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Purpose Calcific aortic valve disease (CAVD), has been characterized as a cascade of cellular changes leading to leaflet thickening and valvular calcification. In diseased aortic valves, glycosaminoglycans (GAGs) normally found in the valve spongiosa migrate to the collagen I-rich fibrosa layer near calcified nodules. Current treatments for CAVD are limited to valve replacement or drugs tailored to other cardiovascular diseases. Methods Porcine aortic valve interstitial cells and porcine aortic valve endothelial cells were seeded into collagen I hydrogels of varying initial stiffness or initial stiffness-matched collagen I hydrogels containing the glycosaminoglycans chondroitin sulfate (CS), hyaluronic acid (HA), or dermatan sulfate (DS). Assays were performed after 2 weeks in culture to determine cell gene expression, protein expression, protein secretion, and calcification. Multiple regression analyses were performed to determine the importance of initial hydrogel stiffness, GAGs, and the presence of endothelial cells on calcification, both with and without osteogenic medium. Results High initial stiffness hydrogels and osteogenic medium promoted calcification, while for DS or HA the presence of endothelial cells prevented calcification. CS was found to increase the expression of pro-calcific genes, increase activated myofibroblast protein expression, induce the secretion of collagen I by activated interstitial cells, and increase calcified nodule formation. Conclusion This study demonstrates a more complete model of aortic valve disease, including endothelial cells, interstitial cells, and a stiff and disease-like ECM. In vitro models of both healthy and diseased valves can be useful for understanding the mechanisms of CAVD pathogenesis and provide a model for testing novel therapeutics.

The electrical properties of magnetic sensing devices fabricated from anisotropic materials are not easily extracted. Here we present a method for determining the resistance matrix for an anisotropic device with multiple electrical contacts placed in a perpendicular magnetic field. By using the methods developed by Van der Pauw and Wasscher, the analysis for the anisotropic system is reduced to the equivalent problem for an isotropic sample, which can then be solved using methods developed previously. As a result, the method works in the case of structures with an arbitrary number of asymmetric extended contacts at large magnetic field strength. In addition to the extraction of nonisotropic resistivities, the resistance matrix can be used to analyze the Hall effect for anisotropic plates.

Introduction: Calcific aortic valve disease (CAVD) is an active pathological process leading to severe valve calcification. Late-stage CAVD is characterized by increased leaflet stiffness, disorganized collagen bundles and the deposition of glycosaminoglycans, such as chondroitin sulfate (CS), in the fibrosa layer. However, many details of the cellular pathological cascade remain unknown. Animal models such as mice, rabbits, and pigs are used in understanding human CAVD, but mice do not have similar anatomy, rabbits cannot spontaneously develop atherosclerotic lesions, and pigs require long, expensive and complex studies. Here we utilize microfluidic devices of the aortic valve fibrosa to model late-stage CAVD. Hypothesis: We assessed the hypothesis that microfluidic calcification will increase with increased shear rates and CS content. Methods: Valve-on-a-chip devices contained a hydrogel of 1.5 mg/mL collagen I-only healthy controls or 1.5 mg/mL collagen I with 1 mg/mL or 20 mg/mL CS. Porcine aortic valve interstitial cells (PAVIC) were embedded within and endothelial cells (PAVEC) were seeded onto the matrix. Steady shear stress at 1 dyne/cm 2 and 20 dyne/cm 2 were applied using a peristaltic pump for 14 days. Alizarin Red S (ARS), an assay to assess calcium deposition, was used to quantify calcific nodule formation. Scanning electron microscopy with energy dispersive x-ray (SEM/EDX) was used to further analyze sample mineralization. Results: Co-cultures in the presence of increasing shear stress and CS exhibit increased calcific nodule formation compared to static controls, both qualitatively and quantitatively (n≥3). SEM revealed the microstructure of calcified nodules and EDX confirmed calcium phosphate mineralization with physiologically-relevant calcium to phosphorous ratios (Ca/P= 0.88 - 1.4). Conclusions: These results show that in vitro calcification is driven by shear stress in the presence of PAVEC and CS. As seen in ex vivo studies of human calcification, these microfluidic-derived nodules are similarly composed of a range of naturally-occurring calcium phosphates. Given that CAVD has no targeted therapy, the creation of a physiologically relevant model of the aortic valve can provide a test bed for novel therapeutic interventions.

Calcific aortic valve disease (CAVD), has been characterized as a cascade of cellular changes leading to leaflet thickening and valvular calcification. In diseased aortic valves, glycosaminoglycans (GAGs) normally found in the valve spongiosa migrate to the collagen I-rich fibrosa layer near calcified nodules. Current treatments for CAVD are limited to valve replacement or drugs tailored to other cardiovascular diseases.Porcine aortic valve interstitial cells and porcine aortic valve endothelial cells were seeded into collagen I hydrogels of varying initial stiffness or initial stiffness-matched collagen I hydrogels containing the glycosaminoglycans chondroitin sulfate (CS), hyaluronic acid (HA), or dermatan sulfate (DS). Assays were performed after 2 weeks in culture to determine cell gene expression, protein expression, protein secretion, and calcification. Multiple regression analyses were performed to determine the importance of initial hydrogel stiffness, GAGs, and the presence of endothelial cells on calcification, both with and without osteogenic medium.High initial stiffness hydrogels and osteogenic medium promoted calcification, while for DS or HA the presence of endothelial cells prevented calcification. CS was found to increase the expression of pro-calcific genes, increase activated myofibroblast protein expression, induce the secretion of collagen I by activated interstitial cells, and increase calcified nodule formation.This study demonstrates a more complete model of aortic valve disease, including endothelial cells, interstitial cells, and a stiff and disease-like ECM. In vitro models of both healthy and diseased valves can be useful for understanding the mechanisms of CAVD pathogenesis and provide a model for testing novel therapeutics.

Endothelial to mesenchymal transformation (EndMT) is a process in which endothelial cells gain a mesenchymal-like phenotype in response to mechanobiological signals that results in the remodeling or repair of underlying tissue. While initially associated with embryonic development, this process has since been shown to occur in adult tissue remodeling including wound healing, fibrosis, and cancer. In an attempt to understand the role of EndMT in cancer progression and metastasis, we present a multiscale, three-dimensional, in silico model. The model couples tissue level phenomena such as extracellular matrix remodeling, cellular level phenomena such as migration and proliferation, and chemical transport in the tumor microenvironment to mimic in vitro tissue models of the cancer microenvironment. The model is used to study the presence of EndMT-derived activated fibroblasts (EDAFs) and varying substrate stiffness on tumor cell migration and proliferation. The simulations accurately model the behavior of tumor cells under given conditions. The presence of EDAFs and/or an increase in substrate stiffness resulted in an increase in tumor cell activity. This model lays the foundation of further studies of EDAFs in a tumor microenvironment on a cellular and subcellular physiological level.

