Difference In Cycle Time Research Articles

Quality And Productivity Analysis Of The Putty Dispenser In The Armature Balancing Process

An electric motor is a device that converts electrical energy into mechanical energy. One of its important components is the armature which functions as the center of movement. Armature is paired with another component of electric motor. In order to achieve a good quality of electric motor, armature quality must be controlled through a standard experiment called balancing test. An adhesive material called putty will be added into armature if the balancing test result is not up to standard. This study conducted in one of automotive industry in Indonesia. The company face a problem in balancing test process. Putty addition carried by factory workers only based on their estimation, resulting in the mass of putty used not in accordance with predetermined standards and also inconsistent, so that the balancing process takes a long time. This research offer a solution for the problem, i.e. putty dispenser to replace the manual putty-picking process with a standardized semi-automatic one. The research objective is to analyze the quality and productivity of the putty dispenser tool design in the armature balancing process. Through 100 armature samples consist of type A and type B, this study examines the quality of the putty mass provided using the most frequently occurring value and uses the independent T-test method to examine the hypothesis that there is a real difference in cycle time before and after the putty dispenser tool. Frame strength testing was also carried out using Solidworks software simulation with 632 N loading. The results of the research on the putty dispenser tool are that the frame used is proven safe, a decrease in cycle time with a percentage of 34.16%, an increase in productivity of 34.13%, also improved quality through the aspects of %NG reduction of 42.29%, and a standardized and constant putty mass of 100 mg for armature type A and 200 mg for armature type B.

Cycle Time Analysis Of AS/RS (Automated Storage & Retrieval System) Using SCADA

AS/RS is not just a replacement for conventional warehouses, but has become a key element in modern manufacturing systems. However, in its use there are still problems and shortcomings, including the unavailability of a system that can control, supervise, and acquire data from AS/RS and the cycle time when AS/RS performs data storage and retrieval tasks is still below industry standards. To overcome this, a system that is generally called SCADA (Supervisory, Control, and Data Acquisition) is needed. This research uses Arduino Mega 2560 as an AS/RS controller, while the VTSCADA application is used to build a SCADA system on AS/RS. This research uses two approaches. First, calculating the AS/RS cycle time when performing storage and retrieval tasks. Second, comparing the cycle time of the storage system and the retrieval system. The first test results show that the fastest cycle time in the storage system occurs at storage rack point 1 with a time of 3.17 seconds, while the fastest cycle time in the retrieval system occurs at retrieval point 1 with a time of 12.74 seconds. The second test resulted in a difference in cycle time between the storage and retrieval systems, namely 0.42 seconds at storage point 1, 0.38 seconds at storage point 2, 0.51 seconds at storage point 3, 0.31 seconds at storage point 4, and 0.43 seconds at storage point 5. It can be concluded that the application of SCADA to AS/RS is able to increase the cycle time of AS/RS.

Correlative Analyses of Cereblon (CRBN), cMYC, IRF4, BLIMP1, and XBP1 with Clinical Outcomes in Stratus (MM-010), a Phase 3b Study of Pomalidomide (POM) + Low-Dose Dexamethasone (LoDEX) in Patients (pts) with Relapsed/Refractory Multiple Myeloma (RRMM)

Correlative Analyses of Cereblon (CRBN), cMYC, IRF4, BLIMP1, and XBP1 with Clinical Outcomes in Stratus (MM-010), a Phase 3b Study of Pomalidomide (POM) + Low-Dose Dexamethasone (LoDEX) in Patients (pts) with Relapsed/Refractory Multiple Myeloma (RRMM)

Self-adjusting multi-objective scheduling based on Monte Carlo Tree Search for matrix production assembly systems

As a response to the low utilization of production lines in the context of an increasing number of product variants with significant differences in cycle times, line-less modular assembly concepts known as matrix production have evolved. Whilst the many degrees of freedom a matrix production offers provide different ways to react to disturbances and balance utilization, it also increases the complexity for scheduling exponentially. For real-time scheduling high solution quality and high efficiency are needed. This paper contributes a multi-objective scheduling approach based on Monte-Carlo Tree Search that self-adjusts to the scheduling problem to improve solution quality and execution time.

