Instantaneous Intensity Research Articles

Photoperiod mediates the differential physiological responses of smaller Thalassiosira pseudonana and larger Thalassiosira punctigera to temperature changes

Global warming is altering both phytoplankton-experienced temperature and light-exposure duration through shifting their niches from low to high latitudes. We explored the growth, physiology, and compositions of a smaller Thalassiosira pseudonana and a larger Thalassiosira punctigera, temperate marine centric diatoms, in responses to a matrix of temperatures (12, 15, 18, and 21 °C) and photoperiods (light:dark cycles of 4:20, 8:16, 16:8, and 24:0). Both T. pseudonana and T. punctigera grew faster under medium temperature and longer photoperiod, under the expected optimal instantaneous light intensity. The biovolume-based pigments content of T. pseudonana responded largely to temperature, while that of T. punctigera responded more to photoperiod duration than to temperature. In T. pseudonana, shortest photoperiod enhanced cellular protein content and alleviated their temperature dependency. Continuous growth light reduced the photosynthetic capacity of T. pseudonana at the lowest temperature and reduced that of T. punctigera across temperatures. Moreover, we found the increasing temperature linearly increased the dark respiration rate (Rd) and molar ratio of carbon to nitrogen (C:N) of T. pseudonana but decreased that of T. punctigera, with the scattered effects of photoperiod. Our results demonstrated that responses of diatoms Thalassiosira across photoperiods and temperatures vary with species and possibly with cell size, suggesting that the poleward shift of the niches of phytoplankton in nature might cause a change in community structure.

Numerical investigation on heat transfer characteristics during melting of lauric acid in a slender rectangular cavity with flow boundary condition

This paper is devoted to numerically investigating the melting mechanism and thermal behavior of phase change material (PCM) in a slender rectangular cavity with heat transfer fluid (HTF) flowing over one side and the other sides thermally insulated. Hot air and lauric acid are selected as the HTF and PCM in current work, respectively. A parametric study is performed by varying the velocity of the HTF in a range of 2, 3, 4, 5 m/s and temperature of 70, 75, 80°C. Dimensionless analysis for the melting process is conducted by introducing a group of dimensionless numbers. The results show that despite the declining heat transfer rate from bottom up along the wall, the melting rate is relatively large in upper part of the cavity due to the dominance of natural convection. Different from the tube flow situation, increasing the Reynolds number or the Stefan number both have significant positive effects on the melting process, and the variations of relevant parameters are described quantitatively. Furthermore, an analogy analysis of dimension is carried out by dividing the whole process into three stages reasonably, based on which a series of new correlations are developed to predict the instantaneous melting fraction and heat transfer intensity during the melting process.

An open-source Abaqus implementation of the phase-field method to study the effect of plasticity on the instantaneous fracture toughness in dynamic crack propagation

Brittle and ductile dynamic fracture in solids is a complex mechanical phenomenon which attracted much attention from both engineers and scientists due to its technological interests. Modeling cracks in dynamic cases based on a discontinuous description is difficult because it needs additional criteria for branching and widening. Due to the very short time scales and the spatial complexity of the dynamic problem, its experimental analysis is still very difficult. Therefore, researchers still have to rely on numerical simulations to find a deeper explanation for many observed phenomena. This study is set out to investigate the effect of plasticity on dynamic fracture propagation. On the other hand, the diffuse phase-field formulation makes it possible to initiate, propagate, arrest or even branch cracks while satisfying the basic principles of thermodynamics. An implicit, staggered elastoplastic version of the phase-field approach was implemented in the commercial finite element code Abaqus through the UEL option. By means of simple examples we show that localized ductile deformations first increase both resistance and toughness. Then, after a maximum value, the resistance starts to decrease with a significant increment in energy dissipation. By favoring shear deformation over tensile failure the fracture pattern changes. First the branching disappears, then the crack propagation angle changes and becomes a shear band. Finally, we observed the increment of the instantaneous dynamic stress intensity factor during the acceleration stage of the crack without introducing a rate dependent critical fracture energy. We explained this phenomenon with the increasing roughness of the fracture surface.

