Femtosecond transient absorption measurements of the ci-trans isomerization of the visual pigment rhodopsin clarify the interpretation of the dynamics of the first step in vision. We present femtosecond time-resolved spectra as well as kinetic measurements at specific wavelengths between 490 and 670 nm using 10-fs probe pulses centered at 500 and 620 nm following a 35-fs pump pulse at 500 nm. The expanded spectral window beyond that available (500-570 nm) in our previous study [ Vision is initiated when a photon is absorbed by the seven a-helical, membrane-bound protein called rhodopsin (1). After optical excitation, the 11-cis-retinal prosthetic group of rhodopsin is converted to an all-trans primary photoproduct in an efficient and apparently barrierless isomerization reaction ( Fig. 1). This product, which was first identified as bathorhodopsin in low-temperature absorption experiments, has an absorption maximum of =z560 nm (2). (13) with 35-fs pump and 10-fs probe pulses centered at 500 nm. Subsequently, Callender and co-workers (14) presented 300-fs time resolution data at 620 nm, which they interpreted in terms of a 200-fs twisting process on the excited-state surface, followed by a 3-ps excited-state to ground-state photoproduct transition. To resolve this disagreement, we present here a more complete series of femtosecond experiments on rhodopsin in which the probe wavelength range is extended to the red by using 10-fs pulses centered at 620 nm. Narrow-bandwidth kinetic traces at a selection of probe wavelengths as well as differential spectral measurements extending from 490 to 670 nm have been obtained. These results establish, in agreement with our earlier report, that the formation time for the rhodopsin photoproduct is 200 fs, and they provide key evidence that clarifies the interpretation of the primary photochemistry of vision. EXPERIMENTAL PROCEDURESThe method for generating 35-fs pump pulses at 500 nm as well as 10-fs probe pulses centered at 500 and 620 nm have been described elsewhere (12,13,15). The experimental configuration used to obtain differential transmittance spectra and time-resolved measurements is identical to that used in ref. 13. Briefly, the average pump power is ==3 ,W at a repetition rate of400 Hz. The pump (==0.5 mJ/cm2) and probe (O0.04 mJ/cm2) beams are crossed in a 0.3-mmjet offlowing bovine rhodopsin (15 OD/cm in ammonyx-LO). The flow rate is sufficient to replace the photolyzed sample between successive pump pulses. Two methods are used to measure transient changes in absorption (AT/T) as a function ofprobe delay time after photolysis of the rhodopsin. Differential spectra at particular pump-probe delay times are obtained by dispersing the probe pulse in a spectrometer after it passes through the sample and imaging it onto a dual diode array. Kinetic information at specific wavelengths is obtained by filtering the probe pulse after the sample (-"7-nm bandpass) and combining differential detection with lock-in amplification as the pump-probe delay time is continu...

A two-phase high-entropy oxide with orange color and good light absorbance is introduced as a photocatalyst for hydrogen production.

High‐temperature dielectric materials for capacitive energy storage are in urgent demand for modern power electronic and electrical systems. However, the drastically degraded energy storage capabilities owing to the inevitable conduction loss severely limit the utility of dielectric polymers at elevated temperatures. Herein, a new approach based on the in situ preparation of oxides onto polyimide (PI) films to high‐temperature laminated polymer dielectrics is described. As confirmed by computational simulations, the charge injection at the electrode/dielectric interface and electrical conduction in dielectric films are substantially depressed via engineering the in situ prepared oxide layer in the laminated composites. Consequently, ultrahigh dielectric energy densities and high efficiencies are simultaneously achieved at elevated temperatures. Especially, an excellent energy density of 1.59 J cm−3 at a charge–discharge efficiency of above 90% has been achieved at 200 °C, outperforming the current dielectric polymers and composites. Together with its excellent discharging capability and cyclic reliability, the laminate‐structured film is demonstrated to be a promising class of polymer dielectrics for high‐power energy storage capacitors operating at elevated temperatures. The facile preparation method reported herein is readily adaptable to a variety of polymer thin films for energy applications under extreme environments.

Photocatalytic hydrogen generation on low-bandgap black ZrO2 produced by high-pressure torsion.

In this study, we use observational and numerical model data from the Coupled Air Sea Processes and Electromagnetic Ducting Research (CASPER) field campaign to describe the mean refractive conditions offshore Duck, North Carolina. The U.S. Navy operational numerical weather prediction model known as the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) performed well forecasting large-scale conditions during the experiment, with an observed warm bias in SST and cold and dry biases in temperature and humidity in the lowest 2000 m. In general, COAMPS underpredicted the number of ducts, and they were weaker and at lower height than those seen in observations. It was found that there is a noticeable diurnal evolution of the ducts, more over land than over the ocean. Ducts were found to be more frequent over land but overall were stronger and deeper over the ocean. Also, the evaporative duct height increases as one moves offshore. A case study was chosen to describe the electromagnetic properties under different synoptic conditions. In this case the continental atmospheric boundary layer dominates and interacts with the marine atmospheric boundary layer. As a result, the latter moves around 80 km offshore and then back inland after 2 h.