A direct analytical method for determining the Resistance Matrix of a Hall disk with an arbitrary number of extended peripheral contacts has been developed. The method does not require the use of any conformal mappings. It works also in the case of large magnetic fields. The resulting explicit formulas involve the angular coordinates of the asymmetrical contacts ends, the sheet resistance, and the Hall angle θH as inputs. The formulas are obtained through the calculation of some definite integrals of analytical functions with integrable singularities at the end of the peripheral contacts. The method can be used for determining the sheet resistance and the Hall mobility of a circular plate with extended contacts on its boundary by utilizing two measurements similar to those used by van der Pauw's method for pointlike contacts.

Objective: Calcific aortic valve disease (CAVD) is a progressive disease ranging from aortic sclerosis to severe aortic stenosis. Current treatments include total valve replacement and drug interve...

The paper presents an analytical theory for a disk-shaped Hall plate having three peripheral contacts and a point contact at the center. The central contact is modeled as a Corbino source. Its potential function contains a multivalued function. On the boundary, besides the exit contact, the positions of the other two (sensing) contacts were determined in such a way as to maximize the Hall voltage. The numerical results show that, in the case of this type of sensing element (referred to as the Hall-Corbino element), the Hall voltage is more than six times larger than that corresponding to a Hall disk having only peripheral contacts.

Objective: In calcific aortic valve disease (CAVD), glycosaminoglycans (GAGs) such as chondroitin sulfate (CS) and hyaluronic acid (HA) are present in the normally collagen-rich aortic valve fibros...

The accelerated growth of heat load in high-density data centers presents challenges to the design of effective cooling solutions. Both energy efficiency and the information technology (IT) equipment reliability are key requirements. Localized hybrid air-water cooling systems such as Rear Door Heat eXchangers (RDHXs) are an effective means to achieve these requirements. In this paper, the transient aerodynamic and thermal performance of a commercial RDHX was investigated experimentally. The RDHX was attached to an isolated server cabinet with a controllable heat load. A localized containment system was used to direct the airflow to the equipment in the cabinet that emanates from a single perforated tile within the enclosure. The water flow rate and supply water temperature to the RDHX was controlled, and a grid of 36 air velocity/temperature sensors was employed to monitor the airside of the cooling system. The cooling performance of the RDHX in an air blower failure scenario was investigated. The failure scenario was designed to diminish different parts of the overall system. The impact on the IT equipment and the cabinet outlet temperatures was assessed. Also, there was a significant reduction in the airflow to the IT equipment. The impact of the reduced airflow on different parts of the cabinet as well as the cooling performance of the heat exchanger was characterized during both failure and recovery.

We previously demonstrated how the Sn3Ag4Ti alloy can robustly bond onto silicon via selective laser melting (SLM). By employing this technology, thermal management devices (e.g., micro-channels, vapor chamber evaporators, heat pipes) can be directly printed onto the electronic package (silicon die) without using thermal interface materials. Under immersion two-phase cooling (pool boiling), we compare the performance of three chip cooling methods (conventional heat sink, bare silicon die and additively manufactured metal micro-fins) under high heat flux conditions (100 W/cm^2). Heat transfer simulations show a significant reduction in the chip temperature for the silicon micro-fins. Reduction of the chip operating temperature or increase in clock speed are some of the advantages of this technology, which results from the elimination of thermal interface materials in the electronic package. Performance and reliability aspects of this technology are discussed through experiments and computational models.

Normal fibroblasts are present within the extracellular matrix (ECM). They can become activated, leading to increased proliferation and ECM protein secretion such as collagen type I to promote tissue remodeling. These cells are also involved in adult pathologies including cancer metastasis and cardiac and renal fibrosis. One source of activated fibroblasts is endothelial to mesenchymal transformation (EndMT), in which endothelial cells lose their cell–cell and cell–ECM adhesions, gain invasive properties, and become mesenchymal cells. While EndMT is well characterized in developmental biology, the mechanisms and functional role of EndMT in adult physiology and pathology have not been fully investigated. A microfluidic device with an incorporated three-dimensional ECM chamber was developed to study the role of combined steady fluid shear stress magnitudes and transforming growth factor-βeta 1 (TGF-β1) on EndMT. Low (1 dyne per cm2) steady shear stress and TGF-β1 exposure induced EndMT in endothelial cells, including upregulation of mesenchymal protein and gene expression markers. Cells exposed to TGF-β1 and high (20 dynes per cm2) steady shear stress did not undergo EndMT, and protein and gene expression of mesenchymal markers was significantly downregulated. Mesenchymally transformed cells under static conditions with and without TGF-β1 showed significantly more collagen production when compared to fluidic conditions. These results confirm that both low shear stress and TGF-β1 induce EndMT in endothelial cells, but this process can be prevented by exposure to physiologically relevant high shear stress. These results also show conditions most likely to cause tissue pathology.

The basic relationships for a Hall plate with N non-symmetric contacts placed in an arbitrary magnetic field are a set of N - 1 relationships that are necessary and sufficient for the existence of a complex electrostatic potential function. By the application of the boundary conditions, they turn into a linear system of N - 1 compatibility conditions involving the terminal voltages and currents. The construction of the basic relationships requires the positions of the contact extremities on the real axis of the canonical domain (the upper half-plane) as well as the electric and magnetic parameters of the Hall device. The conduction and resistance matrices can be obtained easily from the basic relationships. They give an effective method for predicting the performance of both horizontal and vertical Hall effect devices and provide a useful method for designing these types of planar devices.

