Periodic Bursts Research Articles

Gravity-induced seismicity modulation on planetary bodies and their natural satellites

Ground-based monitoring of seismicity and modulation by external forces in the field of planetary seismology remains equivocal due to the lack of natural observations. Constrained by the natural observations (including Earthquakes, Moonquakes, and Marsquakes) and theoretical models, we present the variation in gravitational acceleration “g” of different solar system objects, combined with external harmonic forcings that are responsible for seismicity modulation on the planetary bodies and their natural satellites. From the global diversity in seismicity modulation, it has been observed that the plate-boundary regions on the Earth exhibit both short and long-period seismicity modulation. In contrast, the stable plate interior regions appear to be more sensitive to long-period seismicity modulation, however, lacking in short-period modulation. The deep Moonquakes are susceptible for both the lunar tidal period (13.6 days and 27 days) and long-period pole wobble modulation (206 days), whereas shallow emergent type moonquakes show a seismic periodicity at the lunation period (29.5 days). Further, the seasonal variation with an annual seismicity burst and seismic periodicity at polar wobble periods for high-frequency Marsquakes captured by InSight lander indicate a natural origin. Whereas diurnal and semi-diurnal periodicity along with Phobos’ tidal period, indicate possible artifacts due to different detection probabilities and non-seismic noise in the Martian environment. We argue that, in the context of rate-state-dependent fault friction, the gravity-induced resonance destabilization model appears to be better agreement with the contrast and relative diversity in seismicity modulation linked to the Earth, Moon, and Mars.

Switching dynamics of a Filippov memristive Hindmash–Rose neuron model with time delay

Considering the existence of magnetic induction effect with different intensities in the process of subthreshold and suprathreshold oscillations of bioelectrical activities, a non-smooth feedback strategy for memristive current with time delay is proposed, and then a four-dimensional Filippov Hindmarsh–Rose (HR) neuron model is established. The local stability and bifurcation patterns of delayed subsystems are qualitatively analyzed. Accordingly, the discriminant formula for the direction and stability of periodic solutions generated by Hopf bifurcation is obtained on the center manifold. Importantly, the stability of subsystems has switching behavior, which is accompanied by abundant hidden electrical activities under the effect of time delay. The theoretical analysis clarifies that the proposed feedback strategy leads to complex sliding mode dynamics, including sliding segments, various equilibrium points and sliding bifurcations. Meanwhile, the analytical conditions for motions of grazing, sliding, and crossing are developed and verified based on the flow switching theory. Moreover, the mechanism and evolutive rule of the self-excited and hidden sliding electrical activities are revealed by the fast-slow variable dissection method. Finally, it is verified that the time delay can not only induce bistable structures composed of the quiescent state and periodic bursting, but also eliminate the hidden sliding dynamics.

Подкритическая конвекция в коллоидах и жидких бинарных смесях с положительной термодиффузией

The paper analyzes convection of molecular binary mixtures and colloids with positive thermal diffusion that occurs in the case of heating from below and below the equilibrium stability threshold for a homogeneous liquid. The convection is pulsed in nature and is realized in the form of periodic bursts. Positive thermal diffusion displaces the heavy component into the upper cold layers of the liquid. There, the heavy component accumulates in the boundary layer, forming a growing unstable density stratification. When the inhomogeneity exceeds the critical value for a given geometry, a convective surge occurs, and the heavy component moves down to a stable position. The study has found the critical thickness of the boundary layer, the critical concentration difference at the boundaries of the cavity, and the time at which instability occurs. Based on the analysis of the problem of the concentration profile dynamics under the influence of gravitational sedimentation and thermal diffusion, experimental facts are explained – periodic convective bursts of the binary mixture in channels and in the Hele-Shaw cell below the critical Rayleigh number. The described mechanism probably explains the convection observed by other experimenters in a horizontal flat layer of magnetic fluids below the critical Rayleigh number at Ra < 1708.

