Energy Input Rate Research Articles

Production of coco-vinegar in a bubble biofermentor

The economic value of coconut water can be increased through its conversion into a functional drink of coco vinegar powder having antioxidant and anti-diabetic properties. The fermentation of coconut water into coco-vinegar is more beneficial and cheaper than the chemical routes. Nevertheless, to guarantee product stability and increase the fermentation rate, the fermentation process must be controlled. Bubble bio-fermentation is an applicative technique in upgrading the production scale and in preserve the coco vinegar quality due to its unique characteristics i.e.: simple design, fixed part, controlled flow and agitation, uniform space-time, larger contact area, lower energy input, larger capacity, and higher mass transfer rate. This research objective was to investigate the influence of the parameter process i.e. sugar and alcohol concentration towards the formation of acetic acid in the coconut water fermentation. The research showed that bubble fermentation of coconut water was proven as a potential method for the coco vinegar production process. The bubble bio-fermentation of coconut water conducted by the addition of 8% of sugar, 10% of ethanol and 15% of Acetobacteracetii inoculum and fermentation process for 21 hours was able to give a vinegar having acetic acid concentration up to 1.04%.

Sea surface current response patterns to tropical cyclones

Abstract Tropical cyclones (TCs) are strong synoptic systems which induce strong sea surface currents. This paper first cross-checks a detailed surface current response to specific TCs Rammasun (2014), Kalmaegi (2014) and Sarika (2016) based on buoy/mooring observations as well as a three-dimensional numerical model (three-dimensional version of the Price-Weller-Pinkel model, 3DPWP) and a one-dimensional semi-analytical model which simplifies the driving forcing into wind stress and Coriolis force, then estimates the impact of all possible tropical cyclones using the semi-analytical model. The results show that the sea surface current response to the kinetic energy input of TCs, which is dependent on the TC configurations (translation speed, size and intensity) and the environmental configurations (Coriolis frequency and upper ocean stratification), can be represented by two simple parameters, namely the TC nondimensional translation speed (S) and the TC wind force parameter ( V ~ c ) or TC wind energy parameter ( E ~ ). S represents a combined effect of TC translation speed, size and Coriolis frequency, determines the structure of surface current response. V ~ c or E ~ represents a combined effect of TC intensity, mixed layer depth and Coriolis frequency, determines the intensity of surface current response or wind energy input into surface currents. Ekman-like divergence dominates the sea surface current response when S is small (0 5). The response pattern with S > 5 was rarely studied before. The three values range of S take up ~30.36%, ~69.36% and ~0.28% of all recorded TCs during 2001–2017, which explains why the second response pattern with 0.4 5 has been rarely studied before. Besides, the surface rightward bias is greatest at S = 2.5 (S = 1.45) for current speed (kinetic energy input rate). V ~ c ( E ~ ) determine the amplitude of current speed (wind energy input into currents). This work provides a simple and easy-to-use method to estimate the surface current response pattern to TCs when TCs and associated environmental configurations are given, which may help to improve the parameterization of TCs in regional and climate modeling. It also suggests that S is a better index than TC translation speed to classify TCs when studying the oceanic response.

L-mode to H-mode transition triggered by sawtooth-induced heat flux in EAST

H-modes induced by sawtooth events can be often observed in discharges with marginal auxiliary power injection in EAST. Poloidal flow shear at the very plasma edge, increasing ∼25% up to the threshold value, is observed just before the L-H transition by means of a fast reciprocating probe array in EAST. This suddenly risen poloidal flow shear, caused by the increased turbulent driven Reynolds force, is motived by the heat pulse originally released by a sawtooth crash at the plasma core. Associated with the critical poloidal flow shear, the local turbulent decorrelation rate increases significantly. The increased turbulent decorrelation rate compensated by nonlinear energy transfer rate from the turbulence to the low-frequency shear flows, exceeding the turbulence energy input rate, is sustained for several hundred microseconds till the turbulence quench happening.

