In a word, one needs to study the light source optimization choic

In a word, one needs to study the light source optimization choice and design method combination for different detection tasks and work environments.Moreover, the small proportions of the target defects relative to the entire picture in a micrograph, uneven surface illumination for high curvature surfaces and natural metal textures all contribute to make contrast of defect regions and background regions small, and image segmentation comparatively difficult. PCNN has been widely used in every field of image processing, such as denoising [17], segmentation [18], fusion [19] and feature extraction [20], but the elementary PCNN model framework is complex, and there are multiple undetermined parameters such as attenuation constants, amplification coefficients and connect coefficients.

Most parameters are configured by artificial tests, which affect PCNN image processing speed and make it difficult to implement automatic image processing. Richard [21] used a genetic algorithm for setting optimum PCNN parameters, yet the key of genetic algorithms is the accurate setting of parameters such as variation and cross operator, which, if not set properly, will destroy the developmental stability. Particle Swarm Optimization (PSO) is an efficient search strategy [22], which features quick convergence and requires less parameter settings. Chao [23] used a PSO to search for the best parameter value of a generalized diffusion coefficient function that was used for anisotropic diffusion defect detection in low-contrast surface images.

The PSO algorithm is used to automatically set PCNN optimization key parameters by fitness function of maxima between cluster variances, which carries out automatic PCNN image processing.The paper is organized as follows: Section 2 introduces the structure of the Anacetrapib gyroscope pivot bearing dimension measurement and surface detection system; Section 3 presents task-oriented illumination system design methods; Section 4 presents self-adaptive parameter settings obtained Carfilzomib by integrating the PSO algorithm and PCNN; Section 5 describes experimental results and comparisons. Finally, some conclusions and future development are illustrated in Section 6.2.?Detection System Design2.1. System FrameworkThe shape of a gyroscope pivot bearing is shown in Figure 1.

For middle-aged and older subjects, high blood pressure is an imp

For middle-aged and older subjects, high blood pressure is an important indicator for cardiovascular selleck diseases, which are amongst the leading figure 1 cause of sudden deaths globally.Vital sign monitoring Inhibitors,Modulators,Libraries Inhibitors,Modulators,Libraries systems will, therefore, involve monitoring one or more of the following:blood glucose level;blood pressure;pulse rate;electrocardiograph (ECG) patterns;respiration rate;respiration effectiveness (e.g., blood oxygen saturation).These are discussed in more detail in the following sections.2.1. Monitoring Blood PressureTraditionally, monitoring of blood pressure is performed Inhibitors,Modulators,Libraries in a clinic with trained Inhibitors,Modulators,Libraries personnel by mounting inflatable pressure cuffs with stethoscopes to the patient��s arm��the so-called auscultatory method.

Inhibitors,Modulators,Libraries This type of measurement does not achieve continuous monitoring and the patient is required to be in a certain posture in the clinical environment, which causes the white-coat effect. The white-coat effect is known to be the falsification of BP measurements, usually with transient peaks in BP, due to the stress caused by being present in a clinical environment [4]. Inhibitors,Modulators,Libraries Current alternatives are ambulatory monitoring and home-monitoring devices, where patients can monitor their own BP.One of the common techniques used in ambulatory/home monitoring devices is the oscillometric method. Home monitoring devices generally include a fully automatic inflatable cuff which can be mounted on the patient��s wrist and measures the blood pressure of the radial artery by relating external pressure Inhibitors,Modulators,Libraries with the magnitude of arterial Inhibitors,Modulators,Libraries volume pulsations.

Although oscillometric monitoring systems are convenient to avoid the transient rise of BP due to the white-coat effect, the periodic interruptions of the blood Drug_discovery flow and continuous usage of such devices may cause unwanted side effects, such as sleep disruptions at night-time, skin irritations and an increase in stress levels Entinostat [5]. Vasotrac (Medwave Inc., Arden Hills, MN) is an example of a watch-type ambulatory non-invasive BP monitoring device [6,7]. It includes a circular sensor (this must sit on top of the radial artery in the wrist), a digital monitor and a disposable adhesive plaster to estimate the location of artery.

After collection of data, the sensor response is taken and processed by a controller unit and displayed on the digital screen. Although Vasotrac is a cuff-less device, an external pressure is required for reliable measurements. selleck screening library Vasotrac is a good alternative for infrequent ambulatory monitoring; it is, however, unsuitable for continuous monitoring.Many different methods have been used to measure BP non-invasively. For example, the ultrasonic method, introduced in 1961, relates the Doppler shift of the ultrasound response and the velocity of blood [8].

