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The Genetic Algorithm-Extreme Learning Machine (GA-ELM) neural network algorithm is proposed to model the relevant characteristics of GaN pseudomorphic high electron mobility transistor (P-HEMT) large signal. This algorithm solves the over-fitting problem of the Back Propagation (BP) neural network algorithm in the prediction data. It has the characteristics of fast calculation speed, so it can greatly save calculation processing time. It can also randomly generate the connection weights of the input layer, the hidden layer and the threshold of the hidden layer neurons, avoiding errors in parameter selection. In order to verify the superiority of the algorithm, the modeling effects of the BP neural network algorithm model, the Genetic Algorithm-Back Propagation (GA-BP) neural network algorithm model and the GA-ELM neural network algorithm model are compared in this paper. The results show that the proposed GA-ELM neural network algorithm model has the highest accuracy.

Purpose High-speed Indium Phosphide (InP) HBTs have been widely used to design high-speed analog, digital and mixed-signal integrated circuits. The purpose of this study is to propose a new parameter extraction procedure for determining an improved T-topology small-signal equivalent circuit of InP heterojunction bipolar transistors (HBTs). Design/methodology/approach The alternating current crowding effect is considered through adding the intrinsic base capacitance in the small-signal equivalent circuit. All of the circuit parameters are extracted directly without using any approximation. Findings The extraction technique is more easily understood and clearer than other extraction methods, as the equations are derived from the S-parameters by peeling peripheral elements from small-signal models to get reduced ones and extracting each equivalent-circuit parameter using each equation. Originality/value To validate the presented parameter extraction technology, an n-p-n emitter-up InP HBT was analyzed adopting the method. Excellent agreement between measured and modeled S-parameters is obtained up to 40 GHz.

In the application of classical graph theory, there always are various indeterministic factors. This study studies the indeterministic factors in the connected graph by employing the uncertainty theory. First, this study puts forward two concepts: generalized uncertain graph and its connectivity index. Second, it presents a new algorithm to compute the connectivity index of an uncertain graph and generalized uncertain graph and verify this algorithm with typical examples. In addition, it proposes the definition and algorithm of α -connectivity index of generalized uncertain graph and verifies the stability and efficiency of this new algorithm by employing numerical experiments.

Uncertain differential equations are important mathematical models in uncertain environments. This paper investigates uncertain multi-dimensional and multiple-factor differential equations. First, the solvability of the equations is analyzed. The α-path distributions and expected values of solutions are given. Then, structure preserving uncertain differential equations, uncertain Hamiltonian systems driven by Liu processes, which possess a kind of uncertain symplectic structures, are presented. A symplectic scheme with six-order accuracy and a Yao-Chen algorithm are applied to design an algorithm to solve uncertain Hamiltonian systems. At last, numerical experiments are given to investigate four uncertain Hamiltonian systems, which highlight the efficiency of our algorithm.

an improved small-signal model for the GaN pseudomorphic high electron mobility transistor (P-HEMT) process is proposed in this paper. Experimental studies have found that a high positive bias voltage usually damages or destroys the Schottky grid. In order to solve this problem, a method of extracting parasitic inductance and parasitic resistance using low gate bias voltage technology is proposed. Experimental research found that the parasitic circuit parameters will change with the bias voltage. New intrinsic resistance (RL) and intrinsic inductance (Lds) are introduced into the intrinsic equivalent circuit to suppress its bias dependence to solve this problem. At the same time, it is found that there is a time delay phenomenon in the parasitic parameter model, so the RC network (Rpds and Cpds, Rpgd and Cpgd) is introduced to represent this phenomenon. It is successfully applied to model a GaN P-HEMT. Excellent agreement between measured and modeled S-parameters is obtained from 0.5 to 20.5 GHz.

A new direct parameter-extraction technique applied to the small-signal equivalent circuit of heterojunction bipolar transistor (HBT) is presented. The method is based on first determining the parasitic elements and then the intrinsic elements analytically. Concerning the intrinsic parameters, all the elements are extracted using exact closed-form equations derived in terms of S-parameters by reducing the small-signal models to the simplified using peeling algorithm. The validity of the new extraction methodology is demonstrated by applying it to a 1 × 15 µm2 InP HBT device within the frequency range of 0.1---40 GHz.

