Application Of Pulses Research Articles

Improving NonViral Gene Delivery Using MHz Bursts of Nanosecond Pulses and Gold Nanoparticles for Electric Field Amplification.

Gene delivery by the pulsed electric field is a promising alternative technology for nonviral transfection; however, the application of short pulses (i.e., nanosecond) is extremely limited. In this work, we aimed to show the capability to improve gene delivery using MHz frequency bursts of nanosecond pulses and characterize the potential use of gold nanoparticles (AuNPs: 9, 13, 14, and 22 nm) in this context. We have used bursts of MHz pulses 3/5/7 kV/cm × 300 ns × 100 and compared the efficacy of the parametric protocols to conventional microsecond protocols (100 µs × 8, 1 Hz) separately and in combination with nanoparticles. Furthermore, the effects of pulses and AuNPs on the generation of reactive oxygen species (ROS) were analyzed. It was shown that gene delivery using microsecond protocols could be significantly improved with AuNPs; however, the efficacy is strongly dependent on the surface charge of AuNPs and their size. The capability of local field amplification using AuNPs was also confirmed by finite element method simulation. Finally, it was shown that AuNPs are not effective with nanosecond protocols. However, MHz protocols are still competitive in the context of gene delivery, resulting in low ROS generation, preserved viability, and easier procedure to trigger comparable efficacy.

Ultrasound sensitive O2 microbubbles radiosensitize murine breast cancer but lead to higher metastatic spread.

The inadequate level of oxygenation in tumors has been shown to correlate not only with greater invasiveness of cancer cells, but also with a reduction in their sensitivity to anticancer therapies. Over the years, many attempts have been made to increase the oxygenation level of cancer, but most of them have been ineffective. We investigated the heterogeneous response of tumor tissue to phospholipid-coated oxygen microbubbles (OMB) in murine tumors in vivo using oxygen and hemoglobin saturation mapping and the influence of OMB treatment on microvasculature, perfusion, and radiotherapy effectiveness. Intravenous administration of OMB followed by ultrasound pulse leads to increased oxygenation of a tumor, found mainly in the vicinity of tumor vessels, while intratumoral delivery resulted in areas of increased pO2 more evenly distributed within the tumor. Furthermore, hemoglobin contributes little to the increase in tumor oxygenation caused by oxygen microbubbles. Extensive vasculature disruption was observed in the groups treated with both oxygen/nitrogen microbubbles and ultrasound pulse. This therapy also led to a reduction in the coverage of the vessels by pericytes, while the density of the microvessels was unchanged. Radiotherapy with a single dose of 12Gy reduced tumor growth by 50% in all treated groups. Unfortunately, at the same time, the number of macroscopic metastases in the lungs increased significantly after intravenous administration of oxygen/nitrogen microbubbles and the application of an ultrasound pulse. In conclusion, ultrasound-sensitive oxygen microbubbles are effective in delivering oxygen to tumor tissue, thus increasing the effectiveness of radiotherapy. However, cavitation effects and destruction of the integrity of tumor vessels result in greater spread of cancer cells in the host organism.

Nonlinear optical properties and transient absorption in Hibiscus Sabdariffa dye solution probed with femtosecond pulses

Highly conjugated organic molecules are attractive chromophores for nonlinear optics due to their significant third-order nonlinear response near the absorption bands located in the broad spectral range from 200 to 900 nm. In this work, we report on the wavelength-dependence of one- and two-photon absorption processes in Hibiscus sabdariffa organic dye excited by femtosecond (fs) laser pulses centered at 1030 nm and 515 nm. Z-scan and transient absorption (TA) techniques have been employed to investigate the absorption and relaxation processes in the target dye. The dye is found to have a significant negative nonlinear absorption coefficient (β) of value ∼ −2.7 × 10−11 cm/W at 515 nm probing laser pulses, while it has a positive value equal to +2.1 × 10−13 cm/W when 1030 nm laser pulses were employed. The TA decay measurements using 40 fs laser pulses, centered at 515 nm wavelength, reveal that the dye exhibits a short relaxation time of ∼3 ps attributed to the involvement of the excited state proton transfer (ESPT) process in the Hibiscus dye solution. Moreover, our time-integrated fluorescence measurements revealed that no fluorescence emission could be detected. The application of ultrashort pulses of ∼40 fs duration enabled the tracking of ESPT in the Hibiscus dye, which was not detected in previous studies that employed laser pulses of picoseconds and nanoseconds duration.