Objectives For electronic nicotine delivery systems (ENDS), also commonly called e-cigarettes, coil temperature is a factor in the potential production of toxic chemical constituents. However, data are lacking regarding the temperatures that are achieved in the latest generation of these devices. Fourth-generation ENDS are capable of producing heating coil temperatures well above e-liquid boiling points, and allow the user to monitor and set the heating coil temperature during a puff. In this study, we evaluate the accuracy and consistency of the temperature measurement and control settings for different brands of fourth-generation ENDS. Methods A study was performed using three commercially available, fourth-generation ENDS. The atomizer coil temperatures were obtained from the device (using the EScribe software) reading and from thermocouples attached to the coils during simulated puffing conditions. In addition, aerosol temperatures were measured inside the atomizer and at the mouthpiece. Results Measured temperatures varied widely across samples taken from the same brand. For example, thermocouple measurements for one unit were 40 Celsius (°C) below the 300 °C set point, while another unit of the same brand exceeded the set point by more than 100 °C. We observed a significant variation in temperature (approximately 100 °C) along the length of the coil in some cases. Conclusions The possibility of wide temperature variation across ENDS samples, as well as variations between maximum coil temperatures and internal temperature readings, may have implications for studies that seek to determine correlations between coil temperature and toxin generation.

The rapid growth in the number of data centers combined with the high-density heat dissipation of computer and telecommunications equipment has made energy efficient thermal management of data centers a key research area. Localized hybrid air–water cooling is one approach to more effectively control the cooling when there is wide variation in the amount of dissipation in neighboring racks while the traditional air cooling approach requires overprovisioning. In a closed, hybrid air–water cooled server cabinet, the generated heat is removed by a self-contained system that does not interact with the room level air cooling system. Here, a hybrid-cooled enclosed cabinet and all its internal components were characterized experimentally in steady-state mode (e.g., experimentally determined heat-exchanger effectiveness and IT characterization). Also, a comprehensive numerical model of the cabinet was developed and validated using the experimental data. The computational model employs full numerical modeling of the cabinet geometry and compact models to represent the servers and the air/water heat exchanger. The compact models were developed based on experimental flow and thermal characterization of the internal components. The cabinet level model has been used to simulate a number of operating scenarios relevant to data center applications such as the effect of air leakage within the cabinet. The effect of the air side and the water side failure of the cooling system on the IT performance were investigated experimentally. A comparison was made of the amount of time required to exceed the operating temperature limit for the two scenarios.

Alterations in shear stress, mechanical deformation, extracellular matrix (ECM) composition and exposure to inflammatory conditions are known to cause endothelial to mesenchymal transformation (EndMT). This change in endothelial phenotype has only recently been linked to adult pathologies such as cancer progression, organ fibrosis, and calcific aortic valve disease; and its function in adult physiology, especially in response to tissue mechanics, has not been rigorously investigated. EndMT is a response to mechanical and biochemical signals that results in the remodeling of underlying tissues. In diseased aortic valves, glycosaminoglycans (GAGs) are present in the collagen-rich valve fibrosa, and are deposited near calcified nodules. In this study, in vitro models of early and late-stage valve disease were developed by incorporating the GAGs chondroitin sulfate (CS), hyaluronic acid, and dermatan sulfate into 3D collagen hydrogels with or without exposure to TGF-β1 to simulate EndMT in response to microenvironmental changes. High levels of CS induced the highest rate of EndMT and led to the most collagen I and GAG production by mesenchymally transformed cells, which indicates a cell phenotype most likely to promote fibrotic disease. Mesenchymal transformation due to altered ECM was found to depend on cell-ECM bond strength and extracellular signal-regulated protein kinases 1/2 signaling. Determining the environmental conditions that induce and promote EndMT, and the subsequent behavior of mesenchymally transformed cells, will advance understanding on the role of endothelial cells in tissue regeneration or disease progression. © 2017 Wiley Periodicals Inc. J Biomed Mater Res Part A: 105A: 2729-2741, 2017.

The effectiveness of heat exchangers strongly influences the thermal performance of data center cooling systems. Rear door heat exchangers, in-row and overhead coolers, and fully contained water cooled cabinets are some examples of liquid and hybrid cooling systems used in data centers. Modeling the dynamic behavior of heat exchangers is important for the design of control strategies to improve energy efficiency. In this paper, an existing 2-D model of the transient temperature response of an unmixed-unmixed cross flow heat exchanger, of the type that is widely used in data center cooling equipment, is solved numerically. A detailed analysis of the transient response to a step, ramp, or exponential change in the hot fluid inlet temperature is conducted. The heat capacity rate ratio (E), thermal resistance (R), capacitance ratio (V), and number of transfer units are varied over a wide range to determine their influence on the heat exchanger dynamic thermal performance under different transient input conditions. In addition, the thermal response to the magnitude and time period of the transient input functions are evaluated. The modeling results are used to analyze specific data center cooling scenarios, and provide a means for predicting the transient behavior of heat exchangers used in data center cooling equipment.

Reduced-order thermal models are necessary to enable real-time assessment of the optimum operating and control conditions to improve data center energy efficiency. A 3D computational fluid dynamics (CFD) and heat transfer model of a basic raised floor, air cooled, hot aisle/cold aisle data center configuration was developed and simulation results were used to generate snapshots for initializing compact models based on the Proper Orthogonal Decomposition (POD) and the Nonlinear Principle Component Analysis (NLPCA) methods. The specific focus of the study was to numerically investigate how the thermal trends can be affected by the long-term transient flow patterns associated with leakage and how the compact models (e.g. POD and NLPCA) can be utilized for much faster implementations and characterizations of the transient flows. Using both the POD and the NLPCA method, good agreement was achieved between the full simulation results and the compact models for predicting the dynamically developed local flow structure over a range of transient cooling air supply operating conditions. In addition, the NLPCA method was implemented to better characterize the nonlinear aspects of the CFD results. The benefits of using both the POD and NLPCA methods are discussed in relation to constructing compact models as real-time predictive tools. A systematic use of the compact models has also been proposed, to enable more robust thermal management and control of data centers.

Full-scale data center thermal modeling and optimization using computational fluid dynamics (CFD) is generally an extremely time-consuming process. This paper presents the development of a velocity propagation method (VPM) based dynamic compact zonal model to efficiently describe the airflow and temperature patterns in a data center with a contained cold aisle. Results from the zonal model are compared to those from full CFD simulations of the same configuration. A primary objective of developing the compact model is real-time predictive capability for control and optimization of operating conditions for energy utilization. A scheme is proposed that integrates zonal model results for temperature and air flow rates with a proportional–integral–derivative (PID) controller to predict and control rack inlet temperature more precisely. The approach also uses an Artificial Neural Network (ANN) in combination with a Genetic Algorithm (GA) optimization procedure. The results show that the combined approach, built on the VPM based zonal model, can yield an effective real-time design and control tool for energy efficient thermal management in data centers.

