The rising power density of modern electronic devices causes severe non-uniform temperature distributions and multiple hotspots, posing a major challenge to thermal management. A fundamental trade-off has long plagued cooling systems: reducing hotspot temperatures typically requires higher flow rates or more fins, which inevitably increases pressure drop and cooling energy consumption. This “heat transfer enhancement versus pressure drop penalties” dilemma is particularly critical for energy-intensive data centers. This study demonstrates a potential pathway to mitigate this trade-off by synergistically optimizing fin geometry and jet inclination angle in a microchannel heat sink. Using a two-factor design involving three fin configurations and five inclination angles, we investigate the effects of fin geometry and jet inclination on thermal and hydraulic performance. The key finding is that the RS + 2° configuration simultaneously reduces both hotspot temperature and pressure drop. Compared to the conventional non-inclined RS case, it reduces the peak hotspot temperature by 3.98 K while reducing the pressure drop by 49 %. Flow topology analysis indicates that this notable improvement stems from a pronounced change from normal impingement to streamlined entry, which alleviates inlet blockage and promotes intensive three-dimensional mixing. Furthermore, robustness analyses across a wide operating envelope confirm that RS + 2° consistently outperforms conventional finless designs. Specifically, it yields a maximum temperature reduction of 58.87 K under low flow rates and an 11.2 % pressure drop improvement under high flow rates, while maintaining a stable temperature deviation of 5.5 K. This study provides a quantitative foundation and a scalable strategy for mitigating the classic “heat transfer enhancement versus pressure drop penalty” trade-off in next-generation cooling systems.

With the deepening of sustainable development goals, improving the energy efficiency of buildings has become a global focus. This work designs a coupled heating system combining wall attachment ventilation (WAV) and radiant panels (single and composite layouts) and proposes the thermal comfort variation rate per unit energy consumption (Delta PMV/Delta Q) as a new performance indicator. Through computational fluid dynamics (CFD) simulations and full-scale experiments, the effects of radiant panel layouts, supply air velocity (V), supply air temperature (Ts), and radiant temperature (Tr) are analyzed based on key indicators, including the predicted mean vote of occupant and room (PMVoc, PMVro), draught rate of occupant and room (DRoc, DRro), and energy consumption (Q). Furthermore, a multi-objective assessment is conducted according to the orthogonal experiment and single-factor analysis, employing the Entropy weight-TOPSIS method for comprehensive optimization. The results indicate that composite-panel layouts outperform single-panel layouts in thermal comfort, with the south-west (SW) layout achieving near-neutral PMVoc (-0.04) and low DRoc(8.9 %). Ts exhibits a more significant impact on thermal environment than Tr, albeit with higher Q, while V shows relatively minor influence. Through multi-objective optimization, the optimal configuration is determined as V = 1.6 m/s, Ts = 27 degrees C, Tr = 27.2 degrees C. With this configuration, the system reaches peak performance: PMVoc= 0.01, DRoc= 4.83 %, PMVro =-0.17, DRro = 3.68 %, and Q = 96,719.27 kJ. This work provides theoretical foundations and practical guidance for optimizing the design of convective-radiant coupled heating systems in buildings.

This study addresses the absence of theoretical frameworks for designing infrared suppression devices under radial dimensional constraints. Conventional unconstrained-space designs exhibit significant limitations in radially confined installations, while traditional long mixing tubes produce detectable infrared signatures at a 45 degrees infrared detection angle. Under these constraints, this research systematically analyzes the influence mechanisms of key parameters, including central plug diameter ratio (A), lobe width (W), lobe-to-mixing tube spacing (L), and lobe outward penetration angle (theta). The analysis focuses on enhancing core high-temperature flow cooling and entrainment efficiency. A compact long-funnel layout with a reduced mixing tube-to-funnel ratio is proposed to mitigate detectable infrared signatures at a 45 degrees infrared detection angle, and key funnel contour design criteria are derived from this innovative layout. The results indicate that: (1) Optimal core cooling under radial constraints should prioritize adjusting the A to 0.91 followed by coordinated W optimization. This strategy yields core cooling performance comparable to solely increasing A, but achieves an additional 1.1% higher entrainment coefficient and a 3.95% lower pressure loss; (2) Entrainment enhancement under radial constraints should prioritize reducing the Wand theta. Under identical flow performance, the latter provides superior infrared suppression, yielding a further 4.01% reduction in the mixing tube wall temperature; (3) Long-funnel configuration should maintain a first-stage outlet diameter greater than the heat shield's (Df_out >= Ds_out) while avoiding an overly funnel reduced expansion angle (beta), so as to prevent thermal reflux and maintain overall system performance.