Analysis of Near-wall Coherent Structure of Spiral Flow in Circular Pipe Based on Large Eddy Simulation

Based on the large eddy simulation method, this study performed the three-dimensional transient numerical analysis of the near-wall flow field of the spiral flow in a circular pipe and applied the sub-grid model of the kinetic energy transport. The low-speed bands, streamwise vortices and hairpin vortices of the spiral flow in the near-wall region of the circular pipe are determined using the Q criterion. The ejection and sweeping of coherent structures are identified using the velocity vector of the near-wall region; moreover, the two methods of creating the hairpin vortices are established by the image time series. The results demonstrate that the development directions of the near-wall bands, streamwise vortices and hairpin vortices of the spiral flow in the circular pipe develop along the path of the spiral line. The average spanwise period of the low-speed bands in the near-wall region is approximately 120 wall units, the length is more than 900 wall units and the height is not more than 40 wall units. The separation distance of the streamwise vortices is about 119 wall units. It has a certain angle with the wall (approximately 22°). The average burst period of a hairpin vortices is less than 0.015 s.

Mapping the landscape of PSC-CM research through bibliometric analysis.

The discovery of pluripotent stem cell-derived cardiomyocytes (PSC-CMs) has not only deepened our understanding of the pathogenesis and progression of heart disease, but also advanced the development of engineered cardiac tissues, cardiac regenerative therapy, drug discovery and the cardiotoxicity assessment of drugs. This study aims to visualize the developmental trajectory of PSC-CM research over the past 18 years to identify the emerging research frontiers and challenges. The literature on PSC-CMs from 2007 to 2024 was retrieved from the Web of Science and PubMed databases. Bibliometrix, VOSviewer and CiteSpace software were used for statistical analysis and visualization of scientific literature. Previous clinical trials were summarized using data from the ClinicalTrials.gov database. A total of 29,660 authors from 81 countries and regions published 6,406 papers on PSC-CMs over the past 18 years. The annual output of PSC-CM research experienced a general upward trend from 2007 to 2021, reaching its peak in 2021, followed by a notable decline in 2022 and 2023. The United States has emerged as the most influential nation in this field, with Stanford University being the most prolific institution and Joseph C. Wu standing out as the most productive and highly cited scholar. Circulation Research, Circulation, and Nature have been identified as the most co-cited journals. Organ-on-a-chip, 3D bio-printing, cardiac microtissue, extracellular vesicle, inflammation, energy metabolism, atrial fibrillation, personalized medicine etc., with a longer burst period, and maturation of PSC-CMs, with the highest burst strength of 27.19, are the major research focuses for rigorous investigation in recent years. Cardiac organoid is emerging as a promising key research frontier. While the clinical trials of stem-cell-mediated treatment for heart diseases shows promise, significant challenges remain. Further research is imperative to optimize protocols, enhance cell delivery methods, and establish standardized practices to improve clinical outcomes. In conclusion, several major research hotspots, including engineered cardiac tissue and maturation, exosome-based regenerative therapy, inflammation response, energy metabolism, atrial fibrillation, and personalized medicine etc. will continue to attract substantial interest from investigators worldwide. Cardiac organoids to in vitro recapitulate the intricate human heart is emerging as a promising key research frontier. Significant challenges persist in the clinical trials of stem-cell-mediated therapies for heart diseases.

Main Problems and Outcomes of the Activities of the Organization for Democracy and Economic Development – ODED in 1997–2022

Introduction. The article analyzes the main directions and trends of the development of ODED as an international organization from its formation in 1997 to the present events of 2022. The author summarizes the activities of this structure over more than 20 years of its existence. Results and Discussion. The author concludes that despite periodic bursts of activity, the overall activities of this organization have been largely declaratory in nature and have not led to any significant practical results. Although the Organization for Democracy and Economic Development – ODED, which includes Ukraine, Moldova, Georgia, and Azerbaijan, has repeatedly raised the issue of including the union in global transportation routes for energy supplies, no major projects have been implemented. According to the author, the main reason for this has been the politicized nature of the organization, which was initially created primarily to counter Russia’s integration aspirations in the post-Soviet space with the support of Western actors such as the EU, NATO, and the United States. Conclusion. In reality, the ODED member countries have different goals on the international stage and have virtually no common economic interests. As a result, today ODED primarily serves as a negotiating platform for a small range of issues.

