Production Speed Research Articles

Supporting military maintenance and repair with additive manufacturing

Abstract The purpose of the study is to explore whether Additive Manufacturing (AM) can support the military maintenance and repair of combat troops at isolated tactical level maintenance sites. The study also sought an explanation as to how AM could be organised in military logistics. The subject was approached from a systemic perspective. A system dynamics modelling was used as an impact assessment method. When selecting the parameters used in the model, the 3D printing data of the spare parts printed on the MTLB armoured personnel carrier (APC) were utilised. With simulation, we identified several key nodes for replacing or enhancing conventional military logistics with an AM added supply chain. As a result of the study, it was identified that by adding metal AM to the mechanised battalion organic maintenance and repair at the field level, it can produce spare parts whose use will improve APC recovery in the event of failure. We found that the relatively slow production speed of AM is the most influential factor in the use of the method. This study introduces a new perspective on reviewing the potential of AM in military logistics.

Engineering practice of underground heat injection-enhanced gas extraction in low-permeability coal seams

ABSTRACT The heat injection mechanism for improving gas desorption, coal seam gas pressure, and coal seam permeability in the Yangquan mining area was investigated via theoretical analysis. This analysis was conducted to address the problems of poor permeability, difficult gas extraction, and low extraction efficiency of 15# coal seam. An underground heat injection-enhanced gas extraction technology was proposed; accordingly, a heat injection-enhanced gas extraction system was developed and appropriate extraction methods were devised. The findings of an industrial test on 15# coal seam in the coal mine show that the proposed technology not only increased the amount of gas extracted but also halved the extraction time and realized efficient gas extraction. Two mature underground heat injection-enhanced gas extraction methods were established. These methods have similar gas production principles in that the gas production speed and gas concentration in the heat injection stage are relatively low, while the average degree of improvement in the extraction stage after heat injection can reach more than 50 times. The average degree of improvement in gas production speed and gas concentration after the second heat injection is greater than that after the first.

