undertaken a multi-site, multi-wavelength observing campaign on the archetypal O stars ζ Puppis (O4 I(n)f) and ζ Ophiuchi (O9.5 V). Both stars are well known for the strength of their line profile variations (lpv's), and represent extremes of O spectral type and luminosity class. UV time-series spectroscopy of ζ Pup and ζ Oph is described by Prinja et al. (Ap.J. 1992, 390, 266), and Howarth et al. (Ap.J. 1992, submitted) respectively. The optical spectroscopic results of ζ Oph are reported by Reid et al. (1992, ApJ submitted), of which some of the principal results are given here.

During late April, and early May, 1989, we obtained high-resolution, high signal-to-noise optical spectra of the late O-type, rapid rotator ζ Oph. Time-series analysis, using the CLEAN algorithm, has shown that the characteristic lpv seen in HeI λ447lÅ, Si III λλ4552, 4567, 4575Å, and MgII λ448lÅ can be satisfactorily represented as a set of 4 sinusoids. No substantial variation is observed in HeII λ4541, or NIII λ4517Å. We attribute this behaviour to a combination of equatorial gravity-darkening and a latitudinally-confined origin for the lpv.

The phase changes over the line profiles indicate repetitive patterns of axial symmetry, rotating prograde in the co-rotating frame of the star. The periods are 3.339 hours (-m = 4), 2.435 hours (-m = 5 or -m = 6), 1.859 hours (-m = 9 ± 1), and either 1.366 hours or 1.292 hours (-m = 11 ± 1); -m represents the spatial frequency around the stellar equator. The first three periods confirm those found at earlier epochs, and we conclude that some lpv characteristics are reproduced over at least a 2-year interval.

Since no commensurate superperiod (|m|P) exists, and since the super-periods are less than our estimated minimum rotation period for ζ Oph (> 18 hours), we reject a rotational modulation origin for the lpv and conclude that the star is undergoing multi-mode, sectorial, non-radial pulsations.

A low temperature process for laser dehydrogenation and crystallization of hydrogenated amorphous silicon has been studied. The key feature of this process is the removal of hydrogen from the amorphous silicon thin films while crystallizing the films at the same time. Studies of transient phenomena, hydrogen loss, and crystallinity, using transient reflectivity analyses, transmission electron microscopy and quadrupole mass spectrometry, find that hydrogen out-diffusion depends strongly on film structure and the melt duration controlled by the laser energy density. Utilizing this process, for which the maximum temperature is 350 °C, both high quality polycrystalline and amorphous silicon TFT's have been fabricated on the same Corning 7059 glass substrate.

Melt spinning was used to rapidly quench V2CrA11-xBx and Ti3Nb6Mo3Si4 alloys. Melt spinning had very little effect on the crystal structure of the V2CrA11-xBx alloys. However, a new (NbTiMo)3 Si A–15 phase was found by rapid quenching of the Ti3Nb6Mo3Si4 alloys; the lattice parameter was 5.08 Å. Melt spinning increased the Vickers microhardness values of the V2CrA11-xBx alloys from 500 to 750, and of the Ti3Nb6Mo3Si4 alloys from 1000 to as high as 1675. Melt spinning increased the superconducting transition temperature of the Ti3Nb6Mo3Si4 alloys from 1.9 to 3.4K.

It has become fashionable in educational circles to pay homage to what is described as ‘cultural activities’ in schools, particularly those schools in which the clientele is drawn from a culturally different community. Such an addition to the curriculum content of schools is a response to the concern that schools are somehow irrelevant to the needs of the client group. While the latter point may indeed be true, this paper argues that curriculum decisions in the area of ‘culture’ are deceptively simple.

In following a suggestion of S. Chowla to apply a method of C. Hooley [3] to obtain an asymptotic formula for the sum ∑ r(n)r(n+a), where r(n) denotes the number of representations of n≤x

n as the sum of two squares and is positive integer, we have had to obtain non-trivial estimates for the error term in the asymptotic expansion of

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