In this paper, the study of a Ka-band GaAs HBT VCO is reported with particular emphasis on achieving low-phase noise while using direct coupled varactor. A push–push cross-coupled VCO configuration is employed to achieve high oscillation frequency and low-phase noise. The measured oscillation bandwidth spans from 30.2 to 28.6[Formula: see text]GHz with a tuning range of 1.6[Formula: see text]GHz, while the phase noise at 1[Formula: see text]MHz of frequency offset from the carrier at 29.3[Formula: see text]GHz is [Formula: see text][Formula: see text]dBc/Hz. The VCO consumes 28.2[Formula: see text]mW from 3[Formula: see text]V supply and occupies an area of [Formula: see text][Formula: see text]mm. The FOM of the VCO achieves [Formula: see text][Formula: see text]dBc/Hz.

The static polarization wind imaging interferometer (SPWII) is a device used to measure wind velocity and temperature of the upper atmosphere. In this paper, the principle of SPWII is expounded. Using the four-side pyramid prism and polarizer array, four intensity interferograms of different phase differences form on the four subareas of the CCD which is located at the focal plane of the imaging lens. The wind velocity and temperature can be derived from the interferograms. Using the approximation and the antitheses, we analyze the influences of the wavelength bandwidth on the measured wind velocity and atmospheric temperature. According to the design requirements of the SPWII, the errors of the wind velocity and the atmospheric temperature are less than 5 m/s and 5 K when the incident wavelength bandwidth is in the range of [−3.08, 3.08] nm. The range is estimated and verified by simulations. These results are helpful for the realization and data processing of the SPWII.

Tetrapod zinc oxide (T-ZnO), being a kind of nano-material, has large specific surface area and surface binding energy, which will make it sensitive to the ambient gas condition. So the field emission properties will be influenced by the gas adsorption when being applied as the cathode materials of field emission devices. Carbon monoxide is the main residual gas in T-ZnO field emission devices. In this paper, carbon monoxide was introduced into a field emission device with T-ZnO emitters. The field emission currents of tetrapod ZnO were compared before and after exposure to CO.

To study the mechanism of current degradation of a cold cathode, the outgassing measurement of a field emission diode with tetrapod zinc oxide (ZnO) cathode has been taken with a quadrupole mass spectrometer (QMS) in an ultra-high vacuum (UHV) system. It was found that the H2, CO2, CO, and CH4 were outgassed from the diode during the working process. The partial pressure of outgassing increases with the increased emission current density. The field emission properties of the cold cathode, such as turn-on field, threshold field and the emission current density, were largely related to the pressure of the outgases. From the outgassing experimental results, the relation between the emission current degradation and the outgassing of field emission devices has been found. Due to the outgassing, the work function of ZnO cold cathode increases, while the field enhancement factor decreases. Therefore, the outgassing plays very important role in the current degradation for the field emission devices (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Copyright @ 2008 American Vacuum Society / American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Vacuum Science and Technology Part A: International Journal Devoted to Vacuum, Surfaces, and Films, 26(2), Article number 239 and may be found at http://scitation.aip.org/content/avs/journal/jvsta/26/2/10.1116/1.2827512. The design of a micro chamberquadrupolemass spectrometer (MCQMS) having a small total volume of only 20 cm3, including Faraday cup ion detector and ion source, is described. This MCQMS can resist a vacuum baking temperature of 400–500 °C. The quadrupole elements with a hyperbolic surface are made of a ceramic material and coated with a thin metal layer. The quadrupole mass filter has a field radius of 3 mm and a length of 100 mm. Prototypes of this new MCQMS can detect a minimum partial pressure of 10−8 Pa, have a peak width of ΔM=1 at 10% peak height from mass number 1 to 60, and show an excellent long-term stability. The new MCQMS is intended to be used in residual gas analyses of electron devices during a mutual pumping and baking process. National Key Basic Research Program, the Chinese 111 Project Grant and Program for New Century Excellent Talents in University.

