Control of thermoforming process parameters to manufacture surfaces with pin-based tooling

Many manufacturing processes used to mass produce parts rely on expensive and time consuming tooling. These processes include sheet metal forming, injection molding, casting, and thermoforming. The time invested in design and development of tooling can be justified for high-production volumes. However, for low-volume production and customized products, the tooling investment cannot be amortized. Flexible tooling has been developed to address the needs of smaller production volumes. Reconfigurable pin tooling is an example of flexible tooling that relies on a matrix of adjustable-height pins to produce approximate surfaces. A key challenge in pin-based tooling is achieving accurate high quality surfaces due to the undulations caused by the pins in mimicking the desired shape. This research studies the effects of process parameters on surface quality. A testbed pin tool and thermoformer are fabricated to support this research. The pin tool comprises of a 10 by 10 matrix of square pins. Each pin measures 0.25 inch by 0.25 inch by 2.5 inches and is actuated manually using screws. Twenty-one exploratory and thirty-two shape specific experiments were conducted with 12 inch by 12 inch polystyrene sheets to check the feasibility of producing undulation-free surfaces. The parameters that influence the quality of the surfaces are heating time, sheet thickness, and sheet to fixture distance. Surface quality is measured by conformance with respect to the tool and the intensity of undulations. The surface-reproducibility and the measurement-repeatability errors were determined to be ±0.0045 mm and ±0.00027 mm respectively. The surface quality can be improved by reducing intensity of undulations by controlling the process parameters. The quality of thermoformed surfaces using the pin tool is a function of heating time and the intended shape

Modeling Energy Expenditure and Recovery in Cycling

The power-duration relationship, comprised of the parameters Critical power (CP) and work capacity (ϒ), has been used to model energy expenditure in cycling. For modeling recovery, the W\u27bal model has been used but lacks validation. Additionally, existing literature has not focused on quantifying or estimating the inherent trial-to-trial variability at the subject level, called the intra-individual variability (IIV), of CP and ϒ, posing challenges in modeling and optimization of performance. Thus, the objectives of this research are (i) to establish a method to quantify the IIV of CP and ϒ as determined from the 3-minute all-out test (3MT), (ii) to develop a testing protocol to understand expenditure and recovery of power and ϒ, (iii) to establish ϒ recovery profiles in terms of recovery power (Prec) and recovery duration (trec), and (iv) to present a case of cycling performance optimization using the energy management system based on athlete-specific models. Competitive amateur cyclists participated in two cycle ergometer studies: (i) repeatability of 3MTs to quantify IIV and (ii) intermittent cycling, in the laboratory to establish ϒ recovery profiles. The studies included an incremental ramp test to determine gas exchange threshold (GET), two or four 3MTs to determine CP and ϒ, and nine intermittent cycling tests to understand recovery of ϒ. From the repeated 3MT study, a new method was proposed to compare any two pairs of the 3MT at the individual level and estimate the IIVs associated with CP and ϒ. In the second study, a statistically significant two-way interaction effect between Prec and trec on ϒ recovery was observed followed by simple main effects seen only with respect to Prec at each trec. This indicates that Prec has a greater influence on the recovery of ϒ in a recovery interval lasting 2-15 minutes that follows a semi-exhaustive exertion interval above CP. The overestimation of the actual ϒ-balance at the end of the recovery interval by the W\u27bal models highlights the need for athlete-specific recovery parameters or models. Finally, the optimization tests conducted with one subject provide encouraging signs for the use of individualized recovery models in real-time in-situ performance optimization