Assembly Line Balancing with Method Ranking Positional Weight (case study: XYZ Company)

A company uses several methods to increase productivity in the company. One of method used in increasing productivity is balancing production lines on each work element. Balancing the work track can be done by allocated work elements. The allocation of work elements in the work station can be seen at cycle time. Big difference in cycle time causes some work elements have bottlenecks. In achieving high productivity in a work station company must have a balanced workload. Effectiveness in the production floor aims to make the company achieve the desired production target of consumers. Companies failing to achieve production targets will have a negative impact on the company. The negative impact felt by the company in the form of losses. Ineffectiveness in production summary can be caused by differences between machine capacity and production capacity. Machine capsules that are smaller than the capacity of production cause the work elements must have accumulated. Effective production trajectories can be measured by producing high output with low resource utilization. The reason why companies often experience bottlenecks on a production floor is an imbalance of resources within a factory.

Spatiotemporal gait characteristics of Huntington’s disease during dual-task walking

Purpose: Huntington’s disease (HD) is an neurodegenerative genetic disorder with characteristic gait changes. HD also results in a range of cognitive impairments, such as difficulties to divide attention, or simultaneously monitoring two tasks.Aim: The impact of cognitive and/or motor tasks on HD gait has not been fully elucidated. The aim was to examine gait in HD patients while performing motor and/or cognitive dual-task walking.Methods: Gait was measured with and without performing concurrent cognitive and/or motor tasks. Sixteen HD patients and 24 healthy control (HC) subjects performed a self-paced basic walking task, a dual motor, a dual mental and a combined motor and mental task while walking.Results: Base walk gait parameters are significantly different between HD and HC groups. Same is true for motor, mental and combined tasks comparisons of HD and HC subjects. Gait velocity is also significantly reduced in HD compared to HC for all experimental conditions. Comparison of base walk and mental task performance showing differences in cycle time, stride length, double support time and CV of stride length, while base walk to motor task comparison is different only in stride length. No differences were found when motor and combined tasks were compared to mental task in HD patients.Conclusion: Gait pattern in HD patients while performing motor and/or cognitive dual tasks walking is remarkably preserved. Gait parameters are changed in order to reduce possible falls, and lack of differences of dual tasks gait parameters variability is attributed that patients minimizing risk of falling and preserving stability.

Double-Poling Physiology and Kinematics of Elite Cross-Country Skiers: Specialized Long-Distance Versus All-Round Skiers.

Long-distance cross-country skiers specialize to compete in races >50km predominantly using double poling (DP). This emphasizes the need for highly developed upper-body endurance capacities and an efficient DP technique. The aim of this study was to investigate potential effects of specialization by comparing physiological capacities and kinematics in DP between long-distance skiers and skiers competing using both techniques (skating/classic) in several competition formats ("all-round skiers"). Seven male long-distance (32 [6]y, 183 [6]cm, 76 [5]kg) and 6 all-round (25 [3]y, 181 [5]cm, 75 [6]kg) skiers at high international levels conducted submaximal workloads and an incremental test to exhaustion for determination of peak oxygen uptake (VO2peak) and time to exhaustion (TTE) in DP and running. In DP and running maximal tests, TTE showed no difference between groups. However, long-distance skiers had 5-6% lower VO2peak in running (81 [5] vs 85 [3]mL·kg-1·min-1; P = .07) and DP (73 [3] vs 78 [3]mL·kg-1·min-1; P < .01) than all-round skiers. In DP, long-distance skiers displayed lower submaximal O2 cost than all-round skiers (3.8 ± 3.6%; P < .05) without any major differences in cycle times or cyclic patterns of joint angles and center of mass. Lactate concentration over a wide range of speeds (45-85% of VO2peak) did not differ between groups, even though each workload corresponded to a slightly higher percentage of VO2peak for long-distance skiers (effect size: 0.30-0.68). The long-distance skiers displayed lower VO2peak but compensated with lower O2 cost to perform equally with the all-round skiers on a short TTE test in DP. Furthermore, similar submaximal lactate concentration and reduced O2 cost could be beneficial in sustaining high skiing speeds in long-duration competitions.