Enhanced resistive switching uniformity in HfO2/TiO2 NWA memristor for synaptic simulation

In this article, we fabricated a memristive device with a Cu/HfO2/TiO2 nanowire array (NWA)/FTO structure through a hydrothermal method and atomic layer deposition. The devices exhibit good resistive switching properties, including low set voltages (∼1 V), good retention (>104 s), and multilevel storage. Compared with the Cu/TiO2 NWA/FTO device, Cu/HfO2/TiO2 NWA/FTO devices exhibit better uniformity, which could be due to the difference between the dielectric constants of TiO2 and HfO2. Under the application of consecutive voltage pulses, some synaptic functions were mimicked, including long-term potentiation/depression, paired-pulse facilitation, and spike timing dependent plasticity.

Quantized topological response in trapped quantum gases

In this letter, we propose a quantized topological response in trapped 1D quantum gases. The experimental protocol for the response requires the application of an instant optical pulse to a half-infinite region in an asymptotically harmonic trap and measuring the density distribution. We show that the corresponding linear response is described by a universal quantized formula in the thermal dynamical limit, which is invariant under local continuous deformations of the trapping potential $V$, atom distribution $f_\Lambda$, the spatial envelope of the optical pulse $\Theta_p$, and the measurement region $\Theta_m$. We test the statement by various numerical analysis, the result of which is consistent with the analytical prediction to high accuracy. We further show that a short but finite optical pulse duration only results in a violation of the quantization near the transition time, which suggests that quantized response could be observed in realistic experiments. We also generalize our results to non-linear quantized topological responses for atoms in higher dimensional harmonic traps.

Effect of Process Parameters on Arc Shape, Macroscopic Features, and Microhardness in Pulsed GMA–Additive Manufacturing

Gas metal arc welding-based additive manufacturing (GMA–AM) is a promising, low-cost approach to fabricate large-scale and complex geometry components using layer-by-layer deposition of metals. However, the low forming accuracy of GMA–AM still limits its one-off industrial application due to the strong and nonlinear interactions between arc–droplet transfer and molten pool. To fully understand the influential mechanism of this inherent interaction in the GMA–AM process to precisely control the part accuracy, the arc–droplet transfer behavior in the GMA–AM process with different current waveforms was firstly studied experimentally. The phenomena of the arc swing and the differing droplet transfer with the increase in deposited height were interpreted. The thermal force status of the molten pool and its balance boundary conditions were also theoretically analyzed. Finally, the microstructure and the hardness of the AM parts with different cooling times were tested and analyzed. The experimental results demonstrate that using the spray droplet transfer mode can generate a stable AM process under direct current application conditions, but it easily ends the AM process at the third or fourth layer deposition owing to excessive heat input. A more highly accurate deposition morphology can be obtained in one droplet per pulse mode under pulsed current application conditions, which also indicates that the AM process with a constant current welding supply is stabler and easily produces better deposition than the process with a constant voltage welding supply. With the increase in cooling time, the microstructure evolved from fine ferrite to equiaxed ferrite and to columnar ferrite combined with acicular ferrite with a lower proportion of pearlite in the vertical direction of the part, and the average hardness changed to ~168 HV (bottom), ~175 HV (middle), and ~250 HV (top). The analysis indicates that the heat accumulation of the molten pool is a critical factor that affects the deposition accuracy. To this end, a novel strategy that uses the heat accumulation to compensate for the energy formed in the molten pool is proposed to further reduce the arc heat input and weaken the heat accumulation, and its feasibility is discussed.

High‐Throughput Screening Thickness‐Dependent Resistive Switching in SrTiO3 Thin Films for Robust Electronic Synapse

AbstractThe functionalities and applications of oxide thin films are highly dependent on their thickness. Most thickness‐dependent studies on oxide thin films require the preparation of independent samples, which is labor‐intensive and time‐consuming and inevitably introduces experimental errors. To address this challenge, a general strategy based on high‐throughput pulsed laser deposition technology is proposed to precisely control the thin‐film thickness in local regions under similar growth conditions. The as‐proposed synthesis strategy is demonstrated using typical complex oxide materials of SrTiO3 (STO). Consequently, high‐throughput STO thin films with nine gradient thicknesses ranging from 10.1 to 30.5 nm are fabricated. Notably, a transition from the unipolar to the bipolar resistive switching mode is observed with increasing STO thickness. Moreover, a physical mechanism based on the heterostructure‐mediated redistribution of oxygen vacancies is employed to interpret the transition between the two memristive patterns. The screening of STO thin films with different resistive switching behaviors revealed that the STO thin film with a thickness of 20.3 nm exhibit excellent conductance modulation properties under the application of electrical pulses as well as significant reliability for the emulation of various synaptic functions, rendering it a promising material for artificial neuromorphic computing applications.