To address the challenge of balancing infrared suppression performance and flow resistance in ship exhaust cooling systems, this study conducts a comprehensive performance analysis and multi-objective optimization of a lobed ejector-based infrared suppression (IRS) device. Validated computational fluid dynamics simulations, incorporating a custom infrared radiation calculation program, are employed to evaluate the key performance indicators: infrared radiation intensity (I) in the 3-5 mu m band and pressure drop coefficient (Cd). Single-factor analysis reveals the distinct influences of four critical geometric parameters (lobe external expansion angle alpha, lobe internal expansion angle (I, mixing tube diameter Dmt, and nozzle-mixing tube distance Ld) on I and Cd. A coupled optimization framework integrating response surface methodology, non-dominated sorting genetic algorithm II, and technique for order preference by similarity to ideal solution is implemented for multi-objective optimization. This approach successfully identifies an optimal design (alpha = 3.01 degrees, (I = 15.29 degrees, Dmt = 1640.27 mm, Ld =-499.88 mm) that achieves a remarkable 30.09 % reduction in infrared radiation while simultaneously decreasing pressure loss by 7.12 %, effectively improving stealth performance and energy efficiency. This study innovatively applies multi-objective optimization to IRS device design, filling a gap in the relevant field and facilitating the development of new-generation stealth ships.

The experimental study examines the transient heat transfer performance of spray cooling when subjected to swing excitation, utilizing a swinging spray cooling apparatus. The findings suggest that the transient heat transfer process of spray cooling can be divided into two stages: rapid cooling and slow cooling. The major heat dissipation primarily occurs during the rapid cooling stage. In transient heat transfer processes, applying swinging excitation to the spray chamber also leads to liquid accumulation inside. Increasing the swing amplitude(0 degrees to +/- 135 degrees) and reducing the swing frequency (1.5-0 Hz) both result in greater liquid accumulation depth, although this depth is significantly lower compared to the amount of liquid accumulation under steady heat transfer conditions at the same operating conditions. A moderate level of liquid accumulation can enhance heat transfer during the rapid cooling phase. However, during the slow cooling phase, when there is a higher level of liquid accumulation, it leads to an increase in convective heat transfer resistance, exacerbating the fluctuations in the cooling curve during this period. Increasing the flow rate (0.46-1.16 L/min) and decreasing the spray height (54.7-14.7 mm) prove beneficial in enhancing the heat transfer performance of spray cooling.

This study addresses wall thermal shock within a restricted radial space in conventional central cone nozzle by proposing a hybrid IRS configuration integrating arc-transition lobed nozzle and central cone. It reduces the mixing tube wall temperature (Tmix,ave) by 8.3 % compared to linear design. Concurrently, to resolve the inherent conflict between core temperature reduction and wall heat dissipation in central cone optimization, the further investigations are conducted on the diameter ratio (A = D/Phi 2) and axial position (Ld) of central cone. It shows that increasing A enhances high-angle thermal shielding while increasing low-angle hot wall exposure, and boosts upstream mixing with limited downstream improvement. Furthermore, when A reaches its extremal value of 1, adjustments to Ld show marginal effects on mid and downstream vortex development, with performance discrepancies primarily governed by core thermal mainstream distribution variations within the mixing tube. Finally, a multi-objective optimization framework combining genetic aggregation and CRITIC weighting achieves coordinated improvements: 2.96 % reduction in the Tmix,ave, 1.26 % decrease in the funnel average exit temperature (Tout,ave), and 3.58 % increase of entrainment coefficient (eta) at optimal A = 1, Ld = 298.75 mm compared with the fundamental solution. This methodology establishes a transferable framework for precision IRS design through coordinated parameter optimization, demonstrating strong engineering applicability.