A weighting scheme is proposed to re-scale the distance

A weighting scheme is proposed to re-scale the distance selleck chem Y-27632 between two data points and thus the classification accuracy could be improved. Another solution for analysis of odor mixture is to directly determine the concentration of each component present in the examined mixture by analyzing the response pattern. Regression such methods are applied Inhibitors,Modulators,Libraries in this paper to build odor models. The component concentrations are estimated by solving Inhibitors,Modulators,Libraries a weighted and constrained least-squares problem, in which each of the squared error term is weighted to reflect the reliability of each estimated sensor response.The rest of this paper is organized as follows: Firstly, the proposed methods for analyzing mixed odors will be described in Section 2.

Then, the data collection methods and experimental results will be provided to evaluate and support the proposed methods in Section 3.

Finally, Section 4 will conclude the contribution Inhibitors,Modulators,Libraries of this work.2.?The Proposed Analysis MethodsTraditionally, an electronic nose is Inhibitors,Modulators,Libraries not designed to analyze mixed odors but merely to differentiate between different smells. This paper proposes to determine the components that are most significant in a mixture by analyzing the sensor response pattern Inhibitors,Modulators,Libraries of the odor mixture. This work is based on the following two assumptions [13�C15]:? Homogeneity: The sensor response to an odor is proportional to the odor concentration.? Linear Additive: The sensor response to a mixture is equal to the linear summation of the sensor response to each of its Batimastat components.

Based on the assumption of homogeneity, the normalized Inhibitors,Modulators,Libraries Inhibitors,Modulators,Libraries mixed odor dataset could be categorized according to the contained components without considering the concentration of each component. For example, the categorization results for odors of three components would be like the one shown in Figure 1. The response pattern inhibitor Regorafenib of the examined odor would then be classified to one of the predefined classes by using a classification method. However, the sensors may not provide enough useful information sufficient enough to classify an odor. A method of dimensionality reduction, such as PCA and LDA, can then be applied to select the significant features to achieve a better result of data partition.

However, both Inhibitors,Modulators,Libraries PCA and LDA require solving a complex matrix eigenvalue problem in order to find the projection directions. AV-951 In this paper, a simple local weighting scheme is proposed to properly weight each feature for a class.Figure 1.A schematic plot of the normalized data set of mixed odors consists of three odor components: table 1 A, B and C. The data points are partitioned into seven component sets according to the contained odor components: A, B, C, AB, BC, CA, and ABC.2.1. Locally Weighted Nearest Neighbor (LWNN)Assume that there are N predefined classes.

The triggering of the earthquake is sometimes initiated by the ch

The triggering of the earthquake is sometimes initiated by the change in the magnetic field in Sun-Earth environment which influences the faulting further. Before the occurrence of this severe earthquake a bright aurora selleck inhibitor was seen in the sky of Japan. It is possible to correlate better the triggering of the active fault in the Honshu area of Japan with the sudden change in the magnetic Inhibitors,Modulators,Libraries shield Inhibitors,Modulators,Libraries of the earth due to the impact of CME from Sun. The effect of earth directed CME would not only trigger the earthquake, but affect the w
The GRaphical Electromagnetic COmputing SAR (GRECOSAR) simulation tool has been developed at UPC [1, 2].

The possibility to process Inhibitors,Modulators,Libraries any complex geometry within flexible and Inhibitors,Modulators,Libraries totally controlled scenarios has provided a new benchmark for carrying out a set of SAR research activities that are difficult to be done with real data.

Examples are exhaustive scattering studies where the Inhibitors,Modulators,Libraries dispersion behavior of targets is evaluated for the widest range of observation conditions possible or performance tests where current and/or new sensor designs are evaluated according to particular specifications.GRECOSAR has been designed to deal Inhibitors,Modulators,Libraries with any type of SAR sensor operating at any band, resolution and mode with polarimetric and interferometric capabilities. Its processing efficiency is high and only needs from a simple PC to process realistic and highly detailed 3D models. Up to now, two main types of scenarios with dielectric materials can be managed: maritime and urban.

The former is very realistic as ship motions, bearing and velocity are considered as well as a surrounding dynamic sea.

