Direct Temperature Measurements Research Articles

Melting Point Certified Reference Materials for Organic Substances: Development Perspectives

The field of the melting point measurements of high-purity organic substances today includes a large number of measuring instruments used in the field of medicine, biology, and the production of perfumery and cosmetic products.The purpose of the research is to identify the features and justify approaches to the development of melting point certified reference materials of organic substances provided with metrological traceability to the SI base measurement units «temperature» (°C).The objectives of the research included justification of the choice of substances-candidates for CRMs; determination of the certification procedure for RMs; establishment of restrictions affecting the certification procedure; estimation of uncertainty for certified values of the melting point CRMs.In the course of the research, a state analysis of metrological assurance in the field of melting point measurements was performed. An overview of the reference complex designed to measure the melting point and purity of organic substances in the range from +40 °C to +250 °C is presented, its functional diagram is given. The basic requirements for substancescandidates for CRMs are identified. The study presents the results of determining the melting point of benzophenone, benzoic acid, succinic acid, anthracene, and caffeine obtained by direct measurements of the phase transition temperature and by indirect measurements based on recording the moment of optical transparency of the substances under study. The results of interlaboratory comparisons on samples of the studied substances are presented, which made it possible to obtain reliable data on the temperature of the emergence of optical transparency at different heating rates. A method for reconciling the results is proposed; it consists in presenting the certified value of the melting point determined by the method of direct measurements of the phase transition temperature in the thermodynamic mode, as well as the certified values of the optical transparency temperature at various heating rates as additional characteristics of the substance in the passports of the developed CRMs. Research objectives for further work are formulated.The theoretical significance of the results obtained lies in the development of theoretical and methodological approaches to the certification of melting point CRMs based on pure organic substances, which make it possible to improve the measurement accuracy in the field of thermal analysis at a higher quality level.

On the Use of Temperature Measurements as a Process Analytical Technology (PAT) for the Monitoring of a Pharmaceutical Freeze-Drying Process.

The measurement of product temperature is one of the methods that can be adopted, especially in the pharmaceutical industry, to monitor the freeze-drying process and to obtain the values of the process parameters required by mathematical models useful for in-line (or off-line) optimization. Either a contact or a contactless device and a simple algorithm based on a mathematical model of the process can be employed to obtain a PAT tool. This work deeply investigated the use of direct temperature measurement for process monitoring to determine not only the product temperature, but also the end of primary drying and the process parameters (heat and mass transfer coefficients), as well as evaluating the degree of uncertainty of the obtained results. Experiments were carried out with thin thermocouples in a lab-scale freeze-dryer using two different model products, sucrose and PVP solutions; they are representative of two types of commonly freeze-dried products, namely those whose structures are strongly nonuniform in the axial direction, showing a variable pore size with the cake depth and a crust (leading to a strongly nonlinear cake resistance), as well as those whose structures are uniform, with an open structure and, consequently, a cake resistance varying linearly with thickness. The results confirm that the model parameters in both cases can be estimated with an uncertainty that is in agreement with that obtained with other more invasive and expensive sensors. Finally, the strengths and weaknesses of the proposed approach coupled with the use of thermocouples was discussed, comparing with a case using a contactless device (infrared camera).

Method of determining thermal diffusivity on the basis of measurements of linear displacements

An innovative, relatively simple method of non-stationary determination of thermal diffusivity with the use of linear displacement measurements is proposed. This method is dedicated mostly to materials with an extensive internal structure (porous building materials, i.e. concrete, ceramics, wood, etc.), where the thermal parameters should take into account the heterogeneity of the structure (relatively large samples are required). The main difference between the proposed method and the methods known from the literature is that in order to determine the thermal diffusivity, it is only necessary to measure changes in the length of the sample during cooling or heating. This is an alternative to methods based on direct or indirect measurement of the surface temperature of the sample. The proposed method was tested on samples made of plexiglass. The obtained results were compared with the reference results obtained from measurements with the use of commercial measuring equipment (Netzsch HFM 446), which allows to determine the thermal conductivity coefficient and specific heat with high accuracy. Good agreement of the obtained results was obtained. The uncertainty analysis of the proposed method showed that it is at the level of 3%, which is sufficient in the case of building materials.