EEG in ICU: what the intensivist should know

The EEG is the record of brain electrical fields, characterized by a high temporal resolution but a limited spatial resolution. EEG is largely available, noninvasive and recorded at the patient’s bedside. The main interest of EEG in intensive care unit (ICU) is the detection of seizures or status epilepticus and the investigation of confusion or persistent coma. The EEG can also be useful for the diagnosis of encephalopathy, encephalitis and brain death. EEG allows the assessment of the initial severity of a primary cerebral insult (after cardiac arrest (CA), traumatic brain injury or stroke), as the brain injury severity is correlated with the predominant frequency, the background continuity and the mean amplitude of recorded electrical brain activities. Finally, EEG represents the most widely tool use in recent surveys examining current neuro-prognostication practices after CA, as “highly malignant” patterns (i.e., suppression with or without periodic discharges and burst suppression) remain highly correlated with poor neurological outcome. In this review, we summarize EEG signal generators, recording modalities, interpretation, potentials confounding factors and prognostic values of the different EEG patterns. Finally, we assess the perspective for the future of ICU, as continuous EEG monitoring (cEEG) and quantitative analysis of the EEG (qEEG).

Enhancing protein delivery for tissue regeneration: Development of AGR2-loaded hydrogels with controlled release properties

The growth factor Anterior Gradient 2 (AGR2) has been shown to have an effective role in tissue regeneration, but remained largely unexplored in localized tissue engineering applications. Alginate beads have been proven as safe carriers for protein encapsulation, but they suffer from fragility and uncontrolled protein release. For such alginate systems, little is known about how changes in concentrations and ion-crosslinking affect protein release and accumulation in 3-D matrices. To address these questions, an engineered interpenetrating polymer network (IPN) has been used to synthesize a novel hybrid system consisting of AGR2 loaded beads composed of calcium-crosslinked sodium alginate (SA) and carboxymethyl cellulose (CMC). These beads are embedded in films consisting of SA and polyvinyl alcohol (PVA), using a simple ion gelation technique. We assess protein release kinetics and accumulation within the hybrid system by varying polymer concentrations and cross-linking parameters. The IPN hybrid system maintains controlled release over two weeks, without an initial burst period. Through this approach efficicnt delivery of AGR2 is achieved which in turn effectively mediates cell migration and proliferation, resulting in excellent cell viability and complete wound closure. The described release system opens new perspectives in tissue engineering.

Memristive Hopfield neural network dynamics with heterogeneous activation functions and its application

Activation functions play a crucial in emulating biological neurons within artificial neural networks. However, the exploration of neural networks composed of various activation functions and their associated dynamics have not been noticed yet. This paper proposes a novel method by introducing heterogeneous activation functions into a memristive Hopfield neural network for the first time. The special feature of the proposed model lies not only in its ability to mimic the diversity of brain neurons, providing a more realistic and adaptable frame for artificial neural networks but also in its rich dynamic properties suitable for engineering applications. Theoretical and experimental investigations into the dynamics of the memristive Hopfield neural network are conducted, employing phase portraits, bifurcation diagrams, Lyapunov exponent spectra, 0–1 tests, and bi-parameter dynamic maps. Complex dynamical behaviors, including periodic bursting, chaotic bursting, and chaotic state jump are revealed by the numerical simulations. Furthermore, a hardware implementation of the proposed neural network is designed and validated through circuit simulation software, which is consistent with the numerical simulation and confirms the validity of the proposed model. Finally, an encryption scheme based on the chaotic bursting is also proposed and evaluated. Results demonstrate that the chaotic bursting attractor exhibits excellent randomness, making it well-suited for image encryption applications. The novel exploration of heterogeneous activation neuronal networks in this paper may pave the way for further research in the field of more bionic networks with complex dynamical behaviors and their applications.