ECONOMIC PSYCHOLOGY ANALYSIS OF RECYCLERS' EMOTIONAL STABILITY IN CLOSED-LOOP SUPPLY CHAIN UNDER UNCERTAINTY

BackgroundIn today's society, with the sustainable development of economy, material products are rich and diverse. The production speed of products has far exceeded people's needs. Emission reduction and environmental protection have become people's new pursuit. Closed loop supply chain should consider not only product life cycle and recycling, but also economic and environmental benefits. It has become the focus of scholars all over the world. Closed loop supply chain refers to the complete supply chain cycle from procurement to final sales, including product recovery and reverse logistics supported by life cycle. It is a highly complex process. In the closed-loop supply chain, the simplest form is composed of manufacturers, retailers and recyclers. Recycler is the most critical link in the new closed-loop supply chain system, which is not available in the traditional supply chain. Therefore, this paper mainly studies the change of recyclers when exogenous variables fluctuate from the perspective of economic psychology.Research Objects and MethodsMost scholars use short-term static methods when studying the uncertainty of recyclers in closed-loop supply chain. It is particularly important to analyze the uncertain factors in the closed-loop supply chain. In order to analyze this problem, this paper first improves the closed-loop supply chain model of capital flow and logistics coupling, so as to better simulate the real closed-loop supply chain. Secondly, the sensitivity analysis function of Vensim software is used to simulate the impact of exogenous variables on the inventory value and capital value of recyclers in the closed-loop supply chain model. At the same time, in order to verify the impact of recyclers' emotional stability, this study adopts the following scale. The communication anxiety scale adopts 15 questions of the Interaction Anxiety Scale (IAS) compiled by Leary, with a single dimension and a 5-level score, from 1 to 5 to “very inconsistent”. The higher the score, the greater the degree of social anxiety. The emotion regulation self-efficacy scale adopts the emotion regulation self-efficacy scale (RES) revised by Caprara. The 12 questions are divided into three dimensions: expressing positive emotions, managing depression / pain and self-efficacy of managing anger / anger, with 4 questions in each dimension. A 5-level score is adopted, from 1 to 5, which means “very inconsistent” to “very consistent”. The higher the score, the higher the degree of self-confidence in regulating their emotions. In the study, Cronbach's α The coefficient is 0.80. The aggression scale adopts the aggression scale (bpaq) compiled by Buss and PerryThe scale has 29 questions and is divided into four dimensions: physical aggression, verbal aggression, anger and hostility. The higher the score, the stronger the attack. In this study, Cronbach's α The coefficient is 0.85. The depression questionnaire adopts Beck's revised depression Inventory-II (BDI-II). The questionnaire has 21 questions, with a single dimension. The higher the total score, the heavier the degree of depression. The data were obtained by spss19 0 and amos17 0 for analysis.Resultsthe 19 exogenous variables were divided into four categories: Manufacturer related parameters, retailer related parameters, recycler related parameters and other related parameters. The sensitivity of these 19 parameters to recycler inventory and capital in closed-loop supply chain is simulated and analyzed. Through the comparative analysis of sensitivity chart, it can be seen that the manufacturer's inventory adjustment time, the retailer's safety inventory coefficient, the retailer's smoothing time, the retailer's inventory adjustment time, the collector's fixed expenditure and the collector's initial inventory value are positively correlated. And have a significant impact on collectors' inventory and emotional stability. The reason is that appropriate time adjustment helps to reduce work pressure and naturally improve job satisfaction.Conclusionin the closed-loop supply chain, the fluctuation of the same exogenous variable in the same range has a more significant impact on the recycler's inventory than on the recycler's capital. For recyclers, the decline of inventory value has a positive impact on the capital of recyclers, while the decline of capital value has a negative impact on the capital of recyclers. The impact of retailer order smoothing time on recycler inventory and capital is uncertain. Therefore, recyclers should strengthen fund management, establish insurance mechanism and prepare reserves to prevent the impact of external variable fluctuations on recyclers' funds. At the same time, in view of the uncertainty caused by exogenous variables related to manufacturers and retailers on recyclers' funds and inventory, recyclers need to deal with it through information sharing, compensation mechanism, incentive and other ways.AcknowledgementsSupported by a project grant from National Natural Science Foundation of China (Grant No.71764019), the National Social Science Foundation of China (Grant No.19BGL187), the Planning Project of Philosophy and Social Science of Inner Mongolia (Grant No.2021NDB082), Inner Mongolia Natural Science Foundation (Grant No.2021MS07016 and 2020MS07020) and Research Center for Resources, Environment and Energy Development Strategic.

Experimental, analytical, and numerical investigations on the flexural and fatigue behavior of steel thin-walled X-section beam

Thin-walled hollow shapes are of great interest in many industries with weight constraints, due to their availability, low price, and strength-to-weight ratio. This paper presents the development, calculation, and production of a thin-walled X-section beam design with a unique section geometry. This hollow X-section beam geometry is a beam that has been developed to use shape-connected jaws on the beam and to use less bolts and mounting elements, and to easily change the positions of the parts mounted on the beam. The bending strength of this unique beam section was investigated, and the fatigue damage of the beam was also handled with technological methods. Using both experimental stress measurements and finite element solution, the static and fatigue strength of the beam were calculated with computer-aided engineering software. The FEM solution was performed nonlinearly by defining the linear elastic and plasticity properties of the material. Validation studies were carried out in the laboratory using three-point and four-point bending tests. These traditional experiments were supported by strain gauge technology that measures strain with 0.05% accuracy. The weight and bending strength of the X-section beam were compared with the hollow section square beam. X-section beam (S355J0H) has 13% lower bending strength than 120 × 120 × 8 mm (S355J0H) beam; however, it is 37% lighter. ANSYS-analytical test results of difference are 3.95%, and ANSYS-experimental test results of difference are 0.85%. Experiments showed that a ∼22% increase in strength is found in these corners depending on the production method. The fatigue behavior of the X-section beam was determined with the nCode DesignLife software using validated FEM solutions and fatigue curves of the materials. X-section beam developed for shape–connected assembly systems can be used especially in the formation of chassis with its superior assembly ability and bending strength, increasing functionality, and production speed.

