Direct Modulation Research Articles

Entomotoxic potential of hydroalcoholic extract of Eragrostis plana Nees in experimental model of Nauphoeta cinerea Olivier

The objective of this study was to evaluate the entomotoxic activity of the hydroalcoholic extract of Eragrostis plana Nees in an experimental model of cockroaches (Nauphoeta cinerea Olivier), for a possible bioinsecticide. For this purpose, aerial parts of E. plana were grounded to obtain the hydroalcoholic extract (EACA), after preparing the concentrations of (0.5; 2.5; 5.0; 12.5; 25.0; 50.0 100.0 μg g-1 per animal) a saline solution was used to control the treatment. To determine the receptors and pathways involved in responses to EACA doses of E. plana, a treatment with the drug octopamine and its inhibitor phentolamine were prepared. The effect of EACA on behavioral activities (grooming) and on cardiac activity were tested. All data were expressed as mean ± standard deviation, being analyzed by the two-way ANOVA test, followed by the Tukey test, considered significant when p<0.05. After carrying out the experiment, it was found that EACA induced a significant effect on leg grooming at all concentrations, except for the concentration of 100 μg g-1 per animal, but the same did not modulate antenna grooming. Regarding the receptors and pathways involved, it was observed that octopamine alone and together with the extract, had a significant effect on leg grooming, while phentolamine, together with the extract, influenced antennae grooming. Regarding the effect of the extract on the semi-isolated heart, it was noticed that the same doses that affected grooming, affected heart rate by decreasing it. At no concentration, at the end of the treatment, there was no recovery of the heart rate. The results point to a direct modulation of octopaminergic and cholinergic pathways in the insect nervous system.

Advancing frequency locking: Modified FPGA-Guided direct modulation spectroscopy for laser stabilization

In this paper, we propose a cost-effective laser frequency locking scheme based on frequency modulation spectroscopy (FMS) for precision measurements and experiments in various fields. We demonstrate that by digitally modulating the detected signal frequency using a Field-Programmable-Gate-Array (FPGA) driven by a home-built lock-in and a proportional–integral–derivative (PID) control system, our system achieves higher precision, user-friendliness, and versatility. Our system generates a 20 V peak-to-peak amplified voltage to a piezo transducer (PZT), which enables a mode-hop free laser scan of approximately 2 ±0.2 GHz. We directly modulate the detected saturation absorption signal with a sinusoidal waveform, then demodulate it to obtain multiple zero crossing locking points on the D2 transition of Cs at 852.35 nm. We optimized the system for three commonly used atomic transitions and found that researchers can select any of the zero crossing peaks for frequency stabilization depending on their experimental requirements, we locked the laser at the crossover transition. We measured the long-time frequency fluctuation and power spectral density and found that the frequency fluctuation of the laser is much less than the natural line width of the D2 transition of Cs. Our results demonstrate that our laser frequency locking scheme is effective and practical for precision measurements and experiments in various fields.

A Simplified Volterra Equalizer Based on System Characteristics for Direct Modulation Laser (DML)-Based Intensity Modulation and Direct Detection (IM/DD) Transmission Systems

The nonlinear Volterra equalizer has been proved to be able to solve the problem of nonlinear distortion, but it has high computational complexity and is difficult to implement. In this paper, a simplified second-order Volterra nonlinear equalizer designed for intensity modulation/direct detection systems based on direct modulated laser is proposed and demonstrated, taking into account the characteristics of the system. It has been proved that the received signal of direct modulation laser/direct detection system can be expressed in Volterra series form, but its form is too complex, and the device parameters should also be considered. We re-derived it and obtained a more concise form. At the same time, we proposed a method to simplify the second-order Volterra nonlinear equalizer without relying on device parameters. The performance of the proposed Volterra nonlinear equalizer is evaluated experimentally on a 56 Gb/s 4-ary pulse amplitude modulation link implemented by using a 1.55 µm direct modulation laser. The results show that, compared with the traditional Volterra nonlinear equalizer, the receiver sensitivity of the equalizer is only reduced by 0.2 dB at most, but the complexity can be reduced by 50%; compared with diagonally pruned Volterra nonlinear equalizers, the complexity of the equalizer is the same, but the reception sensitivity can be improved by 0.5 dB.