A mechanistic analysis of particle flow in a pulsatile circulating dual fluidized bed for chemical looping technology based on CDF-DEM simulation

This paper presents a three-dimensional computational fluid dynamic–discrete element method (CFD-DEM) model using Geldart class D particles for studying the fluid flow pattern in a circulating dual fluidized bed (CDFB) for chemical looping dry reforming of methane (CLDRM). The system design comprised a high-velocity air reactor (AR) also known as riser fluidized bed, a riser tube, a cyclone chamber, a fluidizing bed fuel reactor (FR), and a connecting loop, which closes the loop between AR and FR. The particles distribution, volume fraction, flow pattern, velocity and their circulation between the AR (riser) and FR (second fluidized bed) in CDFB were deeply investigated. The results showed that the CLDRM system experiences a pressure imbalance between the reduction and oxidation zones, causing solid particles to undergo a highly intricate and turbulent pulse flow. As a result, the operation of the system is alternately governed by two flow regimes: bubbling fluidization and pulsatile circulating fluidization. The burst of a high pressure pulses provide the pressure head required for circulation of the particles. The pulses also led to the intermittent transportation of particles ― in the form of particles clusters ― from high-pressure area to the region with a lower pressure.

Josephson junction oscillator embedded in the microcontroller: Pseudo-random number generation and combination synchronization

Dynamical scrutiny of the resistive capacitive inductive shunted Josephson junction (JJ) oscillator (RCLSJJO), microcontroller realization, pseudo-random number generation (PRNG) and combination synchronization are achieved in this paper. Numerical probing led to the establishment that the RCLSJJO is characterized by regular behaviors, bistable periodic-2-oscillations, periodic bursting characteristics and various shapes of chaotic dynamics. Thereafter, the vast dynamical characteristics obtained theoretically are realized by the microcontroller realization with qualitative agreements. Moreover, a chaos-based PRNG is designed by using chaotic RCLSJJO and linear feedback shift register (LFSR) as post-processing unit. Satisfactory results are obtained from the NIST 800–22 test suite and the randomness of binary data generated from the proposed RCLSJJO-based PRNG is confirmed for chaos-based digital applications. Lastly, the combination chaos synchronization of two drive and one response RCLSJJO is proven thanks to the theoretical analysis.

Evaluating the Effects of Rewards and Schedule Length on Response Rates to Ecological Momentary Assessment Surveys: Randomized Controlled Trials.

Ecological momentary assessments (EMAs) are short, repeated surveys designed to collect information on experiences in real-time, real-life contexts. Embedding periodic bursts of EMAs within cohort studies enables the study of experiences on multiple timescales and could greatly enhance the accuracy of self-reported information. However, the burden on participants may be high and should be minimized to optimize EMA response rates. We aimed to evaluate the effects of study design features on EMA response rates. Embedded within an ongoing cohort study (Health@NUS), 3 bursts of EMAs were implemented over a 7-month period (April to October 2021). The response rate (percentage of completed EMA surveys from all sent EMA surveys; 30-42 individual EMA surveys sent/burst) for each burst was examined. Following a low response rate in burst 1, changes were made to the subsequent implementation strategy (SMS text message announcements instead of emails). In addition, 2 consecutive randomized controlled trials were conducted to evaluate the efficacy of 4 different reward structures (with fixed and bonus components) and 2 different schedule lengths (7 or 14 d) on changes to the EMA response rate. Analyses were conducted from 2021 to 2022 using ANOVA and analysis of covariance to examine group differences and mixed models to assess changes across all 3 bursts. Participants (N=384) were university students (n=232, 60.4% female; mean age 23, SD 1.3 y) in Singapore. Changing the reward structure did not significantly change the response rate (F3,380=1.75; P=.16). Changing the schedule length did significantly change the response rate (F1,382=6.23; P=.01); the response rate was higher for the longer schedule (14 d; mean 48.34%, SD 33.17%) than the shorter schedule (7 d; mean 38.52%, SD 33.44%). The average response rate was higher in burst 2 and burst 3 (mean 50.56, SD 33.61 and mean 48.34, SD 33.17, respectively) than in burst 1 (mean 25.78, SD 30.12), and the difference was statistically significant (F2,766=93.83; P<.001). Small changes to the implementation strategy (SMS text messages instead of emails) may have contributed to increasing the response rate over time. Changing the available rewards did not lead to a significant difference in the response rate, whereas changing the schedule length did lead to a significant difference in the response rate. Our study provides novel insights on how to implement EMA surveys in ongoing cohort studies. This knowledge is essential for conducting high-quality studies using EMA surveys. ClinicalTrials.gov NCT05154227; https://clinicaltrials.gov/ct2/show/NCT05154227.