Effect of Sub-Contractor Selection on Construction Project Success in Turkey

The construction industry leads the national economy in developing countries. It involves industrial requirements, such as developing technologies, related expertise, demand variability, high production speed and progress. Firms in the industry use subcontractors to produce fast, effective solutions. Therefore, projects’ success varies depending on subcontractors’ rather than general contractors’ performance. This study aimed to develop a model of selection criteria for subcontractors and measure their impact on project success. Construction firms using subcontractors were chosen as the target group. Data on the selection of subcontractors from 93 construction firms that employ subcontractors in their projects were collected through a survey. The impact of the subcontracting selection factor on projects’ overall performance was presented with five hypotheses and modeled using a structural equation model. The weight of each selection factor in the subcontracting selection and the impact on the overall project were designated in the model by determining the standardized regression weights (β). Four hypotheses were accepted and one rejected. This study may contribute to the prequalification conditions in the process of selecting subcontractors in the future.

New Expansions In The Economic Production Quantity Model Containing Defective Products

The basic assumption in classical production quantity models is that all of the products produced are free of defect. But in real life, this assumption is not always valid. EPQ models were examined for the situation where the proportion of defective products is a random variable and fits a certain probability distribution. When the literature reviewed, it is seen that the scanning speed of defective products is accepted as equal to the production rate. In this study, a model was developed under the condition that the scanning speed is smaller than the production rate. In addition, a sample problem solution was made with the assumption that the defective product ratio is random variable and corresponds to the normal distribution and uniform distribution.

Analisis kandungan klorofil pada familia orchidaceae terhadap cekaman kekeringan

Family Orchidaceae has 25.000 to 30.000 species which are divided into 5 subfamilies. Moon orchids and earth orchids are examples of plants from the Orchidaceae family. Orchid cooperatives in Indonesia have high economic value. In the cultivation of orchids, there are obstacles that occur, namely drought which can inhibit growth. Drought stress causes a slow increase in leaf area and affects stomata or photosynthesis which can reduce the speed of plant productivity. Drought stress control can be done by using superior varieties that are resistant to drought serum by adding a compound to the growing media. The purpose of the journal review is to determine the types of compounds that can be used for plants to be resistant to drought stress in the Orchidaceae family. The results of a review of several journals showed that PEG 6000 compounds and growth regulators (ZPT) could increase chlorophyll a, chlorophyll b and total chlorophyll in plantlets which decreased under drought stress conditions

3D-Printed Disease Models for Neurosurgical Planning, Simulation, and Training.

Spatial insight into intracranial pathology and structure is important for neurosurgeons to perform safe and successful surgeries. Three-dimensional (3D) printing technology in the medical field has made it possible to produce intuitive models that can help with spatial perception. Recent advances in 3D-printed disease models have removed barriers to entering the clinical field and medical market, such as precision and texture reality, speed of production, and cost. The 3D-printed disease model is now ready to be actively applied to daily clinical practice in neurosurgical planning, simulation, and training. In this review, the development of 3D-printed neurosurgical disease models and their application are summarized and discussed.

Intervention of resource allocation strategies on spatial spread of epidemics.

Medical resources are crucial in mitigating epidemics, especially during pandemics such as the ongoing COVID-19. Thereby, reasonable resource deployment inevitably plays a significant role in suppressing the epidemic under limited resources. When an epidemic breaks out, people can produce resources for self-protection or donate resources to help others for treatment. That is, the exchange of resources also affects the transmission between individuals, thus, altering the epidemic dynamics. To understand factors on resource deployment and the interplay between resource and transmission we construct a metapopulation network model with resource allocation. Our results indicate actively or promptly donating resources is not helpful to suppress the epidemic under both homogeneous population distribution and heterogeneous population distribution. Besides, strengthening the speed of resources production can significantly increase the recovery rate so that they reduce the final outbreak size. These results may provide policy guidance toward epidemic containment.

Experimental Evaluation of Water Control for Continuous Packer in Buried Hill Fractured Gas Reservoir: A Case Study of HZ 26-6 Condensate Gas Field