Interrogating direct NLRP3 engagement and functional inflammasome inhibition using cellular assays

As a key regulator of the innate immune system, the NLRP3 inflammasome responds to a variety of environmental insults through activation of caspase-1 and release of the proinflammatory cytokines IL-1β and IL-18. Aberrant NLRP3 inflammasome function is implicated in numerous inflammatory diseases, spurring drug discovery efforts at NLRP3 as a therapeutic target. A diverse array of small molecules is undergoing preclinical/clinical evaluation with a reported mode of action involving direct modulation of the NLRP3 pathway. However, for a subset of these ligands the functional link between live-cell target engagement and pathway inhibition has yet to be fully established. Herein we present a cohort of mechanistic assays to both query direct NLRP3 engagement in cells, and functionally interrogate different nodes of NLRP3 pathway activity. This system enabled the stratification of potency for five confirmed NLRP3 inhibitors, and identification of two reported NLRP3 inhibitors that failed to demonstrate direct pathway antagonism.

Benzydamine plays a role in limiting inflammatory pain induced by neuronal sensitization.

Benzydamine is an active pharmaceutical compound used in the oral care pharmaceutical preparation as NSAID. Beside from its anti-inflammatory action, benzydamine local application effectively reliefs pain showing analgesic and anaesthetic properties. Benzydamine mechanism of action has been characterized on inflammatory cell types and mediators highlighting its capacity to inhibit pro-inflammatory mediator's synthesis and release. On the other hand, the role of benzydamine as neuronal excitability modulator has not been yet fully explored. Thus, we studied benzydamine's effect over primary culture DRG nociceptors excitability and after acute and chronic inflammatory sensitization, as a model to evaluate nociceptor response. Benzydamine demonstrated to effectively inhibit neuronal basal excitability reducing its firing frequency and increasing rheobase and afterhyperpolarization amplitude. Its effect was time and dose-dependent. At higher doses, benzydamine induced changes in action potential wavelength, decreasing its height and slightly increasing its duration. Moreover, the compound reduced neuronal acute and chronic inflammatory sensitization. It inhibited neuronal excitability mediated either by an inflammatory cocktail, acidic pH or high external KCl. Notably, higher potency was evidenced under inflammatory sensitized conditions. This effect could be explained either by modulation of inflammatory and/or neuronal sensitizing signalling cascades or by direct modulation of proalgesic and action potential firing initiating ion channels. Apparently, the compound inhibited Nav1.8 channel but had no effect over Kv7.2, Kv7.3, TRPV1 and TRPA1. In conclusion, the obtained results strengthen the analgesic and anti-inflammatory effect of benzydamine, highlighting its mode of action on local pain and inflammatory signalling.

Effects of modulator therapies on endocrine complications in adults with cystic fibrosis: a narrative review.

Cystic fibrosis is a monogenic disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) protein, which transports chloride ions in secretory organs. Modulator therapies are small molecules that correct CFTR dysfunction and can lead to a wide range of benefits for both pulmonary and extrapulmonary complications of cystic fibrosis. With advancements in airway, antimicrobial and nutritional therapies and now introduction of modulator therapies, most people living with cystic fibrosis in Australia are now adults. For adults with cystic fibrosis, endocrine manifestations such as cystic fibrosis-related diabetes, metabolic bone disease, and reproductive health are becoming increasingly important, and emerging evidence on the endocrine effects of CFTR modulator therapies is promising and is shifting paradigms in our understanding and management of these conditions. The management of cystic fibrosis-related diabetes will likely need to pivot for high responders to modulator therapy with dietary adaptions and potential use of medications traditionally reserved for adults with type 2 diabetes, but evidence to support changing clinical care needs is currently lacking. Increased attention to diabetes-related complications screening will also be required. Increased exercise capacity due to improved lung function, nutrition and potentially direct modulator effect may have a positive impact on cystic fibrosis-related bone disease, but supporting evidence to date is limited. Fertility can improve in women with cystic fibrosis taking modulator therapy. This has important implications for pregnancy and lactation, but evidence is lacking to guide pre-conception and antenatal management. Provision of multidisciplinary clinical care remains ever-important to ensure the emergence of endocrine and metabolic complications are optimised in adults with cystic fibrosis.