The effect of ultrasonic intensity on physicochemical properties of Chinese fir

Cavitation intensity is affected by ultrasonic intensity (UI) and is a key parameter to describe experimental results during ultrasonic treatment. The relationship between the UI and physicochemical properties of Chinese fir was investigated. In this study, four frequencies (25, 28, 40, and 59kHz) were used at the same intensity of 240W and the same duration of 35min. The UI during the ultrasonic treatment was determined, and the chemical components were determined. The chemical structure, crystallinity, morphology, and extractives of wood were respectively analyzed by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and gas chromatography-mass spectrometry (GC-MS). The results showed that higher crystallinity was associated with a larger integrated area under the curve of the ultrasonic intensity (UIA). The largest UIA was observed at 25kHz, followed by those at 40, 59, and 28kHz. The relative content of hemicellulose was strongly affected by the ultrasonic treatment. No chemical reactions were observed in the wood, whereas the ultrasonic treatment affected the torus of the bordered pits and facilitated the migration of extractives. In general, the higher the UIA, the stronger the effect of the cavitation was. The most significant changes in the physicochemical properties were observed at 25kHz. The instantaneous ultrasonic intensity (IUI) changed over time, and the UIA was closely associated with changes in the physicochemical properties of the wood. The results of this study demonstrate that UI has a significant influence on the physicochemical properties of wood.

Phase reconstruction of high-order harmonics by quantum path interference

SynopsisWe present a method to retrieve the phase of XUV light generated through high-order harmonic generation, by observing the intensity dependence of the interference pattern in the far-field. This interference pattern arises from electron trajectories in the generation process. These trajectories spend different time in the continuum and the phase of the generated light will therefore depend differently on the instantaneous intensity of the driving field. By changing the intensity of the driving field the phase of the contributing trajectories can be extracted.

Development and applications of schlieren system for measuring characteristics of supersonic molecular beam

Supersonic molecular beam injection (SMBI) is an effective fueling method for the magnetic fusion plasmas. The fueling method was first proposed in the HL-1 tokamak, and now has been applied to several tokamaks and stellarators. Pulsed molecular beam passes from a Laval type nozzle and has a high instantaneous intensity, high directionality and deep deposition in the plasma. The fueling efficiency is higher than the gas puffing efficiency. In addition, it is widely used for controlling plasma density and investigating plasma physics. To further improve the fueling capability in future fusion devices, it is highly desirable to optimize the characteristic of the SMB and further investigate the interactions between the molecular beam and the plasma. In this paper, a schlieren diagnostic system is developed to measure the parameters of molecular beam, and the testing application is performed. The schlieren system, which is based on the schlieren photography, is designed with the zigzag optical path and equipped on the SMBI testing platform to measure the characteristics of the supersonic molecular beam. In order to verify the effectiveness of the system, a series of tests is carried out with different nozzle shapes under atmospheric and vacuum conditions. The beam profiles of CO<sub>2</sub> and D<sub>2</sub> under different background pressures are obtained. The testing results indicate that the directionality of the integrated Laval nozzle is much better than that of the pinhole nozzle. The schlieren system provides a testing tool for optimizing the supersonic molecular beam.

Effects of different light conditions on ammonium removal in a consortium of microalgae and partial nitrifying granules

Ammonium removal by a coupling process of microalgae (Chlorella sorokiniana) with partial nitrifying granules was evaluated in batch reactors illuminated in a wide range of light intensities (0, 100, 450, and 1600 μmol photons m−2 s−1). Ammonium oxidation performance for different light exposure time showed that the granules had a light stress tolerance at 1600 μmol photons m−2 s−1 for up to 12 h, but continuous illumination induced severe inhibition on nitrifying bacteria thereafter. Ammonium removal efficiencies at the end of tests were 66%, 62%, 5%, and −10% (due to ammonification) for 0, 100, 450, and 1600 μmol photons m−2 s−1, respectively. The nitrogen mass balance shows co-occurrence of microalgal growth taking up 24% of fed ammonium and nitrifying bacteria oxidizing 38% of fed ammonium at 100 μmol photons m−2 s−1, while both nitrification and microalgal growth are inhibited at light intensity above 450 μmol photons m−2 s−1. In comparing results from this study with previous results, it was found that the ammonium removal pathway, i.e., nitrification or microalgal uptake, is regulated more strongly by daily average light intensity than by instantaneous light intensity. Empirical model equations to estimate the oxygen balance in consortium reactors categorized the effect of daily average light intensities on process performance as follows: (i) below 27 μmol photons m−2 s−1: insufficient oxygen for nitrification; (ii) 27 to 35: sufficient oxygen for nitrification via nitrite; (iii) 35 to 180: sufficient oxygen for nitrification via nitrate; (iv) above approximately 200–300: oversaturated dissolved oxygen, excess free ammonia and/or intensive light inhibitions.

