One-hour Period Research Articles

Seasonal Variations of Saltation Activity on A High Plains Saline Playa: Yellow Lake, Texas

The Southern High Plains region of West Texas and eastern New Mexico is often described as a flat elevated tableland. Spaced across this vast and otherwise featureless plain are 21 large closed basins containing approximately 40 irregularly shaped saline playas. Yellow Lake, located on the Yellow House Ranch northwest of Lubbock, Texas, is among the largest of the High Plains saline playas. This paper represents the first report of a 4-yr. study of saltation activity at Yellow Lake. From December 30, 1998, to January 1, 2003, a fast-response piezoelectric saltation sensor was used to collect a continuous record of aeolian activity at a point on the playa surface. Since saltation activity is often associated with dust emissions, the saltation record also provides information regarding seasonal patterns of dust emissions from the Yellow House Basin. Results suggest that blowing events can occur at any time of the year when conditions are favorable; however, the necessary conditions are rarely satisfied. As a result, the saltation record is characterized by many hours of inactivity punctuated with brief periods of occasionally intense aeolian activity. From December 30, 1998, to January 1, 2003, saltation activity was detected for only 7% of the hours measured. Although there can be substantial deviations from one year to the next, it was found that saltation activity tends to peak during winter months when winds are moderately strong and precipitation is at a minimum. Hourly saltation activity values occasionally approached unity during intense winter blowing events, indicating nearly continuous sediment transport over a one-hour period. Saltation activity is at a minimum during summer months when winds are often weak and wet conditions prevail. Although winds are typically strongest during the spring season, the playa is relatively stable due to high threshold values produced by significant spring precipitation. This contrasts sharply with the surrounding cropland, which tends to be most active during the spring season.

The effect of changing pressures on dural puncture and leak with various spinal needles on an in vitro model

Postdural puncture headache is one of the most serious complications of spinal anesthesia. In this study, spinal needles of various types and shapes were used to investigate the amount of fluid leakage in dural puncture under various levels of pressures. Dura samples received from 10 cadavers were fixed in an in vitro model. The dural punctures were inflicted with 22 G, 25 G, and 27 G Quincke; 25 G Withacre; 25 G, 27 G Pencan, and 26 G Atraucan spinal needles. The fluid, which leaked during the process, was collected under the pressures of 0, 25, 50, 100, and 150cm H2O in one-hour period for each level. The holes in the dura were studied under light microscope. While 22 G and 25 G Quincke needles were used, the fluid leakage directly correlated the amount of liquid, the diameter of the needle, and the pressure used. The puncture of 25 G Withacre and 25 G Pencan presented a leakage which did not significantly vary with the liquid pressure and was of lesser amount. In 26 G Atraucan, 27 G Pencan, and 27 G Quincke inflicted punctures, little liquid was collected and it did not vary with differing pressures. Thus, no significant correlation was established between the needle diameter and the puncture.It was concluded that the sharp-ended needles could not endure changes in the pressure. However, those needles with a very thin diameter and a pencil tip were considered as safe tools for anesthetical practices.

Endocrine stress response in jugular-vein cannulated rats upon multiple exposure to either diethyl-ether, halothane/O2/N2O or sham anaesthesia.

The main objective of this study was to assess the endocrine stress response to multiple anaesthesia followed by sham anaesthesia in order to detect any memory effects. For this purpose, jugular-vein cannulated rats were subjected to either sham, diethyl-ether or halothane/O2/N2O anaesthesia, and their plasma ACTH, corticosterone, glucose, adrenaline and noradrenaline levels measured. The study had three separate experiments, each consisting of a control and treatment group. In two experiments, the rats were exposed to high or low concentrations (40-15%) of diethyl ether, using either a jar containing cotton soaked in diethyl ether or a vaporizer. In the third experiment, rats were exposed to halothane/O2/N2O. Control animals underwent sham anaesthesia. Blood samples were taken 6 min before and at 5, 15 and 55 min after starting the exposure (t = 0 min). For each variable, the dt5 (level at t = 5 min minus that at t = -6 min) and the cumulative levels over the one-hour period as determined by the area under the curve (AUC) were calculated. Further, the peak levels (Cmax) were determined. The mean time needed to induce anaesthesia was 68, 121 and 55 s for exposure to high and low concentrations of diethyl ether and to halothane/O2/N2O, respectively. Increased noradrenaline and adrenaline dt5 levels were observed only after the first exposure to the high concentration of diethyl ether. Multiple anaesthesia sessions using either diethyl ether or halothane/O2/N2O did not clearly influence adrenaline and noradrenaline levels. Diethyl ether induced a sharp rise in plasma ACTH and glucose levels, irrespective of the concentration used. The response of the ACTH and glucose was similar for single and multiple exposure. An increased response of ACTH, corticosterone and glucose to sham anaesthesia following multiple induction of anaesthesia was observed for the high concentration of diethyl ether only. Halothane/O2/N2O raised plasma glucose without differences between single and multiple anaesthesia sessions. Upon sham anaesthesia following multiple exposures to halothane/O2/N2O, glucose levels were significantly increased. This study indicates that repeated anaesthesia in rats can elicit an increased stress response during subsequent handling and change of environment.