As an advanced infrared suppression technique, water spray can significantly reduce the ship exhaust temperature, but its application may cause flow loss and bring additional energy consumption to the ship engine. In this study, the regression orthogonal design is combined with the analytic hierarchy process-entropy (AHP-entropy) method, and is innovatively used for the multi-objective optimization of water spray setting of a marine infrared suppression (IRS) device. Relations between optimization objectives and spray parameters are developed based on the regression orthogonal experiment. The influences of droplet diameter (x1), droplet velocity (x2), water flow rate (x3), and spray angle (x4) on the device infrared radiation and pressure loss are revealed by visual analysis of the regression eqs. A comprehensive assessment for the importance of device performance indicators is conducted with the combination of AHP and entropy methods. Under the consideration of both subjective and objective effects, the indicator weights are reasonably allocated. The final optimization results show that at the spray setting of x1 = 20 mu m, x2 = 80 m/s, x3 = 2.032 kg/s, and x4 = 30 degrees, compared with no-spray case, the radiation intensity of the device can decrease by 69.62 % with only 1.90 % increase of the pressure drop coefficient.

Due to energy shortage and environmental pollution, vehicles and aircraft powered by Li-ion batteries have now received widespread attention. Among various types of battery thermal management systems (BTMSs), the aircooled BTMS is still the preferred choice due to its affordability, longevity, and simplicity. To ensure the reliable operation of electric vehicles and aircraft at different altitudes, it is extremely meaningful and significant to study the thermal behavior of batteries at different altitudes. Therefore, for the investigation of altitude impact, this paper firstly proposes an indirect decoupling method to address the limitations of using ambient temperature as a single variable. Based on this, several different configurations of air-cooled BTMS have been investigated through numerical simulation. Then, for the tapering-type BTMS with the best thermal performance, the battery behavior at different altitudes is investigated and the influence law of sheer altitude factor is summarized. Subsequently, to address the thermal performance issues at higher altitudes, this research proposes three optimization measures, which include increasing inlet velocity, decreasing inlet temperature, and incorporating phase change material (PCM) layers, respectively. Ultimately, the entropy weight-TOPSIS method is adopted to seek the optimal measure at different parameters. The results indicate that as altitude increases from the standard altitude to 4000 m, the maximum temperature rises significantly, exceeding the permissible temperature range of Li-ion batteries. Besides, in order to effectively confine the maximum temperature within the permissible temperature range at an altitude of 4000 m, the inlet velocity should be increased by at least 2 m/s or the inlet temperature should be reduced by at least 3 degrees C. Among all optimized solutions, the solution with the addition of 0.4 mm PCM layers is the best based on the comprehensive evaluation of multiple indicators.

This paper conducts a multi-objective comparative study on various ventilation–radiant coupled heating systems that combine mixing ventilation (MV) and displacement ventilation (DV) with ceiling, side wall, and floor radiant heating. The aim is to explore the differences in indoor environmental quality (IEQ) and human thermal comfort under different system configurations, as well as the impact of the radiant temperature in the radiant modules and the supply air temperature in the ventilation module on system performance. The research results show that the combination of displacement ventilation and floor radiant heating (DV-F) performs the best in terms of thermal comfort and energy efficiency. In this configuration, the Predicted Mean Vote (PMV) for the indoor environment and human thermal comfort is close to neutral (−0.15 to 0.35), the Draught Rate (DR) is significantly lower than in other systems (3.7% to 4.4%), and the ventilation efficiency is relatively high. In addition, a comprehensive evaluation of different system configurations using the CRITIC weight method further verified that the DV-F configuration with a radiant temperature of 26.2 °C to 28.2 °C and a supply air temperature of 26 °C to 28 °C is superior. This study provides theoretical guidance for the design and optimization of heating systems.

This study investigated the heat transfer characteristics of immersion spray cooling under coolant leakage conditions using experimental methods. Combining high-speed imaging technology to analyze the fluid flow characteristics inside the spray chamber, the study revealed the mechanism behind the formation of heat transfer abrupt changes during leakage. The research findings indicate that at low spray heights(d <= 14.7 mm), droplet impingement heat transfer dominates, and the coolant increases the resistance to droplet impingement and heat transfer resistance, leading to decreased heat transfer performance with increasing coolant depth(0 <= xi <= 2). Conversely, at high spray heights (d = 24.7-44.7 mm), convective heat transfer of the coolant plays a primary role, and the coolant can enhance heat transfer. Two heat transfer abrupt changes were observed during the leakage process: the first abrupt change resulted from air entrainment by droplets enhancing liquid disturbance, and the second abrupt change was caused by the synergistic effect of bubble entrainment, droplet impingement, and coolant convective heat transfer. By introducing dimensionless heat transfer coefficient H, spray Reynolds number Re1, and coolant Reynolds number Re2, a dimensionless correlation including coolant was established. When Re2 ranges from 1000 to 35,000, Re1 is the key parameter determining the heat transfer mechanism.