РАСПРЕДЕЛЕНИЕ ОСТАТОЧНЫХ НАПРЯЖЕНИЙ ПРИ СВАРКЕ В УСЛОВИЯХ НИЗКИХ КЛИМАТИЧЕСКИХ ТЕМПЕРАТУР

The investigation of residual welding stresses is extremely essential for the choice of efficient structural forms of designed welded structures and for the correct choice of technological welding methods for manufacturing welded structures. In spite of the substantial data amount obtained as a result of the investigations carried out earlier the distributions of residual stresses and their impact upon working capacity of welded joints carried out during welding under conditions of low climatic temperatures is studied insufficiently. Actually there are no works on experimental investigations of residual stresses of welding under cold climatic conditions. 
 The purpose of the work consists in the investigation of the character of residual stress distribution in end welded joints of structural steel St3sp after welding under low climatic temperature conditions by power sources with pulse and constant parameter measurements. 
 To investigate residual stresses there was carried out plate welding at room and negative air temperatures. There were chosen and carried out two welding modes: pulse-arc welding with modulated current with the frequency of 1.67Hz and direct current welding. The definition of residual stresses was carried out with the use of X-ray method based on the measurement of material lattice micro-deformations caused by their effect.
 On the basis of the investigation results it was revealed that a welding temperature affects a value and a character of weld stresses. At air temperature decrease up to -45ºC irrespective of the welding mode chosen the increase of a tensile residual welding stress level in welded joints by 40…50% is observed. In comparison with dc welding during welding with modulated current there are formed residual stresses with a lower level of mean values both at room (+20ºC) temperature, and at negative one (-45ºC). The increase of a tensile residual stress level during welding under cold air conditions is connected with the necessity to increase the rate of energy input at welding, and also with the increase of steel strength properties at temperature decrease.

Subsurface cleavage of diamond after high-speed three-dimensional dynamic friction polishing

To unfold the promise of diamond as an advanced technical material, single-crystal diamonds (SCDs) and polycrystalline diamonds (PCDs) were smoothed by high-precision three-dimensional movement dynamic friction polishing (3DM-DFP) to achieve the ultra-smooth surface with roughness <5 nm (even 1 nm) more effectively. However, this inevitably leads to subsurface damage growth, i.e., subsurface defects evolved from nearly damage free to partial defects, and to cleavage faults beneath the SCD surface, resulting from mechanical fatigue and/or the rate of energy input by increasing the linear polishing velocity (from 12 m s−1 to 60 m s−1). In this study it was elucidated, for the first time, the subsurface uniform tile-roof-like cleavage faults and its formation mechanism of diamond after 3DM-DFP at the superhigh speed of linear sliding velocity of 60 m s−1. And the generated subsurface damage would be extended to about 10 μm in depth of the (100) SCD and manifested as micro-cleavage fault region, transition area and compressive zone. Meanwhile, two Raman peaks of 1425 cm−1 (first-order) and 2200 cm−1 (second-order) are assigned to the subsurface damage, which is the amorphous carbon (quasi sp3 + sp2) resulting from the cleavage along (111) crystal planes, based on the fine analysis of Raman spectroscopy and the study of subsurface defect evolution in different types of diamonds. Moreover, the assignment of concomitant peaks of 1750 cm−1 (localized defects) and 2100 cm−1 (sp1 chains) were revealed.

Frequency and energy characteristics of a Cu – Ne laser at different durations of the leading edge of the excitation pulse

The lasing characteristics of a copper vapour laser in a tube with forced heating, having a length of 50 cm and a diameter of 2 cm, excited by a train of pulses are investigated. Comparative studies of the frequency and energy characteristics of the laser are performed with a leading edge duration of the excitation pulse of ∼25 ns (when the capacitance discharges through a thyratron and a magnetic compression line) and ∼3 and 1 ns (using circuits with a high-speed switch – kivotron). It is shown that a decrease in the leading edge duration gives rise to an increase in the optimal pulse repetition rate up to ∼30 kHz, the generation efficiency up to 3.2 % and the generation power per unit length over 100 W m−1. The results obtained confirm the concept of limiting the frequency and energy characteristics of a copper vapour laser due to the insufficient rate of energy input into the plasma at high prepulse electron concentrations.

