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Open Access Publications from the University of California

Scholarly Works (138 results)

  • Article
  • Peer Reviewed
UCLA Previously Published Works (2023)
The challenge in optimizing biohybrid photoelectrodes lies in identifying kinetic bottleneck and energy loss of photoinduced electron transfer. In this issue of Joule, Friebes group describes a method for synchronized spectroscopic and electrochemical measurements of biophotoelectrode in operando, which indicates the electron transfer bottleneck steps and the energy loss processes.
    Cover page: Investigating limitations of biohybrid photoelectrode using synchronized spectroelectrochemistry.
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2024)
    Hybrid systems that integrate synthetic materials with biological machinery offer opportunities for sustainable and efficient catalysis. However, the multidisciplinary and unique nature of the materials-biology interface requires researchers to draw insights from different fields. In this Perspective, using examples from the area of N2 and CO2 fixation, we provide a unified discussion of critical aspects of the material-microbe interface, simultaneously considering the requirements of physical and biological sciences that have a tangible impact on the performance of biohybrids. We first discuss the figures of merit and caveats for the evaluation of catalytic performance. Then, we reflect on the interactions and potential synergies at the materials-biology interface, as well as the challenges and opportunities for a deepened fundamental understanding of abiotic-biotic catalysis.
      Cover page: Performance evaluation and multidisciplinary analysis of catalytic fixation reactions by material-microbe hybrids.
      • Article
      • Peer Reviewed
      Indoor Environmental Quality (IEQ) (2014)
      Thirty female and 30 male college students, who had naturally acclimatized to hot-humid climate, were exposed to seven temperature/humidity combinations in a climate chamber, and they were surveyed all year long at their classrooms and dormitories. They dressed in 0.5 clo in the chamber tests, while their subjective and physiological responses were collected. In the field study the subjects were surveyed while the thermal parameters around their body were measured. Results show no significant differences in thermal sensitivity to temperature changes or in neutral temperatures, based on our chamber and field studies with the same group of subjects. Both genders were equally satisfied with temperatures, although females tended to be more dissatisfied in cool temperatures, and males tended to be more dissatisfied in warm temperatures in the chamber tests; however the differences disappeared when they can adjust their clothing in the field. 
        Cover page: Gender differences in thermal comfort in a hot-humid climate
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2024)
        Methane (CH4) and nitrous oxide (N2O) are major greenhouse gases that are predominantly generated by microbial activities in anoxic environments. N2O inhibition of methanogenesis has been reported, but comprehensive efforts to obtain kinetic information are lacking. Using the model methanogen Methanosarcina barkeri strain Fusaro and digester sludge-derived methanogenic enrichment cultures, we conducted growth yield and kinetic measurements and showed that micromolar concentrations of N2O suppress the growth of methanogens and CH4 production from major methanogenic substrate classes. Acetoclastic methanogenesis, estimated to account for two-thirds of the annual 1 billion metric tons of biogenic CH4, was most sensitive to N2O, with inhibitory constants (KI) in the range of 18-25 μM, followed by hydrogenotrophic (KI, 60-90 μM) and methylotrophic (KI, 110-130 μM) methanogenesis. Dissolved N2O concentrations exceeding these KI values are not uncommon in managed (i.e. fertilized soils and wastewater treatment plants) and unmanaged ecosystems. Future greenhouse gas emissions remain uncertain, particularly from critical zone environments (e.g. thawing permafrost) with large amounts of stored nitrogenous and carbonaceous materials that are experiencing unprecedented warming. Incorporating relevant feedback effects, such as the significant N2O inhibition on methanogenesis, can refine climate models and improve predictive capabilities.
          Cover page: Nitrous oxide inhibition of methanogenesis represents an underappreciated greenhouse gas emission feedback.Creative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          Indoor Environmental Quality (IEQ) (2013)