Influence of cloud cover on the relationship between the sky view factor and nocturnal urban heat islands

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 79:127-137 (2019) - DOI: https://doi.org/10.3354/cr01584 Influence of cloud cover on the relationship between the sky view factor and nocturnal urban heat islands Guixin Zhang1, Guangxing Zhang2, Chuxuan Zhou3, Shanyou Zhu2,* 1School of Geography Science and 2School of Remote Sensing and Geomatics Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, PR China 3National Meteorological Center, China Meteorological Administration, Beijing 100081, PR China *Corresponding author: zsyzgx@163.com ABSTRACT: Cloud amounts, their spatial distribution, and the sky view factor (SVF) all have effects on the nocturnal upwelling longwave radiation and result in different degrees of urban-rural radiation cooling, which are widely investigated in studies of the urban heat island phenomenon. Currently, most research studies discuss the influence of synoptic conditions and urban geometric morphology on urban heat islands. Here we attempted to determine the influence of cloud cover on the relationship between the SVF and nocturnal urban heat islands by calculating the SVF considering the cloud amount and its distribution. The Adelaide central urban area of South Australia was selected as the study area, and we used urban 3-dimensional building data with a spatial resolution of 1 m and field measurement meteorological data, as well as ceilometer-observed cloud data. We sequentially analyzed the influence of cloud amount on the instantaneous nocturnal urban heat island intensity (UHII), SVF, and SVF-UHII relationship. The SVF-UHII feature space was then constructed to explain the nocturnal urban heat island. The results reveal that there are high negative correlations between the total cloud amount and UHII, while the correlations change with site location. The cloud amount has an effect on the defined SVF. SVFs at all sites gradually increase with the cloud amount, and the SVF differences between various sites decrease with increasing cloud amount. The SVF-UHII feature space can be preliminarily used to explain and simulate the UHII at some sites under different cloud cover conditions, and the mean relative error of the simulated UHII for the example data was 20%. KEY WORDS: Cloud cover · Sky view factor · Urban heat island · Feature space Full text in pdf format PreviousNextCite this article as: Zhang G, Zhang G, Zhou C, Zhu S (2019) Influence of cloud cover on the relationship between the sky view factor and nocturnal urban heat islands. Clim Res 79:127-137. https://doi.org/10.3354/cr01584 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 79, No. 2. Online publication date: December 05, 2019 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2019 Inter-Research.

Study the safeguarding performance of shear thickening gel by the mechanoluminescence method

This work reports the potential of a full-field, simple-setup and user-interactive method to study the safeguarding property of shear thickening gel (STG) by converting the invisible force/energy information to visible mechanoluminescence. Both the instantaneous intensity and force signals under impact prove the phase change of STG from viscous liquid state to rubbery state. The illumination images, presenting the energy maps, directly visualize the remarkably expanded impact area and phase change induced energy absorption, promoting the understanding of safeguarding mechanisms. The shear thickening property and viscoelastic deformation of STG significantly expand the impact area by almost 5 times, spreading and dissipating force/energy significantly. Moreover, the phase change accompanied by cracks is observed clearly, which is demonstrated to be beneficial to the energy absorption and contributes to the further enlargement of the impact area.

Observation of femtosecond infrared luminescence in gold

Femtosecond infrared luminescence in Au was observed using the upconversion technique. The instantaneous luminescence intensity for a sample with an appropriate surface roughness was three orders of magnitudes higher than that for a flat film and comparable to the hot luminescence in InAs. The time-resolved spectra from 0 to 1 ps exhibited broad features spreading from 0.3 to 1.04 eV, indicating a continuous joint density of states around the Fermi energy. In terms of a simple model that considers nonthermal and thermal carriers for describing the hot luminescence, most of the characteristic behaviors are semiquantitatively understood.