A Non-Intrusive Particle Temperature Extraction Methodology Using Infrared and Visible-Image Sequences for High-Temperature Particle Plumes

Abstract The direct measurement of particle temperatures in particle-laden flows presents a unique challenge to thermometry due to the flow's transient and stochastic nature. Previous attempts to measure the bulk particle temperature of a dilute particle plume or particle curtain using intrusive and non-intrusive methods have been mildly successful. In this work, a non-intrusive method using a high-speed infrared (IR) camera and a visible-light camera to yield an indirect particle temperature measurement technique is developed and tested. The image sequences obtained from the IR camera allow for the calculation of the apparent particle temperature, while the visible-light image sets allow for the calculation of the plume opacity as a function of flow discharge position. To extract the true particle temperature, a post-processing algorithm based on Planck's radiation theory was developed. The results were validated through a series of lab-scale tests at the University of New Mexico using a test rig capable of generating particle curtains at various temperatures. The temperature profiles extracted from the methodology presented were compared to the temperature data measured during experimental measurements yielding agreement of the bulk particle temperature of the plume within 10% error. The methods described here will be developed further to estimate the heat losses from the falling particle receiver at Sandia National Laboratories.

Direct Measurement of Beam-Induced Heating on Accelerator Pipes With Fiber Optic Sensors: Numerical Analysis Validation

In the field of accelerator physics it is crucial to account for heating caused by the passage of high intensity beams into accelerator components. This phenomenon is known as Radio Frequency (RF) Beam Induced Heating (BIH) and requires, other than an accurate design stage, to constantly monitor temperature-related parameters during the accelerator operations. This enables to warn for critical malfunctions and to prevent possible damages. Monitoring needs to meet various requirements, such as multiplexing capabilities, distributed sensing possibilities, and robustness in harsh environments. Fiber Bragg Grating sensors (FBGs) have been proven to be an ideal solution that meets all these requirements. This study aims to validate the use of FBGs for direct measurement of RF BIH. A section of the beam pipe in the CERN Large Hadron Collider was modeled in terms of impedance, and the resulting RF BIH was computed based on the traveling beam. The results of the numerical simulation were compared with experimental data obtained by FBGs installed along the beam pipe. The analysis shows that FBGs can be a valuable beam diagnostic tool for monitoring accelerated high energy particle beams by measuring RF BIH and may provide useful insights for improving the design and operation of future accelerators. The study highlights the significant advancements of FBG technology in direct temperature measurement and assessment of RF BIH and serves as a promising solution for mitigating RF BIH in the demanding environment of particle accelerators.

Blind PV temperature model calibration

The determination of module temperature in a photovoltaic (PV) system is a crucial factor in PV modelling and the assessment of system health status. However, the scarcity of on-site temperature measurements poses a challenge, and existing PV temperature models encounter difficulties in accurately estimating temperatures in systems characterized by unique structural or locational attributes. This paper introduces a novel approach that enables the calibration of PV temperature models without relying on direct temperature measurements. Referred to as blind calibration, this method eliminates the requirement for temperature measurements, thus offering a promising solution to the aforementioned challenges. The method is validated using three datasets, demonstrating accurate PV temperature (TPV) estimation with mean absolute errors below 2 °C. The findings highlight the suitability of the proposed approach for various PV system types, while acknowledging limitations regarding certain system configurations.