100-kHz RM calcium ion NIR laser

The experimental study of the laser on RM 4p2P3/2∘ - 3d2D5/2 (λ=854.2nm) and 4p2P1/2∘ - 3d2D3/2 (λ=866.2nm) transitions in a singly ionized calcium with active medium volume of 97 cm3 has been carried out. Excitation was performed with the periodic bursts containing 200 pulses each. It is shown that the laser pulse energy enters the steady-state mode during the burst. When the frequency of pulses inside the burst equaled to 90 kHz the steady-state value of the laser energy was 59 mJ, which corresponds to the average output power of 5.3 W. The measured power ratio between lines with λ=854.2nm and λ = 866.2 nm under optimum conditions amounted to 1.7, with radiation pulse duration of 20 ns. Experimental results for lasers on atom RM-transitions operating at pulse repetition frequency f≥100 kHz are reviewed. It is demonstrated that at such f values the energy characteristics of the Ca+ laser are comparable with those of lasers on atom RM transitions of other metals. An analysis of the mechanisms preventing further increase in the average output power when the pulse repetition frequency is increased above 100 kHz is presented.

OR06-05 Differential Regulation Of Transcriptional State Switching Revealed By Endocrine Disruptor Chemicals

Abstract Disclosure: C. Day: None. P. Yasar: None. J. Rodriguez: None. Gene regulation is complex, involving the coordination of hundreds of proteins that function to control genome accessibility, mediate enhancer-promoter interactions, and initiate transcription. At individual loci, transcriptional initiation is stochastic in time, resulting in short periods of nascent RNA synthesis known as transcriptional bursts. Some genes switch between periods of transcriptional bursting and long periods of inactivity. These variable periods of inactivity can last days and lead to gene expression heterogeneity in cancer cells. Here we investigate how transcriptional bursting of estrogen regulated genes is modulated by low affinity estrogen receptor alpha (ERα) ligands, specifically endocrine disruptor chemicals (EDCs). Using live cell MS2-imaging of the estrogen responsive TFF1 gene, we observed that cells treated with genistein or Bisphenol A (BPA) exhibited burst initiation and duration kinetics which were indistinguishable from cells induced with Estradiol (E2). However, there was a 50% reduction in the number of active alleles in BPA treated cells. Our data suggest that BPA treated cells can activate TFF1 alleles that are in transcriptionally permissive states, while E2 and genistein can additionally switch alleles from a repressed state to a transcriptionally permissive state. To understand the contribution of the enhancer on state switching, we deleted the nearby enhancer and observed a similar number of active alleles between cells treated with E2 or BPA. Taken together, our work reveals that ERα and the TFF1 enhancer have roles in activation and state switching at a heterogeneously expressed gene. Our results also highlight different modes of regulation for endocrine disruptor chemicals at the same gene. Presentation: Thursday, June 15, 2023

A New Compact Model for Third-Order Memristive Neuron With Box-Shaped Hysteresis and Dynamics Analysis

This paper proposes a new compact model and presents circuit-theoretical analysis for a third-order memristive neuromorphic element fabricated by S. Kumar et al. The proposed model mainly consists of a box-shaped resistor model and a simplified piecewise-linear memristor model. Since the dynamic behavior of the box-shaped hysteresis in the quasi-static current-voltage curve is mostly unexplored, we firstly extract the box-shaped resistor model and construct its oscillators. The coordinate system shifting method and dynamic route analysis method are used to reveal the operating mechanism of box-shaped resistor-based oscillators. Both the theoretical analysis and simulation verification indicate that the box-shaped hysteresis characteristic facilitates the generation of neuromorphic action potentials. The proposed new compact model not only captures quasi-static characteristics, but also includes dynamic behaviors, such as action potential, periodic spiking, and periodic bursting. The influences of the model parameters are further investigated to reveal the mechanism of the neuromorphic behaviors in the box-shaped hysteresis and positive differential resistance regions. Simulation results manifest the feasibility of the proposed model and the correctness of the presented analysis methods, which pave the way to the optimized design of memristive devices and the research of neuromorphic dynamics.