The computation time for predicting optimum thermal operating conditions in data center facilities using compact thermal modeling tools is significantly reduced compared to a three dimensional, simulation-based optimization methodology. However, applying compact models to configurations outside of the geometry and operating conditions used for model development often results in inaccurate predictions. In order to model a complicated geometry, a potential remedy is to partition the room layout into a finite number of characteristic zones to which the compact models readily apply. Here, a multiple hot aisle/cold aisle data center configuration was analyzed using CFD simulations of the entire room. The room was then partitioned into two zones and the full room simulations were used to quantify the air flow across the inter-zonal partitions. The inter-zonal conditions are then used to extend the solution results from a single zone to a multiple zone configuration. Two specific room configurations are considered where the computer room air conditioning units (CRACs) are located either at the same end or opposite ends of the cold aisle. The method is found to work well when the CRACs are located at opposite ends of the cold aisles.

Modeling the thermal environment for data centers, including prediction of airflow and temperature distributions, is generally an extremely time-consuming process using full-scale CFD analysis. Reduced order models are necessary in order to provide real-time assessment of cooling requirements. The use of a coarse-grained zonal model is being investigated as a predictive tool, and this article details the development and implementation of a three-dimensional, pressurized zonal model. To construct and validate the zonal model, a basic data center configuration was analyzed using a finite volume software package. The calculated flow fields provide the spatial flow coefficients required in the zonal model, which is based on the power law method (PLM). A physically-based mapping between the controllable spatial mass flow rate and temperature distribution was obtained. Good agreement (within 10% average relative error) was obtained between the zonal model predictions and the CFD results. These preliminary resul...

Thermal modeling of some nano-scale devices requires attention to multiple length scales and physical phenomena, ranging from continuum level heat diffusion to atomic-scale interactions and phonon confinement. At the nanometer-scale, thermal phenomena such as ballistic phonon transport may be important. The present paper uses a multiscale thermal modeling approach including diffusion in the Boltzmann Transport Equation (BTE) to study heat transport in several applications like Silicon on Insulator transistors, Si thin films with heat pulse, a Si thin film sandwiched between two bulk layers of Silicon dioxide as in solar cells. Analytical solutions of both a multilayered Fourier model and a simple gray BTE with and without a diffusion term in the steady state are computed. Thermal modeling and analysis of some of these applications is performed using the COMSOL Multiphysics finite element software package. The BTE model with and without diffusion for multilayers is discussed for interface conditions involving reflectance and transmittance of phonons. The results obtained from the models are compared to existing published results for Si/Si, Si/Diamond layers and are found to be in good agreement.

To control energy usage in data center rooms, reduced order models are important in order to perform real-time assessment of the optimum operating conditions to reduce energy usage. Here computational fluid dynamics (CFD) simulation-based Artificial Neural Network (ANN) models were developed and applied to a basic hot aisle/cold aisle data center configuration in order to predict thermal operating conditions for a specified set of control variables. Once trained, the ANN-based model predictions were shown to agree well with the CFD results for arbitrary values of the input variables within the specified limits. In addition, the ANN model was combined with a cost function based multi-objective Genetic Algorithm (GA), which enabled the operating conditions to be inversely predicted for specified values of the output variable (e.g., server rack inlet temperatures). The ANN-GA optimization approach considerably reduces the total computation time compared to a fully CFD-based response surface optimization methodology. Consequently, operating conditions are capable of being reliably predicted in seconds, even for configurations outside of the original ANN training set. These results show that an ANN based model can yield an effective real-time thermal management design tool for data centers.

Excess temperatures on concentrating photovoltaic (PV) modules can lead to a decrease in electrical efficiency and irreversible structural damage. Therefore, designing an appropriate cooling system becomes necessary for the lifetime and performance of concentrating PV (CPV) modules. The basic design considerations for cooling systems include low and uniform cell temperatures, minimal pumping power, high PV efficiencies, and system reliability. In this paper, a 3-D multiphysics computational model for a hybrid concentrating photovoltaic/thermal (HCPV/T) water collector is developed. The collector consists of a solar concentrator, 40 silicon cells connected in series, and a multichannel liquid cooling system with heat-recovery capability. A conjugate heat transfer model is used, assuming laminar flow through either parallel or tree-shaped branching cooling channels. The temperature distributions within the PV cells are determined for different cooling strategies. Comparisons are made by considering the thermal and electrical performances, such as PV cell temperature, electrical efficiency, and outlet water temperature, between a system incorporating tree-shaped channel networks and one having straight parallel channel cooling arrays. For identical convective surface area and pumping pressures in both configurations, the tree-shaped branched channel cooling networks yield lower PV cell temperatures and more uniform temperature distributions within the PV cells. Additionally, a finite-element mechanical analysis is used to estimate the fatigue life of the PV modules based on the temperature profiles obtained from both cooling channel configurations under a specified pumping pressure. The model results predict that the fatigue life of the module with the branched channels is almost twice that of the module with straight channels.

Aisle containment is increasingly being used in data center cooling solutions because of the benefits of segregating the cold and hot air streams which reduces mixing and enhances energy savings. Containment can be integrated into legacy raised floor or non-raised floor local cooling systems such as in-row coolers. However, containment is not always entirely effective due to leakage. Although containment systems providing better sealing are becoming available, significant leakage exists in currently operational sites. The impact of leakage can be significant leading to backflow, the Venturi effect or entrainment. Comparisons between Cold Aisle Containment (CAC) and Hot Aisle Containment (HAC) indicate that there is a slight advantage of the latter in terms of ambient room temperature, failure scenarios and heat exchanger efficiency, although CAC systems can be easier to install. Detailed comparisons between both containment solutions are not widely available. Each containment approach has different behavior characteristics and air flow paths. For instance, leakage can introduce different flow and temperature conditions at server inlets depending on whether CAC or HAC is being used. An experimental characterization of containment was carried out at the ES2 research data center lab at Binghamton University [1] along with detailed numerical modeling. The numerical model was validated based on the experimentally measured flow rate of the perforated tiles in the cold aisles. Also, for the different types of IT equipment modeled in the simulations, experimentally measured flow impedance and fan curves were utilized. The details of the containment including leakage at the bottom and sides of the racks, the mounting rails, blanking panels and door seams were characterized experimentally and then incorporated in the computational model. Fan curves for the three CRAH blowers were used to accurately represent the targeted flow rates. This study focuses on three containment configurations: cold aisle containment and hot aisle containment and chimney (with a drop ceiling). In first two cases, the CRAH flow rate is controlled based on the pressure difference that was measured by three sensors inside and outside of the containment and for the third case, the CRAH flow rate was controlled based on IT required air flow. The water flow rate of the CRAH unit is also controlled based on the air return temperature and total heat load in the room so as to maintain the supply air temperature set point. The temperature and pressure fields in the aisles and at the server inlets and outlets are monitored for all the cases with leakage.