Transcranial application of magnetic pulses for improving brain drug delivery efficiency via intranasal injection of magnetic nanoparticles.

As the blood-brain barrier (BBB) hinders efficient drug delivery to the brain, drug delivery via the intranasal pathway, bypassing the BBB, has received considerable attention. However, intranasal administration still has anatomical and physiological limitations, necessitating further solutions to enhance effectiveness. In this study, we used transcranial magnetic stimulation (TMS) on fluorescent magnetic nanoparticles (MNPs) of different sizes (50, 100, and 300 nm) to facilitate MNP's transportation and delivery to the brain parenchyma. To validate this concept, anesthetized rats were intranasally injected with the MNPs, and TMS was applied to the center of the head. As the result, a two-fold increase in brain MNP delivery was achieved using TMS compared with passive intranasal administration. In addition, histological analysis that was performed to investigate the safety revealed no gross or microscopic damages to major organs caused by the nanoparticles. While future studies should establish the delivery conditions in humans, we expect an easy clinical translation in terms of device safety, similar to the use of conventional TMS. The strategy reported herein is the first critical step towards effective drug transportation to the brain.

Population density gratings produced by a pair of nonharmonic unipolar rectangular attosecond pulses in a resonant medium

Recently, the possibility of obtaining non-harmonic unipolar electromagnetic pulses with a specific electric field strength’s dependence on time (e.g. a rectangular pulse) has been actively discussed in optics. Unipolar pulses have a nonzero electric area and a wide spectrum: from zero frequency up to the visible region. This could open up wide application of such pulses, for example, for faster and more efficient control of the quantum systems’ properties with a high temporal resolution compared to conventional bipolar multicycle pulses. In this paper, based on an approximate solution of the time dependent Schrödinger equation and a numerical solution of the equation system for the density matrix, we show the possibility of creating electromagnetically induced population density gratings in an atomic medium using a pair of unipolar rectangular attosecond light pulses that do not overlap in the medium. The formation of such gratings can be explained on the basis of the concept of ‘interference’ of electric pulse areas, recently introduced into optics.

Ultrasound can increase biofilm formation by Lactiplantibacillus plantarum and Bifidobacterium spp.

The main goal of this research was to study the effect of an Ultrasound (US) treatment on biofilm formation of Lactiplantibacillus plantarum (strains c19 and DSM 1055), Bifidobacterium animalis subsp. lactis DSM 10140, Bifidobacterium longum subsp. longum DSM 20219, and Bifidobacterium longum subsp. infantis DSM 20088. From a methodological point of view, each microorganism was treated through six US treatments, different for the power (10, 30, or 50% of the net power, 130 W), the duration (2, 6, or 10 min) and the application of pulses (0 or 10 s). After the treatment, a biofilm of the strains was let to form on glass slides and the concentration of sessile cells was analyzed for 16 days. Biofilms formed by untreated microorganisms were used as controls. As a first result, it was found that US significantly increased the concentration of sessile cells of B. longum subsp. infantis, while for some other strains US treatment could not affect the formation of biofilm while improving its stability, as found for L. plantarum DSM1055 after 16 days. The variable mainly involved in this positive effect of US was the duration of the treatment, as biofilm formation and stability were improved only for 2 min-treatments; on the other hand, the effect of power and pulses were strain-dependent. In conclusion, the results suggest practical implication of a US pre-treatment for various fields (improvement of adhesion of microorganisms useful in food or in the gut, biomedical and environmental industries), although further investigations are required to elucidate the mode of action.

Quantum sensing of control errors in three-level systems by coherent control techniques

Quantum coherent control of a quantum system with high-fidelity is rather important in quantum computation and quantum information processing. There are many control techniques to reach these targets, such as resonant excitation, adiabatic passages, shortcuts to adiabaticity, and so on. However, for a single pulse to realize population transfer, the external tiny error has a trivial influence on the final population. The repeated application of the same pulse will greatly amplify the error effect, making it easy to be detected. Here, we propose to measure small control errors in three-level quantum systems by coherent amplification of their effects, using several coherent control techniques. For the two types of Hamiltonian with SU(2) dynamic symmetry, we analyze how the fidelity of population transfer are affected by Rabi frequencies fluctuation and static detuning deviation, based on the pulse sequence with alternating and same phases, respectively. It is found that the sensitivity of detecting these errors can be effectively amplified by the control pulse sequences. Furthermore, we discuss the efficiency of sensing the two errors with these control techniques by comparing the full width at half maximum of the population profiles. The results provide an accurate and reliable way for sensing the weak error in three-level quantum systems by applying repeatedly the coherent control pulse.