          Moving air cools human body.  In warm environments, fans can provide comfort using less energy than air-conditioning. The savings in HVAC energy is substantial, and greater if fans enable buildings to be successfully conditioned by natural ventilation or evaporative cooling systems, instead of chillers. Although there are many laboratory studies for desk fans and personalized fans, the tests for ceiling fans are rare, mainly from early studies in 1980s.  The purpose of this study is to examine cooling effect of an integrated low-wattage ceiling fan on people in warm environments when air comes from different directions with different speeds.  We conducted 96 human subject tests in an environmental chamber.  Sixteen college students each experienced 6 air movement conditions: two different air speeds and three different air directions from the fan toward the subject-from front, side, or right above the head. The difference in thermal comfort and thermal sensation generated by fixed and oscillating fans was also investigated. The temperature and humidity conditions for the tests were 28 °C and 50% RH. The two air velocities were selected based on previous experiments conducted with human subjects in our environmental chamber. The two hour test schedule included two five minute breaks when subjects were asked to be away from the fans, simulating conditions in real offices when people are away from fans. 

          Subjective responses about thermal sensation, comfort, temperature satisfaction, perceived air quality, and preferred air movement were obtained periodically during the test, including the break periods. The results show that the ceiling fan is capable of providing thermal comfort under the tested warm condition. 

            Cover page: Enabling Energy-Efficient Approaches to Thermal Comfort Using Room Air MotionCreative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            Indoor Environmental Quality (IEQ) (2018)
            Over-cooling happens commonly in air-conditioned buildings that costs energy and results in discomfort complaints. There are many reasons causing overcooling, and HVAC engineers and researchers have proposed several approaches to prevent it from happening. In this paper, we describe a field study to show how the overcooling and energy use were significantly reduced by lowering maximum and minimum supply air flowrate setpoints, while providing personal comfort systems for occupants. The study was conducted over 16 months in two office spaces of a campus building with high HVAC energy expenditure and frequent cold complaints. The initial visit and measurements showed that the spaces were over-ventilated, causing cold discomfort in several workstations. We provided personal comfort systems to 26 occupants (heated/cooled chair, footwarmer, legwarmer based on occupants’ own choices) to maintain comfort, and gradually reduced the maximum and minimum supply air volume setpoints, to reduce the air-conditioning intensity and to let the office ambient temperature float. We increased occupants’ satisfaction rate from 56% to over 80%, meanwhile lowered HVAC zone energy use by 60% in heating and 40% in cooling.
              Cover page: Reducing building over-cooling by adjusting HVAC supply airflow setpoints and providing personal comfort systemsCreative Commons 'BY-NC-SA' version 4.0 license
              • Article
              • Peer Reviewed
              UCLA Previously Published Works (2022)
              Ultra-high performance liquid chromatography-high-resolution mass spectrometry (UPHLC-HRMS) is used to discover and monitor single or sets of biomarkers informing about metabolic processes of interest. The technique can detect 1000s of molecules (i.e., metabolites) in a single instrument run and provide a measurement of the global metabolome, which could be a fingerprint of activity. Despite the power of this approach, technical challenges have hindered the effective use of metabolomics to interrogate microbial communities implicated in the removal of priority contaminants. Herein, our efforts to circumvent these challenges and apply this emerging systems biology technique to microbiomes relevant for contaminant biodegradation will be discussed. Chlorinated ethenes impact many contaminated sites, and detoxification can be achieved by organohalide-respiring bacteria, a process currently assessed by quantitative gene-centric tools (e.g., quantitative PCR). This laboratory study monitored the metabolome of the SDC-9™ bioaugmentation consortium during cis-1,2-dichloroethene (cDCE) conversion to vinyl chloride (VC) and nontoxic ethene. Untargeted metabolomics using an UHPLC-Orbitrap mass spectrometer and performed on SDC-9™ cultures at different stages of the reductive dechlorination process detected ~10,000 spectral features per sample arising from water-soluble molecules with both known and unknown structures. Multivariate statistical techniques including partial least squares-discriminate analysis (PLSDA) identified patterns of measurable spectral features (peak patterns) that correlated with dechlorination (in)activity, and ANOVA analyses identified 18 potential biomarkers for this process. Statistical clustering of samples with these 18 features identified dechlorination activity more reliably than clustering of samples based only on chlorinated ethene concentration and Dhc 16S rRNA gene abundance data, highlighting the potential value of metabolomic workflows as an innovative site assessment and bioremediation monitoring tool.
                Cover page: Metabolome patterns identify active dechlorination in bioaugmentation consortium SDC-9™.Creative Commons 'BY' version 4.0 license
                • Article
                • Peer Reviewed
                Indoor Environmental Quality (IEQ) (2014)