GRECOSAR has been mainly used for scattering studies of complex targets. Most of the efforts have been focused to ships for which few information about their dispersion characteristics was available. This is essential Inhibitors,Modulators,Libraries for developing more efficient scattering-based classification methods that can fulfill the new monitoring demands for SAR imagery (see IMPAST [3] and DECLIMS Inhibitors,Modulators,Libraries [4] projects). In this framework, a large number of polarimetric scattering maps with resolutions around centimeters have been generated for different ship geometries and environmental parameters.

Their analysis with Coherent Target Decompositions (CTD) [5, 6] have revealed certain dispersion stability Anacetrapib along the radar aspect angle.

The cause is the presence of Permanent Polarimetric Scatterers (PePS) that have a high Radar Cross Section (RCS) and Batimastat a well-defined scattering pattern, which remains constant within a large solid angle [7, 8]. The spatial and polarimetric selleck chemical Idelalisib distribution of PePS has appeared to be particular for each vessel model, characterizing its macro-scale features. This has allowed the definition of a feature set from which a new quantitative manner for ship discrimination is possible [7].

The static weighing of

The static weighing of AMN-107 vehicles in highways has several disadvantages, including being time consuming, expensive, and dangerous on heavily travelled roads.The concept of Weigh-In-Motion (WIM) was introduced more selleck chemical than fifty years ago [1]. WIM is the process by which the static weights of vehicles are determined by measuring wheel Inhibitors,Modulators,Libraries load while the vehicles are in motion. There are several advantages of weighing vehicles while they are in motion rather than at rest [2], which include savings in time and cost, and being safer to operate on busy roads.Traditional highway WIM systems tended to use weighing devices set in Inhibitors,Modulators,Libraries the road in one lane [3]. Many such systems Inhibitors,Modulators,Libraries are still in use, including some developed in recent years.

Wear and tear is severe, often resulting in a short lifespan.

Unless the approach pavement is particularly Inhibitors,Modulators,Libraries smooth, these systems Inhibitors,Modulators,Libraries are often inaccurate because the devices are subject to large load fluctuations depending on vehicle speed, vehicle suspension characteristics and road roughness [4]. Inhibitors,Modulators,Libraries Many new technologies such as Multi-sensor WIM [7], Fiber-optic WIM [8-10] and Capacitive sensor WIM [11] were developed for improving accuracy and longer lifespan. Unfortunately, although the current WIM technologies offer many advantages, they still suffer from high installation and maintenance costs and low accuracy. Bridge-WIM [5-6, 20-21] could supply vehicle weight data rapidly and at a low cost, but it is hard to obtain separate axle weights as the bridge is under stress from the moment the vehicle enters the span.

A novel sensor system is proposed for measuring wheel loads of vehicles on highways.

The proposed approach Inhibitors,Modulators,Libraries is based on the concept of monitoring strain response in the surface of rigid pavement affected by the moving vehicular loads. Multiple embedded Inhibitors,Modulators,Libraries concrete strain sensors are deployed in a freeway lane to directly measure the dynamic strain response of the pavement. The strain response is related to the instantaneous, dynamic wheel load on the pavement Carfilzomib by the passage of vehicles in the vicinity of the strain sensor. The measurements can be processed to filter out noise and extract important features of the dynamic load.

Batimastat The relation between pavement response and the dynamic load can be obtained through calibration using a known wheel load vehicle.

The article is organized by the following selleck chemical Cabozantinib parts: Section 1 �C Introduction; Section 2 �C Description of the measurement method; Section LCL161? 3 �C Experimental test bench; Section 4 �C Experimental results and analysis; Section 5 �C Conclusion.2.?Description of the methodologyCurrent WIM systems are mainly based on three types of sensors: bending plate, piezoelectric and single load cells. All three sensors must be located in the path of the vehicle. The sensors register the vertical dynamic tire forces provided by the passing vehicles.

Autologistic regression modeling has been already introduced in r

Autologistic regression modeling has been already introduced in remote sensing studies as a classification approach of satellite together data, however it has been limited to binary classification selleck chemicals schemes as for instance in flood zonation and burned land Inhibitors,Modulators,Libraries mapping [26, 27]. Finally, the ML classified image was upgraded to contextual by considering typicality, a measure which indicates the strength of class membership [28].2.?Study AreaThe study area is located in the uppermost part of the Kassandra Peninsula in NC Greece (Figure 1). Although each place is unique, depending on how environmental parameters Inhibitors,Modulators,Libraries and human actions are spatially integrated, our study area seems to be characteristic and representative of many landscape types found across Greece.