Activation, Decay Heat, and Waste Disposal Analyses for the ARIES-AT Power Plant

Detailed activation, decay heat and waste disposal calculations of the ARIES-AT design are performed to evaluate the safety aspects of the device. The high initial activity of the SiC highly irradiated components translates directly into a higher initial decay heat for these structures than for the well-protected steel-based components. However, after a one-hour cool-down period, the SiC decay heat drops by two decades to levels comparable to the steel-based components. The decay heat of the LiPb coolant was found to exceed that of the SiC components for several days after shutdown. This implies that a loss of flow accident (LOFA) event is more critical than a loss of coolant accident (LOCA) event for LiPb/SiC systems. Regarding waste disposal, all structures can easily meet the Class C Low-Level Waste (LLW) requirements established for the ARIES power plants. Many components could qualify as Class A LLW after a 100-year storage period after selection of low activation materials and control of the Nb and Mo impurities in ferritic steel. A purification system will be required to remove the 210Po and 203Hg generated by Pb during operation.

EMG activity and pain development in fibromyalgia patients exposed to mental stress of long duration

Objective: To examine the distribution of stress-induced upper-body pain in fibromyalgia patients, and the possible association of pain with electromyographic activity in muscles near the sites of pain development. Methods: Fifteen fibromyalgia patients and 15 pain-free subjects were exposed to low-level mental strain over a one-hour period. EMG was recorded from frontalis, temporalis, trapezius, and splenius capitis. Pain in the corresponding locations was recorded before the test, every 10 minutes during the test, and the 30-minute posttest period. Results: The fibromyalgia patients developed pain during the test in all the above body locations. Pain development in all locations associated with trapezius EMG activity, but not with EMG activity in underlying muscles for forehead, temples, and neck. Conclusion: Stress-induced pain in fibromyalgia patients is not generally caused by muscle activity. The trapezius EMG response may be part of a general stress response that cause pain independently of motor activity in muscles.

Effect of animal density and trough placement on drinking behavior and dehydration in slaughter horses

One of the issues in the debate over the regulation of the transport of horses to slaughter plants is whether slaughter horses will consume water on board the trucks in which they are transported. The effect of horse density and trough placement on latency to drink and the amount of time spent drinking water on-board a semi-trailer were determined in three experiments using 19, 20, and 24 slaughter-type horses. The horses were deprived of access to feed and water for four hours prior to and for eight hours during transportation. Transport in a commercial 16-m long, single-deck, open-topped semi-trailer commenced at 1200 h and lasted until 2000 hours, followed by a one-hour watering period. In Experiments 1 and 2, the trailer was divided into four 2.4×3.6-m compartments into each of which two steel water troughs (25×90 cm) were hooked on the inside of the trailer after transportation ended and immediately prior to the watering period. Each compartment contained four to six horses. The troughs were placed along one side of the trailer in Experiment 1 and placed on opposite corners of each compartment in Experiment 2. In Experiment 3, the trailer was divided into two 2.4×7.2-m compartments each containing 12 horses and two troughs were staggered on the opposite walls of each compartment (four troughs per compartment). Three of the 19 horses were blocked from drinking by other horses in Experiment 1, five of the 20 horses were blocked from drinking in Experiment 2, and all horses drank in Experiment 3. All horses that drank initiated their first drink within 15 minutes of water entering the troughs in Experiments 1 and 2 and within 25 min for Experiment 3. Total serum protein, Na, and Cl were not significantly different between trough placements (Exp. 1 and 2) (P>.52) or between densities in Experiments 1 and 2 (P>.16). The larger compartment (2.4×7.2 m) and group size (12 horses) in Experiment 3 provided adequate maneuvering room so that all of the horses could get access to water when the water troughs were placed on both sides of a compartment at .8m of trough per 2.4 m of wall. Providing slaughter horses with access to water onboard trucks appears to be a useful method of reducing dehydration.

