Frequency-dependent Changes Research Articles

On chip glucose sensing using guided waves at terahertz frequencies

This paper demonstrates an on-chip anhydrous D-glucose sensor using a coplanar stripline (CPS) on a thin (1 m) silicon nitride membrane at terahertz (THz) frequencies. A thin layer ( 10 m) of D-glucose was placed in close proximity to the CPS and the transmission response was measured using a modified THz-TDS setup. The D-glucose introduces frequency-dependent changes to the effective permittivity of the CPS resulting in a modified spectral response at the receiver. Measurement results show absorption signatures at 1.42 THz and 2.07 THz corresponding to the first two significant resonances beyond 1 THz for D-glucose allowing for label-free detection. The frequency-dependent attenuation coefficient was estimated by simulation for several D-glucose layer thicknesses using a modified Lorentz model. Measurement results align with simulations and other literature that use free-space THz radiation. This work verifies on-chip THz sensing of D-glucose and presents a pathway toward on-chip sensing of other materials at THz frequencies.

Comprehensive analysis of Ni0.4Cu0.2Zn0.4Fe2-4xSn3xO4 nanospinel ferrites: Structural, electrical, and dielectric characterization through advanced techniques

This study extensively investigates Ni0.4Cu0.2Zn0.4Fe2-4xSn3xO4(x ≤ 0.10) nanospinel ferrites, denoted as NCZFe2-4xSn3xO4 NSFs, focusing on their structural, morphological, electrical, and dielectric characteristics. Utilizing various techniques such as SEM, EDX, TEM, XRD, and impedance analysis, the research confirms the cubic spinel structure and composition of the nanoferrites. The substitution of Sn4+ ions into Ni0.4Cu0.2Zn0.4Fe2O4 NSFs is explored, with a thorough examination of dielectric and electrical parameters up to 1.0 MHz and temperatures ranging from 20 to 180 °C. Complex impedance spectroscopy is employed to represent these parameters in a logarithmic 3D graph, revealing insights into ac/dc conductivity, activation energies, dissipation factor, dielectric constant, and loss. The study observes adherence to the power-law frequency rule in ac conductivity and highlights the impact of temperature and substitution ratios on grains, grain boundaries, and elemental composition. The investigation suggests a conduction mechanism involving electron and polaron hopping, and ionic contributions. Dielectric parameters show frequency-dependent changes that relate the dielectric constant to space charge polarization, inhomogeneous dielectric structure, impurities, and grains/grain boundaries. Cole-Cole impedance plots display semicircles dependent on substitution ratios and temperature, emphasizing contributions from grains, grain boundaries, and ionic mobilities. The Nyquist plots of Cole-Cole impedance functions further underscore substantial complexity in the conduction mechanism of the substituted NCZFe2-4xSn3xO4NSFs.

Observations of interstellar scattering of six pulsars using Polish LOFAR station PL611

ABSTRACT We present the preliminary results of 4 yr of observations of the scattering of pulsar radiation in the interstellar medium using the Low Frequency Array (LOFAR) PL611 station located in Lazy near Krakow. In this work we show the initial results for six pulsars from our observing campaign. We used the HBA antennas of the station, with a central frequency of 154 MHz and a 72 MHz bandwidth and we were able to detect the frequency-dependent change in the pulse profiles. Splitting the bandwidth into a number of separate sub-bands we obtained independent scatter time estimates, which allowed for the estimation of the scattering frequency scaling slope for each individual observation. Our project has been accumulating data for more than 4 yr and as a result we are in a position to study the time variability of the scattering parameters over this period. We detected significant changes in the scatter time and its frequency scaling for at least two of pulsars. The average values of the frequency scaling index for the six pulsars selected for this work are below the range of values predicted by the simple thin screen model of interstellar scattering. This is in accordance with previous results shown for both higher dispersion measure pulsars observed in the past, as well as the more recent LOFAR observations and other projects similar in the observing frequency. We also discuss the advantages of using individual LOFAR stations (or similar instruments) for this kind of research.