The fragmented landscape consists of small patches of forested land, interchanged Inhibitors,Modulators,Libraries with agriculture and rangelands. The forested land mainly consists of Aleppo Inhibitors,Modulators,Libraries pine (Pinus halepensis) and dense shrubs (maquis), Inhibitors,Modulators,Libraries the latter which occasionally dominate the overstory within the Inhibitors,Modulators,Libraries stands. In these ecosystems, the main species present in the understory are Quercus conferta, Quercus ilex and Pistacia lentiscus. As in the majority of Mediterranean forests, the landscape is quite heterogeneous with regards to stand structure and composition.Figure 1.Location of the study area and colour composite (RGB: TM-743) of the Landsat TM image used in the study.

The study area belongs to the Mediterranean type climate and the bioclimate is characterized as semi-arid with severe summer droughts and relatively high humidity throughout the year.

The study area is subject to strong human influence and high tourist pressure Inhibitors,Modulators,Libraries which justifies the fragmented character of the landscape. The relief Inhibitors,Modulators,Libraries of the area is rather gentle with mild slopes resulting in non-severe topographic shading.3.?Materials and Methods3.1. Image Data PreprocessingA Landsat-5 Thematic Mapper image Dacomitinib (path 184; row 032) was acquired on 11 May 1997. Haze removal was applied to the LANDSAT TM image by subtracting the amount by which each band’s histogram is shifted from the origin due to atmospheric scattering. Following this dark pixel subtraction approach, the minimum value of each spectral channel was subtracted from each pixel brightness in that channel [29].

The Landsat TM image was orthorectified using 54 ground control points identified on 1:5,000 scale orthophotographs produced from a 1996-1997 national aerial photography campaign and a digital elevation model constructed from contour lines of 20 m increment. Orthorectification ensured that spatial inaccuracies caused by the irregular terrain would be Site URL List sellectchem 1|]# minimized. The total root mean square error (RMS error) was about 0.6 of a pixel.3.2. Data analysis3.2.1. Classification SchemeInitially, six informational classes (Table 1) were identified after a field survey and photo interpretation of the orthophotographs.

The method employed to extract features from the sensor

The method employed to extract features from the sensor JQ1 molecular weight transients is based on the discrete wavelet transform [8, 12] and the pattern recognition makes use of simple support vector machine algorithms [13-16].2.?Experimental2.1. Set-upTo achieve a flow-modulation capable sniffer, a closed loop system was designed which was based on a PC-controlled peristaltic selleck chemicals Pazopanib Inhibitors,Modulators,Libraries pump and two three-way electro valves. Figure 1 shows the configuration devised. The stainless-steel sensor chamber housed three commercially-available Taguchi 8-series sensors (i.e. TGS-800,822 and 826). The Inhibitors,Modulators,Libraries system had two operating modes (cleaning phase and measurement phase). In the cleaning configuration, pure dry air enters the system through the first electro valve and cleans the peristaltic pump, the sensor chamber and the evaporation chamber.

Solid arrows in Figure 1 mark the flow of clean air in this mode. In the measurement mode, air re-circulates Inhibitors,Modulators,Libraries in the closed circuit indicated by dashed arrows in Inhibitors,Modulators,Libraries Figure 1. Initially, Inhibitors,Modulators,Libraries the flow is kept constant at 250 sccm and a calculated quantity of a given pollutant in the liquid phase is sprayed into the evaporation chamber using a chromatographic syringe (since temperature, Inhibitors,Modulators,Libraries pressure and system volume were known, the volume of liquid to be injected could be calculated with the ideal gas theory [11]). This allows for obtaining the steady-state response of the sensors. Then, a square-wave flow modulation at a given frequency is initiated, which allows for measuring the transient response of the sensors.

Inhibitors,Modulators,Libraries The system can generate other types of waveforms such as sinusoids or sawtooth functions, although they have not been used in this study.Figure 1.Experimental set-up during flow modulation Inhibitors,Modulators,Libraries experiments.A microcontroller commands Batimastat the speed of the peristaltic pump, which directly translates into different flow rates. A PC programmed with a in-house-written program communicates with the microcontroller so that the user can select the flow rate and the frequency and type of waveform that is applied to modulate the flow. Via this program, the PC commands the microcontroller to open or close the electro valves and to change the configuration of the system depending upon AV-951 the operating phase.