Apse-alignment in narrow-eccentric ringlets and its implications for the ϵ-ring of Uranus and the ring system of (10199) Chariklo

The discovery of ring systems around objects of the outer Solar System provides a strong motivation to apply theoretical models in order to better estimate their physical and orbital parameters, which can constrain scenarios for their origin.We review the criterion for maintaining apse-alignment across a ring and the balance between the energy input rate provided by a close by satellite and the internal dissipation rate occurring through ring particle collisions that is required to maintain ring eccentricity, as derived from the equations of motion governing the Lagrangian-displacements of the ring-particle orbits. We use the case of the ϵ-ring of Uranus, to calibrate our theoretical discussion and illustrate the basic dynamics governing these types of ring.In the case of the ring system of (10199) Chariklo, where the evidence that the rings are eccentric is not conclusive, we apply the theory of apse-alignment to derive information about the most plausible combination of values of the surface density and eccentricity-gradient, as well as the masses and locations of their postulated but - presently undetected - shepherd-satellites.When the balance conditions that we predict are applied to the ring system of (10199) Chariklo, we are able to estimate the minimum mass of a shepherd satellite required to prevent eccentricity decay, as a function of its orbital location, for two different models of dissipation. We conclude that the satellite mass required to maintain the m = 1 eccentric mode in the ring, would be similar or smaller than that needed to confine the rings radially.Our estimation of the most plausible combinations of eccentricity gradient and surface density consistent with apse-alignment are based on a standard model for the radial form of the surface density distribution, which approximately agrees with the optical depth profile derived by the stellar occultations. We find a diverse range of solutions, with combinations of eccentricity gradient and surface mass density that tend to minimize required enhanced collisional effects, having adopted estimated values of the form factor of the second degree harmonic of the gravitational potential.

Detecting and understanding co-benefits generated in tackling climate change and environmental degradation in China

China is facing the challenge of climate change and environmental protection in line with the promotion of sustainable development goals. Climate, environmental, and economic policy can each individually impact the effectiveness of other policies in the process of implementation. Understanding synergies among policy measures and identifying the co-benefits of environmental sustainable development generated by them is the focus of the paper. Because of existing restrictions in current research methods, the research community lacks the capacity to detect the interrelation among environmental, economic, and social development. Co-benefit research has gradually become an important area on sustainable development. Based on endogenous economic growth theory, we build a modified endogenous growth model to determine the optimal rates of economic growth, environmental pollution, energy input, and other factors in the context of co-benefits. Further empirical analysis is given which is missing in previous studies in this field. The empirical analysis reveals that China’s actual GDP, consumption, energy input, and physical capital growth rates are much higher than the optimal growth rate. However, the human capital and environmental pollution control growth rates are slower than the optimal values. Although China has a rapid growth in economy, the optimal level of comprehensive co-benefits has not been reached yet.

Plasma catalytic steam methane reforming for distributed hydrogen production

Abstract Steam methane reforming (SMR) via thermal catalytic approach is one of the dominant sources of industrial hydrogen, however it proceeds with slow response and low specific productivity. Here we demonstrate a plasma catalytic SMR for distributed hydrogen production, for which warm plasma by gliding arc discharge initiates the reaction, followed by Ni-based catalyst in a heat-insulated reactor without extra heating. In terms of the plasma alone process, specific energy input (SEI), steam/CH4 ratio (S/C) and total inlet flow rate (Ft) contribute to the methane conversion. In parallel, SEI and S/C account for the decrease in C2Hx selectivity hence the increase in selectivity of CO and CO2, while with Ft all the selectivity is approximately constant. The reaction pathway represented by the selectivity can be influenced by SEI and S/C rather Ft. To utilize the heat and active species with the reaction in plasma zone, Ni/CeO2/Al2O3 catalyst bed is coupled. For the coupled process, the conversion approaches the thermodynamic equilibrium values, with the favorable dismissed C2Hx selectivity thus the complete selectivity to CO and CO2. The coupled process was maintained steady for six hours, and the methane conversion of 90% at total hydrogen (t-H2) production rate of 2.7 SLM is achieved under optimum conditions of SEI, S/C, Ft and gas hourly space velocity (GHSV) of 110 kJ/mol, 3, 3 SLM and 18,000 ml·g−1 h−1. Compared to 59% and 2.3 kW h/Nm3 of the plasma alone process, such a coupled process achieves the energy efficiency (of methane to t-H2) of 75% and the low energy cost of 1.5 kW h/Nm3. Consequently, our approach of plasma catalytic SMR features the merits of rapid response, compact system and high specific productivity, which can be anticipated for the emerging needs of distributed hydrogen generation.

