Extreme heat events increasingly threaten public health, particularly in rapidly urbanizing areas like Maricopa County, Arizona. This study addresses gaps in identifying communities most vulnerable to extreme heat and heat waves by creating a Heat Vulnerability Index (HVI) that integrates often-overlooked populations. Utilizing US census data, satellite imagery, chronic illness prevalence rates, and unhoused population data, this HVI assesses vulnerability across census tracts in Maricopa County's diverse urban-rural landscape. Principal components analysis identified nine factors influencing heat vulnerability: (1) socioeconomic disadvantage; (2) isolation; (3) elderly populations; (4) chronic illness; (5) environmental risks; (6) African American race and language barriers, (7) Native American and unemployment status; (8) lack of housing and male; and (9) mobile home residents. Model validation found that heat-related mortality rate increased with heat vulnerability. Despite statistical limitations from data resolution and timeframe, this study integrates unhoused data into vulnerability assessments, emphasizing the need for equitable approaches that include underserved communities to address extreme heat vulnerability.
Occupational heat exposure is a growing public health concern in Japan, where hot, humid summers contribute to heat-related illnesses (HRIs). To characterise the thermophysiological responses of Japanese outdoor workers to summer heat exposure and explore the effect of a practical pre-cooling approach. Two field-based experiments were conducted in August-September. In Experiment 1, heart rate (HR) and core body temperature (CT) were continuously monitored under routine working conditions. In Experiment 2, workers performed their duties after pre-work ingestion of a 100 g carbohydrate-electrolyte ice slurry. HR and CT were assessed using non-invasive wearable sensors, and subjective thermal perception was recorded during the workday. Under high environmental heat stress (maximum Wet Bulb Globe Temperature: 30.2 ± 2.4 °C and 29.4 ± 2.1 °C), both CT and HR increased significantly during midday and afternoon periods. No significant differences were observed between the conditions in terms of HR, CT, or subjective thermal perception. Japanese outdoor workers exhibited a sustained elevation in thermo-physiological strain during summer. A low-volume pre-cooling strategy did not measurably modify these responses, indicating a limited physiological impact under real-world conditions.
Thermal storage combustion technology is one of the most efficient methods for treating volatile organic compounds (VOCs), with the rotary regenerative thermal oxidizer (R-RTO) representing the latest generation. However, research on R-RTOs remains scarce and rarely considers the impact of rotation on the flow dynamics and heat transfer. This study employed simulations using the standard k-ε model with enhanced wall function, porous media model, species transport model, Finite-Rate/Eddy-Dissipation combustion model, and the Sliding Mesh method. After validating the simulation accuracy, the velocity and temperature distributions and heat transfer patterns within the channels of the regenerator were investigated. The following conclusions were drawn: The gas flow was uniform within the regenerative chamber but became nonuniform in the lower section of the chamber and within the oxidation chamber owing to the structural and flow directions. This nonuniformity also affected the uniformity of the temperature distribution. A small portion of the gas within the combustion chamber exhibited a short residence time. During rotary valve rotation, inlet gas flow short-circuiting occurred, causing severe fluctuations in the inlet/outlet pressure difference and flow rate, and reducing the VOC removal efficiency. An analysis of the thermal storage media channels revealed that the channel length and inlet air velocity significantly affected the heat transfer coefficient. However, the impacts of these two parameters (length and velocity) and the switching time on thermal efficiency were minor. Furthermore, the switching time had little impact on the heat transfer coefficient.
Low-density, selective grazers with restricted habitat requirements may be particularly vulnerable to extinction under hotter, drier conditions expected across Africa's drylands with climate change. We evaluated how spatiotemporal variation in vegetation greenness and environmental heat load influenced movements of sable antelope, a water-dependent African grazer with selective resource requirements. We recorded hourly Global Positioning System (GPS) locations of 10 sable antelopes (Hippotragus niger) in Bwabwata National Park, Namibia, for up to 24 months, with concurrent hourly measurements of environmental heat load. As conditions became hotter and vegetation became browner during the dry season, home ranges increased in size and elongated towards the Kavango River. The 24-hour mean hourly displacement distance of sable antelopes increased in response to increased heat load and brown vegetation exposure, primarily due to more frequent long-distance movements to the Kavango River during the late dry season. Using Hidden Markov Models (HMMs), we identified four behavioural states of movement from GPS movement tracks: resting, foraging, local movement, and relocating. The relocating state, which was generally associated with directed movements to surface water, predominated during the late dry season. Sable antelopes increased both relocating and local movements, while decreasing foraging when exposed to high heat loads and brown vegetation. As conditions become increasingly hotter and drier, and resource availability becomes more unpredictable in space and time, species with specific resource requirements may face increased risk of extirpation, as walking farther to meet water requirements may compromise their already precarious energy balance during periods of resource limitation.