Moreover, the PC records the sensor response (i.e. sensor conductivity) at the rate of 2 samples per second.Figure selleck compound 2 shows that after a few modulation periods (e.

g. 2) the transient pattern of the sensors becomes highly selleck chemicals Tofacitinib reproducible. In practice, a measurement would take 2 periods of the modulation frequency to complete.Figure 2.Dynamic response of three sensors. The flow modulation is applied from 550 s onwards.Additionally, a temperature sensor was located inside the sensor chamber (placed perpendicular to the flow and between the chamber inlet and the gas sensors) so the effect of flow modulation in the temperature of the chamber (and hence in the operating temperature of the sensors) could be estimated.

Sea-based sources are discharges coming from ships

Sea-based sources are discharges coming from ships inhibitor Veliparib or offshore platforms. Oil pollution from sea-based sources can be accidental or deliberate. Fortunately, the number of marine accidents and the volume of oil released accidentally are on the decline. On the other side, routine Inhibitors,Modulators,Libraries tanker operations can lead still to the release of oily ballast water and tank washing residues. Furthermore, fuel oil sludge, Regorafenib chemical structure engine room wastes and foul bilge water produced by all type of ships, also end up in the sea. In the last decade maritime transportation has been growing Inhibitors,Modulators,Libraries steadily. More ships also increase the potential number of illegal oil discharges. Both oil tankers and other kinds of ships are among the suspected offenders of illegal discharges.

The different tools to detect and monitor oil spills are vessels, airplanes, and satellites.

Vessels, especially if equipped with specialised radars, can detect oil at sea but they can cover a very limited area. The vessel, however, remains necessary in case oil sampling is required. The main systems to monitor sea-based oil pollution are the use of airplanes and satellites Inhibitors,Modulators,Libraries equipped with Synthetic Inhibitors,Modulators,Libraries Aperture Radar (SAR). SAR is an active microwave sensor, which Inhibitors,Modulators,Libraries captures two dimensional images. The brightness of the captured image is a reflection of the properties of the target-surface. The possibility of detecting an oil spill in a SAR image relies on the fact that the oil film decreases the backscattering of the sea surface resulting in a dark formation that contrasts with the brightness of the surrounding spill-free sea.

Spaceborne SAR sensors are extensively used for the detection of oil spills in the marine environment, as they are independent from sun light, they are not Inhibitors,Modulators,Libraries affected Inhibitors,Modulators,Libraries by cloudiness, they cover large areas and are more cost-effective GSK-3 than air patrolling.Radar backscatter values from oil spills are very Inhibitors,Modulators,Libraries similar to backscatter values from very calm sea areas and other ocean phenomena named ��look-alikes�� (e.g. currents, eddies). Figure 1 presents an example of a verified oil spill and a verified look-alike on a SAR image. Several studies aiming at oil spill detection have been conducted.

The first comprehensive publications on the subject [1-5] concerned methodologies to distinguish oil spills from look-alikes. Solberg et al. [1] presented an automatic statistical approach while Del Frate et al.

17-DMAG fda [2] used a neural network classifier. Espedal and Wahl [3] used wind Carfilzomib history information to detect oil spills, Espedal et al. [4] focused on detection near offshore platforms and Fiscella et al. [5] used a probabilistic approach for detection and discrimination. The first reconnaissance study for the Mediterranean Sea using more that 1600 SAR images was given by Pavlakis et al. [6]. The second wave of interest on the subject came some years later, with new techniques and methodologies [7-14]. De Souza meantime et al. [7] presented and intelligent system to extract features from oil slicks, Keramitsoglou et al.

In this paper, we used LC as the solvent which was mixed with 3 w

In this paper, we used LC as the solvent which was mixed with 3 wt% of the spiropyran powder. The alignment of the nematic LC (Merck E7) possessed a long-range order and its molecular shape was rod-like. The molecular shape of the doped spiropyran in the liquid crystal was also rod-like in shape. The relationship between spiropyran at small concentrations selleck chemicals and the LC are similar to a guest-host relationship. Therefore, the doped spiropyran possessed order alignment due to the anchoring force of the liquid crystal. By incorporating a nematic LC lamina to enable the SP to retain a long-range order, the electrical properties were enhanced in a nematic orientation tailored to ion transportation [15].Figure 1.Scheme of the electrode of traditional mode 1 sensor with specific pattern employed for an one-dimensional cantilever beam.