Abstract Although research into water control completion techniques is now relatively mature, there are still difficulties in controlling water in fractured gas reservoirs in the sea. Unlike oil reservoirs, submerged gas reservoir development still faces some problems. To explore the water control mechanism of buried hill fractured gas reservoir, based on the parameters of well HZ26-6-2 in HZ 26-6 condensate gas field, the water control experiment of the continuous packer in the bottom water gas reservoir was completed through the design of experimental parameters, the design of buried hill fractured formation, and the process design of continuous packer. Studies have shown that the continuous packer water control technology delays the water coning rate and makes the water propulsion more uniform. The water breakthrough time and gas production are slightly different for different fractured gas reservoirs, and the network fracture model has a short gas recovery period and fast gas production speed. Continuous packer water control can improve natural gas recovery by 14.3% in fractured gas reservoir. Based on fracture dredging ability, sand accumulation and filling degree, and drilling and production strategy, the influencing factors of horizontal well water control effect in buried hill fractured gas reservoir are discussed and summarized. The research results are aimed at establishing a development model of water control for buried hill gas reservoirs and providing good technical support for rational and scientific water control of horizontal Wells in offshore condensate gas fields. The findings of this study can help for a better understanding of water control of horizontal wells in offshore condensate gas fields.

Direct synthesis of graphene by blowing CO2 bubble in Mg melt for the seawater/oil pollution

It is urgent to improve the quality and reduce the cost of graphene for widespread applications. In this work, a simple and cost-effective vapor-liquid reaction route to produce few-layer graphene was developed for the seawater/oil separation. The method can not only achieve direct synthesis of graphene by blowing CO2 bubbles into magnesium (Mg) melt, but also realize efficient extraction of graphene assisted by molten salt. The defect density and production speed of graphene were controlled by adjusting the size and growth time of the CO2 bubble in molten Mg. In addition, the wrinkled morphology of as-fabricated graphene also formed due to the disordered restacking of curly surface. Seawater pollution caused by oil spills could be absorbed within by the wrinkled graphene. This novel method represents a great opportunity to solve the problem of excessive CO2 emission in a sustainable future. In addition, it could be applied to the industrial production of graphene powder easily and also paves a new path for the synthesis of other nanomaterials.

Analysis of Animation Peripheral Design Ability Based on Artificial Intelligence

With the development of communication technology and hardware technology, only continuous innovation in animation production can meet the development needs of the times. Animation has recently received substantial interest in special education. New forms of representation, including animation, multimedia, and virtual reality, are some of the key developments that education technology has made possible. Animation software is an influential mass media, communication, and education platform. Progressive improvements in technical methods along with the expansion of knowledge and skills have resulted in an increase in variety as well as the speed of production of new products for animation. In this study, we propose an Advanced Animation Teaching Model (AATM) based on Design-Oriented Learning Approach (DOLA). Design-based learning is the incorporation of design projects in classrooms so that students can acquire creative solutions and learn curriculum content by participating in actual, cross-curricular challenges. This model keeps pace with the times to meet the needs of the modern market. It combines introduction to animation, color composition, color psychology, composition basis, spatial perspective, animation scene design, and visual art design-related theories to form the theoretical basis for the major. The results showed the trends of animation used in education and the strengths of animation to improve the learning of students and enhance the thinking ability of the students.

APPLICATION OF 3D PRINTING TECHNOLOGY IN MEDICINE

Currently, 3D-printing technology is almost universally used in various fields, and the list of materials used in 3D-printing is becoming more and more extensive. One of the most popular and imoirtant areas for the application of this technology is medicine, or rather transplantology. The ability to create layouts based on individual anatomical features, the accuracy of the virtual analogue and the high production speed make 3D-printing extremely promising in organ transplantation. At present, there is already experience of creating artificial organs and body parts using this method. Expanding the range of use of 3D-printing in medicine will make it possible to cure many diseases, which will improve the quality of people’s lives. This article provides a brief overview of the history of 3D printing and its application in medicine.

Multivariate optimization of mechanical and microstructural properties of welded joints by FSW method