Portable air cleaners (PACs) have shown promising potential in reducing the risk of SARS-CoV-2 infection by effectively removing pollutant particles and optimizing airflow patterns. This study focused on a simulated scenario where an infected source and a susceptible person engage in conversation within a naturally ventilated room. By combining the Eulerian fluid method with the Lagrangian particle tracking model, a comprehensive insight into indoor airflow patterns and the dispersion of virus-laden droplets was gained. As deposited droplets may be resuspended or in contact thereby increasing the potential risk of infection, the deposition of droplets of different sizes in different susceptible areas was also specifically analyzed. The impacts of three variables, namely the configuration of the PAC's opening, air flow rate, and positioning, on the transmission of virus-laden droplets were investigated. The results highlighted the significant role of PAC utilization in effectively capturing droplets emitted by the infected source and reducing virus concentration in the vicinity of the susceptible person, thereby mitigating the risk of transmission. Notably, the design and orientation of the suction opening emerged as crucial factors. Among the various cases studied, the optimal control and prevention performance against the virus was achieved with a virus concentration reduction rate of 97.4% when the PAC had an opening configuration with a larger single-sided suction opening facing the infected source, an airflow rate of 200 m3 h-1, and was positioned at the center of the tabletop between the infected source and the susceptible person. This research underscored the importance of employing PACs with appropriate settings to enhance indoor air quality and minimize the potential for SARS-CoV-2 transmission in similar scenarios.

For the application of spray cooling in aircraft, it is necessary to further scientifically demonstrate whether highintensity external excitation adversely affects the heat transfer characteristics. In this paper, a swing spray cooling experimental device is established to systematically study the heat transfer stability of spray cooling under different swing excitation conditions. The experimental results show that swing excitation leads to fluid accumulation in the spray chamber, which intensifies unsteady flow and significantly deteriorates heat transfer stability. The amount of fluid accumulation is positively correlated with swing amplitude(theta = 0 degrees to +/- 135 degrees) and negatively correlated with swing frequency(f = 0 Hz to 1.67 Hz), in the case of theta = 135 degrees and f = 0.5 Hz, the maximum fluid accumulation depth reaches 9.50 cm. Fluid accumulation causes continuous fluctuations in wall temperature and heat flux during the swing process. The stronger the swing excitation, the more significant the fluctuations, in the case of theta = 135 degrees and f = 0.5 Hz, the wall temperature of SSCF is 15.86% higher than that of CSSC. Particularly, when the swing of the spray chamber stops, two significant abrupt heat transfer events occur, accompanied by a large spray height(h = 34.7 mm to 44.7 mm). These events are attributed to a sudden increase in accumulated fluid inertial force and the synergistic effect of droplet impact heat transfer and convective heat transfer of the accumulated fluid, respectively. Among all the spray methods, inverted spray cooling not only ensures cooling capacity equivalent to that of vertical downward spray but also significantly mitigates the impact of fluid accumulation on heat transfer stability.

To mitigate transient thermal shocks in lasers and reduce thermal stresses caused by temperature fluctuations, the use of phase change materials (PCMs) in thermal management systems is a viable solution. This study proposes an innovative two-dimensional transient heat transfer model specifically designed for plate-fin phase change heat exchangers (PFPCHEs). The model meticulously simulates the complex heat transfer phenomena within the heat exchanger, including fluid convection, solid thermal conduction, and the phase change processes of PCM. The convective heat transfer coefficient between fluid and plate is calculated using the Wieting correlation. An advanced pulse-mode experimental test platform was constructed to validate the model, dynamically monitoring and recording outlet temperatures and heat exchange performance for stringent experimental comparison. The research explores the impact of key operating parameters such as initial temperature, flow rate, and inlet temperature of the cooling cycle on the performance of the heat exchanger, providing valuable design and control strategies for transient thermal management of laser systems. The experimental results confirm that the model accurately predicts the dynamic response characteristics and temperature distribution of PFPCHEs under multi-cycle pulse loads, with 96% of the predictions within a 10% error margin. A significant finding is that the initial temperature has negligible influence on the heat transfer characteristics when it is below the solid phase temperature of the PCM. Moreover, by meticulously adjusting the flow rate and inlet temperature of cooling cycle, it is possible to effectively maintain the stability of the outlet temperature throughout the entire pulse cycle. This is crucial for minimizing temperature fluctuations within the thermal management system and extending the service life of electronic components.