Printable carbon nanotubes field emission displays with shadow mask (Shadow Mask CNT-FED) is suggested. A layer of insulator is screen printed on the upper surface of shadow mask, and address electrodes are fabricated on it. MgO film is deposited on shadow mask by electron beam evaporation. Secondary emission electrons escape from MgO film under the bombardment of primary electrons. In the simulation, 93% of the landing electrons are found to be secondary emission electrons. The modulating amplitude of the voltage on the address electrodes is low (∼ 250 V) because of the low-energy secondary emission electrons. The comparable results are also got from the experiments. The modulating amplitude of the voltage is found to increase with the thickness of the insulator. The optimized thickness (40 ∼ 50 μm) and the fabrication process of the insulator are suggested in this research report.

The functional mitochondrial protein alternative oxidase (AOX) gene was used as a marker to analyse the phylogenetic relationship betweenCryptosporidiumisolates. This gene was characterized, and the phylogentic tree was established fromCryptosporidiumisolates and compared to those generated from 18S rRNA and heat-shock protein 70 (HSP70) gene sequences. The present trial aimed at finding out whether the AOX gene is suitable for phylogenetic analysis of theCryptosporidiumgenus. The results revealed that the genusCryptosporidiumcontained the phylogenetically distinct speciesC. parvum,C. hominis,C. suisandC. baileyi, which were consistent with the biological characterization and host specificity reported earlier.Cryptosporidiumspecies formed two clades: one includedC. hominis,C. suis,C. parvumcattle genotypes andC. parvummouse genotype; and the other comprisedC. meleagridisandC. baileyiisolates. WithinC. parvum, both the mouse genotype and the pig genotype I (also known asC. suis) isolates differed from cattle and human (also known asC. hominis) genotypes, based on the aligned nucleotide sequences. The sequence identity of the AOX gene was higher betweenC. meleagridisandC. baileyithan betweenC. meleagridisandC. parvum. The phylogenetic trees showed thatC. meleagridiswas closer toC. baileyithan toC. parvum. This result was inconsistent with the phylogenetic analysis deduced from 18S rRNA and HSP70 gene sequences, respectively. The present results suggest that the AOX gene is not only equally suitable for the phylogenetic analysis ofCryptosporidium, but also provides an outstanding and new approach in determiningCryptosporidiumheredity.

Field emitters of vertical carbon fibers on a silicon substrate are fabricated by catalytic chemical vapor deposition. After an ageing process of 150 min, field emission measurement of the fibers is carried out in a vacuum chamber with a base pressure of 5.0 × 10−4 Pa. The experimental results display that field emission performance of the carbon fibers depends strongly on the vacuum level during the experiments. After the field emission measurement, damage to the carbon fiber field emitters is observed from the scanning electron microscopic images.

A Static Polarizing Atmospheric Michelson Interferometer (SPAMI) system for multiple emission lines is reviewed. It changes the Optical Path Difference (OPD) by Polarization Array (PA) at one time, instead of rotating the polarizer by four times in traditional polarizing Michelson interferometer. This allows the NPAMI system to make simultaneous measurements. PA is a key element cemented by four polarizers with different polarization orientations in the SPAMI system. In practice, assembly error is brought to the polarization array unexpected. It is proved that the temperature and wind velocity measurements are highly depended on the polarization orientations of polarizers in PA. In this paper, the effect of deflection of polarization orientation on temperature and wind velocity are analyzed and discussed. Moreover, a proper approach is proposed to improve the accuracy of alignment.

The basic principle of the static polarization wind imaging interferometer (SPWII) is expounded in this paper. By using trigonometric function and complex amplitude methods, the complex vibration amplitude of each polarization device with deviation from its ideal direction is calculated. The variations of the fringe visibility and optical throughput with deviation angles are given analytically and simulated numerically. According to the design parameters of the SPWII, the air-equivalent length L is equal to 16.14 cm and the total transmissivity is greater than 0.4. When the polarization directions of each polarization device are all in the ideal directions, the total optical throughput can be maintained at about 16.4% of the incident optical intensity. When the polarization directions of each polarization device are all 2° deviated from the ideal positions, the total optical throughput is decreased by 0.08%. This work would be useful for the realization and data processing of the SPWII.