This paper investigates the microstructural and mechanical properties in the joining of aluminum sheets using the friction stir welding (FSW) method. First, the microstructural properties are investigated, and then the effect of process parameters on the grain size, defect formation, microhardness, and fracture energy is discussed. The grain size in the stir zone is remarkably refined compared to the base metal, while the microhardness is reduced due to the annealing effects of the FSW. According to the findings, the material integrity in the stir zone is the most critical aspect in determining the value of absorbed energy in the fracture test. The existence of a cavity in the stir zone severely reduces the fracture energy, while the negative effects of the weld line remnant defect on the fracture energy are negligible. For each pin profile and rotational speed, the safe window of traverse speed for defect-free joint production is widened from the conical cylinder pin to the square pin and then to the threaded pin. The ratio of rotational speed to traverse speed (w/v) is the most important parameter in determining almost all characteristics of a joint produced by a specific tool. For each type of pin profile, there is a minimum amount for this ratio, below which the defect formation is very likely to the occurrence. The lowest w/v ratio required to generate a defect-free weld with the conical cylinder pin tool is nearly 2. While that is desirably lowered to 1.6 and 1.25 for square and threaded pin tools, respectively. For all three pin shapes, the hardness value is increased by increasing the traverse speed and decreasing the rotational speed. The grain size and Charpy impact fracture energy values are also reduced by decreasing the rotational speed and increasing the traverse speed. While, a power regression curve (that is very similar to the Hall-Petch relationship) is fitted well to describe the relationship between hardness and grain size, a second-order equation is fitted to the results of fracture energy vs. hardness and grain size. Furthermore, based on the obtained results, it can be concluded that the fracture energy value is more sensitive to the pin profile compared to other outputs of this research (i.e., hardness and grain size). Using the neural network, a relationship was obtained between the input parameters of the process, such as traverse speed, rotational speed, and tool shapes, with the mechanical and microstructural properties of the joints. This relationship was then used in a hybrid multiobjective optimization to find the optimal process parameters. As the best compromise option, hybrid multiobjective optimization proposes a traverse speed of 309 mm/min, a rotational speed of 495 rev/min, and a threaded cylinder pin shape.

Impact of winding on nanoimprinted surfaces in roll‐to‐roll nanoimprint lithography

AbstractRoll‐to‐Roll manufacturing aims at scaling ultraviolet‐ and thermally cured nanoimprint lithography (UV‐NIL, T‐NIL) to commercial production speeds and volumes. Winding is the only convenient way of storing large quantities of nanoimprinted webs as they await unwinding in sequential R2R processes with distinct transport speeds. At production speeds, the imprinted resin is still chemically evolving when the imprinted web enters the winder, through a phenomenon called dark curing. The viscoelastic resin at various curing stages deforms under the contact pressure due to winding. This study is concerned with the impact of the contact pressure on the imprinted peak heights and potentially the functionality of the nanoimprinted surface. We develop a multiscale numerical model of the winding of the imprinted web. First the evolving properties of the resin through time are characterized, combining the effect of dark curing and viscoelasticity on the time‐dependent properties. Second, a finite element model of the imprinted web uses the resin mechanical properties to determine the effective properties of the imprinted web. Finally, the winding model determines the pressure and resulting strain of the imprints in the wound roll. The surface creep is quantified. This prediction will establish how and how long the imprinted materials should be wound.

RPEM: Design and Realization of Reconfigurable Power Electronic Modules

A series of novel externally reconfigurable power electronic modules (RPEMs) are invented to increase the flexibility of power modules and their application purposes. In this article, the concept of RPEMs, their switching arrangements, and power-module-based architectural design are demonstrated. An RPEM is then designed, analyzed through simulations, and compared with the conventional fixed-configuration power electronic modules. The sizes of the power modules and used power terminals are kept similar to avoid any differences in power loop inductance values solely due to various trace pad sizes. In addition, similar gate/source pads and signal pins are used for all of the designed power modules to have constant switching dynamics in all modules. The comparison results show that the internal parasitic inductance and performance are still comparable with the conventional modules despite having high configurability. The designed RPEM and a conventional full-bridge (FB) power module are fabricated and characterized. The experimental tests show that the difference between the overshoot voltages on both RPEM and FB power modules is less than 2%. Such flexibility without compromising the power module performance decreases the engineering time for designing different power modules for various power electronic converters; hence, the production speed can be improved while decreasing the overall module cost.

Simulation Software for Transition-Edge Sensor Performance Prediction

Transition-edge sensors (TES) are outstanding calorimeters based on the steep superconductive transition of a metallic film. Among other photon detectors, they are renowned for the fine energy resolution, the photon-number resolving (PNR) capability and an extremely low dark count rate. Due to the broad detection spectrum, from gamma-ray to visible and submillimetre wavelengths, TESs are highly sought-after in a great variety of fields, such as X-ray detection and quantum technologies. Each of these fields demands a step forward in TESs performance with regards to the recovery time and energy resolution. Here we present a program, primarily capable of predicting the performance of TESs. Using established theoretical and empirical methods we developed a software that allows the users to choose active area, thickness, and material composition of a TES and to calculate its performance. Furthermore, the software can simulate TES properties at different working points. The aim of the software is to minimize the production cost and speed up the overall process for the creation of new devices with improved performance.