In this experimental study a unique configuration of a isolated cabinet with IBM Rear Door Heat exchanger was utilized. This experimental test setup is located in the ES2 data center laboratory at Binghamton University. The cabinet was populated by 16 servers (2 RU) and one 9 RU server simulator. With this equipment a maximum of about 15.9 kW can be generated. Localized cold aisle containment was employed in order to provide a more uniform inlet air temperature to the IT equipment. A single perforated tile is located in front of the cabinet within the containment enclosure. Two types of tiles with 65% and 22% open perforation area were used in different experiments. On the water side of the heat exchanger, a control system maintains the water temperature (by controlling three-way valve) and the water flow rate (by controlling pump speed). The control system also can monitor and collect water supply and return temperature data. For the experimental air side measurements a Mobile Temperature/Velocity Mesh (MTVM) was developed in order to measure air temperature/velocity at the front and rear of the cabinet. This sensor system obtains measurements on a grid in a 2D plane and the data is transferred via a network connection.

In traditional data centers chilled air flow is delivered to the IT equipment through the raised floor plenum and perforated tiles. Variation of power load in different racks in the same aisle increases the possibility of over cooling of some IT and hot spots in others. Additional solutions like cold and hot aisle containment, chimneys, etc are employed to prevent the mixture of hot and cold air in data centers. In order to avoid this problem, localized hybrid cooling solutions are used in recently designed data centers. By putting the cooling source closer to the heat load, the localized cooling capacity is more controllable and this significantly increases the energy efficiency. On the other hand, data center energy efficiency is not the only consideration, but other operational conditions need to be considered. In the current study, a commercial hybrid cooled, enclosed server cabinet is studied empirically and numerically. The CFD numerical model used here has been validated with different steady-state cases in an earlier study. In the model, the cabinet is made up of different parts such as: IT equipment (servers and server simulator), multifunction rear door, heat exchanger box, recirculation deflector and side panels. Each part is characterized and validated based on experimental results. The total heat that was generated by the IT is removed by a V-shaped heat exchanger that is located within the cabinet. The performance of the system was investigated at different operational stages.

Wetting, phase change, and reaction in high temperature systems (e.g., a liquid metal on a metal substrate) are complex phenomena that are only partially understood. These phenomena occur in joining processes, thin film processing and sintering among others. Dissolutive wetting is characterized by chemical and physical processes that span a broad range of spatial and temporal scales. While experiments are difficult to conduct, there have been a number of experimental investigations of dissolutive wetting in metal–metal systems and a short review of these studies is presented. Although limited, recently there have been studies comparing results, such as spreading rate and dissolution depth, from experiments to those from computational simulations. For dissolutive wetting in metal systems it is difficult to observe much of the spreading process experimentally. Computational models may provide better understanding of many aspects of dissolutive wetting. Models of dissolutive wetting incorporate knowledge from chemical thermodynamics, phase transformations, capillary behavior, and multi-phase transport. A number of computational models have appeared in the literature over the last 10 years. Dissolutive wetting has been studied using a broad range of approaches from molecular dynamics to continuum based models at the drop scale that include hydrodynamic transport using different levels of sophistication. We present a comprehensive review of the modeling approaches that have been used to study dissolutive wetting.

With the ever increasing heat loads dissipated by computer hardware, the ability to accurately characterize the cooling requirements in data centers is becoming crucial. Computational fluid dynamics modeling has proven in many cases to be adequate in providing a general understanding of the thermal environment in data centers. However, almost all analyses of data centers to this day are conducted in steady state. The effect of changes in hardware configurations and cooling resources on server rack inlet temperatures and airflow through servers has not been adequately investigated. This paper introduces transient modeling of data centers with changing power dissipations and computer room air-conditioning (CRAC) airflow rates. Transient modeling proves advantageous in monitoring temperature fluctuations due to airflow changes, which in some cases leads to insufficient cooling. In addition, modeling server thermal mass is shown to be important for transient analysis, as it can lead to overshoots in temperatures. Another segment of this paper looks at the effect of introducing thermal characteristics curves into CRAC modeling on server inlet temperature. All the cases presented show that fixed CRAC supply temperature is a non-valid assumption.

The Boltzmann Transport Equation (BTE) with the single Relaxation Time Approximation (RTA) can be employed to simulate energy transport in the sub-continuum regime, as long as the particle assumption for the heat carriers is valid. Here, analytical and numerical solutions of the BTE in one space dimension are obtained for two different sets of boundary conditions. For the steady case, numerical solutions obtained are found to be identical (to within purely numerical error) to the analytical solutions. Transient solutions are obtained using the Lattice Boltzmann Method (LBM). Additionally, the impact of introducing a diffusive term in the BTE is investigated. When the diffusive model is solved, an increasing gradient (but no jump) in the temperature at the boundaries is observed as the Knudsen number (Kn) increases. The results for the transient case are compared to those obtained from the Fourier solution for small values of Kn. It is observed that the BTE with an added diffusion term is applicable for all Kn.

The article presents an axi-symmetrical model for determining the total damping coefficient of a periodic perforated microelectromechanical systems (MEMS) microstructure for cases where the lubrication approximation yielding the Reynolds’ equation is no longer appropriate. Damping is modeled by solving for the viscous flow in an approximation of the periodic cell geometry using an equivalent axi-symmetrical cylindrical flow domain. Using the Stokes approximation of the incompressible Navier–Stokes (N–S) equations with harmonic time behavior, an analytic solution is obtained yielding an explicit formula for the damping coefficient. Additionally, two numerical models were implemented based on the finite element method. Numerical solutions were obtained for the linearized, viscous acoustic equations (time harmonic) and the steady, incompressible N–S equations. The results given by the analytical formula compare well with those obtained from the FEM solutions and with measured values for MEMs microstructures found in the literature.