Nonequilibrium Ionization States within Galactic Outflows: Explaining Their O vi and N v Column Densities

Abstract We present a suite of one-dimensional spherically symmetric hydrodynamic simulations that study the atomic ionization structure of galactic outflows. We track the ionization state of the outflowing gas with a nonequilibrium atomic chemistry network that includes photoionization, photoheating, and ion-by-ion cooling. Each simulation describes a steady-state outflow that is defined by its mass and energy input rates, sonic radius, metallicity, and UV flux from both the host galaxy and metagalactic background. We find that for a large range of parameter choices, the ionization state of the material departs strongly from what it would be in photoionization equilibrium, in conflict with what is commonly assumed in the analysis of observations. In addition, nearly all the models reproduce the low N v to O vi column density ratios and the relatively high O vi column densities that are observed.

Launching of hot gas outflow by disc-wide supernova explosions

Galactic gas outflows are driven by stellar feedback with dominant contribution from supernovae (SN) explosions. The question of whether the energy deposited by SNe initiates a large scale outflow or gas circulation on smaller scales -- between discs and intermediate haloes, depends on SN rate and their distribution in space and time. We consider here gas circulation by disc-wide unclustered SNe with galactic star formation rate in the range from {$\simeq 6\times 10^{-4}$ to $\simeq 6\times 10^{-2}~M_\odot$~yr$^{-1}$~kpc$^{-2}$, corresponding to mid-to-high star formation observed in galaxies. We show that such disc-wide SN explosion regime can form circulation of warm ($T\sim 10^4$ K) and cold ($T<10^3$ K) phases within a few gas scale heights, and elevation of hot {($T>10^5$ K)} gas at higher ($z>1$ kpc) heights. We found that the threshold energy input rate for hot gas outflows with disc-wide supernovae explosions is estimated to be of the order $\sim 4\times 10^{-4}$~erg~s$^{-1}$~cm$^{-2}$. We discuss the observational manifestations of such phenomena in optical and X-ray bands. In particular, we found that for face-on galaxies with SF ($\Sigma_{_{\rm SF}}>0.02~M_\odot$~yr$^{-1}$~kpc$^{-2}$), the line profiles of ions typical for warm gas show a double-peak shape, corresponding to out-of-plane outflows. In the X-ray bands, galaxies with high SF rates ($\Sigma_{_{\rm SF}}>0.006~M_\odot$~yr$^{-1}$~kpc$^{-2}$) can be bright, with a smooth surface brightness in low-energy bands ($0.1\hbox{--}0.3$~keV) and patchy at higher energies ($1.6\hbox{--}8.3$~keV).}

Surfactant and non-surfactant radical scavengers in aqueous reactions induced by pulsed corona discharge treatment

The choice of energy input rate in treatment of aqueous media with gas-phase pulsed corona discharge (PCD) requires quantification of reactive oxygen species (ROS) reactions dependent on oxidation kinetics. The role of surfactant and non-surfactant OH-radical scavengers in PCD was studied in respect of oxidation of phenol, oxalic and humic acid. Phenol reacts fast, whereas oxalate is known to selectively react with OH-radicals. Humic acid oxidation is slow. Rapid energy intake is advised for oxidation induced exclusively by radical reactions, such as humics, whereas abatement of admixtures reacting with both surface-borne and long-living oxidants benefits from reduced pulse repetition frequency.

Is spontaneous generation of coherent baroclinic flows possible?

Geophysical turbulence is observed to self-organize into large-scale flows such as zonal jets and coherent vortices. Previous studies of barotropic $\unicode[STIX]{x1D6FD}$-plane turbulence have shown that coherent flows emerge from a background of homogeneous turbulence as a bifurcation when the turbulence intensity increases. The emergence of large-scale flows has been attributed to a new type of collective, symmetry-breaking instability of the statistical state dynamics of the turbulent flow. In this work, we extend the analysis to stratified flows and investigate turbulent self-organization in a two-layer fluid without any imposed mean north–south thermal gradient and with turbulence supported by an external random stirring. We use a second-order closure of the statistical state dynamics, that is termed S3T, with an appropriate averaging ansatz that allows the identification of statistical turbulent equilibria and their structural stability. The bifurcation of the statistically homogeneous equilibrium state to inhomogeneous equilibrium states comprising zonal jets and/or large-scale waves when the energy input rate of the excitation passes a critical threshold is analytically studied. Our theory predicts that there is a large bias towards the emergence of barotropic flows. If the scale of excitation is of the order of (or larger than) the deformation radius, the large-scale structures are barotropic. Mixed barotropic–baroclinic states with jets and/or waves arise when the excitation is at scales shorter than the deformation radius with the baroclinic component of the flow being subdominant for low energy input rates and insignificant for higher energy input rates. The predictions of the S3T theory are compared with nonlinear simulations. The theory is found to accurately predict both the critical transition parameters and the scales of the emergent structures but underestimates their amplitude.