Production layout improvement by using line balancing and Systematic Layout Planning (SLP) at PT. XYZ

PT. XYZ is a wood processing company which produce semi-finished wood with production system is make to order. In the production process, it can be seen that the production line is not balanced. The imbalance of the production line is caused by the difference in cycle time between work stations. In addition, there are other issues, namely the existence of material flow pattern is irregular so it resulted in the backtracking and displacement distance away. This study aimed to obtain the allocation of work elements to specific work stations and propose an improvement of the production layout based on the result of improvements in the line balancing. The method used in the balancing is Ranked Positional Weight (RPW) or also known as Helgeson Birnie method. While the methods used in the improvement of the layout is the method of Systematic Layout Planning (SLP). By using Ranked Positional Weight (RPW) obtained increase in line efficiency becomes 84,86% and decreased balance delay becomes 15,14%. Repairing the layout using the method of Systematic Layout Planning (SLP) also give good results with a reduction in path length becomes 133,82 meters from 213,09 meters previously or a decrease of 37.2%.

Improving Assembly Line Balancing Using Moodie Young Methods on Dump Truck Production

Dump truck is a transportation equipment to facilitate the process of loading and unloading. The company has 7 work stations different cycles time. The difference in cycle time at each work station causes a bottleneck on the line balancing production. The bottleneck occurring in the line balancing production causes a delay in the completion of the product. Delays in delivery of goods certainly gives a bad impact to the company. Therefore, companies need to balance the line balancing production to reduce bottlenecks that cause delayed product completion time. Bottleneck minimization will increase the efficiency of the assembly line balancing. Line balancing aims to obtain a smooth flow of production that resulting maximum line balancing efficiency. One method of line balancing is by using Moodie Young method. The result of the calculation with Moodie Young method obtains an increase of line efficiency by 75% from the actual method. This method is also reduce balance delay from 53.86% to 19.18% the decline in smoothness index to be 597,57. It can be concluded that the Moodie Young Method is better than the actual method.

Online Monitoring of a Sequencing Batch Reactor Treating Domestic Wastewater

Domestic wastewater consists of considerable concentrations of pollutants that can boost water eutrophication if not treated before final discharge, which could damage the ecosystem and negatively affect human health. Sequencing batch reactor (SBR) technology is considered a promising biological wastewater treatment technology to address these issues. In recent years, SBR selection has increased as an effective technology for the treatment of domestic and industrial wastewaters due to its setup simplicity and ease of operation. However, many researchers have reported differences in cycle time. The importance and originality of this study is that it explores the parameters of pH, temperature, oxidation-reduction potential (ORP) and dissolved oxygen (DO) throughout the SBR cycle to predict the end of the treatment cycle. A laboratory-scale SBR was used in this study with a five-litre working volume. It was equipped with four electronic sensors (probes) to monitor the pH, ORP, temperature and DO. The SBR was operated under constant aeration, 1.0 l/min, ±12 C° temperature and 6h cycle time. Each cycle of the SBR operation included Fill (30minutes), React (240minutes), Settle (30minutes), Draw (30minutes) and Idle (30minutes). Influent and effluent samples were analysed for COD, ammonia-N and nitrate-N. The pH, ORP and DO values at the end of the 6h HRT treatment cycle were between 6.6-7.9, 147-169mV and 4.6-6.6mg/l respectively. The results show complete degradation of COD and nitrogen compounds was seen when the DO profile increased due to bacterial respiration. The results prove that online monitoring of SBR operating parameters could significantly predict the end of the treatment cycle, and the pH, DO and ORP profiles could be used as onsite process control parameters.

The Impact of Vacuum-Drying on Efficiency of Hardwood Products Manufacturing

Many wood product manufacturers are trying to increase competitiveness by implementing continuous improvement programs such as lean manufacturing. However, the lumber drying process can significantly affect manufacturing time and inventory size, thus limiting how “lean” the entire process can become. The goal of this research was to determine how vacuum drying technology could support lean manufacturing concepts relative to conventional drying technology in hardwood manufacturing. Two flooring manufacturers with drying operations were modeled, and simulations were used to determine differences in cycle time and work-in-process inventory. The total cycle time of vacuum drying was 78% and 90% less than conventional drying. Work-in-process inventory was reduced by 57% and 52%. The reduction of work-in-process inventory in the drying process represents a potential cost savings of $7.3 million and $13.6 million per year for each manufacturer, respectively. The reduction in inventory carrying costs, faster drying rates, and reduced cycle time demonstrate that vacuum drying could significantly improve the competitiveness of hardwood flooring manufacturers.