РОЛЬ ГИДРОТЕРМАЛЬНОЙ ДИНАМИКИ В ЗАРОЖДЕНИИ ЖИЗНИ НА ЗЕМЛЕ

In framework of the inversion concept one more required condition for the origin of life has been substantiated: multilevel fluctuations of physic-chemical parameters (in addition to the three accepted: availability of organic matter, aqueous medium, and source of energy). Taking this condition into consideration, hydrothermal systems were preferable medium for the origin of life on early Earth, in comparison with ocean. Hydrothermal environments are characterized by an extremely wide range of temperature, pressure, pH, and concentrations of components gradients. Multilevel fluctuations availability has been corroborated by means of thermodynamic estimations and direct measurements of pressure and temperature during the monitoring in some of the Kamchatka peninsula hydrothermal systems. The monitoring database mathematical processing reveals at least three levels of pressure fluctuations: 1) irregular macro fluctuations (with big amplitudes); 2) regular micro oscillations (with smaller amplitudes and periods about 20 minutes); 3) sudden pressure changes and fluctuations with periods lower than 5 minutes. High correlation between pressure, temperature, and concentrations of chemical components is also detected both in hydrothermal systems of Kamchatka and Slovenia. A lot of data on pressure and temperature dynamics in hydrothermal fluid, obtained by many researchers, can be applicable for investigation of the origin-of-life process.

Comparison of Ablation Performance between Octopus Multipurpose Electrode and Conventional Octopus Electrode.

To compare Octopus multipurpose (MP) electrodes, which are capable of saline instillation and direct tissue temperature measurement, and conventional electrodes for radiofrequency ablation (RFA) in porcine livers in vivo. Sixteen pigs were used in this study. In the first experiment, RFA was performed in the liver for 6 minutes using Octopus MP electrodes (n = 15 ablation zones) and conventional electrodes (n = 12 ablation zones) to investigate the effect of saline instillation. The ablation energy, electrical impedance, and ablation volume of the two electrodes were compared. In the second experiment, RFA was performed near the gallbladder (GB) and colon using Octopus MP electrodes (n = 12 ablation zones for each) with direct tissue temperature monitoring and conventional electrodes (n = 11 ablation zones for each). RFA was discontinued when the temperature increased to > 60℃ in the Octopus MP electrode group, whereas RFA was performed for a total of 6 minutes in the conventional electrode group. Thermal injury was assessed and compared between the two groups by pathological examination. In the first experiment, the ablation volume and total energy delivered in the Octopus MP electrode group were significantly larger than those in the conventional electrode group (15.7 ± 4.26 cm3 vs. 12.5 ± 2.14 cm3, p = 0.027; 5.48 ± 0.49 Kcal vs. 5.04 ± 0.49 Kcal, p = 0.029). In the second experiment, thermal injury to the GB and colon was less frequently noted in the Octopus MP electrode group than that in the conventional electrode group (16.7% [2/12] vs. 90.9% [10/11] for GB and 8.3% [1/12] vs. 90.9% [10/11] for colon, p < 0.001 for all). The total energy delivered around the GB (2.65 ± 1.07 Kcal vs. 5.04 ± 0.66 Kcal) and colon (2.58 ± 0.57 Kcal vs. 5.17 ± 0.90 Kcal) were significantly lower in the Octopus MP electrode group than that in the conventional electrode group (p < 0.001 for all). RFA using the Octopus MP electrodes induced a larger ablation volume and resulted in less thermal injury to the adjacent organs compared with conventional electrodes.

Use of the CFD Tool to Analyze the Aeration Comportment in a Horizontal Silo

Storage in vertical and horizontal silos is commonly used worldwide, and its better understanding is essential to acquire and maintain product quality of the stored products.Environmental temperature inside the silos is the main factor that drives mass loss, grain biological activity, pest development and product respiration. Thus, the study of temperature behavior at several layers of the product throughout time is necessary to diminish loss and achieve higher storage time with minimum quality loss, profit, and yield. Aeration is a formidable tool that allow the maintenance of temperature and consequently becomes an important preventive method to avoid the problems stated before. Direct measurement of temperature in all directions inside the silo requires numerous expensive equipment and labor force and requires a large amount of time to provide valuable and trusty data. For these reasons, CFD (computational fluid dynamics) was utilized to solve this problem. CFX software satisfactory demonstrated velocity behavior within the horizontal silo containing wheat; however, the aeration ducts configuration did not offered support to the correct silo aeration.