We consider a model for the solidification of an ideal ternary alloy in a mushy layer that incorporates the effects of thermal and solutal diffusion, convection and solidification. Our results reveal that although the temperature and solute fields are constrained to the liquidus surface of the phase diagram, the system still admits double-diffusive modes of instability. Additionally, modes of instability exist even in situations in which the thermal and solute fields are each individually stable from a static point of view. We identify these instabilities for a general model in which the base-state solution and its linear stability are computed numerically. We then highlight these instabilities in a much simpler model that admits an analytical solution.

Thermal management of device-level packaging continues to present many technical challenges in the electronics industry. In a device/heat sink assembly, the highest resistance to heat flow typically comes from the thermal interface material (TIM). The thermal conductivities of TIMs remain in the range of 1-4 W/mK due to the properties and structure of small dispersed solids in polymer matrices. As a result of the rising design power and heat flux at the silicon die, new ways to improve the effective in situ thermal conductivity of interface materials are required. This paper analyzes a unique TIM enhanced with ultrahigh-density wafer-level thin film-compliant interconnects referred to as smart three axis compliant (STAC) interconnects. MEMS technology is used to directly fabricate STAC interconnects onto a silicon wafer and embed them into the TIM to provide an enhanced conductive path between the die/package and the heat sink. Here, results from a theoretical analysis of the thermal conduction in a TIM embedded with STAC interconnects are reported. The objective of the study is to provide comprehensive design strategies for effective implementation of this type of TIM for specific applications. Parametric studies are performed to examine the thermal resistance of the microinterconnect-enhanced TIM for varying materials, configurations, and geometry of the microinterconnects. A periodic element model of a chip-TIM configuration with top heat sink is used to evaluate the conductive effect of the microinterconnects. In addition, an investigation of the conductive transport in a more complicated chip stack is considered. A 3-D thermal analysis is conducted for a multichip stack package with and without through-silicon vias. The numerical results show that the microinterconnects significantly improve the thermal performance of the TIM. Finally, further steps toward achieving a chip-level design optimization and fabrication process using a STAC microinterconnect structured TIM is proposed.

PurposeThe purpose of this paper is to consider double‐diffusive convection in a heated porous medium saturated with a fluid. Of particular interest is the case where the fluid has a stabilizing concentration gradient and small diffusivity.Design/methodology/approachA fully‐coupled stabilized finite element scheme and adaptive mesh refinement (AMR) methodology are introduced to solve the resulting coupled multiphysics application and resolve fine scale solution features. The code is written on top of the open source finite element library LibMesh, and is suitable for parallel, high‐performance simulations of large‐scale problems.FindingsThe stabilized adaptive finite element scheme is used to compute steady and unsteady onset of convection in a generalized Horton‐Rogers‐Lapwood problem in both two and three‐dimensional domains. A detailed study confirming the applicability of AMR in obtaining the predicted dependence of solutal Nusselt number on Lewis number is given. A semi‐permeable barrier version of the generalized HRL problem is also studied and is believed to present an interesting benchmark for AMR codes owing to the different boundary and internal layers present in the problem. Finally, some representative adaptive results in a complex 3D heated‐pipe geometry are presented.Originality/valueThis work demonstrates the feasibility of stabilized, adaptive finite element schemes for computing simple double‐diffusive flow models, and it represents an easily‐generalizable starting point for more complex calculations since it is based on a highly‐general finite element library. The complementary nature of h‐adaptivity and stabilized finite element techniques for this class of problem is demonstrated using particularly simple error indicators and stabilization parameters. Finally, an interesting double‐diffusive convection benchmark problem having a semi‐permeable barrier is suggested.

A dissolutive wetting model is employed to study the dynamics of axisymmetric Bi–Sn alloy drops spreading on Bi. The liquid drop surface is assumed to be a spherical cap, while the isothermal model for solute transport with simplified hydrodynamics computes the evolution of the solid–liquid interface. Simulations are performed on a millimeter scale to model experiments. The evolution of the drop radius, the flow and solute concentration profiles near the triple junction, the contact line mobility relationship, the apparent contact angles and the shape of the dissolution boundary during spreading are investigated as functions of initial Sn concentration, model parameters and initial conditions. Good agreement is obtained when compared with the experiments for the cases where diffusion is the dominant transport mode. The shape of the solid–liquid interface is predicted better when the initial experimentally determined dissolution boundary is implemented as the starting point of the subsequent simulation.

A variational formulation and C1 finite element scheme with adaptive mesh refinement and coarsening are developed for phase-separation processes described by the Cahn–Hilliard diffuse interface model of transport in a mixture or alloy. The adaptive scheme is guided by a Laplacian jump indicator based on the corresponding term arising from the weak formulation of the fourth-order non-linear problem, and is implemented in a parallel solution framework. It is then applied to resolve complex evolving interfacial solution behavior for 2D and 3D simulations of the classic spinodal decomposition problem from a random initial mixture and to other phase-transformation applications of interest. Simulation results and adaptive performance are discussed. The scheme permits efficient, robust multiscale resolution and interface characterization. Copyright © 2008 John Wiley & Sons, Ltd.

In this paper, we consider an adaptive finite element approach for reliable, efficient solution of a class of continuum models for tumour-induced angiogenesis. The ideas are demonstrated using an established three equation reaction/transport model that simulates aspects of tumour-induced angiogenesis in a deterministic manner. The weak variational formulation and finite element approximation scheme for the model are developed, and a statistical approach for concurrent adaptive mesh refinement and coarsening is described. The appropriate form of the model and solution dependence on choice of parameters are explored. Computational results are presented for 1D, 2D and 3D geometry models. The effectiveness of the open-source, parallel adaptive software library (LibMesh) that is being developed in the CFDLab at the University of Texas is also demonstrated. Copyright © 2006 John Wiley & Sons, Ltd.