PT202 Predictors of the coronary in-stent restenosis

PT202 Predictors of the coronary in-stent restenosis

Elbow Joint Fatigue and Bench-Press Training

Bench-press exercises are among the most common form of training exercise for the upper extremity because they yield a notable improvement in both muscle strength and muscle endurance. The literature contains various investigations into the effects of different bench-press positions on the degree of muscle activation. However, the effects of fatigue on the muscular performance and kinetics of the elbow joint are not understood fully. To investigate the effects of fatigue on the kinetics and myodynamic performance of the elbow joint in bench-press training. Controlled laboratory study. Motion research laboratory. A total of 18 physically healthy male students (age = 19.6 ± 0.8 years, height = 168.7 ± 5.5 cm, mass = 69.6 ± 8.6 kg) participated in the investigation. All participants were right-hand dominant, and none had a history of upper extremity injuries or disorders. Participants performed bench-press training until fatigued. Maximal possible number of repetitions, cycle time, myodynamic decline rate, elbow-joint force, and elbow-joint moment. We observed a difference in cycle time in the initial (2.1 ± 0.42 seconds) and fatigue (2.58 ± 0.46 seconds) stages of the bench-press exercise (P = .04). As the participants fatigued, we observed an increase in the medial-lateral force (P = .03) and internal-external moment (P ≤ .04) acting on the elbow joint. Moreover, a reduction in the elbow muscle strength was observed in the elbow extension-flexion (P ≤ .003) and forearm supination-pronation (P ≤ .001) conditions. The results suggest that performing bench-press exercises to the point of fatigue increases elbow-joint loading and may further increase the risk of injury. Therefore, when clinicians design bench-press exercise regimens for general athletic training, muscle strengthening, or physical rehabilitation, they should control carefully the maximal number of repetitions.

Increased Activity of Prothrombinase Fgl-2 in Peripheral Blood Mononuclear Cells of Patients with B-Cell Lymphoma.

AbstractAbstract 2665 Background:Hematologic and solid tumors are associated with hypercoagulability the reason for which has not been delineated. Prothrombinase named fibrinogen-like protein 2 (FGL-2) is a 70 kD transmembrane protein that was found to have a quality of a serine protease capable of directly cleaving prothrombin to thrombin. FGL-2 is synthesized by monocytes, T-lymphocytes and endothelial cells. FGL-2 protein and its mRNA have been previously found within different tumor cells. Aim:To study the role of FGL-2 in patients with lymphoproliferative disorders. Our hypothesis is that upregulation of FGL-2 activity in patients with B-cell malignancies may contribute to tumorigenesis via generation of thrombin leading to increased angiogenesis and spread/metastasis of malignant cells. Methods:Thrombin generation reflecting FGL-2 activity was measured in homogenized peripheral blood mononuclear cells (PBMC) from 29 patients with active lymphoproliferative disorders and 107 normal controls. Informed consent was obtained from every participant. PBMC extracts were incubated with an equal volume of human prothrombin (final concentration10 μM) for 30 min at 37 °C. Thrombin generation was measured at 405 nm using an automated plate reader after addition of chromogen S-2238. The thrombin activity of each sample was calculated by comparison with absorbance curve generated by known concentrations of human thrombin. FGL-2 was immunoprecipitated (IP) from PBMC with an anti-FGL-2 antibody and EZview Red Protein A Affinity Gel (sigma # P6486). The activity of IP FGL-2 was measured by thrombin generation assay. The expression of FGL-2 was analyzed in HUVEC and PBMC in the presence or absence of IF-γ at 20 ng/ml. Total RNA was isolated using RNAqueous™ (Ambion #AM1912) and RT-PCR, analysis was performed using Rotor-gene RG-3000 (Corbett). The difference in cycle time (ΔCT) was measured by comparing FGL-2 gene with ABL-1 gene (house keeping gene). The relative quantification was calculated by the formula RQ= 2−ΔCT. HUVEC were transfected with 0.5 μM SiRNA synthesized complementary to FGL-2 (Target SiRNA) using Dharmacon ON-TARGET plus SMART pool reagent (Thermo Fisher Scientific) according to manufacturer instructions. FGL-2 expression following addition of target SiRNA was compared to that obtained following addition of non-specific (non-target) SiRNA. Student’s t-test was used for all comparisons. Results:As shown in the table, almost 3-fold increase in FGL-2 activity in PBMC was observed among patients with active B-cell lymphoma, either aggressive or indolent, as compared to that of healthy controls (p<0.0001 for all comparisons). No difference in FGL-2 activity in PBMC between patients with aggressive and indolent lymphoma was observed (p=0.68).Three-fold increase in thrombin generation was obtained in PBMC from the patients following IP, similarly to that observed in non-IP PBMC. A significant increase in mRNA of FGL-2 was found in either PBMC of lymphoma patient or HUVEC treated with IF-γ. In HUVEC the increase in FGL-2 mRNA was inhibited by 80% following treatment with specific SiRNA. Conclusions:1.There is increased activity of prothrombinase FGL-2 in PBMC of patients with B-cell lymphoma. Possible correlation between increased mRNA and protein activity of FGL-2 and B-cell lymphoma burden will be evaluated.2.The mechanistic effect of FGL-2 on tumorigenesisangiogenesis will be studied.Control subjects (N=107)Indolent B-cell lymphoma: FL, MCL, MZL, SLL (n=16)Aggressive B-cell lymphoma: DLBC, BL (n=13)All B-cell lymphoma (n=29)Mean ± SD (ng/ml)142.2 ± 118.4427.1 ± 219.2389.3 ± 267.5410.2 ± 238.3Range (ng/ml)0–439180–948153–1011153–1011P valueP<0.0001*P<0.0001*P<0.0001*FL – follicular lymphoma; MCL – mantle cell lymphoma; MZL – marginal cell lymphoma; SLL – small lymphocytic lymphoma; DLBCL – diffuse large B-cell lymphoma; BL – Burkitt’s lymphoma*compared to the control group. Disclosures:No relevant conflicts of interest to declare.