All-Organic PTFE Coated PVDF Composite Film Exhibiting Low Conduction Loss and High Breakdown Strength for Energy Storage Applications

Plastic film capacitors are widely used in pulse and energy storage applications because of their high breakdown strength, high power density, long lifetime, and excellent self-healing properties. Nowadays, the energy storage density of commercial biaxially oriented polypropylene (BOPP) is limited by its low dielectric constant (~2.2). Poly(vinylidene fluoride) (PVDF) exhibits a relatively high dielectric constant and breakdown strength, making it a candidate material for electrostatic capacitors. However, PVDF presents significant losses, generating a lot of waste heat. In this paper, under the guidance of the leakage mechanism, a high-insulation polytetrafluoroethylene (PTFE) coating is sprayed on the surface of a PVDF film. The potential barrier at the electrode-dielectric interface is raised by simply spraying PTFE and reducing the leakage current, and then the energy storage density is increased. After introducing the PTFE insulation coating, the high-field leakage current in the PVDF film shows an order of magnitude reduction. Moreover, the composite film presents a 30.8% improvement in breakdown strength, and a 70% enhancement in energy storage density is simultaneously achieved. The all-organic structure design provides a new idea for the application of PVDF in electrostatic capacitors.

Self-healing magnetorheological elastomers based on thermoreversible Diels–Alder networks

Magnetorheological (MR) elastomers are a class of stimuli-responsive materials of which the damping and stiffness can be reversibly tailored by applying magnetic fields. However, concerns such as fatigue damage, insufficient MR efficiencies with low loadings of magnetic particles or highly crosslinked elastomers, and lack of reprocessability remain unaddressed for conventional MR elastomers. To this end, a series of self-healing MR elastomers (SHMRE) were prepared based on thermoreversible Diels–Alder covalent crosslinks. The application of magnetic pulses yielded pre-aligned magnetic particles chains within the curing matrix which strongly influenced the SHMRE rheological properties. The resulting composites do not only exhibit a large MR effect but also efficient self-healing properties at room temperature. We found that the particle loading and the field-induced orientation of the aggregates affect the magnitude of the MR response, the mechanical strength and the healing efficiency. In addition, the MR response is also strongly influenced by the temperature. With a temperature increase from room temperature to 70 °C, a change in the MR response from 90% to 462% is observed while the SHMRE retain a solid viscoelastic state at 50 wt% particles loading. Interestingly, the thermoreversible features of the synthesized networks also allow potential reprocessability of SHMRE when heating these systems above the gel transition temperature (89 °C–90 °C). The final low viscous state makes it possible for the magnetic particles to be potentially restructured as chains by applying a magnetic field, which are retained upon cooling when the solid network state is recovered. The proposed SHMRE systems are shown to be a highly efficient and reprocessable solution to substitute classical MR elastomers in a wider context of generalized MR materials.

Role of root hair elongation in rhizosheath aggregation and in the carbon flow into the soil

One of the most prominent changes in the rhizospheric soil structure is associated with the formation of a strongly bound soil layer in the surroundings of the root, which is named rhizosheath. In this study, we investigated how root hair elongation, a ubiquitous root morphological trait, affect the stability of rhizosheath aggregates. Using 13CO2 pulse labeling, we tracked the fate of root-derived 13C inputted into the rhizosheath of two Zea mays L. genotypes with contrasting root hair elongation: a mutant with root hair defective elongation (rth3) and a corresponding wild type (WT). In addition, we also investigated the differences between two 13CO2 labeling approaches (single vs. multiple pulse labeling) in the distribution of 13C in the rhizosheath aggregates. We were able to demonstrate that the rhizosheath aggregate stability and the resulting aggregate size distribution follows the same mechanisms irrespective of the root hair elongation. This result reinforces the assumption that other soil properties are more decisive for the soil structure formation in the rhizosheath in comparison to root hair elongation. The majority of recently deposited root-derived C (57%) was found in the macroaggregates. Increasing the number of pulses (multiple pulse labeling approach) resulted in a higher 13C enrichment of the rhizosheath aggregates fractions in comparison to the application of a single pulse. While both labeling approaches resulted in a similar distribution of 13C in the rhizosheath aggregates, the higher enrichment given by multiple pulse labeling allowed the separation of significant differences between the genotypes in plant C allocation in the rhizosheath.