Heat stress is a major constraint to sustainable poultry production in tropical regions. This study evaluated the effects of Lactobacillus plantarum 1582-fermented red onion bulb extract (LFRO), supplied through drinking water, on growth performance, cecal microbiota, and excreta gas emissions in heat-stressed yellow-feather chickens. A total of 300 one-day-old male Rilai chicks were assigned to four treatments in a completely randomized design with five replicate pens of 15 birds each: unsupplemented control or LFRO at 25, 50, or 100 mg/L in drinking water. Birds were reared for 70 days under natural chronic tropical heat stress, with the temperature-humidity index predominantly within the severe-to-very severe range (28.9-31.1). Supplementation with 100 mg/L LFRO increased final body weight and body weight gain, reduced feed intake, and improved feed conversion ratio over the whole trial. The European Production Efficiency Index and Broiler Performance Efficiency Factor were also highest in the 100 mg/L group. Cecal 16 S rRNA sequencing showed no major changes in alpha- or beta-diversity, but several selected bacterial genera were modulated. LFRO at 50 and 100 mg/L reduced ammonia emission from excreta, whereas the other measured gases were not affected. This study shows LFRO at 100 mg/L is a natural drinking water supplement that improves feed efficiency and gut microbial balance in yellow-feathered chickens exposed to chronic tropical heat stress.
For semiconductor devices operating under elevated temperatures, especially in high-insolation regions, the intrinsic thermal degradation of optoelectronic performance poses a fundamental challenge. Herein, we report a heat-activated interfacial polarization strategy that uniquely converts this performance loss into a substantial gain. By incorporating electron-deficient N-heteroaromatic cations into lead-iodide perovskites, we induce a thermally driven electron cloud deformation at the organic-inorganic interface. This process establishes a reversible interfacial dipole that reshapes the electrostatic landscape, lowering charge-transport barriers and effectively screening deep trap states. As a result, carrier mobility increases by ∼100-fold and trap density reduces by ∼80% upon heating from 300 to 363 K, directly inverting the conventional thermal-roll-off trend. The universality of this mechanism is demonstrated across 1D, 2D, and 3D perovskite systems, all exhibiting pronounced photocurrent enhancement with temperature. As a proof-of-concept application, fire-warning detectors based on this strategy achieve 100-fold and 1000-fold enhanced responsivity to flame-signal infrared irradiation and smoke-marker NO2 gas, respectively, under identical heating conditions. This work establishes thermal energy as a functional asset rather than a performance liability, opening new avenues for thermally robust and smart optoelectronics.
Autonomous thermoelectric power generation under uniform heating, without an external cold reservoir, remains an open challenge for self-powered Internet-of-Things (IoT) sensors. This work shows that, for a fixed single-walled carbon nanotube (SWCNT) p-n junction film, circuit, and adhesive-bonded device structure, the substrate alone produces a substrate-dependent transition between continuous power generation and high-sensitivity heat-flux sensing. Across three flexible substrates, cycloolefin polymer (COP), polyimide (PI), and polyethylene naphthalate (PEN), substrate infrared absorptivity and per-unit-area thermal inertia jointly govern the sign, magnitude, and temporal evolution of the output voltage. COP (absorbance 0.34; transmittance 45.8% at 8.8 µm) heats the film preferentially, sustaining a stable in-plane gradient and delivering +0.38 mV at steady state. PI and PEN, with near-complete absorption, transiently invert the gradient, producing excursions of -0.58 and -0.96 mV; the larger PEN response reflects 2.4-fold greater thermal inertia, yielding -45 µV/K per junction pair. A transient thermal model and thermographic imaging reproduce these dynamics and indicate that the substrate optical contrast, rather than the interfacial factors common to all devices, principally governs the switching. For the present device structure and testing conditions, these results establish a substrate-engineering framework for dual thermoelectric functions in a single SWCNT architecture.