Field-based measurements of personal erythemal ultraviolet exposure through a common summer garment.

The research in this paper quantifies the solar erythemal UV exposures to the skin through a common summer garment during outdoor activities. The erythemal exposures under the garment for the wet white garment exceeded a MED (minimum erythemal dose) at some anatomical sites in summer for a two-hour period. An erythemal exposure of 1.7 MED, in excess of the occupational limit for UV exposure, was measured under the white garment during swimming for a one-hour period. Clothing must form an important component of a UV protection strategy. However, it must be realised that total UV protection is not provided and significant UV exposures may be received beneath the garment, particularly for a white garment in the wet state. This re-enforces the necessity of a combination of several UV prevention strategies to minimise UV exposure.

Cardiovascular Surgery Without Cardiopulmonary Bypass in Patients with Heparin-Induced Thrombocytopenia Type II Using Anticoagulation with Recombinant Hirudin

Cardiovascular Surgery Without Cardiopulmonary Bypass in Patients with Heparin-Induced Thrombocytopenia Type II Using Anticoagulation with Recombinant Hirudin

Effects of Indoor Pyrotechnic Displays on the Air Quality in the Houston Astrodome

ABSTRACT Fine and coarse particulate mass samples were collected during baseball games with pyrotechnic displays and control games without displays. The average fine and coarse particulate masses were 173 and 141 mg/m3, respectively, for the one-hour period immediately following the pyrotechnic displays. The particulate matter generated by the pyrotechnic displays was composed of the following elements (arranged from most to least abundant): K, S, Mg,Ti, Cl, Si, Ca, Al, Sr, V, Zn, Mn, and Pb. Although the average particulate mass concentrations were high during the first hour, the ventilation system reduced the concentrations by up to 41% during the second hour after the display.

PIXE ANALYSIS OF SUSPENDED PARTICULATE MATTER ORIGINALLY COLLECTED FOR BETA-RAY ABSORPTION MASS MONITORING

A method of transferring suspended particulate matter (SPM) from the used filter of a beta-absorption mass monitor to a polycarbonate filter for subsequent PIXE analysis has been developed. The method allows determination of the relative elemental composition of SPM. It was demonstrated that PIXE analysis can detect S , Cl , Fe and Zn in SPM sampled over a one-hour period.

Noninvasive near infrared spectroscopy monitoring of regional cerebral blood oxygenation changes during peri-infarct depolarizations in focal cerebral ischemia in the rat.

Intermittent peri-infarct depolarizations (PID), which spread from the vicinity of the infarction over the cortex, have been reported in focal ischemia. These depolarizations resemble cortical spreading depression except that they damage the cortex and enlarge the infarct volume possibly because of compromised oxygen delivery. The main purpose of this study was to evaluate the noninvasive technique of near-infrared spectroscopy (NIRS) for the identification of PID and to evaluate its capability for further pathophysiological studies. We used male barbiturate-anesthetized Wistar rats (n = 10) in which middle cerebral artery occlusion had been performed with a surgical thread. Middle cerebral artery occlusion resulted in a drop in parietally measured regional cerebral blood flow (laser Doppler flowmetry) to 31 +/- 8% of baseline flow. Six +/- 4 minutes after the induction of focal ischemia, 5 +/- 2 direct current deflections were recorded during a one-hour measurement period which may be regarded as PID. Measuring regional cerebral blood oxygenation changes with a NIRO 500 revealed dynamic concentration changes in the three chromophores oxyhemoglobin [HbO2], deoxyhemoglobin [Hb], and the oxidized form of cytochrome aa3 [CytO] during PID. Typically, an initial slight decrease of [HbO2] (-6.1 +/- 1.7 arbitrary units [AU] and an increase of [Hb] (+11.5 +/- 7.7 AU) were followed by an increase of [HbO2] (+10.8 +/- 4.7 AU) and a decrease of [Hb] (-4.7 +/- 5.5 AU); [CytO] decreased during the depolarizations (-2.0 +/- 1.2 AU). We conclude that NIRS can detect typical PID-associated changes in blood oxygenation. We hypothesize that during the course of PID, unlike "normal" spreading depression, hypoxygenation precedes hyperoxygenation of the microcirculation in a given cortex volume as the depolarization wave propagates through hemodynamically compromised to intact tissue. This would accord with the known damaging effect of PID. The NIRS "fingerprint" of PID encourages the search for PID during early stroke in patients.