Detection of intended and unintended emissions from Starlink satellites in the SKA-Low frequency range, at the SKA-Low site, with an SKA-Low station analogue

Context. Intended and unintended radio emissions from satellites can interfere with sensitive radio telescopes in the frequency ranges of key experiments in astrophysics and cosmology. We detect strong intended and unintended electromagnetic radiation from Starlink satellites at the site of the future SKA-Low facility in Western Australia, using an SKA-Low prototype station known as the Engineering Development Array version 2 (EDA2). Aims. We aim to show that Starlink satellites are easily detectable utilising a configuration of low frequency radio antennas representative of an SKA-Low ‘station’ and that our results complement similar findings with the LOFAR telescope. Methods. Utilising the EDA2 at frequencies of 137.5 MHz and 159.4 MHz, we detected trains of Starlink satellites on March 17 and 18, 2023, and November 16 and 17, 2021, respectively, via the formation of all-sky images with a frequency resolution of 0.926 MHz and a time resolution of 2 s. Time differencing techniques were utilised to isolate and characterise the transmissions from Starlink and other satellites. Results. We observed Starlink satellites reaching intensities of 106 Jy beam−1, with the detected transmissions exhibiting a range of behaviours, from periodic bursts to steady transmission. The results are notable because they demonstrate that Starlink satellites are detected in the SKA-Low frequency range, transmitting both intentionally and unintentionally. Follow-up work and discussion are needed to identify the cause of this unintentional radiation as it has the potential to interfere with SKA-Low science. It is likely that the transmission levels will need to be reduced by orders of magnitude to bring the impact on radio astronomy to potentially manageable levels. Conclusions. Our results indicate that both intended and unintended radiation from Starlink satellites will be detrimental to key SKA science goals without mitigation. A continued conversation with SpaceX could potentially result in future mitigations which the EDA2 instrument could efficiently monitor and characterise at the SKA-Low site.

Development of space-resolved EUV spectrometers working at 5–138 Å for profile observation of high-Z impurity ions in EAST plasma

In order to observe the radial profile of impurity line emission in a short wavelength range and to study the transport of metallic impurity ions intrinsically existing in plasma, two pairs of space-resolved extreme ultraviolet (EUV) spectrometers working at 5–138 Å were newly established on EAST tokamak. A back-illuminated complementary metal oxide semiconductor (CMOS) detector with a small pixel size of 6.5 × 6.5 μm2 and a varied-ling-spacing (VLS) concave holographic grating with a central density of 2400 grooves/mm allows the EUV spectrometers have good spectral resolution. A precise wavelength calibration is performed with cubic polynomial fitting using well-known emission lines from light impurity ions. The radial intensity profile of Cu XX at 12.570 Å and Cu XXI at 10.392 Å were observed successfully by space-resolved EUV spectrometers during H-mode discharge. The rapid change in the W XXXIII radial profile during the impurity burst period was clearly observed with sufficient intensity. The results show that the newly developed space-resolved EUV spectrometers have excellent performance in impurity diagnostics.

A lytic phage to control multidrug-resistant avian pathogenic Escherichia coli (APEC) infection.

The inappropriate use of antibiotics has led to the emergence of multidrug-resistant strains. Bacteriophages (phages) have gained renewed attention as promising alternatives or supplements to antibiotics. In this study, a lytic avian pathogenic Escherichia coli (APEC) phage designated as PEC9 was isolated and purified from chicken farm feces samples. The morphology, genomic information, optimal multiplicity of infection (MOI), one-step growth curve, thermal stability, pH stability, in vitro antibacterial ability and biofilm formation inhibition ability of the phage were determined. Subsequently, the therapeutic effects of the phages were investigated in the mice model. The results showed that PEC9 was a member of the siphovirus-like by electron microscopy observation. Biological characterization revealed that it could lyse two serotypes of E. coli, including O1 (9/20) and O2 (6/20). The optimal multiplicity of infection (MOI) of phage PEC9 was 0.1. Phage PEC9 had a latent period of 20 min and a burst period of 40 min, with an average burst size of 68 plaque-forming units (PFUs)/cell. It maintained good lytic activity at pH 3-11 and 4-50°C and could efficiently inhibit the bacterial planktonic cell growth and biofilm formation, and reduce bacterial counts within the biofilm, when the MOI was 0.01, 0.1, and 1, respectively. Whole-genome sequencing showed that PEC9 was a dsDNA virus with a genome of 44379 bp and GC content of 54.39%. The genome contains 56 putative ORFs and no toxin, virulence, or resistance-related genes were detected. Phylogenetic tree analysis showed that PEC9 is closely related to E. coli phages vB_EcoS_Zar3M, vB_EcoS_PTXU06, SECphi18, ZCEC10, and ZCEC11, but most of these phages exhibit different gene arrangement. The phage PEC9 could successfully protect mice against APEC infection, including improved survival rate, reduced bacterial loads, and organ lesions. To conclude, our results suggest that phage PEC9 may be a promising candidate that can be used as an alternative to antibiotics in the control of APEC infection.