In this paper, a fully integrated Ku-band voltage controlled oscillator (VCO) with low phase noise is presented in a GaAs heterojunction bipolar transistor (HBT) technology. A cross-coupled configuration is employed to achieve low phase noise, and to achieve high output power, the largest HBT and higher bias current are adopted. The implemented VCO demonstrates that the oscillation frequency is from 13.77[Formula: see text]GHz to 14.8[Formula: see text]GHz, with a maximum 4.83[Formula: see text]dBm output power at 13.77[Formula: see text]GHz. The phase noise of the VCO is [Formula: see text]100.2[Formula: see text]dBc/Hz at 1[Formula: see text]MHz offset from 14.36[Formula: see text]GHz oscillation frequency. The VCO consumes 61.2[Formula: see text]mW from 6[Formula: see text]V supply and occupies an area of 0.51[Formula: see text]mm[Formula: see text][Formula: see text]mm. Finally, the figure-of-merits (FOMs) for VCOs are discussed.

Image quality is one of the decisive factors for consumers when buying electronic display. White point is an important aspect affecting image quality evaluation. The paper investigated the preferred white-point setting for natural images considering content dependency. Images were generated by changing white-point from original image to different extent via image processing. The averaged preferred white point setting is close to previous research. In addition, the preferred white point settings are also investigated for desaturated images and blurred ones. The preferred white point for desaturated images is a little yellowish compared with those for original images. However, the preferred white point is not changed statistically when images are blurred.

Data fusion is meanly used in data integration and data processing. In this paper, an object-oriented algorithm of data fusion is presented. Firstly, neural network theory was employed in the identification and location fixing of target in a certain area at discrete time. Then an experimental model was setup. In the given model, adaptive resonance theory of neural network was adopted and a double-layer self-organized neural network was established. This provided a new method to implement neural network using data fusion algorithm.

Zinc oxide is a wide band gap semiconductor (WBGS). Its band bending, which usually favors field emission by lowering surface barrier and bringing more electrons to the bottom of conduction band, can be quite dramatic under high field. In the last few years, different kinds of ZnO nano-materials has been synthesized and applied as the cathode materials for field emission. For better application of ZnO in commercial field emission devices, long-term current stability is one of the most important aspects to be ensured. So in this paper, the field emission behavior of screen printing tetrapod ZnO will be studied by exposing to CO, which is the main residual gas in sealed tetrapod ZnO (T-ZnO) field emission device.

In order to study whether the ambient gases affect the emission current stability of the cathode, the cathode should be the same one. In addition, the working condition should be kept constant except the ambient gas condition, so that other factors, which may also lead to the emission current degradation of the cathode, can be avoided. Only the influence from the residual gases will be concerned. For this consideration, an experimental system was set up, as shown in Fig. 1. It consisted of a vacuum system with a quadrupole mass spectrometer (QMS) and FE device opening set to introduce the residual gases inside the FE device into the analysis system.

Plasmon coupling of dimers of Ag nanoparticles is studied by the EELS as shown in Fig 1a [1]. The spectroscopic images in the above Fig. 1a are extracted from 2.8eV, 3.4eV and 3.6eV respectively, where one can see the preferable exciting points of the features around the Ag nanoparticles. With the aid of DDA calculation(Fig. 1b), the three features are identified as the in-phase plasmon coupling, non-coupling and anti-phase coupling modes. The in-phase mode is able to conduct the light transportation due to its dipolar nature, which redshifts from the 3.4eV at large spacings to 2.7eV near touching (Fig. 1c). Such behaviour is also observed in the chain of 3 and 4 nanoparticles. The experiment provides clear evidence on the plasmon coupling of Ag nanoparticles. Extracting the dopant states in the Co-doped ZnO nanoparticles [2]. In order to assign the dopant-introduced states in the low-loss EELS, we employ both the core-loss EELS and the valence EELS on the same Co-doped ZnO nanoparticles by spatially mapping the dopant concentration distribution via the core-loss EELS (Fig 2a 2b 2c) and simultaneously by identifying the dopant features in the accumulated valence EELS via the measured dopant richness (Fig 2d). Three Coincidentally-growing Co dopant states are successfully determined in Fig. 2e. The experimental inputs feed the first-principles calculation, which generates full electronic structure of the doped ZnO nanoparticles. The experiment supports the carrier mediated room-temperature magnetism, which is a main confusion with current dilute magnetic semiconductors.