A Continuous Infusion of Acyclovir for Severe Hemorrhagic Varicella

To the Editor: Severe infections with varicella–zoster virus are common in immunocompromised hosts.1 Hemorrhagic varicella is serious and frequently fatal. We describe a case of hemorrhagic varicella that was resistant to a conventional regimen of acyclovir but was successfully treated by a continuous infusion of acyclovir. A 40-year-old woman with leukemia treated with various chemotherapies was admitted with fever, general fatigue, and generalized hemorrhagic bullae without a dermatomic distribution (Figure 1A and Figure 1B). A Tzanck smear of the bullae was positive. The patient had had varicella in childhood. An intravenous infusion of 250 mg of acyclovir over a one-hour period every . . .

Swell-preventing effect of intermittent exercise on lower leg during standing work.

This study investigated the effectiveness of several possible exercises for performance during standing work in order to prevent lower leg swelling and relieve subjective complaints. Volume changes in the lower leg were measured using bioelectrical impedance plethysmography in 13 healthy male subjects aged 23-36 years. Subjective complaints of leg pain, leg dullness and whole body fatigue were also recorded. Measurements were performed at two-minute intervals during a one-hour period of standing with insertions of one-minute of exercise every 10 min. The exercises were knee-bending, foot-stepping, walking, and heel-raising. The change rates of impedance over one hour were 2.2%, 4.0%, 4.6%, and 6.3%, respectively, indicating that leg volume was increased under all exercise conditions. Among exercises, the swell-preventing effect of knee-bending was strongest, and that of heel-raising was weakest. Heel-raising also yielded the highest number of subjective complaints. Knee-bending, which uses the thigh and calf muscles simultaneously, was considered the most effective for suppressing lower-leg swelling and minimizing subjective complaints.

Calciuric response to an acute acid load in healthy subjects and hypercalciuric calcium stone formers

Excessive animal protein consumption is associated with a greater risk of occurrence of renal calcium stone, presumably because of the attendant endogenous acid production. Indeed, chronic acid load enhances urinary calcium excretion possibly through an increased bone calcium release. Because acute studies are best designed to elucidate the mechanism, renal or extra renal, underlying hypercalciuria in the setting of enhanced acid load, we examined the response of 9 healthy adults (8 males, 1 female, aged 38 +/- 3 years, weight 67 +/- 2 kg) and 34 hypercalciuric recurrent calcium stone formers (31 males, 3 females, aged 44 +/- 2 years, weight 72 +/- 2 kg), without any associated disease, to an oral acid load (NH4Cl 2 mmol/kg body wt). After an overnight fast, each patient and control was studied during one one-hour period before and three two-hour periods after their intake of the acid load. An additional group of four time-control subjects (4 males, aged 33 +/- 2 years, weight 66 +/- 2 kg) was studied as the experimental groups except that they did not receive the acid load. On baseline, the three groups exhibited similar glomerular filtration rates, net acid excretions, and plasma calcium and magnesium concentrations. However, fasting urine calcium and magnesium excretions were higher in hypercalciuric calcium stone formers than in healthy control or time-control subjects. In time-control subjects, plasma acid base status, net acid excretion, filtered loads of calcium and magnesium, and urinary calcium and magnesium excretions remained unchanged all over the study. By contrast, after the oral acute acid load, net acid excretion increased and urinary pH decreased similarly in patient and control groups; glomerular filtration rate did not change, as well as plasma calcium and magnesium concentrations. Nevertheless, urinary calcium and magnesium excretions markedly increased, in both groups, independently of changes in tubular sodium handling and in plasma parathyroid hormone concentration. The increase in urinary calcium and magnesium excretions that occurred in the absence of any change in the filtered load of calcium and magnesium was therefore mediated by a decrease in tubular calcium and magnesium reabsorption, independent of PTH, but dependent on changes in net acid excretion. A positive linear relationship between urinary calcium and magnesium excretions suggested that the target tubular site for acid load was the thick ascending limb of Henle's loop. Finally, a negative linear relationship was demonstrated between the acid load-induced increase in urinary calcium excretion and fasting urinary calcium excretion; indeed, the lowest calciuric responses were observed in patients with the highest fasting urinary calcium excretion. Thus there was no additional effect of the acid load-induced inhibition on intrinsic defect in tubular calcium reabsorption which suggests that the tubular target site for acid load and the site of calcium transport defect in idiopathic hypercalciuria may be the same.