This paper focused on egg yolk plasma (EYP) and systematically analyzed the critical factors underlying heat-induced EYP instability. 76 °C is the key temperature for phase behavior transformation of EYP, and 72 °C marks the rheological transition point of thermal aggregation rate. Heat induction caused particle size of EYP increase by 6.20 times and emulsifying activity decrease by 6.90%, corresponding to larger and more aggregated emulsion droplets. Protein structure became more compact, with β-sheet content increasing by 32.48% and reduced fluorescence intensity. SDS-PAGE revealed that β-livetin, γ-livetin and apo-LDL were the key proteins involved in heat-induced EYP aggregation. Betaine altered hydrogen bond and water binding to suppress particle growth of EYP proteins, yet lost its protective effect on key proteins at 76 °C. The results clarify the thermal aggregation rules of EYP and liquid egg yolk, and lay a theoretical foundation for the production of thermally stable liquid egg products.
Evaluating children with acute encephalopathy can be challenging, particularly when the presentation overlaps with severe heat-related illnesses like heat stroke. This case describes a 17-month-old boy who initially presented with febrile seizures and encephalopathy after exposure to hot weather in a poorly ventilated car. Despite initial treatment for heat stroke, the child's clinical condition worsened with recurrent seizures, agitation, and dystonia. Infectious, autoimmune, and metabolic work up were unrevealing yet a detailed clinical examination and history taking as the child began to awaken hinted towards an underlying disorder confirmed by detailed genetic testing. This case highlights the diagnostic approach to pediatric encephalopathy and emphasizes a stepwise strategy in narrowing the differential diagnosis through careful clinical observation including the child behavior that can be missed during the acute encephalopathy stage.
Diabetes-associated hyperglycemia reshapes the oral microenvironment, aggravates biofilm-driven inflammation, and compromises the safety and efficacy of orthodontic treatment. Here, we develop a heat treatment-programmed bioactive orthodontic alloy, named NiTi-5Cu (AH), which combines structural functionality with microenvironment-responsive biological activity. By applying a solution-quench-aging process to NiTi-5Cu, we induce near-surface Cu enrichment and a more uniformly active electrochemical state, thereby enabling sustained Cu release. The resulting alloy maintains functional recoverability while exhibiting robust antibacterial and antibiofilm activities against Escherichia coli, Staphylococcus aureus, and Streptococcus mutans. In parallel, NiTi-5Cu (AH) exhibited no cytotoxicity toward human oral epithelial cells, vascular endothelial cells, and macrophages. Moreover, it induced M2-like macrophage polarization, shows favorable hemocompatibility isn both healthy and diabetic rabbits, and does not induce overt developmental or inflammatory toxicity in zebrafish assays. In a type 2 diabetic periodontitis rat model, intraoral placement of the alloy alleviates alveolar bone loss, inflammatory infiltration, and osteoclast activation. Moreover, 16S rRNA sequencing showed treatment-associated differences in oral-swab microbiota composition, while transcriptomic and metabolomic analyses revealed associative changes in inflammatory and metabolic pathways. Collectively, this work establishes a bioactive platform in which heat-treatment-engineered Cu release enables simultaneous antibiofilm regulation and periodontal protection, offering a promising metallic biomaterial strategy for diabetic oral care.
This research assessed the impacts of high protein feeds on the performance of local rabbits under severe chronic heat stress (Temperature-Humidity Index (THI) = 31.47 ± 2). This research used 72 local rabbits aged 42 days of mixed sexes, which were distributed equally into three groups: low-protein (LP), medium-protein (MP) and high-protein (HP), receiving low, medium and high protein feeds containing 16.7%, 18.2% and 19.5% crude protein, respectively. Even though the rabbits were fed ad libitum, rabbits in HP and MP groups showed similar average daily gain and mean body weight, which were significantly higher than LP group by + 7.5% and + 6%, respectively. Feed conversion ratios were significantly lower in MP and HP rabbits than in the LP group, with reductions of 7% and 8%, respectively, reflecting better feed conversion efficiency in the former two groups. Compared to the LP group, both MP and HP groups showed similar improved slaughter weight (+ 7%), skin weight (+ 9%), and cold carcass weight (+ 8%), while showing different improved results for weight of kidneys (+ 6% and + 7%), weight of liver (+ 12% and + 15%), respectively. The LP group had a much higher Perirenal fat content (+ 42%, p < 0.0001) than the HP and MP groups, which showed similar results. Additionally, the height, width, and area of the villus in MP and HP rabbits were improved by 16-25%, indicating better nutrient absorption. The results of this study provide evidence that utilising dietary protein enrichment is beneficial in combating the adverse effects of weather-induced heat stress on the growth of local rabbits.