Rancang Bangun Mesin Pemeras Tebu 3 Roll dengan Penyajian Otomatis

Sugarcane juice can be taken by squeezing sugarcane stalks using a squeeze machine. The existing squeezing machines are still not efficient and relatively low production speed. The main factor of machine performances was on rolls quantity and its arragement. To overcome this problem, we have designed and fabricated the machine with 3-rolls by optimally speed and inter-rolls distance setting. The squeezer rolls were driven by 1-phase motor with fixed speed by the gear ratio setting. The distance and position between the rolls are arranged in such a way that the pressing power is maximized, but it is maintained to avoid stuck. The peeled and cut sugarcane is loaded into the hopper. Then, the sugar cane is drawned and squeezed by rolls. After that, it filtered and stored in the container. This machine is equipped with an automatic system for dispensing sugarcane juice from the container to the glass. The results show that the efficiency of this machine is around 65.1% with 78.1 ml/s production speed. Sugarcane juice produced is relatively clean without contaminated by it dregs

Optimization of logistics business processes to strengthen the company's competitive advantages

The paper highlights one of the modern management approaches – the process approach to management, which allows you to increase the operational efficiency of enterprises, make it flexible and quickly respond to market changes. A certain topic is relevant for the development of any enterprise, because logistics operations management is a source for discovering new prospects, innovative ideas, and stable competitive positions. The authors note that for success in the market, it is not enough to work methodically to improve the products offered, it is necessary to improve logistics business processes, optimizing them taking into account changes in the market situation. The purpose of the paper is to highlight the essence, features, and content of the process approach for optimizing logistics business processes of the enterprise and methods and methods of their implementation as a basis for effectively strengthening competitive advantages. The paper examines the essence of the concept of "business process" and "logistics business process". The key elements of logistics business processes are presented, and the need to manage them to strengthen the competitive advantages of the enterprise is determined. It is indicated that it is necessary to provide for the formation of purposeful behavior of the enterprise in the direction of creating stable competitive advantages by identifying, structuring and managing a system of interrelated and complementary elements of logistics business processes that are the driving forces of economic growth, and their resource environment (technical and technological, personnel, financial, time, legal). The paper presents the key stages of work that should be performed in order to achieve the implementation of a process approach in the logistics activities of the enterprise. The authors substantiate the need to optimize logistics business processes and present methods that can be used in the enterprise, present their strengths and weaknesses. It is noted that the results of optimizing logistics business processes are to reduce time costs for solving typical logistics problems, reduce production costs, improve the quality and speed of production, and improve methods of working with customers.

Persistent CAD activity in memory CD8+ T cells supports rRNA synthesis and ribosomal biogenesis required at rechallenge.

Memory CD8+ T cells are characterized by their ability to persist long after the initial antigen encounter and their capacity to generate a rapid recall response. Recent studies have identified a role for metabolic reprogramming and mitochondrial function in promoting the longevity of memory T cells. However, detailed mechanisms involved in promoting their rapid recall response are incompletely understood. Here, we identify a role for the initial and continued activation of the trifunctional rate-limiting enzyme of the de novo pyrimidine synthesis pathway CAD (carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase) as critical in promoting the rapid recall response of previously activated CD8+ T cells. We found that CAD was rapidly phosphorylated upon naïve T cell activation in an mTORC1-dependent manner, yet remained phosphorylated long after initial activation. Previously activated CD8+ T cells displayed continued de novo pyrimidine synthesis in the absence of mitogenic signals, and interfering with this pathway diminished the speed and magnitude of cytokine production upon rechallenge. Inhibition of CAD did not affect cytokine transcript levels but diminished available pre-rRNA (ribosomal RNA), the polycistronic rRNA precursor whose synthesis is the rate-limiting step in ribosomal biogenesis. CAD inhibition additionally decreased levels of detectable ribosomal proteins in previously activated CD8+ T cells. Conversely, overexpression of CAD improved both the cytokine response and proliferation of memory T cells. Overall, our studies reveal a critical role for CAD-induced pyrimidine synthesis and ribosomal biogenesis in promoting the rapid recall response characteristic of memory T cells.