Effect of sonification types in upper-limb movement: a quantitative and qualitative study in hemiparetic and healthy participants

BackgroundMovement sonification, the use of real-time auditory feedback linked to movement parameters, have been proposed to support rehabilitation. Nevertheless, if promising results have been reported, the effect of the type of sound used has not been studied systematically. The aim of this study was to investigate in a single session the effect of different types of sonification both quantitatively and qualitatively on patients with acquired brain lesions and healthy participants.MethodsAn experimental setup enabling arm sonification was developed using three different categories of sonification (direct sound modulation, musical interaction, and soundscape). Simple moving forward movements performed while sliding on a table with both arms were investigated with all participants. Quantitative analysis on the movement timing were performed considering various parameters (sound condition, affected arm and dominance, sonification categories). Qualitative analysis of semi-structured interviews were also conducted, as well as neuropsychological evaluation of music perception.ResultsFor both the patient and healthy groups (15 participants each), average duration for performing the arm movement is significantly longer with sonification compared to the no-sound condition (p < 0.001). Qualitative analysis of semi-structured interviews revealed different aspects of motivational and affective aspects of sonification. Most participants of both groups preferred to complete the task with sound (29 of 30 participants), and described the experience as playful (22 of 30 participants). More precisely, the soundscape (nature sounds) was the most constantly preferred (selected first by 14 of 30 participants).ConclusionOverall, our results confirm that the sonification has an effect on the temporal execution of the movement during a single-session. Globally, sonification is welcomed by the participants, and we found convergent and differentiated appreciations of the different sonification types.

SkinAid: A Wirelessly Powered Smart Dressing Solution for Continuous Wound-Tracking Using Textile-Based Frequency Modulation.

In this article, SkinAid, a battery-free, low-cost, robust, and user-friendly smart bandage for electrochemical monitoring and sensing of chronic wounds is proposed. The working principle of the bandage is based on direct frequency modulation of a tri-electrode electrochemical sensing of wound data. The electronics and biotelemetry links were realized using low-cost manufacturing process of textile embroidery onto fabric substrate. The transmitter was represented by a bedsheet with novel corrugated crossed-dipole made of Elektrisola-7 embroidered onto gauze fabric. An input RF signal of 1 W was transmitted at 462 MHz from the bedsheet to the all-textile bandage featuring a rectifying circuit, a voltage-controlled oscillator (VCO), an electrochemical sensor, and a 915-MHz dipole for re-transmission of the modulated wound data. We demonstrate that for wound fluid emulated by various uric acid concentrations from 0.2 mM to 1.2 mM, corresponding modulated frequency varies from 1090 MHz to 1145 MHz for signals captured at 25 cm away from the bandage. For pH modulation ranging from 2 to 10, the corresponding modulated frequency was between 800 MHz and 830 MHz for signals received at more than 6 feet away from the bandage. For quick and reliable assessment, two empirical models were developed for the direct frequency modulation as a function of uric acid and pH. To the best of our knowledge, this is the first time an all-textile (fabric-integrated), battery-free and wirelessly powered smart bandage have been proposed for wound monitoring. This result can be used as a first step in developing RFID-type, battery-free, and low-cost 5G/6G smart bandages using millimeterwave and terahertz frequencies where the bedsheet can be host to a MIMO-aided beamforming.

Directional Modulation With Dynamic Distributed Time-Modulated Arrays

Directional Modulation With Dynamic Distributed Time-Modulated Arrays

A Sub-Terahertz High-Speed Traveling-Wave Switch Modulator Based on Dynamically Tunable Double-Resonant Coupling Units

High-speed direct modulation devices are of great significance for the development of high-speed communication systems with large bandwidth, miniaturization, and low complexity. However, an increase in the carrier frequency in the sub-terahertz band and above will negatively impact high-performance direct modulation devices due to the large insertion loss and low on–off ratio. Based on the traveling-wave modulation mechanism, this article adopts the zero-phase-difference amplitude modulator design method. More specifically, a 1- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m small anode Schottky diode is combined with a Z-type matching structure to form a dual-resonant coupling dynamic tunable unit. Interunit coupling is found to further improve the on–off ratio. In this way, high-speed dynamic modulation is performed for the transmission traveling-wave amplitude with low insertion loss and a high on–off ratio. On this basis, a 0.14-THz on–off keying (OOK) high-speed traveling-wave modulator is proposed, and our results showed that a on–off ratio of 25.4 dB could be achieved at the zero-phase-difference point by only using two dynamic structural units. Meanwhile, the control voltage could be adjusted to achieve high-speed modulation with a phase difference of only 3.66 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^\circ$</tex-math> </inline-formula> during the entire control voltage transition, a data rate of 24 Gb/s, and 33.99% sidebands occupation.