Predicting the effects of cycle time variability on the efficiency of electronics assembly mixed-model, zero-buffer flow processing lines

The research literature emphasises the need to use flow processing lines to undertake processing and assembly within low demand volume, high product variety electronics manufacturing environments that have significant levels of product, process and demand variability to contend with. Currently, the presence of such high levels of product, process and demand variability prevents the design of efficient flow processing lines by significantly disrupting the synchronisation of materials movement between work stations, resulting in under-utilisation of manufacturing resources, long lead times and poor delivery reliability. In order to ensure efficient flow processing under such conditions, a range of methods has been developed for both reducing levels of variability and for managing the effects of variability. However, ensuring the effective use of each of these methods requires detailed knowledge of the effects this variability has on the resource requirements of individual workstations. The current research is concerned with the development of predictive models that can quantitatively estimate the amounts of blocking and waiting, on individual workstations along a flow line, arising from differences in cycle times between these workstations. Information derived from such models are able to enable more precise and effective use of the methods used to off-set the effects of cycle time variability.

Automated time study of skidders using global positioning system data

Time study is an important research tool used in comparing productivity of forest harvesting systems across varying conditions. Unfortunately, it has been an expensive tool to apply, involving travel and fieldwork by a crew of technicians plus time in the office to reduce raw data to usable information. In the interests of safety and cost reduction, it would be preferable to have a means of performing autonomous time study that did not involve fieldwork and that produced detailed summaries of machine or system performance over long periods of time. Automated tracking of machine productivity is currently possible on advanced harvesting equipment, notably cut-to-length harvesters, but is not for the predominant tree-length logging systems used in the US south. This paper reports on a data acquisition system used to convert movement and positional data collected using a GPS receiver mounted on tree-length harvesting equipment, primarily skidders, into time study information. The conversion was performed in two stages: reduction of raw position data to a set of measurable, simple events; interpretation of sequences of simple events as machine functions. Simple events were extracted from the raw position data along with time and distance accumulated since the previously occurring event, then passed to the interpretive stage of processing. The stream of simple events was evaluated using a pattern-matching system that combined events into machine functions. Patterns were rules specified using a regular expression syntax that defined machine-specific operational characteristics. Field trials with the data acquisition system on skidders showed it was capable of reproducing measurements obtained from field crews. In two tests measuring total skid cycle time (46 cycles), the automated time study system missed identifying fewer than 10% of the cycles, and of those identified, the difference in cycle time averaged less than 2% (5 s). Although small, the bias was consistent (automated system shorter) and significantly different from 0. Elemental time study was also possible. A three-element cycle (travel empty, grapple, and travel loaded) was identified in 33 of the 36 cycles with differences in element times between clock and automated system measurements being generally less than 10%.