Mechanistic evaluation of the initial burst release of leuprolide from spray-dried PLGA microspheres

Spray-dried poly(lactic-co-glycolic acid) (PLGA) peptide-loaded microspheres have demonstrated similar long-term in vitro release kinetics compared to those produced by the solvent evaporation method and commercial products. However, the difficult-to-control initial burst release over the first 24 h after administration presents an obstacle to product development and establishing bioequivalence. Currently, detailed information about underlying mechanisms of the initial burst release from microspheres is limited. We investigated the mechanism and extent of initial burst release using 16 previously developed spray-dried microsphere formulations of the hormone drug, leuprolide acetate, with similar composition to the commercial 1-month Lupron Depot® (LD). The burst release kinetics was measured with a previously validated continuous monitoring system as well as traditional sample-and-separate methods. The changes in pore structure and polymer permeability were investigated by SEM imaging and the uptake of a bodipy-dextran probe. In vitro results were compared to pharmacokinetics in rats over the same interval. High-burst, spray-dried microspheres were differentiated in the well-mixed continuous monitoring system but reached an upper limit when measured by the sample-and-separate method. Pore-like occlusions observed by confocal microscopy in some formulations indicated that particle swelling may have contributed to probe diffusion through the polymer phase and showed the extensive internal pore structure of spray-dried particles. Continuous monitoring revealed a rapid primary (1°) phase followed by a constant-rate secondary (2°) release phase, which comprised ∼80% and 20% of the 24-hr release, respectively. The ratio of 1° phase duration (t1°) and the characteristic probe diffusion time (τ) was highly correlated to 1° phase release for spray dried particles. Of the four spray-dried formulations administered in vivo, three spray-dried microspheres with similar polymer density showed nearly ideal linear correlation between in vivo absorption and well-mixed in vitro release kinetics over the first 24 h. By contrast, the more structurally dense LD and a more-dense in-house formulation showed a slight lag phase in vivo relative to in vitro. Furthermore, in vitro dimensionless times (tburst/τ) were highly correlated with pharmacokinetic parameters for spray-dried microspheres but not for LD. While the correlation of increases in effective probe diffusion and 1° phase release strongly suggests diffusion through the polymer matrix as a major release mechanism both in vitro and in vivo, a fixed lower limit for this release fraction implies an alternative release mechanism. Overall, continuous monitoring release and probe diffusion appears to have potential in differentiating between leuprolide formulations and establishing relationships between in vitro release and in vivo absorption during the initial burst period.

Rodent abundance, diversity and community structure in a bubonic plague endemic area, northern Tanzania

Abstract Rodent-borne diseases such as bubonic plague remain a significant threat to public health in tropical countries. In plague-endemic areas, little information exists on the factors triggering periodic bursts, thus rendering preparedness strategies for preventing the negative impacts of the deadly zoonosis difficult. In this study, we assessed how species richness, diversity, and community structure of rodents are associated with plague persistence in Mbulu District, Tanzania. Rodent data were collected using the removal trapping technique. We captured 610 rodents belonging to 12 species, with Mastomys natalensis recording highest abundance. There was significantly higher abundance and species richness in persistent than non-persistent plague locality. Also, house premises recorded significantly lower species richness than farm and forest habitats. Additionally, we found three broad rodent community structures that varied significantly between studied habitat types suggesting high rodent populations interaction at fine-scale resource abundance. The high abundance and diversity of plague-susceptible rodent reservoirs suggestively contribute to the plague persistence in the foci. These results may be useful to developing preparedness strategies in these areas to control plague outbreaks.