A 103 fJ/b/dB, 10–26 Gb/s Receiver With a Dual Feedback Nested Loop CDR for Wide Bandwidth Jitter Tolerance Enhancement

A 10–26 Gb/s energy-efficient receiver incorporating a dual-feedback nested loop clock and data recovery circuit (DF-CDR) is proposed. Combining a direct modulation path on voltage-controlled oscillator (VCO) and phase interpolator (PI)-based phase rotator inside a phase locked loop (PLL), it improves high-frequency jitter tolerance by 0.15 UI. An edge-first equalization scheme is proposed to reduce power and hardware overhead of decision feedback equalizers. Meanwhile, it facilitates adaptive equalization of continuous time linear equalizer, and background offset calibration of the receiver frontend. A three-stage latch comparator is adopted to enable high-speed direct feedback equalizer. By applying PRBS-31 test pattern through a 32 dB loss channel, the receiver is error-free and features the best energy efficiency of 103 fJ/b/dB at 26 Gb/s.

Design of a Single-Element Dynamic Antenna for Secure Wireless Applications

We introduce a new technique for secure wireless applications using a single dynamic antenna. The dynamic antenna supports a constantly and rapidly changing current distribution that generates a radiation pattern that is static in a desired direction and dynamic elsewhere. This imparts additional modulation on the signal and obscures information transmitted or received outside of the information beam, thus achieving directional modulation. Dynamic currents are supported by a single feed that is switched between separate ports on a single antenna, generating two different radiation patterns without changing the physical shape of the antenna. We introduce the theoretical concept by exploring an ideal complex dynamic radiation pattern that remains static in a narrow desired direction and is dynamic elsewhere. The impact on the transmission of information is analyzed, showing that the information beam narrows as the modulation order increases, and design constraints on the spatial width of the information beam as a function of modulation format are determined. We design and analyze a 2.3 GHz two-state dynamic dipole antenna and experimentally demonstrate secure wireless transmission. We demonstrate the ability to change the information beamwidth and steer the information beam experimentally in real time, and to maintain high throughput in the information beam while obscuring the information elsewhere. In contrast to multiport or array-based antennas, our approach introduces a novel rapidly switched single-element technique for secure wireless applications that can be used independently from the rest of the wireless system, essentially operating as a “black box” for an additional layer of security.

Phase-shifting the circadian glucocorticoid profile induces disordered feeding behaviour by dysregulating hypothalamic neuropeptide gene expression

Here we demonstrate, in rodents, how the timing of feeding behaviour becomes disordered when circulating glucocorticoid rhythms are dissociated from lighting cues; a phenomenon most commonly associated with shift-work and transmeridian travel ‘jetlag’. Adrenalectomized rats are infused with physiological patterns of corticosterone modelled on the endogenous adrenal secretory profile, either in-phase or out-of-phase with lighting cues. For the in-phase group, food intake is significantly greater during the rats’ active period compared to their inactive period; a feeding pattern similar to adrenal-intact control rats. In contrast, the feeding pattern of the out-of-phase group is significantly dysregulated. Consistent with a direct hypothalamic modulation of feeding behaviour, this altered timing is accompanied by dysregulated timing of anorexigenic and orexigenic neuropeptide gene expression. For Neuropeptide Y (Npy), we report a glucocorticoid-dependent direct transcriptional regulation mechanism mediated by the glucocorticoid receptor (GR). Taken together, our data highlight the adverse behavioural outcomes that can arise when two circadian systems have anti-phasic cues, in this case impacting on the glucocorticoid-regulation of a process as fundamental to health as feeding behaviour. Our findings further highlight the need for development of rational approaches in the prevention of metabolic dysfunction in circadian-disrupting activities such as transmeridian travel and shift-work.