The effects of ion bombardment on the field emission of screen printed tetrapod zinc oxide cathodes are reported. The field emission characteristics of this cathode degrade strongly after Ar ion bombardment for 10min at an energy of 3keV and ion current of 5µA. The emission current density decreases from 1.65 to 0.32mA/cm2 at 4.50V/µm field strength, while the turn-on field increases from 2.16 to 3.11V/µm at a current density of 0.1µA/cm2. This result demonstrates that the field emission of the ZnO emitters severely degrades upon ion bombardment. The emission degradation can be attributed to a lower value of the field enhancement factor β, which is caused by changes of the morphology, and a higher work function ϕ, which is caused by changes of the surface composition of ZnO.

Tetrapod zinc oxide (T-ZnO), being a kind of nano-scale material, has a large specific surface area and high surface binding energy, which will make it sensitive to ambient gases; hence, the field emission (FE) properties of this ZnO nanomaterial will be influenced by gas adsorption. The effect of methane on the field emission of T-ZnO emitters was investigated. It was found that CH 4 enhanced the field emission substantially. By curve fitting we are able to describe the experimental results adequately as a function of the methane pressure. The increase of the field emission is caused by a lower work function of the ZnO-emitters.

The Ba and BaO evaporation rates of a thermionic cathode have been measured at 145K and 170K above the typical operating temperature being about 1033K. According to the measurement result, the relationship between cathode lifetime and operation temperature has been discussed. A comparison life test also be done between a poisoned but reactivated cathode and a normal one under the same condition. We found almost the same emission current at the beginning but different current decrease speed and Ba evaporation rate at the course of the life test.

Evaporation of carbon nanotubes (CNT) cathodes and the degradation of its field emission are reported in this paper. After 100h at 1323K the emission current density decreases from 6.50 to 0.20mA/cm2 at 7.50V/µm field strength, while the turn-on field increases from 1.92 to 2.45V/µm at a current density of 0.1µ/cm2. The C+-ion current in a mass spectrometer has also been measured to compare the CNT evaporation at different cathode temperatures between 1173K and1373K. The results indicate that the CNT evaporation rate increases greatly at temperatures above 1100K. Scanning electron microscopy (SEM) images show that the emission degradation can be mainly attributed to the decreased value of field enhancement factor β, which is caused by CNT evaporation.

The true outgassing from cathodes is often masked by the production of gases released by phosphors in field emission displays (FEDs). The outgassing characteristics of CNT cathode and ZnO cathode for application in FEDs are presented. Quadropole mass spectrometer[QMS] has been used to measure the outgassing characteristics from carefully prepared samples of CNT and ZnO cathodes in ultra-high vacuum(UHV) system. We observe that the outgassing rate of Z n O cathode is much lower than it of CNT cathode due to its solid structure, but they have the similar outgassing. It has been shown that the main components of released gases are water vapor, carbon monoxide, carbon dioxide and oxygen.

This paper reports the development and the operation of field emitters with low turn on electric field based on carbon fibres. Field emitters of vertical carbon fibres on silicon substrate were fabricated by the catalyst chemical vapor deposition. The diameter of the fibres is about 3~4 mum and the height is larger than 1 mm. After one aging process of 150 minutes, field emission measurements of carbon fibres were carried out in a vacuum chamber with pressure of 5.0times10-4 Pa. The experimental results showed the turn on electric field is 1.5V/mum and the emission current density rises to 46.7mA/cm2 under the field of 2.8 V/mum. The field emission performance and stability of carbon fibres depends strongly on the vacuum level during the process of the experiments. Damages on carbon fibres were also observed because of ion bombardment

Field emission characteristic and stability of a carbon nanotubes (CNTs) cathode have been studied by testing the emission current at different levels. By monitoring the emission I-V curves, we can obtain a relative stable maximum current from a CNTs cathode, after reaching the maximum current, the emission current fluctuate seriously and sparking can be seen at the site of emission. From the experimental results, the causes of emission instability and sparking is concluded and the influence of the sparking and ion bombardment on the emission performance of a CNTs cathode is obtained

In this paper, the outgassing of field emission display (FED) was studied using vacuum chamber and FED panel. The gas was measured with a quadrupole mass spectrometer (QMS), and the mean gas outgassed from the FED panel is CO when the device is working at about 1000V

We studied the residual gases inside Field Emission Displays (FEDs) with carbon nanotube(CNTs) emitters, and found that the main residual gases inside sealed CNT-FEDs are Ar and CO, both of which are typical residual gases inside electronic vacuum tubes.