THE IMPACT OF UNIONS ON OPERATIONS STRATEGY

This paper explores the effect that unions have on a firm's ability to reengineer manufacturing processes. We begin by exploring the various effects that a union may have in a manufacturing environment. Next, we briefly review how unions may affect managerial initiatives to reengineer processes and improve manufacturing performance. The third section analyzes an existing database to test for differences in cycle time and manufacturing performance between union and nonunion firms. Finally, we discuss the implications of the study for future operations strategy research and note how a different form of union‐management relationships is beginning to evolve.

Rapid thermal annealing of ion implanted 6H-SiC by microwave processing

Rapid thermal processing utilizing microwave energy has been used to anneal N, P, and Al ion-implanted 6H-SiC. The microwaves raise the temperature of the sample at a rate of 200°C/min vs 10°C/min for conventional ceramic furnace annealing. Samples were annealed in the temperature range of 1400-1700°C for 2-10 min. The implanted/annealed samples were characterized using van der Pauw Hall, Rutherford backscattering, and secondary ion mass spectrometry. For a given annealing temperature, the characteristics of the microwave-annealed material are similar to those of conventional furnace anneals despite the difference in cycle time.

The Impacts of Visual Display Units Used for Highly Cognitive Tasks on Learning Curve Models

Abstract This paper compares progress (learning) curves for a task that requires high manual dexterity where information is obtained from a video display unit (VDU) to a manual assembly line task. Sixteen volunteer subjects either assembled peg-boards or performed a task on a VDU. Subjects were randomly assigned to a task or control group for each task. Each subject performed their assigned task for approximately two hours. The peg-board assembly simulated a very low cognitive but highly manual task, and the VDU task simulated a high technological industrial operation. There were no statistical differences in learning between the control and test group for either task. The progress curve rates were 95 percent for the pegboard and 91 percent for the VDU. Steady states for the peg-board and VDU tasks were reached at the 25th and 30th iterations respectively. Subjects then were tested four weeks later. During this 28 day period the test group refrained from participating in any activity that would approximate their assigned task. The control group maintained proficiency by practicing 45 minutes per week. There was no difference between the control and test groups for the peg-board task. Thus, there was no significant forgetting. However, there was a significant difference between the control and test groups for the video task. For the control group (VDU) the cycle time for the first iteration was reduced by 68.0 percent. The group's progress curve rate was 97.4 percent and steady state was reached at the 23rd iteration. Though the test group did improve their cycle time for the first iteration, it was only 33 percent of the control group's improvement. The test group's progress curve rate was 94.5 percent and steady state was reached at the 33rd iteration. This significant difference between the two curves is explained by forgetting. The forgetting rate decrease in learning for the VDU was 3.2 percent. This rate gradually decreased until the 45th iteration where there was no significant differences in cycle time between the two groups. Thus, forgetting occurs in the earlier iterations. To maintain its competitive edge in the world marketplace, industry has begun to implement many processes that rely heavily on VDUs. Inherent in these processes are shorter production runs and multiple set-ups. Traditional curves developed from low cognitive tasks do not reflect the forgetting that occurs in more typical modern industrial tasks. This impacts on industrial engineers and production managers whose operations require information obtained from VDUs. To set standard times for these type tasks, more consideration should be given to forgetting rather than relying totally on the more traditional models.

Cell cycles in cell hierarchies.

In the replacing tissues of the body, namely the bone marrow, testis, and the surface epithelia with their appendages, cell replacement would appear to be achieved using an hierarchically organized proliferative compartment with relatively few ultimate stem cells producing dividing transit cells which eventually differentiate and mature into the functional cells of the tissue. The cell cycle times of the various constituents of the hierarchy differ, and the stem cells apparently have a longer cell cycle than the transit cells. There may be variations in the cell cycle as cells pass through the transit population in some cases, e.g. in the bone marrow, while in others the cycle time remains fairly constant, e.g. in the testis. The difference in the cell cycle time between stem cells and transit cells is not completely unequivocal, and there is little or no difference in cycle time in the epithelium on the dorsal surface of the tongue while in other cases the experimental evidence for long stem-cell cycles is somewhat imprecise. However, the epithelium in the small intestine and the spermatogonia in the testis have been fairly extensively studied and here the evidence clearly shows a lengthening of the cell cycle as more primitive cells are considered.