The introduction of three-dimensional (3D) printing in prosthodontics has revolutionized denture fabrication. However, the concerns remain regarding the mechanical and physicochemical properties of 3D-printed polymethyl methacrylate (PMMA) in comparison to conventional materials. This research was done to evaluate and compare the physicochemical and mechanical properties of a novel 3D-printed PMMA-based denture base material with conventional heat-polymerized PMMA. An in vitro experimental study was conducted on 98 specimens divided into two groups (n = 49 each): Group I (3D-printed PMMA) and Group II (conventional PMMA). Specimens were fabricated using standardized protocols and evaluated for flexural strength, water sorption, surface roughness, surface hardness, impact strength, and solubility as per ISO guidelines. The obtained data were statistically evaluated. Group II demonstrated significantly higher mechanical properties, including flexural strength (92.63 ± 7.54 MPa), hardness (22.74 ± 2.01 VHN), and impact strength (4.05 ± 0.52 kJ/m2) compared to Group I. Conversely, Group I exhibited higher surface roughness (0.42 ± 0.06 μm), water sorption (28.75 ± 3.21 μg/mm3), and solubility (2.94 ± 0.51 μg/mm3). All differences were statistically highly significant (P < 0.001). Strong negative correlations were found between physicochemical and mechanical parameters. Although 3D-printed PMMA offers advantages in digital dentistry, its inferior mechanical properties and higher degradation potential limit its current clinical applicability. Résumé Introduction:L’introduction de l’impression en trois dimensions (3D) en prothèse dentaire a révolutionné la fabrication des prothèses amovibles. Toutefois, des préoccupations subsistent quant aux propriétés mécaniques et physico-chimiques du polyméthacrylate de méthyle (PMMA) imprimé en 3D par rapport aux matériaux conventionnels. Cette étude visait à évaluer et à comparer les propriétés physico-chimiques et mécaniques d’un nouveau matériau de base prothétique à base de PMMA imprimé en 3D avec celles d’un PMMA conventionnel polymérisé à chaud.Matériels et méthodes:Une étude expérimentale in vitro a été menée sur 98 échantillons répartis en deux groupes (n = 49 chacun): le groupe I (PMMA imprimé en 3D) et le groupe II (PMMA conventionnel). Les échantillons ont été réalisés selon des protocoles standardisés et évalués en termes de résistance à la flexion, d’absorption d’eau, de rugosité de surface, de dureté de surface, de résistance au choc et de solubilité, conformément aux normes ISO. Les données obtenues ont fait l’objet d’une analyse statistique.Résultats:Le groupe II a présenté des propriétés mécaniques significativement supérieures à celles du groupe I, notamment en ce qui concerne la résistance à la flexion (92,63 ± 7,54 MPa), la dureté (22,74 ± 2,01 VHN) et la résistance au choc (4,05 ± 0,52 kJ/m²). À l’inverse, le groupe I a affiché une rugosité de surface (0,42 ± 0,06 μm), une absorption d’eau (28,75 ± 3,21 μg/mm³) et une solubilité (2,94 ± 0,51 μg/mm³) plus élevées. Toutes les différences étaient hautement significatives sur le plan statistique (P < 0,001). De fortes corrélations négatives ont été observées entre les paramètres physico-chimiques et mécaniques.Conclusion:Bien que le PMMA imprimé en 3D présente des avantages en dentisterie numérique, ses propriétés mécaniques inférieures et son potentiel de dégradation plus élevé limitent son application clinique actuelle.
Heated tobacco products (HTPs) are marketed as alternatives to conventional cigarettes with a potential reduced risk profile. Yet, their actual impact on cancer and noncancer disease risk remains uncertain and requires rigorous quantitative assessment. In this study, we develop a unified and transparent computational framework for toxicological risk assessment of HTPs, integrating chemical emissions data with compound-specific toxicological thresholds derived from regulatory agencies. Our work (i) systematically reviews and harmonizes existing risk models used in the literature, (ii) formulates generalizable mathematical models for estimating lifetime cancer risk, hazard quotients, and margins of exposure that account for population demographics, smoking habits, and compound characteristics, and (iii) validates these models by reproducing published results and exploring the sensitivity of risk estimates to model parameters and emission sources. Using emissions data from conventional cigarettes and HTPs, we quantify per-compound and aggregated cancer and noncancer risks, and evaluate the relative risk reduction associated with switching from cigarettes to HTPs. The proposed risk analysis models provide a reproducible, extensible, and transparent approach for computational toxicology assessment, and can be readily applied to emerging nicotine and tobacco products within harm-reduction evaluation paradigms.