Targeted Polymersome Delivery of a Stapled Peptide for Drugging the Tumor Protein p53:BCL-2-Family Axis in Diffuse Large B-Cell Lymphoma.

Diffuse large B-cell lymphoma (DLBCL) remains a formidable diagnosis in need of new treatment paradigms. In this work, we elucidated an opportunity for therapeutic synergy in DLBCL by reactivating tumor protein p53 with a stapled peptide, ATSP-7041, thereby priming cells for apoptosis and enhancing their sensitivity to BCL-2 family modulation with a BH3-mimetic, ABT-263 (navitoclax). While this combination was highly effective at activating apoptosis in DLBCL in vitro, it was highly toxic in vivo, resulting in a prohibitively narrow therapeutic window. We, therefore, developed a targeted nanomedicine delivery platform to maintain the therapeutic potency of this combination while minimizing its toxicity via packaging and targeted delivery of a stapled peptide. We developed a CD19-targeted polymersome using block copolymers of poly(ethylene glycol) disulfide linked to poly(propylene sulfide) (PEG-SS-PPS) for ATSP-7041 delivery into DLBCL cells. Intracellular delivery was optimized in vitro and validated in vivo by using an aggressive human DLBCL xenograft model. Targeted delivery of ATSP-7041 unlocked the ability to systemically cotreat with ABT-263, resulting in delayed tumor growth, prolonged survival, and no overt toxicity. This work demonstrates a proof-of-concept for antigen-specific targeting of polymersome nanomedicines, targeted delivery of a stapled peptide in vivo, and synergistic dual intrinsic apoptotic therapy against DLBCL via direct p53 reactivation and BCL-2 family modulation.

Chaos Synchronization of InGaAsP Lasers

The optical output of a semiconductor laser can fluctuate chaotically by modulating its direct current in limited conditions of the modulated current signal parameters in terms of modulation frequency and modulation index. In this work, single, double, and chaotic pulses of an InGaAsP laser with direct current modulation, are numerically presented through a bifurcation diagram. Numerically, the unidirectional optical coupling system realizes chaotic synchronization between two identical InGaAsP lasers with direct current modulation, as the transmitter/receiver configuration. The transmission time for transmitting light from the transmitted laser to the received laser is essential for controlling the quality of chaos synchronization. The transmission time applies on the order of nanoseconds. Chaos synchronization quality is estimated by a correlation plot and calculated by the cross-correlation coefficient. This study observed the best synchronization quality (complete chaos synchronization) when the two lasers are identical. On the other hand, the chaotic synchronization between two non-identical InGaAsP lasers was investigated. In this case, complete chaos synchronization is not found, and the quality of chaotic synchronization was observed to decrease as the mismatch between the parameters of the two lasers increased.

Scalable Metamaterial Integrated Digital Coding Transmitting Bit Array for Concurrent Multistream Direct Antenna Modulation

This letter presents a new type of metamaterial (MTM) integrated digital coding transmitting bit array for wireless communication. The proposed transmitter directly modulates the baseband digital signal on the carrier frequency to each antenna element without using any RF mixers as in conventional homodyne or heterodyne transmitters, thereby simplifying the hardware complexity. Single-tone carrier wave is distributed by an MTM-based power divider and fed to each antenna element of the bit array, the phase of which can be electrically manipulated to realize direct antenna modulation (DAM). Moreover, the code-division multiple access (CDMA) communication method is leveraged to achieve the concurrent multistream data transmission without increasing the hardware intricacy of the system. Experimental verification for concurrently transmitting three different data streams is carried out to demonstrate the validity of the proposed MTM integrated transmitting bit-array architecture.