Rotor Temperature Estimation for Magnetically Suspended Turbo Molecular Pump Based on Flux Linkage Identification

Monitoring rotor temperature is a significant issue for safe operations in magnetically suspended turbo molecular pump (MSTMP). The increase in rotor temperature may cause the irreversible demagnetization of the permanent magnet (PM) and destroy the vacuum environment, eventually affecting the efficiency and security of the MSTMP system. Unfortunately, the direct measurement of the rotor temperature is complicated in practice due to the difficulty of accessing temperature sensors on a rotating shaft. This article proposes a novel rotor temperature estimation method based on the identification of the PM flux linkage. In order to address rank-deficiency in the identification of multiparameters, the resistance is calculated from the measured stator temperature, and two recursive least square (RLS) algorithm segments are combined to identify the inductance and flux linkage. Furthermore, the dynamic factor is introduced into the RLS algorithm to enhance the identification accuracy and convergence rate of the algorithm. The experiment results on the MSTMP test rig, equipped with the infrared temperature measuring module, demonstrate that the identified flux linkage has a good performance for the estimating rotor temperature under different working conditions.

Assessing the ability of satellite sea surface temperature analyses to resolve spatial variability – The northwest tropical Atlantic ATOMIC region

Direct measurements of the sea surface temperature (SST) from multiple platforms deployed during the Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) field campaign are used to evaluate the ability of satellite SST products to accurately represent spatial gradients within the region. The results further provide insight into the suitability of different satellite SST products for application to ATOMIC and other northwest tropical Atlantic scientific analyses. In situ SST measurements from the Research Vessel Ronald H. Brown, Saildrones, and Surface Velocity Program – Salinity (SVPS) drifters were collocated with five daily Level 4 satellite SST analyses and two Level 3 single-sensor satellite SST products during the period from January 1 to February 24, 2020. The absolute accuracy of the satellite products was generally good with random errors on the order of 0.2 K or less, though most exhibited a small cool bias of ∼0.1 K. The biases were not representative of a consistent offset, but rather larger cool biases of a subset of observations influenced the overall statistics. Sub-grid SST variability in the ATOMIC region was small (< 0.03 K) in relationship both to other regions and to uncertainties in the satellite products. Despite their absolute accuracy, the L4 analyses accurately reproduced the spatial SST variability within the ATOMIC domain only on scales of 0.5–1° or more. At the scale of their respective grid resolutions, correlations between satellite-derived and Saildrone-inferred grid-scale SST gradients were low, as the satellite–Saildrone SST differences dominated over small cell-to-cell variability in the region. One reason was the coarser feature resolution of the analyses compared to their grid resolution. Correlations increased with the distance over which the SST values were averaged. Simulations demonstrated that a satellite product precision near 0.05 K was needed to successfully reproduce the observed SST spatial variability at the grid cell level. Comparison with Saildrone observations from the Arctic showed sub-grid SST variability six-times larger and a relaxed satellite accuracy requirement of near 0.5 K in that region, but the satellite product accuracy was also degraded, again hindering the accurate sampling of SST gradients at the scale of the L4 analyses.

Electrothermal Coupling Model With Distributed Heat Sources for Junction Temperature Calculation During Surges

High junction temperature is usually the main factor leading to device failures in high-power working conditions, such as surges or avalanches. It is of great significance to obtain the junction temperature quickly and accurately. Direct measurement of junction temperature is inconvenient, and usually indirect electrical measurement combined with model calculation is used. An electrothermal coupling junction temperature calculation model with distributed heat sources is proposed in this article. This model can accurately and quickly predict the device behavior during the surge process, as well as the voltage drop and temperature changes of each part of the device, without actually performing surge tests. This article describes the theoretical basis and calculation principles of the model. By taking a commercial SiC merged PiN Schottky diode as an example, this article also explains the details of the establishment of the electrical and thermal characteristic models of the device, as well as the calculation steps of the junction temperature by the thermal coupling model. The calculated device voltage drop curve of the device is in good agreement with the measured ones, and the calculated junction temperature curve is more consistent with the device failure mechanism than the one by the traditional RC thermal circuit model.