In this paper, a novel gun of RF power amplifier based on always-on cathode was described. Double hopping electron funnels are fabricated into the devices. RF modulated signal is applied on the aluminum electrode. The process of secondary electron emission, potential distribution and trajectories were simulated. In the simulation model, the primary electrons, which are low energy, emit from the ring cathode with proportional spacing

An efficient method is used to improve the emission stability and uniformity of the field emission from a carbon nanotube (CNT) cathode. In this method, a fully sealed device with CNTs cathode is exhausted by a pumping system. At the same time, this device is baking at a temperature about 400degC and maintains for a few minutes, and an overload current is applied. The overload current can burn the nanotubes which are over-outcrop to the surface. Besides this, successive emission cycles process is designed to aging the cathode and get rid of the residual gas stored in the cathode layer. Consequently, the emission stability and uniformity of a CNTs cathode have been improved apparently

A new triode structure for printable carbon nanotube field emission displays is described in this paper. In the structure, silver paste is printed on the surface of a metal mesh and acts as the gate electrode. Between the gate and the metal mesh is a dielectric layer. MgO film and MgF/sub 2/ film are deposited on the surfaces of the mesh and the funnels by evaporation. A voltage applied on the metal mesh, the primary electrons emit from the CNT cathode and bombard on the surface of the metal mesh with initial energy. The secondary electrons and backscatters are generated. Because of the low energy of the secondary electrons, the gate can control the emission current easily. Therefore the range of the modulate voltage can be withdrawn. The dielectric layer on the surface of the metal mesh must be compact, otherwise silver paste will penetrate in after firing and under high voltage, breakdown of the insulator materials will occur by surface flashover. This paper reports the fabrication process of dielectric layer and the preparation of the materials.

A modified static polarizing wind imaging interferometer (SPWII) for measuring the upper atmospheric wind and temperature is presented. The atmospheric temperature and wind velocity can be derived by observing multiple emission lines. The principle of the SPWII is described. The effects of the dispersion of the quarter wave plates on the derived results are analyzed. Using a simulated annealing algorithm, some multilayer achromatic quarter wave plates (AQWPs) are designed to suppress the errors introduced by the dispersion. Two alternative AQWPs (six- and ten-layer) are obtained. The transmission loss of the interferometer and the measurement errors of atmospheric temperature and wind velocity introduced through dispersion can, through the use of achromatic QWPs, be reduced to below 0.2%, 0.15 K and 0.03 m s−1, respectively.

The influences of ion bombardment on the field emission performance of tetrapod ZnO nanostructures are reported. As the scanning electron microscopy images and photoluminescence spectrum show, the tips of the field emitters are destroyed and the surface state of the field emitters is also changed after the ion bombardment. The ion bombardment has a considerable effect on the field emission properties of the tetrapod ZnO field emitters. After Ar+ ion bombardment with the energy of 3 keV and the ion current of 0.05 μA for 30 min, the turn-on field increases about 63% and the threshold field increases about 77%, respectively. There are two main reasons for the variation in field-emission property: (1) the decrement of the field enhancement factor β, which is caused by the variation in morphology of field emitter; (2) the increment of work function φ, which is caused by the changed concentration of the surface oxygen vacancy.

The authors measured the residual gas spectrum of a field emission display (FED) with carbon nanotube (CNT) emitters and found that the main residual gases inside a sealed CNT FED, containing an evaporated Ba getter, are H2, CH4, CO, Ar, and CO2, all of which are typical residual gases of electronic vacuum tubes. Additionally they also measured the electron stimulated desorption of gases by operating their field emission devices.

A novel gun double hop gun of rf power amplifier based on an always-on ringed cold cathode is suggested. Double hopping electron funnels, including a metal funnel and a glass funnel, are fabricated in. MgO film is deposited around the walls of the funnels by electron beam evaporation. Secondary electrons or backscatters (elastic and inelastic) escape from the dielectric film (MgO) under the bombardment of accelerated electrons and are driven to the exit window of the glass funnel by a modulated voltage. Among the escaping electrons, the ratios of secondary emission electrons, elastic scatters, and inelastic scatters are 90%, 9%, and 1%, respectively. Most of the escaping electrons at the exit window have low energy (