Basal and meal-stimulated colonic absorption.

Few quantitative experiments evaluating colonic absorption of water and electrolytes have been performed using an awake, conscious animal model. The purpose of these experiments was to develop this type of model and evaluate both basal and meal-stimulated colonic absorption of water and electrolytes. Canine Thiry-Vella fistulas were created using a 20 cm segment of distal colon under general anesthesia. Colonic absorption studies were performed using infusion of the Thirty-Vella fistulas with a buffer solution containing [14C]polyethylene glycol. Electrolyte analysis and concentration of radioactivity in the effluent were obtained and used to calculate the net flux of water, sodium, and chloride. Each study consisted of an one-hour basal period and a three-hour experimental period divided into two groups. Group 1 received no meal. Group 2 orally ingested a mixed meal at the completion of the basal hour. In the basal state, water and electrolytes are absorbed from the distal colon at a steady and constant rate. An orally ingested meal produces a statistically significant increase in the rate of absorption, independent of direct colonic luminal contact with the nutrients of the meal given. These studies demonstrate an in vivo quantitative and qualitative measure of mammalian colonic water and electrolyte absorption. An increase in absorption rate occurs in response to a meal that is probably the result of an unidentified neural or humoral signal.

Taste Quality of Milk from Dairy Cows Fed ForageBrassicacv. Tyfon

Tyfon is a relatively new forage Brassica available for use in ruminant rations. It is a member of the Brassicaceae family, which has been reported to contribute to the development of flavor defects in bovine milk. A trial was conducted to evaluate the flavor quality of milk from dairy cows fed Tyfon for a one-hour period of time at either 3, 6, 9, or 12 h prior to milking. The cows consumed a basal total mixed ration consisting of corn and grass silage and a grain mixture. There was not a flavor difference between the milk from the control (no Tyfon) versus the milk from cows fed Tyfon at any of the time points.

Cloud fraction and cloud shadow property retrievals from coregistered TIMS and AVIRIS imagery: the use of cloud morphology for registration

The Thermal Infrared Multispectral Scanner (TIMS) and the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) were operated simultaneously from the ER2 aircraft during a March 1990 test over the Rio Bravo region, Belize. Coregistration of the imagery obtained by these two instruments is necessary to utilize the data effectively. A technique for registering the TIMS imagery to AVIRIS imagery is presented. It takes advantage of the morphology of the fair weather cumulus (FWC) clouds present in the imagery for estimating inter-sensor distortions. It relies on an iterative process in which skew, nearest neighbor sampling, and cross-correlation (1D and 2D) are applied. Comparison between the AVIRIS three-band ratio (3BR) imagery and the coregistered TIMS imagery shows that TIMS is superior in detecting thin cloud and cloud edge pixels, especially over shadowed background. Although the seven scenes analyzed in the study were obtained within the same one-hour time period and over the same geographical region, the optimum temperature threshold for cloud detection, with respect to the background temperature, varies significantly from 2.1 to 3.3/spl deg/C. These values agree with the AVIRIS 3BR cloud fraction equivalent temperature thresholds to within 0.5/spl deg/C. When applying a cloud shadow mask from the AVIRIS near infrared imagery to the coregistered TIMS background imagery, a 1/spl deg/C temperature differential is found between the shadowed and nonshadowed background. This significant radiative cooling by Fair Weather Cumulus cloud shadows could introduce errors in surface emissivity retrievals by other Earth Observing System (EOS) investigators.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Interrater Reliability of Pinch and Grip Strength Measurements in Patients with Cumulative Trauma Disorders

The purposes of this study were to examine the interrater reliabilities of grip, lateral pinch, and tripod pinch measurements in patients with cumulative trauma disorders. Thirtyeight patients with unilateral (n = 28) or bilateral (n = 10) cumulative trauma disorders were tested independently by two hand therapists, during a one-hour period. The tests were completed in a normal hand clinic environment using the standard protocol recommended by the American Society of Hand Therapists. Interrater reliability coefficients for the scores obtained using either a single repetition or the mean of three repetitions were very high (intraclass correlation coefficient [ICC] > 0.87) for all strength measurements. As a result, strength determination in this patiept group, when performed by different hand therapists, may be considered reliable.

Studies of fluoride retention by oral soft tissues after the application of home-use topical fluorides.