DIRECT EXPERIMENT ON THE PASSAGE OF ULTRA-WIDEBAND PULSES OF SUBNANOSECOND DURATION IN THE EARTH’S ATMOSPHERE

The results of the first direct experiments on the passage of pulses of ultra-wideband radiation of subnanosecond duration in the Earth’s atmosphere at a distance of more than 10 km are presented. In contrast to the calculated work, the preservation of the amplitude-time shape of the pulses in the process of increasing the distance is shown. The establishment of this fact is of decisive importance in the practical application of ultra-wideband pulses in new technological developments.

Polarity dependence of CO2 conversion in nanosecond pulsed large gap dielectric barrier discharges

The splitting of carbon dioxide was investigated for a coaxial dielectric barrier discharge, which was operated with nanosecond high-voltage pulses of 500 ns and amplitudes up to 20 kV at ambient temperature and atmospheric pressure. A non-thermal plasma could be established across a gap distance of 4 mm and a length of 90 mm for gas flows of 30–210 sccm of pure CO2 and with admixtures of Argon. The application of high-voltage pulses of either positive or negative polarity resulted in distinct differences in effective conversion and CO production. The highest observed conversion of 6.6%, corresponding to a CO production of 7%, was achieved for positive high-voltage pulses of 20 kV that were applied with a repetition rate of 3 kHz for a ratio of CO2:Ar of 1:2 at a flow rate of 30 sccm. Conversely, an operation with negative high-voltage pulses, for otherwise the same operating parameters, resulted in an effective conversion of only 5.3% and CO production of 5.4%. The corresponding conversion rates for specific energy input (SEI), concerning different operating parameters, could be related to reaction enthalpies that were calculated from thermodynamic functions. The differences in polarity were associated with discharge characteristics, i.e., plasmas appeared more filamentary for positive high-voltage pulses. In this case, a visible plasma could also be established for much lower pulse amplitudes.Graphical

Enhancement of reactive oxygen species production in triple negative breast cancer cells treated with electric pulses and resveratrol.

Triple negative breast cancer (TNBC) is difficult to treat since it lacks all the three most commonly targeted hormone receptors. Patients afflicted with TNBC are treated with platinum core chemotherapeutics, such as cisplatin. Despite the initial effective anticancer effects of cisplatin, TNBC attenuates its effect and develops resistance eventually, which results in tumor reoccurrence. Hence, there is a critical demand for effective, alternative, and natural ways to treat TNBC. Towards this, a promising technique for inhibiting TNBC cell proliferation involves promoting the production of reactive oxygen species (ROS), which triggers pro-apoptotic caspases 9 and 3. Resveratrol (RESV), an active bio compound found in naturally available fruits, such as grapes, is utilized in this research for that. In addition, electrochemotherapy (ECT), which involves the application of electrical pulses (EP), was utilized to enhance the uptake of RESV. MDA-MB-231, human TNBC cells were treated with/out RESV, and eight 600-1,000 V/cm, 100 μs pulses at 1 Hz. The cells were characterized by using various assays, including viability assay, and ROS assay. A TNBC cell viability of as low as 20% was obtained at 24 h (it was 13% at 60 h), demonstrating the potential of this novel treatment. ROS production was the highest in the combination of EP at 1,000 V/cm along with RESV at 100 μmol/L. Results indicate that RESV has the potential as an anti-TNBC agent and that EP + RESV can significantly enhance the cell death to reduce MDA-MB-231 cell viability by increasing ROS production and triggering apoptosis.