Noninvasive platinum thin-film microheater/temperature sensor array for predicting and controlling flow boiling in microchannels

Thermal sensors and actuators are usually introduced at/in micro-channels in two ways: first, in an invasive manner through drilled holes which can lead to leakage problems and a change in channel dimensions and second, mounted in a non-invasive manner outside the channel which reduces heat transfer, accuracy, precision and response time. These problems are multiplied as soon as microchannel boiling with associated rapid thermal effects is investigated. Therefore, in this work, a platinum microheater/temperature sensor array has been developed to provide non-invasive, but nevertheless direct heating and temperature measurement at several locations along microchannels. This array comes without the mentioned disadvantages, resulting in ultra-fast response times that are limited only by the measurement speed of the sensor resistance and linear temperature coefficient of resistance. The working platinum area of each element in the array is only 238 nm thick, 0.1 mm wide and 0.5–2 mm long. The structures can be operated in heating and temperature measurement mode simultaneously. They are integrated into microreactors with the working surface as a side wall of a microchannel and in direct contact with the flowing fluid. Since the structures are deposited on transparent Pyrex glass in a cleanroom process, optical observation of two-phase flow boiling processes is possible for flow regime identification. The maximum operating temperature of the Pt microstructures is 450 °C and the linear temperature coefficient of resistance is about 2.98 × 10−3 °C−1. The relative measurement error of temperature measurements is less than 0.05% due to 2.9 µm thick highly conductive electroplated gold pads which form the electrical contact to the Pt microheaters/T-sensors. The platinum heater structures are capable of generating stationary vapor bubbles with a defined size proportional to the applied heating power. They can also predict two-phase flow boiling regimes (e.g. slug flow), vapor bubble length and frequency via the periodic signal of the measured temperature. Furthermore, they allow accurate calculation of heat transfer coefficients using the exact fluid temperatures measured with the Pt structures at the inlet and outlet of the microchannel, rather than analytically calculated values from temperature measurements outside the channel.

Highly Time Resolved, Combined Temperature, and Heat Flux Measurement Technique Based on ALTP Sensors

Abstract This study demonstrates a new methodology for the simultaneous direct measurement of temperature and heat flux within the same sensing element of heat flux sensors. The methodology is demonstrated for fast-response atomic layer thermopile (ALTP) sensors and makes use of a temperature–resistance correlation. The new methodology enables an inherent comparison and validation of the heat flux density signal of ALTPs. Good agreement is found based on experiments in the stagnation point of a subsonic hot air jet. The results of the mainly convective heat flux densities are compared against a standard coaxial thermocouple, indicating good agreement of mean values and signal characteristics. The simultaneous direct measurement of the temperature and heat flux allows the time-resolved calculation of local heat transfer coefficients and Nusselt numbers. The spectral analysis of the Nusselt number exhibits an excellent signal-to-noise ratio.

Insights Into the Aerodynamic Versus Radiometric Surface Temperature Debate in Thermal‐Based Evaporation Modeling

AbstractGlobal evaporation monitoring from Earth observation thermal infrared satellite missions is historically challenged due to the unavailability of any direct measurements of aerodynamic temperature. State‐of‐the‐art one‐source evaporation models use remotely sensed radiometric surface temperature as a substitute for the aerodynamic temperature and apply empirical corrections to accommodate for their inequality. This introduces substantial uncertainty in operational drought mapping over complex landscapes. By employing a non‐parametric model, we show that evaporation can be directly retrieved from thermal satellite data without the need of any empirical correction. Independent evaluation of evaporation in a broad spectrum of biome and aridity yielded statistically significant results when compared with eddy covariance observations. While our simplified model provides a new perspective to advance spatio‐temporal evaporation mapping from any thermal remote sensing mission, the direct retrieval of aerodynamic temperature also generates the highly required insight on the critical role of biophysical interactions in global evaporation research.

Measuring Skeletal Muscle Thermogenesis in Mice and Rats.