Comparison of Oil‐in‐Water Emulsion between Ultrasonic Irradiation and Mechanical Stirring

AbstractTo compare oil‐in‐water emulsification behaviors between ultrasonic irradiation and impeller stirring, experiments and calculation by mathematical models were performed. For ultrasonic irradiation, the peak diameter of dispersed oil droplets decreased with an increase in input power and reductions in ultrasonic frequency, ratio of dispersed volume, and interfacial tension. For mechanical stirring, it declined with higher mechanical rotation speed. The results calculated by the mathematical models approximately agreed with the experiments. Ultrasonic irradiation was better than mechanical stirring by an impeller for producing a fine emulsion at higher supplied energy rate into liquid, whereas the tendency was inverse for a rough emulsion at lower input energy rate.

Structure and Properties of the Heat-Affected Zone of Low-Alloy Cold-Resistant Steel for Arctic Application

Abstract—The paper presents the results of a comprehensive study of structural and property changes in the most dangerous regions of the heat-affected zone of low-alloy cold-resistant steel with a guaranteed yield strength of 355–390 MPa before and after the post-welding tempering, including those caused by the combined impact of heating temperature under tempering and deformation, compared to base metal. The simulation was performed using a DIL 805 dilatometer and a Gleeble 3800 complex. The results of the investigation of the structure and properties of actual welded joints after welding with different rates of energy input (3.5 and 6 kJ/mm) are presented.

Investigation of minimum laser ignition energies of combustible gas mixtures

Minimum ignition energy (MIE) values for electric spark have been calculated and experimentally evaluated long ago, but for laser ignition significantly higher values were found, as explained, due to shorter duration and smaller size of the laser impact region. The feature of electric breakdown ignition is high energy input rate in the discharge channel. For laser ignition, energy input rate depends on gas spectral absorption. So only a small part of incident laser energy may be deposited in laser spark near breakdown threshold. MIE for certain gas mixture contents and pressure is expected to be independent on the way of energy deposition. There is a mess in published data on laser ignition energies, because authors often do not state whether incident or deposited energy is mentioned. To resolve these discrepancies, minimum pulse energy (MPE) term is suggested for laser impact, and is a more practical one. Although MPE is easy to measure, its value depends a lot on experimental conditions, which are not always properly documented, to reduce this effect, we suggest to consider MPE to laser breakdown energy ratio. We have experimentally evaluated MPE for butane (C4H10) based fuel mixture of different equivalence ratios (φ∼0.5-1.5) and pressures (p∼1-4 bar) at the impact of 1064 nm radiation of nanosecond laser. Efficiency of laser ignition was evaluated by MPE to breakdown threshold ratio.

On the Relationship between the Energy Dissipation Rate of Surface-Breaking Waves and Oceanic Whitecap Coverage

AbstractWave breaking is the most important mechanism that leads to the dissipation of oceanic surface wave energy. A relationship between the energy dissipation rate associated with breaking wave whitecaps and the area of whitecap foam per unit area ocean surface is expected, but there is a lack of consensus on what form this relationship should take. Here, mathematical representations of whitecap coverage and growth-phase whitecap coverage are derived, and an energy-balance approach is used to formulate and in terms of . Both and are found to be linearly proportional to but also inversely proportional to the bubble plume penetration depth during active breaking. Since this depth can vary for breaking waves of different scales and slopes, there is likely no unique relationship between and either or as bubble plume penetration depth must also be specified. Whitecap observations from the North Atlantic are used to estimate bubble plume penetration depth as a function of wind speed and then used with measurements to compute . An estimate of the relative magnitude of to the rate of energy input from the wind to the waves is made. Above wind speeds of about 12 m s−1, is largely balanced by . At lower wind speeds the ratio quickly drops below unity with decreasing wind speed. It is proposed that sea-state-driven variability in both and bubble plume penetration depth are significant causes of variation in whitecap coverage datasets and parameterizations.