Local control model of a human ventricular myocyte: An exploration of frequency-dependent changes and calcium sparks

Local control model of a human ventricular myocyte: An exploration of frequency-dependent changes and calcium sparks

Frequency-dependent changes in the activity of blood enzymes under the action of modulated ultrasound.

Frequency-dependent changes in the activity of blood enzymes under the action of modulated ultrasound.

Real-time monitoring of a 3D blood-brain barrier model maturation and integrity with a sensorized microfluidic device.

A significant challenge in the treatment of central nervous system (CNS) disorders is represented by the presence of the blood-brain barrier (BBB), a highly selective membrane that regulates molecular transport and restricts the passage of pathogens and therapeutic compounds. Traditional in vivo models are constrained by high costs, lengthy experimental timelines, ethical concerns, and interspecies variations. In vitro models, particularly microfluidic BBB-on-a-chip devices, have been developed to address these limitations. These advanced models aim to more accurately replicate human BBB conditions by incorporating human cells and physiological flow dynamics. In this framework, here we developed an innovative microfluidic system that integrates thin-film electrodes for non-invasive, real-time monitoring of BBB integrity using electrochemical impedance spectroscopy (EIS). EIS measurements showed frequency-dependent impedance changes, indicating BBB integrity and distinguishing well-formed from non-mature barriers. The data from EIS monitoring was confirmed by permeability assays performed with a fluorescence tracer. The model incorporates human endothelial cells in a vessel-like arrangement to mimic the vascular component and three-dimensional cell distribution of human astrocytes and microglia to simulate the parenchymal compartment. By modeling the BBB-on-a-chip with an equivalent circuit, a more accurate trans-endothelial electrical resistance (TEER) value was extracted. The device demonstrated successful BBB formation and maturation, confirmed through live/dead assays, immunofluorescence and permeability assays. Computational fluid dynamics (CFD) simulations confirmed that the device mimics in vivo shear stress conditions. Drug crossing assessment was performed with two chemotherapy drugs: doxorubicin, with a known poor BBB penetration, and temozolomide, conversely a specific drug for CNS disorders and able to cross the BBB, to validate the model predictive capability for drug crossing behavior. The proposed sensorized microfluidic device represents a significant advancement in BBB modeling, offering a versatile platform for CNS drug development, disease modeling, and personalized medicine.

Qualitative Characterization of Lead–Acid Batteries Fabricated Using Different Technological Procedures: An EIS Approach

Electrochemical impedance spectroscopy techniques were applied in this work to nine industrially fabricated lead–acid battery prototypes, which were divided into three type/technology packages. Frequency-dependent impedance changes were interpreted during successive charge/discharge cycles in two distinct stages: (1) immediately after fabrication and (2) after a controlled aging procedure to 50% depth of discharge following industrial standards. To investigate their state of health behavior vs. electrical response, three methods were employed, namely, the Q-Q0 total charge analysis, the decay values of the constant-phase element in the equivalent Randles circuits, and the resonance frequency of the circuit. A direct correlation was found for the prediction of the best-performing batteries in each package, thus allowing for a qualitative analysis that was capable of providing the decay of the batteries’ states of health. We found which parameters were directly connected with their lifetime performance in both stages and, as a consequence, which type/technology battery prototype displayed the best performance. Based on this methodology, industrial producers can further establish the quality of novel batteries in terms of performance vs. lifespan, allowing them to validate the novel technological innovations implemented in the current prototypes.

Changes in neural readout of response magnitude during auditory streaming do not correlate with behavioral choice in the auditory cortex

A fundamental goal of the auditory system is to group stimuli from the auditory environment into a perceptual unit (i.e., "stream") or segregate the stimuli into multiple different streams. Although previous studies have clarified the psychophysical and neural mechanisms that may underlie this ability, the relationship between these mechanisms remains elusive. Here, we recorded multiunit activity (MUA) from the auditory cortex of monkeys while they participated in an auditory-streaming task consisting of interleaved low- and high-frequency tone bursts. As the streaming stimulus unfolded over time, MUA amplitude habituated; the magnitude of this habituation was correlated with the frequency difference between the tone bursts. An ideal-observer model could classify these time- and frequency-dependent changes into reports of "one stream" or "two streams" in a manner consistent with the behavioral literature. However, because classification was not modulated by the monkeys' behavioral choices, this MUA habituation may not directly reflect perceptual reports.