Direct Assimilation of Ground-Based Microwave Radiometer Clear-Sky Radiance Data and Its Impact on the Forecast of Heavy Rainfall

Ground-based microwave radiometer (GMWR) data with high spatial and temporal resolution can improve the accuracy of weather forecasts when effectively assimilated into numerical weather prediction. Nowadays, the major method to assimilate these data is via indirect assimilation by assimilating the retrieved profiles, which introduces large retrieval errors and cannot easily be represented by an error covariance matrix. Direct assimilation, on the other hand, can avoid this issue. In this study, the ground-based version of the Radiative Transfer for the TIROS Operational Vertical Sounder (RTTOV-gb) was selected as the observation operator, and a direct assimilation module for GMWR radiance data was established in the Weather Research and Forecasting Model Data Assimilation (WRFDA). Then, this direct assimilation module was applied to assimilate GMWR data. The results were compared to the indirect assimilation experiment and demonstrated that direct assimilation can more effectively improve the model’s initial fields in terms of temperature and humidity than indirect assimilation while avoiding the influence of retrieval errors. In addition, direct assimilation performed better in the precipitation forecast than indirect assimilation, making the main precipitation center closer to the observation. In particular, the improvement in the precipitation forecast with a threshold of 60 mm/6 h was obvious, and the corresponding TS score was significantly enhanced.

Bacteriophages as Potential Clinical Immune Modulators.

Bacteriophages (phages for short) are bacteria-specific viruses that have been drawing attention when it comes to countering the ever-growing antibiotic bacterial resistance, and are being seen as one of the most promising technologies against multi-antibiotic-resistant bacteria. Although bacteriophages are commonly regarded only as anti-bacterial objects unable to directly interact with eukaryotic cell metabolism, an increasing quantity of evidence has indicated that bacteriophages can directly affect cells bacteria in both in vitro and in vivo applications, influencing the behavior of tissues and immune systems. In sight of this new range of applications, several authors have expressed enthusiasm in phage therapy as direct modulators of eukaryotic cells for clinical usage, highlighting the need for further investigations covering the pharmacology of these new "eukaryotic-viruses", as even harmful interactions with eukaryotic cells were detected after phage therapy. The present review aims to cover and highlight mechanisms through which bacteriophages may interact with immune cells, analyzing potential clinical applications and obstacles presented in the use of bacteriophages as anti-inflammatory tools.

Does the Emotional Modulation of Visual Experience Entail the Cognitive Penetrability of Early Vision?

AbstractEmpirical research suggests that motive states modulate perception affecting perceptual processing either directly, or indirectly through the modulation of spatial attention. The affective modulation of perception occurs at various latencies, some of which fall within late vision, that is, after 150 ms. poststimulus. Earlier effects enhance the C1 and P1 ERP components in early vision, the former enhancement being the result of direct emotive effects on perceptual processing, and the latter being the result of indirect effects of emotional stimuli on perceptual processing that automatically capture exogenous attention. Other research suggests that emotional stimuli do not capture attention automatically but attentional capture is conditioned on the context. Since context dependent effects are first registered with the elicitation of N1 ERP component about 170 ms. poststimulus, emotional stimuli affect late vision. However, the early affective modulation of early vision by emotive states threatens the cognitive impenetrability of early vision since emotive states are associated with learning and past experiences. I argue that the emotive modulation of early vision does not entail the cognitive penetrability of early vision. First, the early indirect affective modulation of P1 is akin to the effects of spatial pre-cueing by non-emotive cues and these preparatory effects do not signify the cognitive impenetrability of early vision. Second, because the direct modulation of C1 signifies an initial, involuntary appraisal of threat in the incoming stimulus that precedes any cognitive states.

Direct density modulation of photo-assisted field emission from an RF cold cathode

This paper explores direct density modulation of high-current electron beam emission from an RF cold cathode using optical excitation. We theoretically study the photo-assisted field emission of periodically bunched electron beams of various pulse shapes under the combined excitation of an RF field and an optical field, using an exact quantum model. Both continuous-wave (CW) and pulsed optical fields are considered. The emission current pulse amplitude, pulse width, electron number density per pulse, as well as pulse shape and its harmonic contents are investigated in detail. For CW photon sources in the UV to NIR range (i.e., 200–1200 nm), increasing the optical intensity under an RF bias tends to change the current pulse from a Gaussian to sinusoidal-like shape, thus offering strong flexibility to control the frequency components in beam current emission. Pulsed photon sources combined with an RF field can produce sharp, high-current electron bunches with pulse duration comparable with or even less than that of the optical pulse. A contour map of the density modulation depth is constructed for different combinations of RF and laser fields. The results provide insight into unlocking new opportunities to achieve direct density modulation during electron current emission by optical means.