Skeletal muscle thermogenesis provides a potential avenue for better understanding metabolic homeostasis and the mechanisms underlying energy expenditure. Surprisingly little evidence is available to link the neural, myocellular, and molecular mechanisms of thermogenesis directly to measurable changes in muscle temperature. This paper describes a method in which temperature transponders are utilized to retrieve direct measurements of mouse and rat skeletal muscle temperature. Remote transponders are surgically implanted within the muscle of mice and rats, and the animals are given time to recover. Mice and rats must then be repeatedly habituated to the testing environment and procedure. Changes in muscle temperature are measured in response to pharmacological or contextual stimuli in the home cage. Muscle temperature can also be measured during prescribed physical activity (i.e., treadmill walking at a constant speed) to factor out changes in activity as contributors to the changes in muscle temperature induced by these stimuli. This method has been successfully used to elucidate mechanisms underlying muscle thermogenic control at the level of the brain, sympathetic nervous system, and skeletal muscle. Provided are demonstrations of this success using predator odor (PO; ferret odor) as a contextual stimulus and injections of oxytocin (Oxt) as a pharmacological stimulus, where predator odor induces muscle thermogenesis, and Oxt suppresses muscle temperature. Thus, these datasets display the efficacy of this method in detecting rapid changes in muscle temperature.

Monitoring of shear heating effects during injection molding of rubber to improve the process control

This work aims to get new insights into the “process monitoring tool” proposed by the authors for the online monitoring of the shear heating phenomenon during injection molding of technical rubber parts. The online monitoring is based on direct measurement of the surface rubber temperature (shear heating temperature, TSH) by an infrared thermal camera of the rubber as it leaves the extruder barrel of the injection molding machine. The measured rubber temperature is a process indicator giving the thermal history of the rubber compound injection and process safety. Therefore, this fast process control is applied to industrial applications to investigate the processing behavior of ethylene acrylate (AEM) rubber compounds. In particular, the relationships between TSH vs injection pressure, vs injection speed, vs screw speed rotation and vs screw length over diameter ratio (L/D ratio) and vs AEM rubber compound properties variation due to exceeding the shelf life are investigated. The results show that TSH is manly influenced by the screw L/D ratio, followed by injection pressure and screw speed rotation (especially if are set to higher levels), whereas the injection speed is the least effective parameter to reduce TSH. Furthermore, a previously found robust correlation between the shear heating parameter (ηSH) and the minimum torque measured in rheometric laboratory tests (ML) is used to show the noteworthy deviation from the proportional trend when the AEM rubber compound exceeded it shelf life. Therefore, the coefficient of determination of {text{log}}eta_{{{text{SH}}}} vs ML curves provides a good indication of process stability, while it is running.

Global distribution of the hydrocarbon Golden Zone

The presence of sedimentary sequences located at temperatures ranging between 60 and 120 °C has permitted the identification of hydrocarbon accumulation patterns of economic importance. This thermal range is identified as the “Golden Zone”, where there is a potential co-existence of the petroleum system elements that supports a minimal degree of degradation or transformation of hydrocarbons generated from source rocks, mainly in the hydrocarbon expulsion zone from approximately 120 °C–200 °C. The Golden Zone distribution can be represented on maps to help distinguish regions of relevant hydrocarbon potential.This work presents global Golden Zone distribution maps, estimated using a global geothermal gradient model obtained using the Curie Point Depth (CPD) distribution constrained with geothermal gradients from direct wells temperature measurements and a global model of sedimentary thicknesses obtained from data reported by a diverse array of institutions. The Golden Zone maps show the variations in different geotectonic environments. The depth interval for the Golden Zone varies between 500 m and 3000 m for the top and from 1000 m to 5000 m for the base, with thicknesses ranging between 5 and 3000 m.The Golden Zone distribution estimated shows that along active tectonic margins, the sedimentary sequences tend to be thin, located with abrupt contrasts of the basement, and where one or both isotherms that define the Golden Zone are below the basins, preventing its proper development. Exceptions to this trend are in the forelands and some intermountain basins. In contrast, the passive margins are characterized by Golden Zone regions in which the sedimentary sequences present a wide range of thicknesses within basins of diverse ages and extensions.