Hot walls of the infrared suppression (IRS) device intensify the infrared signature of warships, which is detrimental for attaining infrared stealth. In this work, to effectively reduce the wall temperature, hole cooling technology is innovatively adopted on a marine IRS device. Circular holes are arranged on the mixing tube of the device. Numerical simulations are conducted to predict the temperature and flow distribution. The current research comprehensively analyzes the effects of hole position, number of hole rows, and number of holes on the wall temperature of the mixing tube and heat shield. The air suction rate and the exit temperature of the whole device are considered as well. The results indicate that the air suction and exit temperature of the device do not significantly change with the hole arrangement parameters. As the hole position moves towards the mixing tube outlet, the average temperature of the mixing tube continuously increases, while the maximum temperature of the mixing tube exhibits a peak-and-valley pattern. When the holes with large diameters are located near the mixing tube inlet, a backflow occurs between the mixing tube and the heat shield, causing the heat shield temperature to rise appreciably. Increasing the number of hole rows can reduce the mixing tube temperature, but excessive hole rows lead to an elevation in the heat shield temperature. The optimal configuration for the number of hole rows is found to be 2 with a hole diameter of 80 mm. With the increment in hole number, the average temperature of the mixing tube rises due to the accelerated disappearance of the streamwise vortices behind the holes; however, the maximum temperature of the mixing tube shows a decreasing-then-increasing trend owing to that more streamwise vortices are created. This study paves the way for the practical application of hole cooling technology on marine IRS devices. The findings can provide instructive suggestions for the arrangement of cooling holes.

Phase change energy storage technology holds broad prospects in the field of energy storage for the future. This study numerically simulates the melting process of phase change materials (PCMs) within a triplex tube heat exchanger (TTHX). Initially, the study explores methods and patterns to enhance thermal storage efficiency by altering the shape of the inner tube and adding fins. The addition of fins divides the PCM into multiple segments, resulting in a series of "nine-grid" configurations for the TTHX. Among all the nine-grid configurations, the best one reduces the melting time by 66.5 % compared to the traditional circular inner tube structure, significantly improving the melting level. This leads to the concept of "segmentation," which transforms the melting issue of the entire PCM area into the melting problems of each small segment. Based on the existing segmented shapes, a conceptual model with triangular segments has been further designed, and its superiority has been validated. It ensures thermal storage while reducing the usage rate of fins. In particular, the triangular model integrated with horizontal fins has achieved a 67.7 % reduction in melting time compared to the original configuration. The study indicates that the solid PCM in the middle and lower parts is the most difficult to melt, and the total melting time is directly related to this. Reasonable segmentation requires better coordination between the tube walls and the fins. This research provides constructive references for improving energy storage levels and innovative device design, which is of great significance for energy utilization and resource conservation.

The latent heat energy storage system holds promising application prospects in the field of energy. However, the critical bottleneck remains the melting speed of phase change materials (PCMs). In this study, the melting dynamics of PCM within a triplex-tube heat exchange system are investigated, focusing on the effects of varying the number and arrangement of inner tubes. The system performance with four, five, six, and seven inner tubes is compared, revealing a decrease in melting time with an increasing number of inner tubes. However, excessive numbers do not yield more significant enhancement. A novel arrangement scheme is proposed, recommending six inner tubes. Additionally, the effects of inner tube spacing, upper angle and lower angle are explored. Increasing these parameters initially decreases melting time but then exhibits a reverse trend. Specifically, appropriate spacing enhances coverage area, expediting rapid connectivity of melting areas and thereby augmenting natural convection. While an increase in the upper angle delays PCM melting in the upper half, optimal arrangement enhances lower half PCM melting. Balancing melting rates of three difficult-to-melt areas in the lower half with proper lower angle achieves optimal performance. Compared with the base case, the proposed arrangement with the tube spacing of 40 mm, upper angle of 92 degrees, and lower angle of 62 degrees reduces melting time by 44.8 %. These findings provide a theoretical and experimental foundation for enhancing PCM-based energy storage system performance, offering valuable insights for engineering applications.