Modeling the behavior of anaerobic work capacity in cycling

Models of fatigue are based on physiological parameters such as Critical Power (CP) and Anaerobic Work Capacity (AWC). CP is a theoretical power that can be maintained indefinitely and AWC is a finite anaerobic energy reservoir for efforts above CP. There is an increasing interest in developing mathematical models of energy expenditure and recovery for athletic training and performance. Recently, researchers have developed formal mathematical models that aid in better management of performance. Most available models have originated from cycle ergometer tests due to the ease of measuring power in cycling. The objectives of this research are (i) to develop a testing protocol to understand expenditure and recovery of AWC in cycling, (ii) to establish AWC recovery profiles in terms of recovery powers and durations, and (iii) to combine AWC recovery with expenditure for energy management in cycling. Nine recreational cyclists performed a study which involved a VO2max ramp test to determine gas exchange threshold (GET), a 3-min all-out intensity test (3MT) to determine CP and AWC, and 9 intermittent cycling tests to understand recovery of AWC. Three cyclists completed all tests resulting in a complete profile of the AWC recovery. The results indicate that AWC recovered during recovery decreases with increasing recovery powers. No generic trends were observed in AWC recovery with respect to recovery durations. In addition, the tests indicate the need for individualized models owing to the inherent within-subject variability (WSV) associated with CP and AWC. Quantifying this WSV will aid in accurately modelling and optimizing performance

Mechanisms of Telomere Protection and Deprotection in Human Cells

Telomeres, the nucleo-protein complexes at the ends of linear chromosomes, have critical roles in genome stability, cancer, and aging. Early work by B. McClintock and H.J. Muller demonstrated that eukaryotic chromosome ends contain specialized structures that prevent recognition and processing by the DNA repair machinery. The importance of these structures is illustrated by studies showing that loss of chromosome end protection results in massive genome instability and cell death. Although Muller and McClintock's initial observations were made several decades ago, little progress has been made in understanding the molecular markers that distinguish naturally occurring chromosome ends from de novo DNA double strand breaks, especially in humans. Using a novel system to specifically target proteins of interest to human telomeres, we have uncovered a role for hRAP1 in protecting telomeres from non-homologous end joining (NHEJ). We find that telomeric DNA containing hRAP1, but not TRF2, is protected from NHEJ in vitro. Furthermore, we show that telomeres containing TRF2 but not hRAP1 can be fused by NHEJ in vivo, and we also demonstrate that targeting hRAP1 to telomeres in vivo, even when TRF2 is not detected, is sufficient to protect telomeres from NHEJ. These results identify hRAP1 as a critical mediator of telomere protection and genome stability in humans. Related to this work, we have also identified a new type of telomere dysfunction associated with semi-conservative replication stress at human telomeres. This new type of telomere dysfunction is telomerase and NHEJ-independent and may require the RecQ helicase WRN for its formation, suggesting that it is related to telomere entanglements observed upon induction of replication stress in fission yeast. The finding that this type of dysfunction is conserved from yeast to man is a testament to the underappreciated role of semi-conservative DNA synthesis in maintaining telomere structure and function

An Experimental Protocol to Model Recovery of Anaerobic Work Capacity

Models of fatigue are based on physiological parameters such as Critical Power (CP) and Anaerobic Work Capacity (AWC). CP is a theoretical threshold value that a human can generate for an indefinite amount of time and AWC represents a finite expendable amount of anaerobic energy at intensities above CP. There is an increasing interest in developing mathematical models of energy expenditure and recovery for athletic training and human performance. The objective of this research is to propose and validate a model for recovery of AWC during a post exertion recovery interval of cycling. A cycling ergometer study is proposed which involves a VO2max ramp test to determine gas exchange threshold, a 3-min all-out intensity test to determine CP and AWC, and exertion-recovery interval tests to understand recovery of AWC. The results will be used to build a human in the loop control system to optimize cycling performance

A survey of mathematical models of human performance using power and energy

The ability to predict the systematic decrease of power during physical exertion gives valuable insights into health, performance, and injury. This review surveys the research of power-based models of fatigue and recovery within the area of human performance. Upon a thorough review of available literature, it is observed that the two-parameter critical power model is most popular due to its simplicity. This two-parameter model is a hyperbolic relationship between power and time with critical power as the power-asymptote and the curvature constant denoted by W′. Critical power (CP) is a theoretical power output that can be sustained indefinitely by an individual, and the curvature constant (W′) represents the amount of work that can be done above CP. Different methods and models have been validated to determine CP and W′, most of which are algebraic manipulations of the two-parameter model. The models yield different CP and W′ estimates for the same data depending on the regression fit and rounding off approximations. These estimates, at the subject level, have an inherent day-to-day variability called intra-individual variability (IIV) associated with them, which is not captured by any of the existing methods. This calls for a need for new methods to arrive at the IIV associated with CP and W′. Furthermore, existing models focus on the expenditure of W′ for efforts above CP and do not model its recovery in the sub-CP domain. Thus, there is a need for methods and models that account for (i) the IIV to measure the effectiveness of individual training prescriptions and (ii) the recovery of W′ to aid human performance optimization