Chemical abundances in Seyfert galaxies – IX. Helium abundance estimates

ABSTRACT For the first time, the helium abundance relative to hydrogen (He/H), which relied on direct measurements of the electron temperature, has been derived in the narrow line regions (NLRs) from a local sample of Seyfert 2 nuclei. In view of this, optical emission line intensities [3000 &amp;lt; λ(Å) &amp;lt; 7000] of 65 local Seyfert 2 nuclei (z &amp;lt; 0.2), taken from Sloan Digital Sky Survey Data Release 15 and additional compilation from the literature, were considered. We used photoionization model grid to derive an Ionization Correction Factor (ICF) for the neutral helium. The application of this ICF indicates that the NLRs of Seyfert 2 present a neutral helium fraction of ∼50 per cent in relation to the total helium abundance. We find that Seyfert 2 nuclei present helium abundance ranging from 0.60 to 2.50 times the solar value, while ∼85 per cent of the sample present oversolar abundance values. The derived (He/H)–(O/H) abundance relation from the Seyfert 2 is stepper than that of star-forming regions (SFs) and this difference could be due to excess of helium injected into the interstellar medium by the winds of Wolf–Rayet stars. From a regression to zero metallicity, by using Seyfert 2 estimates combined with SFs estimates, we obtained a primordial helium mass fraction Yp = 0.2441 ± 0.0037, a value in good agreement with the one inferred from the temperature fluctuations of the cosmic microwave background by the Planck Collaboration, i.e. $Y_{\rm p}^{\rm Planck}=0.2471\pm 0.0003$.

A daily temperature rhythm in the human brain predicts survival after brain injury.

Patients undergo interventions to achieve a ‘normal’ brain temperature; a parameter that remains undefined for humans. The profound sensitivity of neuronal function to temperature implies the brain should be isothermal, but observations from patients and non-human primates suggest significant spatiotemporal variation. We aimed to determine the clinical relevance of brain temperature in patients by establishing how much it varies in healthy adults.We retrospectively screened data for all patients recruited to the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) High Resolution Intensive Care Unit Sub-Study. Only patients with direct brain temperature measurements and without targeted temperature management were included. To interpret patient analyses, we prospectively recruited 40 healthy adults (20 males, 20 females, 20–40 years) for brain thermometry using magnetic resonance spectroscopy. Participants were scanned in the morning, afternoon, and late evening of a single day.In patients (n = 114), brain temperature ranged from 32.6 to 42.3°C and mean brain temperature (38.5 ± 0.8°C) exceeded body temperature (37.5 ± 0.5°C, P < 0.0001). Of 100 patients eligible for brain temperature rhythm analysis, 25 displayed a daily rhythm, and the brain temperature range decreased in older patients (P = 0.018). In healthy participants, brain temperature ranged from 36.1 to 40.9°C; mean brain temperature (38.5 ± 0.4°C) exceeded oral temperature (36.0 ± 0.5°C) and was 0.36°C higher in luteal females relative to follicular females and males (P = 0.0006 and P < 0.0001, respectively). Temperature increased with age, most notably in deep brain regions (0.6°C over 20 years, P = 0.0002), and varied spatially by 2.41 ± 0.46°C with highest temperatures in the thalamus. Brain temperature varied by time of day, especially in deep regions (0.86°C, P = 0.0001), and was lowest at night. From the healthy data we built HEATWAVE—a 4D map of human brain temperature. Testing the clinical relevance of HEATWAVE in patients, we found that lack of a daily brain temperature rhythm increased the odds of death in intensive care 21-fold (P = 0.016), whilst absolute temperature maxima or minima did not predict outcome. A warmer mean brain temperature was associated with survival (P = 0.035), however, and ageing by 10 years increased the odds of death 11-fold (P = 0.0002).Human brain temperature is higher and varies more than previously assumed—by age, sex, menstrual cycle, brain region, and time of day. This has major implications for temperature monitoring and management, with daily brain temperature rhythmicity emerging as one of the strongest single predictors of survival after brain injury. We conclude that daily rhythmic brain temperature variation—not absolute brain temperature—is one way in which human brain physiology may be distinguished from pathophysiology.