The outbreak of the COVID-19 pandemic in 2019 has drawn public awareness to the transmission of respiratory infectious diseases. To better comprehend the developments and trends in research on the transmission mechanism of respiratory infectious diseases in the air, the publications in the Web of Science Core Collection database from 2017 to 2023 were utilized to reveal critical information. Herein, the yearly quantitative distribution and the geographical distribution of publications were analysed using a bibliometric method and information visualization technology. In addition, this study focused on the airborne transmission characteristics and influencing factors of respiratory infectious diseases. Research directions in different scenarios were innovatively extracted and the main measures to reduce the infection risk were summarized. Furthermore, some future work suggestions were given. The findings of this study provide several implications that can serve as guidelines for new and experienced researchers to establish a basic framework before initiating future research projects.

A variable geometry auxiliary inlet for a wide-body aircraft environmental control system with moveable deflectors operating in a large mass flow rate range is studied through numerical simulation and wind tunnel tests, which yields a design method for the variable geometry auxiliary inlet with high performance. The characteristics of the flow field are studied by numerical simulation. The results show that the favorable pressure gradient and the roll-up vortices are the major impetus that inhales the incoming flow into the inlet. The law of regulation and the performance variation under different conditions are obtained by wind tunnel test. The flow coefficient increases first but then decreases with the increase in the inlet opening, and the pressure rise ratio and total pressure recovery coefficient increase first and then decrease with the increase in the mass flow rate. In general, under the condition of a high Mach number (Ma > 0.4), the inlet opening of this test configuration should not exceed 50%. The deflectors can maintain the normal work of the environmental control system by moving properly to control the mass flow rate of the auxiliary inlet.

Phase change material (PCM) cooling is a promising approach to battery thermal management, but its wide application is limited by the narrow phase change temperature range. When the PCM temperature is below the melting point, PCM is equivalent to a purely thermally conductive material. When the ambient temperature exceeds the phase change temperature of PCM, PCM melts completely and cannot play the role of battery thermal management. Therefore, a novel petal-type battery thermal management system (BTMS) with dual PCMs is proposed in this paper to solve the environmental adaptability problem of PCM cooling. The thermal performance of the system at different ambient temperatures and different discharge rates is investigated by numerical simulation methods. The results show that the maximum temperature of battery at 2 C discharge rate is 30.49 ℃, 34.16 ℃ and 43.70 ℃ at ambient temperatures of 20 ℃, 30 ℃ and 40 ℃, respectively. Compared with the BTMS filled with a single PCM, the thermal performance of the proposed BTMS is particularly good at the high operating temperature represented by 40 ℃. At lower ambient temperatures such as 20 ℃ and 30 ℃, the thermal performance is not the best, but it fully meets the requirements of battery thermal management. Furthermore, the above BTMS is optimized using fin-reinforced heat transfer technology in this paper. The solution with the optimal fin arrangement can reduce the maximum temperature difference by 36.2% and 42.8% and the maximum temperature rise by 5.53% and 29.19% at 30 ℃ and 40 ℃, respectively.

The existing thermal runaway and barrel effect of energy storage container with multiple battery packs have become a hot topic of research. This paper innovatively proposes an optimized system for the development of a healthy air ventilation by changing the working direction of the battery container fan to solve the above problems. Four ventilation solutions based on fan flow direction control are numerically simulated, and their internal airflow distribution and thermal behavior are analyzed in detail. The results show that the heat dissi-pation effect of optimized solution 4 is significantly better than other solutions, and its average temperature and maximum temperature difference are 310.29 K and 4.87 K. The results are reduced by 1.16 % and 54.36 % respectively compared with the initial scheme. The results show that optimized solution 4 has significantly better heat dissipation than the other solutions, with an average temperature and maximum temperature difference of 310.29 K and 4.87 K respectively, a reduction of 1.16 % and 54.36 % respectively compared to the initial scheme. In summary, the cooling and ventilation solution based on the logical control of the fan direction is feasible and had a certain market prospect due to its simple structure and high economy.