Enhanced graphite recovery by optimising flotation energy input

ABSTRACTThis experimental work on graphite flotation investigated the effect of energy input on flotation performance of three particle size fractions. Results obtained from flotation tests indicated that the required energy input rate increases with the decreasing particle size. The maximum graphite recovery of coarse particles was obtained at 121 J/min, while the optimum recovery of fine particles was obtained at 330 J/min. However, the demand of energy for each coarse particle is slightly higher than that of the fine particle in collision process. Numerical analysis showed that the streamlines have little effect on the trajectories of coarse particles, which can significantly contribute to a higher recovery of coarse particles in comparison with fine particles at the same energy input rate.

Maintaining homeostasis by controlled alternatives for energy distribution in plant cells under changing conditions of supply and demand

Plants depend on light energy for the generation of ATP and reductant as well as on supply of nutrients (inorganic C, N, and S compounds) to successfully produce biomass. Any excess of reducing power or lack of electron acceptors can lead to the formation of reactive oxygen species (ROS). Multiple systems are operating to avoid imbalances and subsequent oxidative stress by efficiently scavenging any formed ROS. Plants can sense an upcoming imbalance and correspondingly adapt to changed conditions not only by an increase of ROS scavengers, but also by using excess incoming light energy productively for assimilatory processes in actively metabolizing cells of growing leaves. CO2 assimilation in chloroplasts is controlled by various redox-regulated enzymes; their activation state is strictly linked to metabolism due to the effects of small molecules on their actual activation state. Shuttle systems for indirect transfer of reducing equivalents and ATP specifically distribute the energy fluxes between compartments for optimal biomass production. Integration of metabolic and redox signals involves the cytosolic enzyme glyceraldehyde-3-P dehydrogenase (GapC) and some of its many moonlighting functions. Its redox- and metabolite-dependent interactions with the mitochondrial outer membrane, the cytoskeleton, and its occurrence in the nucleus are examples of these additional functions. Induction of the genes required to achieve an optimal response suitable for the respective conditions allows for growth when plants are exposed to different light intensities and nutrient conditions with varying rates of energy input and different assimilatory pathways for its consumption are the required in the long term. A plant-specific respiratory pathway, the alternative oxidase (AOX), functions as a site to convert excess electrons into heat. For acclimation, any imbalance is sensed and elicits signal transduction to induce the required genes. Examples for regulated steps in this sequence of events are given in this review. Continuous adjustment under natural conditions allows for adaptive responses. In contrast, sudden light stress, as employed when analyzing stress responses in lab experiments, frequently results in cell destruction. Knowledge of all the flexible regulatory mechanisms, their responsiveness, and their interdependencies is needed when plant growth is to be engineered to optimize biomass and production of any desired molecules.

Out-of-Equilibrium Collective Oscillation as Phonon Condensation in a Model Protein

In the first part of the present paper (theoretical), the activation of out-of-equilibrium collective oscillations of a macromolecule is described as a classical phonon condensation phenomenon. If a macromolecule is modeled as an open system, that is, it is subjected to an external energy supply and is in contact with a thermal bath to dissipate the excess energy, the internal nonlinear couplings among the normal modes make the system undergo a non-equilibrium phase transition when the energy input rate exceeds a threshold value. This transition takes place between a state where the energy is incoherently distributed among the normal modes, to a state where the input energy is channeled into the lowest frequency mode entailing a coherent oscillation of the entire molecule. The model put forward in the present work is derived as the classical counterpart of a quantum model proposed long time ago by H. Fr\"ohlich in the attempt to explain the huge speed of enzymatic reactions. In the second part of the present paper (experimental), we show that such a phenomenon is actually possible. Two different and complementary THz near-field spectroscopic techniques, a plasmonic rectenna, and a micro-wire near-field probe, have been used in two different labs to get rid of artefacts. By considering a aqueous solution of a model protein, the BSA (Bovine Serum Albumin), we found that this protein displays a remarkable absorption feature around 0.314 THz, when driven in a stationary out-of-thermal equilibrium state by means of optical pumping. The experimental outcomes are in very good qualitative agreement with the theory developed in the first part, and in excellent quantitative agreement with a theoretical result allowing to identify the observed spectral feature with a collective oscillation of the entire molecule.