Influence of Electron Acceptor and Electron Donor on the Photophysical Properties of Carbon Dots: A Comparative Investigation at the Bulk‐State and Single‐Particle Level

AbstractCarbon dots (CDs) are extensively studied to investigate their unique optical properties such as undergoing electron transfer in different scenarios. This work presents an in‐depth investigation to study the ensemble‐averaged state/bulk state and single‐particle level photophysical properties of CDs that are passivated with electron‐accepting (CD‐A) and electron‐donating molecules (CD‐D) on their surface. The bulk‐state experiments reveal that in a mixture of these CDs, CD‐A dominates the overall photophyiscal properties and eventually leads to formation of at least two associated geometries, which is dependent on time, concentration, intramolecular electron/charge transfer, and hydrogen bonding. Single‐particle studies, however, do not reveal an “acceptor‐dominating” scenario based on analysis of instantaneous intensity, bleaching kinetics, and photoblinking, indicating that the direct interaction of these CDs may affect their photophysical properties in the bulk state due to formation of hierarchical structural assemblies. Here it is anticipated that these fundamental results will further provide insights toward the understanding of the complex mechanism associated with CD emission, which is one of the key contributors to their successful application. As an immediate application of these functional CDs, it is shown that they can be used as a sensing array for metal ions and serve as a powerful toolbox for their technological applications.

Broadband Characteristics of Chaotic Pulse Trains Associated With Sequential Dart Leaders in a Rocket‐Triggered Lightning Flash

AbstractBased on simultaneous measurements of fast E‐field change, very high frequency radiation and channel mapping, channel base current, and high‐speed video, the characteristics of chaotic pulse trains (CPTs) during propagation of dart leaders in a rocket‐triggered lightning were analyzed. The triggered lightning involved 16 subsequent leader‐return strokes traversing in the same grounding channel. At least five dart leaders showed significant CPT signals during its propagation, with much larger intensity than that in normal leader stage at broadband of low‐frequency–medium‐frequency, very high frequency, and visible light band. All CPTs occurred in the final stage of the leader development, within 150 μs prior to the return strokes. The leader velocity and the charge transfer are both related to the instantaneous intensity of CPT, but the relationship is not always solid when the two parameters are considered individually. Nevertheless, the large product of return stroke charge to 1 ms and the velocity of the leader (QV) could be a reliable proxy/indicator for CPT. All CPTs correspond to a larger local QV with a threshold higher than 1 × 107 C · m/s when CPT is determined as chaotic electric field pulses with magnitude larger than 3 std of the magnitude of E‐fluctuation waveform of the whole flash.

Advancing Opportunistic Sensing in Hydrology: A Novel Approach to Measuring Rainfall With Ordinary Surveillance Cameras

Abstract“Opportunistic sensing” represents an appealing idea for collecting unconventional data with broad spatial coverage and high resolution, but few studies have explored its feasibility in hydrology. This study develops a novel approach to measuring rainfall intensity in real‐world conditions based on videos acquired by ordinary surveillance cameras. The proposed approach employs a convex optimization algorithm to effectively decompose a rainy image into two layers: a pure rain‐streak layer and a rain‐free background layer, where the rain streaks represent the motion blur of falling raindrops. Then, it estimates the instantaneous rainfall intensity via geometrical optics and photographic analyses. We investigated the effectiveness and robustness of our approach through synthetic numerical experiments and field tests. The major findings are as follows. First, the decomposition‐based identification algorithm can effectively recognize rain streaks from complex backgrounds with many disturbances. Compared to existing algorithms that consider only the temporal changes in grayscale between frames, the new algorithm successfully prevents false identifications by considering the intrinsic visual properties of rain streaks. Second, the proposed approach demonstrates satisfactory estimation accuracy and is robust across a wide range of rainfall intensities. The proposed approach has a mean absolute percentage error of 21.8%, which is significantly lower than those of existing approaches reported in the literature even though our approach was applied to a more complicated scene acquired using a lower‐quality device. Overall, the proposed low‐cost, high‐accuracy approach to vision‐based rain gauging significantly enhances the possibility of using existing surveillance camera networks to perform opportunistic hydrology sensing.

In Situ Image Acquisition and Measurement of Microdroplets Based on Delay Triggering.