The heat dissipated by electronic equipment inside data centers is increasing at a rapid rate due to the increasing of performance requirement and package density. This ever increasing power leads to critical challenges of thermal management for these high power density data centers. Energy consumption is also a key issue for high density data centers. Roughly 1.5% of all U.S. electricity consumption in the year 2006 was related to data centers, while that number increased to 2% by the year 2010. In 2013, U.S. data centers consumed approximately 91 billion kilowatt-hours of electricity. This amount of the electricity equals the annual output of 34 500-megawatt coal-fired power plants [1]. Cooling systems constitute a significant portion of the energy consumption of data centers, being approximately 25%∼35% of the total energy usage. Therefore, there is a large potential to save energy by optimizing current existing cooling systems and investigating new cooling technologies, and, at the same time, improving the overall cooling capacity and efficiency. This paper describes and investigates a hybrid cooling technology which utilizes in row coolers in existing raised floor air cooled data centers. The in row cooler functions as a liquid-to-air heat exchanger. In addition to the traditional raised floor cold aisle-hot aisle arrangements, the in row cooler is installed between the IT equipment to enable delivering the liquid coolant medium closer to the IT equipment. The in row coolers intake the hot air from the hot aisle, condition it, and supply the chilled air to the cold aisle. Thus, by extracting a large portion of the heat more directly into the cooling liquid through the in row coolers compared with the perimeter CRAH unit, the overall cooling performance and efficiency can potentially be improved. CFD models for an in row cooler and a representative data center room are developed. Experimentally characterized performance data are used to calibrate and validate the models. The models are then used to conduct a detailed computational analysis to assess the effectiveness of different arrangement configurations of in row cooler units in two rows of racks along one cold aisle. The detailed performance of the entire cold aisle is characterized using the rack inlet air temperature and a temperature nonuniformity factor. The impact of CRAH location and room layout are also investigated. This study is based on a practical problem and the corresponding results and analysis provide basic installation and design guidelines for future equipment upgrading in certain parts of the data center.Copyright © 2015 by ASME

Because of the rapid growth in the number of data centers combined with the high density heat dissipation in the IT and telecommunications equipment, energy efficient thermal management of data centers has become a key research focus in the electronics packaging community. Traditional legacy data centers still rely largely on chilled air flow delivered to the IT equipment racks through perforated tiles from the raised floor plenum. When there is large variation in the amount of heat dissipated by the racks in a given aisle, the standard air cooling approach requires over-provisioning. Localized hybrid air-water cooling is one approach to more effectively control the cooling when there is wide variation in the amount of dissipation in neighboring racks. In a closed hybrid air-water cooled server cabinet, the generated heat is removed by a self-contained system that does not interact with the room level air cooling system. In this study, a comprehensive procedure for CFD validation in a close coupled hybrid cooled enclosed cabinet is described. The commercial enclosure has been characterized experimentally in an earlier study, where the effectiveness values were applied as boundary conditions to the compact heat exchanger model. Here, the previously obtained experimental data are used to validate the results from computational modeling. Two cases with different air flow rates are compared. Very good agreement is achieved, with the maximum overall average error less than 4%. Due to relatively high pressure inside the cabinet, it is possible that air leakage from the cabinet may be responsible for the discrepancy between the model and experimental results. A sensitivity study was applied to the validated model to investigate the effect leakage had on the cabinet’s performance.

The heat dissipated by high performance IT equipment such as servers and switches in data centers is increasing rapidly, which makes the thermal management even more challenging. IT equipment is typically designed to operate at a rack inlet air temperature ranging between 10 °C and 35 °C. The newest published environmental standards for operating IT equipment proposed by ASHARE specify a long term recommended dry bulb IT air inlet temperature range as 18°C to 27°C. In terms of the short term specification, the largest allowable inlet temperature range to operate at is between 5°C and 45°C. Failure in maintaining these specifications will lead to significantly detrimental impacts to the performance and reliability of these electronic devices. Thus, understanding the cooling system is of paramount importance for the design and operation of data centers. In this paper, a hybrid cooling system is numerically modeled and investigated. The numerical modeling is conducted using a commercial computational fluid dynamics (CFD) code. The hybrid cooling strategy is specified by mounting the in row cooling units between the server racks to assist the raised floor air cooling. The effect of several input variables, including rack heat load and heat density, rack air flow rate, in row cooling unit operating cooling fluid flow rate and temperature, in row coil effectiveness, centralized cooling unit supply air flow rate, non-uniformity in rack heat load, and raised floor height are studied parametrically. Their detailed effects on the rack inlet air temperatures and the in row cooler performance are presented. The modeling results and corresponding analyses are used to develop general installation and operation guidance for the in row cooler strategy of a data center.Copyright © 2015 by ASME

A water-cooled, fully-enclosed server cabinet is one type of hybrid cooling technology used in data centers to cool high power IT equipment. These types of cabinets employ a water/air heat exchanger. External chilled water is provided to the heat exchanger and circulating air inside the cabinet is supplied to the server intakes. One advantage of this type of hybrid system is that the heat removed by the water-side can be used for other purposes, which is a potential means for increasing the overall data center energy efficiency. A specific commercial hybrid server cabinet design has been characterized experimentally in this study. The cabinet utilizes a V-shaped, unmixed-unmixed liquid-to-air cross flow heat exchanger. Three robust rear door mounted fans produce the air circulation in the cabinet. They are capable of providing an air flow rate of up to 1.321m3/s (2800 CFM) depending on the air temperature inside the cabinet. In the experiments, the air velocity is measured at different positions at the inlet and outlet of the heat exchanger using an array of velocity sensors. The contribution of each fan to the airflow distribution at the inlet of the heat exchanger is characterized using the measured air velocity data. For the water-side, the flow rate and temperature of the chilled water supply is measured using a vortex flow meter. From the measured air and water flow rates and temperatures, the effectiveness of the heat exchanger is calculated. The experimental results are presented in terms of effectiveness curves for different air and water operating flow rates and the high performance V-shaped heat exchanger is characterized in detail using these results. The heat exchanger performance data provides a better understanding of the design and operation of this type of closed cabinet, which can be used to potentially improve the operating efficiency.

The isothermal dissolutive wetting behavior of various Bi–Sn alloys on pure Bi substrates was studied at 250 °C using the sessile drop technique. Wetted radius and apparent dynamic contact angle were recorded as a function of time. Sequential quenching and metallographic cross-sectioning were employed to investigate the temporal evolution of the S/L interface and the complete configuration of the contact line region. The macroscopic total contact angle was found to be close to 90° during spreading for the majority of Bi–Sn alloys investigated. The contact line mobility relationship, based on apparent dynamic contact angle, showed certain similarities to a universal correlation for partially wetting inert systems. Additional discussions of grain boundary effects and mass transport are presented.