Previous studies have focused on enamel and plaque as the primary sites of fluoride (F) retention in the mouth. The present study was undertaken to evaluate the role of oral soft tissue as a site of F retention by comparing an edentulous subject panel (n = 9) with a fully dentate panel (n = 10). Unstimulated whole saliva samples were collected by having subjects pool saliva for two min. Samples were collected over a 24-hour period after application of a placebo dentifrice (PD; 0.4 ppm F), fluoride dentifrice (FD; 1100 ppm F), fluoride rinse (FR; 226 ppm F), or fluoride gel (FG; 5000 ppm F) delivered in custom trays. There was no statistically significant difference in salivary flow rate between the two panels for any of the treatments. The edentulous panel had higher salivary F levels than the dentate panel, which reached statistical significance (p less than 0.05) for the FD and FG treatments. In a separate study involving the same treatments, F levels at specific soft-tissue sites were measured over a one-hour period by use of absorbent discs placed in different soft-tissue areas of the mouth. The tongue and lower posterior vestibule retained the highest F levels, followed by the upper posterior buccal vestibule and upper anterior labial vestibule, with the lowest F levels retained in the lower anterior vestibule and the floor of the mouth. There was a strong-to-moderate correlation between whole saliva F concentration and F levels at specific soft-tissue sites. This study establishes the importance of oral soft tissue as the major site of F retention in the mouth.

Comparison of collaborative self, peer and tutor assessment in a biochemistry practical

Introduction It has been noted that Higher Education often falls short of its own aims of promoting effective learning, indepen- dence of thought, awareness of alternative approaches to a subject and rational debate. 1 In looking for reasons for this failure, one area of student experience which is being examined is the traditional method of assessment within which staff members exercise unilateral intellectual authority. Undergraduate students entering into univer- sities normally follow a pre-designed programme of learning into which they have no input; they are subjected to pre-determined criteria of assessment without necess- arily being informed about the nature of these criteria, and they have little say in the judgements which are made about them by lecturers and tutors. This situation engenders in students a strong tendency to indulge in surface learning by rote such that the perceived essential facts can be memorised for the purpose of 'passing the exams' rather than engendering a commitment to effective learning processes required to give a deep understanding of the given subject. The traditional system of assessment therefore generates the wrong sort of motivation in students through its emphasis on external rewards and punishments. The system also militates against the notion of developing students' ability to evaluate their own work in ways which are applicable to their future professional work in any given discipline. One possible means of changing the status quo is to make assessment procedures an integral part of the learning process since life-long learning requires that individuals are able not only to work independently but also to assess their own perform- ance and progress. Involvement in the assessment process would hopefully heighten our awareness and knowledge of the student approach to learning and enable students to make rational and objective judgements about their own strengths, weaknesses and range of skills. As previously described by Falchikov, 2 alternatives to traditional assessment practices have fallen into three categories: self assessment, peer group assessment and collaborative assessment. In self assessment the learner judges his or her own performance and products against his or her own criteria. In peer group assessment, peers assess the learner with or without prior discussion, and collaborative assessment requires that learner and tutor discuss and negotiate a commonly agreed set of assess- ment criteria and the final assessment grade. This paper describes an experiment in collaborative peer and self assessment of a first year undergraduate biochemistry laboratory practical experiment. Procedure A laboratory practical project entitled 'Chemical Frac- tionation of Cells and Estimation of Nucleic Acids and Protein' has been used over many years with varying degrees of success. The experiment involves separation of nucleic acid and protein components of a rat liver cell suspension using straightforward extraction procedures followed by colorimetric assays. Students work in pairs with the occasional group of three students working together. The practical is carried out over two three-hour sessions. In this instance, prior to the students coming to the laboratory there was a one-hour discussion period with the primary aim of introducing the students to the concept of involving themselves in the assessment procedure. The first class of 87 students agreed to self-assessment of the practical report. A class representative then agreed to start negotiating with the rest of the class on the key points which would be important for a good report. Thecriteria were then ranked in order through continual discussion and student assignment of a points system. The role of the tutor in this was one of encouragement and support for the students and helping to put issues to a vote if this was deemed necessary. By the end of the discussion period a marking system had been devised with which the class was happy and over which the students had full ownership. A second class of 63 students agreed to peer assessment of the practical report and again a class representative initiated the negotiation phase. This class also decided on the important points which should be made within the report and devised a scoring scheme. Interestingly the two classes decided on different weightings of the marks but to give a true sense of ownership of the assessment criteria no adjustments were made by the tutor. Results (1)