An in situ image acquisition apparatus based on delay triggering for visualizing microdroplets formation is described. The imaging system includes a charge-coupled device camera, a motion control card, a driving circuit, a time delay triggering circuit, and a light source. By adjusting the varying trigger delay time which is synchronized with respect to the signal for jetting, the steady sequential images of the droplet flying in free space can be captured real-time by the system. Several image processing steps are taken to measure the diameters and coordinates of the droplets. Also, the jetting speeds can be calculated according to the delay time interval. For glycerin/water (60:40, mass ratio), under the given conditions of the self-made pneumatically diaphragm-driven drop-on-demand inkjet apparatus, the average of diameter and volume are measured as 266.8 μm and 9944 pL, respectively, and the maximum average velocity of the microdroplets is 0.689 m/s. Finally, the imaging system is applied to measure the volume of 200 microsolder balls generated from the inkjet apparatus. The average diameter is 87.96 μm, and the relative standard deviation is 0.83%. The results show good reproducibility. Unlike previous stroboscopic techniques, the present in situ imaging system which is absence of instantaneous high intensity light employs two control signals to stimulate the microdroplet generator and the charge-coupled device (CCD) camera. Hence, the system can avoid the desynchronization problem of signals which control the strobe light-emitting diode (LED) light source and the camera in previous equipment. This technology is a reliable and cost-effective approach for capturing and measuring microdroplets.

Instantaneous Speckle Structures in a Partially Coherent Optical Wave Field with Broad Frequency and Angular Spectra

We consider the hypothesis of instantaneous volume speckle structures in a partially coherent optical wave field of frequency-broadband radiation from an extended light source. We discuss the spatiotemporal correlation properties of instantaneous speckle structures and the relation of these properties with the spatiotemporal coherent properties of the wave field. We show that the instantaneous speckle structures determine spatial fluctuations of the wave field and its spatial coherent properties. Using numerical calculations of the field of wave perturbations in the near-field diffraction region of the extended light source, we obtain images of instantaneous speckle structures in the longitudinal cross section of the wave field and investigate the correlation properties of the spatial distribution of the instantaneous intensity of the wave field in the direction of its propagation as functions of the width of the frequency spectrum and the width of the angular spectrum of the field. We show that the longitudinal length of instantaneous speckles can be determined either by the width of the frequency spectrum of the field, or the width of its angular spectrum, or, jointly, by the width of the frequency spectrum and the width of the angular spectrum of the field. We find conditions under which instantaneous speckle structures propagate, experiencing decorrelation changes during their propagation, to a distance that is determined by the width of the angular spectrum of the field.

The Role of Electron Trajectories in XUV-Initiated High-Harmonic Generation

High-harmonic generation spectroscopy is a powerful tool for ultrafast spectroscopy with intrinsic attosecond time resolution. Its major limitation—the fact that a strong infrared driving pulse is governing the entire generation process—is lifted by extreme ultraviolet (XUV)-initiated high-harmonic generation (HHG). Tunneling ionization is replaced by XUV photoionization, which decouples ionization from recollision. Here we probe the intensity dependence of XUV-initiated HHG and observe strong spectral frequency shifts of the high harmonics. We are able to tune the shift by controlling the instantaneous intensity of the infrared field. We directly access the reciprocal intensity parameter associated with the electron trajectories and identify short and long trajectories. Our findings are supported and analyzed by ab initio calculations and a semiclassical trajectory model. The ability to isolate and control long trajectories in XUV-initiated HHG increases the range of the intrinsic attosecond clock for spectroscopic applications.

Bulk-state and single-particle imaging are central to understanding carbon dot photo-physics and elucidating the effects of precursor composition and reaction temperature

Carbon dots have garnered attention for their strong multi-color luminescence properties and unprecedented biocompatibility. Despite significant progress in the recent past, a fundamental understanding of their photoluminescence and structure-properties relationships, especially at the bulk vs. single-particle level, has not been well established. Here we present a comparative study of bulk- and single-particle properties as a function of precursor composition and reaction temperature. The synthesis and characterization of multicolored inherently functionalized carbon dots were achieved from a variety of carbon sources, and at synthesis temperatures of 150 °C and 200 °C. Solvothermal synthesis at 200 °C led to quantum yields as high as 86%, smaller particle sizes, and a narrowed fluorescence emission, while synthesis at 150 °C resulted in a greater UV–visible absorbance, increase in nanoparticle stability, red-shifted fluorescence, and a greater resistance to bulk photobleaching. These results suggest the potential for synthesis temperature to be utilized as a simple tool for modulating carbon dot photophysical properties. Single-particle imaging resolved that particle brightness was determined by both the instantaneous intensity and the on-time duty cycle. Increasing the synthesis temperature caused an enhancement in blinking frequency, which led to an increase in on-time duty cycle in three out of four precursors.