A comprehensive continuum model of solid tumor evolution and development is investigated in detail numerically, both under the assumption of spherical symmetry and for arbitrary two-dimensional growth. The level set approach is used to obtain solutions for a recently developed multi-cell transport model formulated as a moving boundary problem for the evolution of the tumor. The model represents both the avascular and the vascular phase of growth, and is able to simulate when the transition occurs; progressive formation of a necrotic core and a rim structure in the tumor during the avascular phase are also captured. In terms of transport processes, the interaction of the tumor with the surrounding tissue is realistically incorporated. The two-dimensional simulation results are presented for different initial configurations. The computational framework, based on a Cartesian mesh/narrow band level-set method, can be applied to similar models that require the solution of coupled advection-diffusion equations with a moving boundary inside a fixed domain. The solution algorithm is designed so that extension to three-dimensional simulations is straightforward.

Calculations of a phase-field model are presented representing the solidification of a pure two-dimensional single-crystal subject to an applied electric current. The effect of Joule heat on growth of a crystal is studied. Results show that the application of an uniform electrical current causes the tip radius to deviate from a constant value that is characteristic of steady-state growth in the absence of current. Additionally, the Peltier effect is shown to affect the symmetry exhibited by the crystal growth form from what would be expected in the absence of current.

Tumor development is influenced by stromal cells in aspects including invasion, growth, angiogenesis, and metastasis. Activated fibroblasts are one group of stromal cells involved in cancer metastasis, and one source of activated fibroblasts is endothelial to mesenchymal transformation (EndMT). EndMT begins when the endothelial cells delaminate from the cell monolayer, lose cell-cell contacts, lose endothelial markers such as vascular endothelial-cadherin (VE-cadherin), gain mesenchymal markers like alpha-smooth muscle actin (α-SMA), and acquire mesenchymal cell-like properties. A three-dimensional (3D) culture microfluidic device was developed for investigating the role of steady low shear stress (1 dyne/cm2) and altered extracellular matrix (ECM) composition and stiffness on EndMT. Shear stresses resulting from fluid flow within tumor tissue are relevant to both cancer metastasis and treatment effectiveness. Low and oscillatory shear stress rates have been shown to enhance the invasion of metastatic cancer cells through specific changes in actin and tubulin remodeling. The 3D ECM within the device was composed of type I collagen and glycosaminoglycans (GAGs), hyaluronic acid and chondroitin sulfate. An increase in collagen and GAGs has been observed in the solid tumor microenvironment and has been correlated with poor prognosis in many different cancer types. In this study, it was found that ECM composition and low shear stress upregulated EndMT, including upregulation of mesenchymal-like markers (α-SMA and Snail) and downregulated endothelial marker protein and gene expression (VE-cadherin). Furthermore, this novel model was utilized to investigate the role of EndMT in breast cancer cell proliferation and migration. Cancer cell spheroids were embedded within the 3D ECM of the microfluidic device. The results using this device show for the first time that the breast cancer spheroid size is dependent on shear stress and that the cancer cell migration rate, distance, and proliferation are induced by EndMT-derived activated fibroblasts. This model can be used to explore new therapeutics in a tumor microenvironment.

Thermoelectric (TE) modules utilize available temperature differences to generate electricity by the Seebeck effect. The current study investigates the merits of employing thermoelectrics to harvest additional electric energy instead of just cooling concentrating photovoltaic (CPV) modules by heat sinks (heat extractors). One of the attractive options to convert solar energy into electricity efficiently is to laminate TE modules between CPV modules and heat extractors to form a CPV-TE/thermal (CPV-TE/T) hybrid system. In order to perform an accurate estimation of the additional electrical energy harvested, a coupled-field model is developed to calculate the electrical performance of TE devices, which incorporates a rigorous interfacial energy balance including the Seebeck effect, the Peltier effect, and Joule heating, and results in better predictions of the conversion capability. Moreover, a 3D multiphysics computational model for the HCPV-TE/T water collector system consisting of a solar concentrator, 10 serially connected GaAs/Ge photovoltaic (PV) cells, 300 couples of bismuth telluride TE modules, and a cooling channel with heat-recovery capability, is implemented by using the commercial FE–tool Comsol Multiphysics®. A conjugate heat transfer model is used, assuming laminar flow through the cooling channel. The performance and efficiencies of the hybrid system are analyzed. As compared with the traditional photovoltaic/thermal (PV/T) system, a comparable thermal efficiency and a higher 8% increase of the electrical efficiency can be observed through the PV-TE hybrid system. Additionally, with the identical convective surface area and cooling flow rate in both configurations, the PV-TE/T hybrid system yields higher PV cell temperatures but more uniform temperature distributions across the cell array, which thus eliminates the current matching problem; however, the higher cell temperatures lower the PV module's fatigue life, which has become one of the biggest challenges in the PV-TE hybrid system.

Water-cooled server racks are typically closed cabinets, so no heat load is removed by the room cooling system in a raised floor data center. Instead, the cooling is provided by a closed system employing an air-water (fin-tube) heat exchanger. This kind of heat exchanger uses chilled water from a central plant, and there is the potential of using the waste heat that is returned. The goal of this study is characterize a specific sealed-door, water-cooled server cabinet under steady state and transient operation. The experimental part of the study is being performed on a Knurr CoolThermTM® rack. In this cabinet, the water/air heat exchanger is located at the bottom. Cooling air is circulated by three rear door mounted fans, the cooled air flows upward in front of the servers. The specific cabinet being tested has the capability to handle 25 kW and has a 30% cooling system energy efficiency. In the experiments, 16 1U servers and a 9U load bank are employed for generating a heat load. Over 100 thermocouples are used to monitor air temperature within different parts of the cabinet. The operating conditions monitored include: water flow rate, water inlet temperature, air flow rate through the servers, air flow rate through the heat exchanger, air temperatures and server power. The internal temperature of the servers is also monitored. From the measured data, the effectiveness is calculated for four different water flow rates and different power dissipation levels. Computational modeling of the air flow and heat transfer in a simplified model of the cabinet is also performed.

This paper evaluates the impact of pressure drop in server racks on the cooling of the IT equipment. The measured impedance curves for servers internal resistance, rack doors, and Cable Management Arms (CMA) are used to estimate the reduction in the cooling airflow rate. In this study, 1 RU and 2 RU servers, and a 9 RU server simulator are used as representative IT equipment. A Computational Fluid Dynamics (CFD) model is used to investigate the influence of the rack structure on the thermal field. The effect of the cooling air flow rate on the temperature of the server's internal components is also studied experimentally.