Heat shock proteins (HSPs) maintain cellular homeostasis and regulate immune responses across species. HSP90 stabilises and activates regulatory proteins, while HSP70 facilitates protein folding and prevents aggregation. In this study, the complete cDNA sequences of Dastarcus helophoroides - HSP70, HSP90, and β-actin (used as a reference for real-time quantitative polymerase chain reaction) - were obtained using rapid amplification of cDNA ends-polymerase chain reaction, and the expression of HSP70 and HSP90 under cold stress was analysed. The full-length cDNA of HSP90 contains a 2346-bp open reading frame (ORF) encoding 781 amino acids with a molecular weight (MW) of 89.6 kDa. The HSP70 cDNA contains a 1911-bp ORF encoding 636 amino acids (MW: 69.7 kDa), and the β-actin cDNA contains a 1131-bp ORF encoding 376 amino acids (MW: 41.7 kDa). Cold stress significantly affected HSP expression: HSP90 expression peaked at -15 °C, with a 9.45-fold increase compared to the control (P < 0.05), whereas HSP70 expression increased markedly at -10 °C, with a 60.42-fold increase compared to the control (P < 0.05). These findings have important biological implications for predicting insect performance under fluctuating thermal environments and for optimising low-temperature storage and release strategies of D. helophoroides in biological control programmes.
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Older adults exhibit heightened vulnerability to heat-related morbidity, yet it remains unclear whether short-term heat acclimation modifies integrative physiological stress responses in aging. We tested whether seven days of passive heat acclimation via warm water immersion alters basal concentrations and acute exercise-heat stress responses of biomarkers reflecting fluid regulation, gastrointestinal epithelial integrity, renal stress, and inflammation in older males. Twelve habitually active older males (median [IQR] age: 68 [64-73] years; V̇O2peak: 34.1 [29.4-36.1] mL O2·kg-1·min-1) completed an exercise-heat stress test before and after seven consecutive days of warm water immersion (~40°C), with rectal temperature maintained at ~38.5°C for the final 60 min. Blood samples were collected before and after each exercise-heat stress test and analysed using linear mixed-effects models (Day x Time). Repeated warm water immersion increased resting renin by 68% [95% CI: 29, 120; P<0.001], while neutrophil gelatinase-associated lipocalin and lipopolysaccharide binding protein decreased by 24% [-40, -4; P=0.023] and 22% [-37, -3; P=0.026] respectively. Exercise heat stress increased aldosterone by 45% [12, 87%, P=0.004], renin by 41% [8, 84%, P=0.01], intestinal fatty acid-binding protein by 52% [26, 85%, P<0.001], and plasma osmolality by 5.6% [2.5, 8.7%, P<0.001]. However, there was no day x time interaction for any biomarker (all P>0.05), indicating that seven days of warm water immersion did not alter the magnitude of the exercise heat stress response. Short-term passive heat acclimation in older males induces selective fluid-regulatory endocrine adaptations consistent with preserved renin-angiotensin-aldosterone system plasticity, while gastrointestinal and renal stress responses to exercise-heat exposure remain unchanged.
To systematically analyze the clinical manifestations, dynamic changes in hematological parameters, traditional Chinese medicine (TCM) tongue characteristics, and syndrome differentiation patterns in children with influenza A during spring, so as to provide clinical evidence for the integrated Chinese and Western medicine diagnosis and treatment of pediatric influenza A in spring. A single-center retrospective study design was adopted. A total of 143 children who visited the Department of Traditional Chinese Medicine of our hospital in the spring of 2024 and 2025 and were initially diagnosed with influenza A were included. General information, initial symptoms, and symptom combinations were collected. Hematological parameters were measured, including white blood cell count (WBC), absolute neutrophil count (NEU), absolute lymphocyte count (LYM), neutrophil-to-lymphocyte ratio (NLR), procalc itonin (PCT), and C-reactive protein (CRP). According to disease duration, patients were divided into three stages: <1 d, >1-≤3 d, and >3-14 d, and trends of change were compared. Tongue characteristics including tongue color, coating texture, and coating color were recorded, and TCM syndrome differentiation types were statistically analyzed. (1) General data and symptom characteristics: Among the 143 children, 78 were male (54.55%) and 65 were female (45.45%), with a mean age of (6.48 ± 3.61) years. The main age group was >5-≤10 years (64 cases, 44.76%). The mean disease duration was (1.82 ± 1.69) d, and 100 cases (69.93%) sought medical care within ≤1 d. Fever was the most common initial symptom (132 cases, 92.31%). The most frequent symptom combination was " fever + cough" (116 cases, 