Мгновенные спекл-структуры в частично когерентном оптическом волновом поле с широкими частотным и угловым спектрами

AbstractWe consider the hypothesis of instantaneous volume speckle structures in a partially coherent optical wave field of frequency-broadband radiation from an extended light source. We discuss the spatiotemporal correlation properties of instantaneous speckle structures and the relation of these properties with the spatiotemporal coherent properties of the wave field. We show that the instantaneous speckle structures determine spatial fluctuations of the wave field and its spatial coherent properties. Using numerical calculations of the field of wave perturbations in the near-field diffraction region of the extended light source, we obtain images of instantaneous speckle structures in the longitudinal cross section of the wave field and investigate the correlation properties of the spatial distribution of the instantaneous intensity of the wave field in the direction of its propagation as functions of the width of the frequency spectrum and the width of the angular spectrum of the field. We show that the longitudinal length of instantaneous speckles can be determined either by the width of the frequency spectrum of the field, or the width of its angular spectrum, or, jointly, by the width of the frequency spectrum and the width of the angular spectrum of the field. We find conditions under which instantaneous speckle structures propagate, experiencing decorrelation changes during their propagation, to a distance that is determined by the width of the angular spectrum of the field.

Fracture behavior of carbon fiber reinforced polymer composites: An optical study of loading rate effects

Crack initiation and growth in single-edge notched unidirectional T800s/3900-2 CFRP laminates are studied under stress wave and quasi-static loading conditions. An optical technique called reflection-mode Digital Gradient Sensing is also extended to study fracture mechanics of CFRP by using it in conjunction with ultrahigh-speed photography to perform full-field measurement of crack-tip deformations in the pre- and post-crack initiation regimes. DGS is capable of measuring two orthogonal surface slopes in the crack-tip vicinity as angular deflection of light rays. A method for extracting crack-tip parameters – the instantaneous crack speed and stress intensity factor (SIF) histories – associated with the stationary and propagating cracks using measured surface slopes is presented. The effect of fiber orientation in the range 0°–60° relative to the initial notch and two loading rates are investigated. Nominally mode-I fracture occurs when the fiber orientation is 0° whereas mixed-mode fractures ensue in others. Besides crack initiation occurrence at higher loads as fiber orientation increases, the SIF histories imply strong fiber bridging at low fiber orientations under quasi-static conditions. Furthermore, this CFRP shows significant loading rate dependence during crack growth. Unlike stress wave loading conditions, an increasing crack growth resistance immediately after crack initiation is seen under quasi-static conditions.

Contention Intensity Based Distributed Coordination for V2V Safety Message Broadcast

In this paper, we propose a contention intensity based distributed coordination (CIDC) scheme for safety message broadcast. By exploiting the high-frequency and periodical features of the safety message broadcast, the application-layer design of the CIDC enables each vehicle to estimate the instantaneous channel contention intensity in a fully distributed manner. With the contention intensity information, the media access control layer design of CIDC allows vehicles to adopt a better channel access strategy compared to the 802.11p. This is because CIDC selects the initial back-off counter for each new packet deterministically, i.e., based on the contention intensity, rather than randomly. The proposed CIDC is modeled, and key performance indicators in terms of the packet collision probability and average contention delay, are derived. It is shown that the proposed change in the initial counter selection leads to a system model completely different from the classic Markov chain based model. Moreover, the proposed CIDC, fully distributed and compatible with the 802.11p, can achieve both a much lower collision probability and a smaller contention delay compared with 802.11p at the cost of a small communication and computation overhead. Extensive simulation results demonstrate the effectiveness of the CIDC in both of the accurate and the erroneous contention intensity estimation scenarios.