                In warm environments, room fans can provide comfort using substantially less energy than air- conditioning. The savings are greater if the fans make it possible to successfully condition the building with natural ventilation or evaporative cooling systems, instead of chillers. Although there are many laboratory studies of comfort using desk fans and personalized fans, tests for ceiling fans are rare, mainly in early studies from the 1980s. This study examines the cooling effect of a low-wattage ceiling fan on occupants when air comes from different directions with different speeds. We conducted 96 human subject tests in an environmental chamber. Sixteen college students each experienced 6 air movement conditions: two different air speeds and three different air directions between fan and subject: from front, side, or right above the head (total eleven configurations). The difference in thermal comfort and thermal sensation generated by fixed and oscillating fans was also investigated. The temperature and humidity conditions for the tests were 28 °C and 50% RH.

                It was found that the majority of subject (70%) perceive the thermal environment without fans comfortable. This number rise to 100% for some configuration with fans. Our subject found that the oscillating air movement had no effect in terms of improved thermal comfort or thermal sensation, but it greatly improves their air quality perception. The subjects did not report any dry eyes discomfort for any of the eleven configurations.

                  Cover page: Enabling energy-efficient approaches to thermal comfort using room air motion
                  • Article
                  • Peer Reviewed
                  Indoor Environmental Quality (IEQ) (2013)
                  A heated/cooled chair was evaluated for its effect on thermal sensation and comfort. Thirty college students participated in 150 1.75-hour tests. Two heated/cooled chairs were placed in an environmental chamber resembling an office environment. The chamber temperatures were set at 16, 18, 25 and 29 °C (60.8, 64.4, 77, 84.2 °F). During the tests the subjects had full control of the chair surface temperature through a knob located on the desk. An additional 64 tests with sixteen subjects were conducted at the same four temperatures but with regular mesh or cushion chairs in order to provide reference results for comparison.  Subjective responses about thermal sensation, comfort, and temperature satisfaction were obtained at 20 minute intervals and eight times before, during, and after a break period. The chair’s energy consumption was monitored continuously. The results show that the heated/cooled chair strongly influences the subjects’ thermal sensation and comfort, providing thermal comfort under all tested conditions, both warm and cool. The average power draw is 27 Watts at 16ºC (60.8 °F), and 45.5 Watts at 29ºC ambient conditions (84.2 °F). 
                    Cover page: Effect of a heated and cooled office chair on thermal comfortCreative Commons 'BY' version 4.0 license
                    • Article
                    • Peer Reviewed
                    Indoor Environmental Quality (IEQ) (2014)
                    A naturally ventilated office building in Alameda, CA with operable windows and ceiling fans was monitored from Oct 2011 to Oct 2012. Physical environmental parameters such as dry-bulb air temperature, humidity, CO2 levels, outdoor wind speed, hourly window positions, heater settings and fan settings were recorded. Occupants were surveyed regularly over a period of one year about their current thermal comfort, thermal acceptability, air movement satisfaction, clothing and noise satisfaction. Occupants wore clothing with a clo value of between 0.5 – 0.6 during summer, and 0.7 – 0.8 during winter. The clo value of the occupants clothing was most closely correlated with the outdoor running mean temperature. Occupants start opening windows when the outdoor is at 16 °C. Window opening was strongly related with occupant’s arrival and outdoor temperature. Fans use was best explained by indoor temperature. Fans were typically turned on during the summer at indoor temperatures above 26 °C. Occupants voted that the thermal environments in the building were acceptable 98% of the time during the year-long survey period.
                      Cover page: Use of adaptive actions and thermal comfort in a naturally ventilated office
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