81.12%), followed by "fever + constipation" (85 cases, 59.44%). (2) Changes in hematological parameters: At the initial visit, 129 cases (90.21%) had LYM below the normal reference range, and 84 cases (58.74%) had elevated PCT. With disease progression, WBC showed a s light downward trend without statistical significance (P > 0.05); NEU gradually decreased, and was lower in the >3-14 d stage than in the <1 d stage (P < 0.05); LYM gradually increased, and was higher in the >1-≤3 d and >3-14 d stages than in the <1 d stage (P < 0.05); NLR gradually decreased, and was lower in the >3-14 d stage than in the <1 d stage (P < 0.05). PCT and CRP increased in the >1-≤3 d stage and decreased in the >3-14 d stage; PCT in the >3-14 d stage was lower than that in the >1-≤3 d stage (P < 0.05), and CRP in the >1-≤3 d stage was higher than that in the <1 d stage (P < 0.05). (3) Tongue characteristics: Red tongue was predominant (134 cases, 93.71%), and the proportion of red tongue increased with disease progression (<1 d 92.00%, >3-14 d 100%). Thick coating was predominant (91 cases, 63.64%), and the proportion increased with prolonged disease duration (<1 d 60.00%, >3-14 d 73.33%). White coating was the most common (89 cases, 62.24%), while the proportion of yellow coating increased with disease progression (<1 d 30.00%, >3- 14 d 60.00%). (4) TCM syndrome differentiation characteristics: The distribution of syndromes was as follows: heat-toxin attacking the lung syndrome (50 cases, 34.97%), wind-heat invading the exterior syndrome (47 cases, 32.87%), wind-cold constraining the exterior syndrome (29 cases, 20.28%), and dampness obstructing the defensive qi syndrome (17 cases, 11.89%). Stratification by sex showed that wind-heat invading the exterior syndrome was slightly more common in males (35.90%), while heat-toxin attacking the lung syndrome was slightly more common in females (38.46%). Stratification by age showed that in the 0-≤5 years and >5-≤10 years groups, wind-heat invading the exterior syndrome was more common (35.71% and 35.94%, respectively), whereas in the >10-16 years group, heat-toxin attacking the lung syndrome predominated (56.52%). Stratification by disease duration showed that the >3-14 d stage had the highest proportion of heat-toxin attacking the lung syndrome (53.33%). Spring influenza A in children was characterized by fever-dominant onset, frequent cough and constipation, early lymphopenia, dynamic inflammatory marker changes, and progressive tongue/coating changes across disease-duration stages. The observed increase in red tongue, thick coating, yellow coating, and heat-related TCM syndromes suggests a possible disease-duration-related shift toward intensified heat signs. These findings may provide exploratory reference for integrated clinical assessment, but they should be interpreted with caution because of the single-center retrospective design, small late-stage subgroup, absence of treatment/outcome data, and lack of standardized digital tongue imaging. Prospective multicenter studies are needed to validate these observations and clarify their clinical value.
Many bacterial chlorogenic acid esterases (ChlEs) exhibit atypical temperature behavior, featuring activities that barely change with temperature and activity maxima that fall below the thermal denaturation point. This work focuses on a ChlE fromLactobacillus helveticus (Lh-ChlE), which has a flat temperature dependence. First, it was determined that conformational changes during Lh-ChlE turnover are not rate-limiting and that the overall rate depends on the chemical step at all temperatures. Next, Lh-ChlE's temperature dependence was investigated using a conformational equilibrium model that assumes the existence of a temperature-dependent equilibrium between an active and an inactive conformation and an activation heat capacity model that postulates a difference in heat capacity between the ground and transition states. Although the equilibrium model recapitulates the data well, it yields an unrealistically low inactivation temperature around 280 K. Circular dichroism spectroscopy suggests that Lh-ChlE does not undergo structural changes at that temperature but may undergo small structural transitions at moderately elevated temperature. The activation heat capacity model describes Lh-ChlE behavior well, yielding an activation heat capacity (ΔCp‡) of approximately -1 kJ mol-1 K-1. Overall, the results suggest that the atypical temperature behavior of Lh-ChlE likely arises from a negative activation heat capacity. This work illustrates that contrasting thermodynamic models for atypical temperature dependence in enzymes can give rise to similar looking fits, even though they have different underlying physical meaning. Our results furthermore encourage additional analysis of the Lh-ChlE transition state structure to better understand the structural features that cause the enzyme's nonzero activation heat capacity.