Experimental Modeling of Cyclists Fatigue and Recovery Dynamics Enabling Optimal Pacing in a Time Trial

Improving a cyclist performance during a time-trial effort has been a challenge for sport scientists for several decades. There has been a lot of work on understanding the physiological concepts behind it. The concepts of Critical Power (CP) and Anaerobic Work Capacity (AWC) have been discussed often in recent cycling performance related articles. CP is a power that can be maintained by a cyclist for a long time; meaning pedaling at or below this limit, theoretically, can be continued for infinite amount of time. However, there is a limited source of energy for generating power above CP. This limited energy source is AWC. After burning energy from this tank, a cyclist can recover some by pedaling below CP. In this paper we utilize the concepts of CP and AWC to mathematically model muscle fatigue and recovery of a cyclist. Then, the models are used to formulate an optimal control problem for a time trial effort on a 10.3 km course located in Greenville SC. The course is simulated in a laboratory environment using a CompuTrainer. At the end, the optimal simulation results are compared to the performance of one subject on CompuTrainer.Comment: 6 pages, 8 figure

Modeling the Expenditure and Recovery of Anaerobic Work Capacity in Cycling

The objective of this research is to model the expenditure and recovery of Anaerobic Work Capacity (AWC) as related to Critical Power (CP) during cycling. CP is a theoretical value at which a human can operate indefinitely and AWC is the energy that can be expended above CP. There are several models to predict AWC-depletion, however, only a few to model AWC recovery. A cycling study was conducted with nine recreationally active subjects. CP and AWC were determined by a 3-min all-out test. The subjects performed interval tests at three recovery intervals (15 s, 30 s, or 60 s) and three recovery powers (0.50CP, 0.75CP, and CP). It was determined that the rate of expenditure exceeds recovery and the amount of AWC recovered is influenced more by recovery power level than recovery duration. Moreover, recovery rate varies by individual and thus, a robust mathematical model for expenditure and recovery of AWC is needed

Ciliary Neurotrophic Factor Induces Genes Associated with Inflammation and Gliosis in the Retina: A Gene Profiling Study of Flow-Sorted, Müller Cells

Ciliary neurotrophic factor (CNTF), a member of the interleukin-6 cytokine family, has been implicated in the development, differentiation and survival of retinal neurons. The mechanisms of CNTF action as well as its cellular targets in the retina are poorly understood. It has been postulated that some of the biological effects of CNTF are mediated through its action via retinal glial cells; however, molecular changes in retinal glia induced by CNTF have not been elucidated. We have, therefore, examined gene expression dynamics of purified Müller (glial) cells exposed to CNTF in vivo.Müller cells were flow-sorted from mgfap-egfp transgenic mice one or three days after intravitreal injection of CNTF. Microarray analysis using RNA from purified Müller cells showed differential expression of almost 1,000 transcripts with two- to seventeen-fold change in response to CNTF. A comparison of transcriptional profiles from Müller cells at one or three days after CNTF treatment showed an increase in the number of transcribed genes as well as a change in the expression pattern. Ingenuity Pathway Analysis showed that the differentially regulated genes belong to distinct functional types such as cytokines, growth factors, G-protein coupled receptors, transporters and ion channels. Interestingly, many genes induced by CNTF were also highly expressed in reactive Müller cells from mice with inherited or experimentally induced retinal degeneration. Further analysis of gene profiles revealed 20-30% overlap in the transcription pattern among Müller cells, astrocytes and the RPE.Our studies provide novel molecular insights into biological functions of Müller glial cells in mediating cytokine response. We suggest that CNTF remodels the gene expression profile of Müller cells leading to induction of networks associated with transcription, cell cycle regulation and inflammatory response. CNTF also appears to function as an inducer of gliosis in the retina