Scheme 1 shows that the spiropyran can be transformed into Inhibitors,Modulators,Libraries a merocyanine (MC) state under UV irradiation, and it also can be reversed to a SP state by irradiating with visible light or by heating.Scheme 1.Spiropyran transformed into a MC state by UV irradiation and reversed by visible light or by heating.In Scheme 1, we can see clearly that the molecular structure of the SP and MC were both rod-like in shape. Figure 2 shows the electrical properties of the LC/SP lamina measured using an impedance analyzer (Agilent 4294A). In our work, the cell was made for measuring the impedance of the LC/SP lamina.Figure 2.Electric properties of the LC/SP employed to replace the traditional electrode for modal sensor applications: (a) impedance and (b) phase measurements of the LC/SP under treatment of shading and UV irradiation using an impedance analyzer (Agilent 4294A).

…We used a polyethylene terephthalate (PET) film coated with indium Inhibitors,Modulators,Libraries tin oxide (ITO) to enclose the LC/SP lamina Inhibitors,Modulators,Libraries (Figure 3). Rubbing the ITO surface using a velvet cloth completed the rubbing requirement to align the liquid crystal. The thickness of the PET and ITO were 188 ��m and 200 nm, respectively. An adhesive containing appropriate spacers (e.g., 20 ��m) was Inhibitors,Modulators,Libraries applied between the two PET+ITO plates. The LC/SP mixture was then siphoned into the cell formed by the PET/ITO plates through capillary action.Figure 3.(a) Scheme of the cell structure composed of 200nm ITO and 20��m spacer when the LC/SP mixture was injected into the cell.

(b) Cell schematic GSK-3 when sample is irradiated by UV and where the electric properties of the LC/SP mixture are measured using …It is clear from Figure 2(a) that the impedance of this LC/SP lamina decreased after UV irradiation. The ratio of the impedance variation represents the ratio between the impedance after and before the UV irradiation. The minimum impedance variation cisplatin mechanism of action ratio was 0.29. The LC/SP mixture underwent 5 minutes of UV irradiation.

1) Further, it might be pointed out that a multi-hop scenario ma

1). Further, it might be pointed out that a multi-hop scenario may thenthereby be too energy-hungry for some specific Inhibitors,Modulators,Libraries body sensors (e.g., the ones close to the care unit) and thus jeopardize their own medical data transmissions. It is therefore assumed that the single-hop star-based topology is the most energy-efficient, because this does not put body sensor��s own medical data transmission at risk, avoiding unnecessary battery replacements.Figure 1.A star-based BSN in a potential medical scenario.In a IEEE 802.15.4 star-based BSN, the beacon-enabled mode appears to allow for the greatest energy efficiency. Indeed, it allows the transceiver to be completely switched off up to 15/16 of the time when nothing is transmitted/received, while still allowing the transceiver to be associated to the network and able to transmit or receive a packet at any time [2].

The beacon mode introduces Inhibitors,Modulators,Libraries the so-called superframe structure (Figure 2).Figure 2.IEEE 802.15.4 MAC superframe structure in beacon-enabled mode (active).As previously mentioned, the superframe structure starts with the beacon, which is a small synchronization packet sent by the BAN coordinator, carrying service information for the BSN maintenance and notifying body sensors about pending data in the downlink. The inter-beacon period is partially or entirely occupied by the superframe, divided into 16 slots. The number of slots at the tail of the superframe may be used as GTS, i.e., they can be dedicated to specific body sensors with no contention (see Figure 2, CFP). This functionality targets very low latency applications, but does not scale properly to highly dense BSNs (i.

e., saturation conditions), since the number of dedicated Inhibitors,Modulators,Libraries Inhibitors,Modulators,Libraries slots would not be sufficient to accommodate more than seven body sensors at a time. In such conditions, it is better to use the contention access mode, where the sparse data is statistically multiplexed. Batimastat In the contention access period, distributed channel accesses in the uplink are coordinated by a slotted CSMA/CA mechanism, while indirect transmission is used in the downlink. As we will see later, the CSMA/CA mechanism has a significant impact on the overall energy and performance of the uplink. According to the slotted CSMA/CA algorithm in [2], a node must sense the channel free at least twice before being able to transmit, this corresponds to the decrement of the so-called contention windows.

The first sense must be delayed by a random delay chosen between 0 and 2BE�C1, where BE is the back-off exponent. This randomness serves to reduce the probability of collision when two nodes simultaneously sense the channel, assess it free and decide to transmit at the same time. When the channel is selleck sensed busy, transmission may not occur and the next channel sense is scheduled after a new random delay computed with an incremented back-off exponent.