The Usefulness of Motor Potentials Evoked Transvertebrally at Lumbar Levels for the Evaluation of Peroneal Nerve Regeneration after Experimental Repair in Rats

Motor evoked potentials (MEPs) are used in neurology as part of a precise diagnostic method to study the transmission of efferent neural impulses at the central and peripheral levels of the nervous system. Previous attempts have been made to apply MEPs in animal studies for evaluating neural transmission at the motor cortex center level to the muscles of the forelimbs and hindlimbs. In clinical and experimental studies, little attention is focused on the significance of the magnetic stimulation of spinal cord structures with the direct recording of the evoked potentials from peripheral nerve motor fibers. The aim of this paper was to evaluate the usefulness of the motor potentials evoked transvertebrally at lumbar levels in the evaluation of experimental peroneal nerve regeneration in rats. The bilateral transmission of efferent impulses in the distal parts of the peroneal and tibial nerves was verified by recordings of evoked potentials following transvertebral magnetic stimulation at lumbar levels (MEPs) and the electrical stimulation of the sciatic nerve in classical electroneurographic (ENG) tests for comparison. Recordings were performed 24 weeks after grafts on surgically treated hindlimbs as well as on non-operated hindlimbs as controls. Both the MEP and ENG stimulations resulted in evoked potentials with larger amplitude values following the application of the magnetic pulses, with more being recorded on the non-operated hindlimbs than on the operated ones when recordings were taken from peroneal nerve branches. We observed statistically significant correlations between the MEP and ENG results for peroneal and tibial nerve amplitude on the non-operated side and peroneal nerve amplitude on the operated side. The recorded latencies of the evoked potentials were shorter in the ENG studies than in the MEPs for the non-operated side. The results demonstrated the phenomenon of regeneration in the motor fibers of the peroneal nerves 24 weeks after grafting in the experimental conditions. In this study, the MEPs were as useful as the ENG studies for evaluating regeneration in the motor fibers of hindlimb nerves in rats, although they were not significantly different. This paper discusses the clinical importance of transvertebral MEPs induced at the lumbosacral and cervical levels with a magnetic field for the diagnostic evaluation of efferent impulse transmission at different levels of the motor pathway.

The Impact of a Pulsed Light Stream on the Quality and Durability of the Cold-Stored Longissimus Dorsal Muscle of Pigs.

The purpose of this study was to investigate the effect of pulsed light application (exposure to a pulsed light beam (PL) of 400 Hz for a period of 60 s, with an energy dose of 600 mW and wavelengths of 660 and 405 nm) on the physicochemical, technological, and sensory properties, as well as the nutritional value and shelf life of cold-storage pig longissimus dorsi muscle. Each muscle was divided into six parts, three of which were control samples, and the rest were exposed to pulsed light. The detailed laboratory tests of the meat were conducted 1, 7, and 10 days after slaughter. The meat was cold stored at +3 °C ± 0.5 °C. The study showed that the application of pulsed light has a favorable effect on lowering the TBARS index, oxidation-reduction potential, and water activity values. In addition, the application of PL had no statistically significant effect on the variation in the perception of selected sensory characteristics of meat. Furthermore, PL processing, as a low-energy-intensive method that can be environmentally friendly and thus have a large potential for implementation, is an innovative way to extend the shelf life, especially of raw meat, without a negative impact on its quality. This is of particular importance for food security (especially in the quantitative and qualitative aspects of food, but also in terms of food safety).

Thermal Analysis of Flip-Chip Bonding Designs for GaN Power HEMTs with an On-Chip Heat-Spreading Layer

In this work, we demonstrated the thermal analysis of different flip-chip bonding designs for high power GaN HEMT developed for power electronics applications, such as power converters or photonic driver applications, with large gate periphery and chip size, as well as an Au metal heat-spreading layer deposited on top of a planarized dielectric/passivation layer above the active region. The Au bump patterns can be designed with high flexibility to provide more efficient heat dissipation from the large GaN HEMT chips to an AlN package substrate heat sink with no constraint in the alignment between the HEMT cells and the thermal conduction bumps. Steady-state thermal simulations were conducted to study the channel temperatures of GaN HEMTs with various Au bump patterns at different levels of current and voltage loadings, and the results were compared with the conventional face-up GaN die bonding on an AlN package substrate. The simulations were started from a single finger isolated HEMT cell and then extended to multiple fingers HEMT cells (total gate width > 40 mm) to investigate the "thermal cross-talk" effect from neighboring devices. Thermal analysis of the GaN HEMT under pulse operation was also performed to better reflect the actual conditions in power conversion or pulsed laser driver applications. Our analysis provides a combinational assessment of power GaN HEMT dies under a working condition (e.g., 1MHz, 25% duty cycle) with different flip chip packaging schemes. The analysis indicated that the channel temperature rise (∆T) of a HEMT cell in operation can be reduced by 44~46% by changing from face-up die bonding to a flip-chip bonding scheme with an optimized bump pattern design.