Effect of microstructure and environmental conditions on the dielectric properties of plasma sprayed Al2O3 insulating coatings

The effect mechanism of microstructure and environmental conditions on the dielectric properties of plasma-sprayed Al2O3 insulating coatings was systematically investigated in this study. Two kinds of Al2O3 powders with different particle sizes were used to deposit the coatings under the same spraying parameters. The microstructures of the coatings (including porosity, pore size, crack density, and phase composition) were analyzed using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and X-ray diffraction (XRD). The dielectric properties (including breakdown strength, resistivity, dielectric constant, dielectric loss, and complex impedance) were characterized by a two-electrode measurement cell. The results indicated that the coating deposited with the larger-sized powder (D50=45.8 μm) exhibited higher porosity, α-Al2O3 content, and connected crack density, than the coating with the other kinder of powder (D50=22 μm). The DC and AC breakdown strengths were found to be related to the porosity of the coatings and the partial discharge in the pores results in the eventual breakdown. The resistivity of the coatings decreased significantly with increasing humidity due to the moisture adsorbed on the pores and cracks. In high-humidity environments, the water molecule enhanced space charge polarization (WESCP), as the main polarization mode, contributed to the dramatic increase of the dielectric constant and dielectric loss. Moreover, the complex impedance and phase angle showed frequency-dependent changes in different environments, suggesting a combined effect of humidity and temperature on the polarization and conductance of coatings. The obtained results of this study could pave the way for the design and application of high-performance plasma-sprayed insulating coatings.

Frequency dependent whole-brain coactivation patterns analysis in Alzheimer's disease.

The brain in resting state has complex dynamic properties and shows frequency dependent characteristics. The frequency-dependent whole-brain dynamic changes of resting state across the scans have been ignored in Alzheimer's disease (AD). Coactivation pattern (CAP) analysis can identify different brain states. This paper aimed to investigate the dynamic characteristics of frequency dependent whole-brain CAPs in AD. We utilized a multiband CAP approach to model the state space and study brain dynamics in both AD and NC. The correlation between the dynamic characteristics and the subjects' clinical index was further analyzed. The results showed similar CAP patterns at different frequency bands, but the occurrence of patterns was different. In addition, CAPs associated with the default mode network (DMN) and the ventral/dorsal visual network (dorsal/ventral VN) were altered significantly between the AD and NC groups. This study also found the correlation between the altered dynamic characteristics of frequency dependent CAPs and the patients' clinical Mini-Mental State Examination assessment scale scores. This study revealed that while similar CAP spatial patterns appear in different frequency bands, their dynamic characteristics in subbands vary. In addition, delineating subbands was more helpful in distinguishing AD from NC in terms of CAP.

Frequency Dependent Changes of Regional Homogeneity in Children with Growth Hormone Deficiency.

Abnormal spontaneous neural activity in children with growth hormone deficiency (GHD) has been found in previous resting-state functional magnetic resonance imaging (rs-fMRI) studies. Nevertheless, the spontaneous neural activity of GHD in different frequency bands is still unclear. Here, we combined rs-fMRI and regional homogeneity (ReHo) methods to analyze the spontaneous neural activity of 26 GHD children and 15 healthy controls (HCs) with age- and sex-matching in four frequency bands: slow-5 (0.014-0.031Hz), slow-4 (0.031-0.081Hz), slow-3 (0.081-0.224Hz), and slow-2 (0.224-0.25Hz). In the slow-5 band, GHD children compared with HCs displayed higher ReHo in the left dorsolateral part of the superior frontal gyrus, triangular part of the inferior frontal gyrus, precentral gyrus and middle frontal gyrus, and right angular gyrus, while lower ReHo in the right precentral gyrus, and several medial orbitofrontal regions. In the slow-4 band, GHD children relative to HCs revealed increased ReHo in the right middle temporal gyrus, whereas reduced ReHo in the left superior parietal gyrus, right middle occipital gyrus, and bilateral medial parts of the superior frontal gyrus. In the slow-2 band, compared with HCs, GHD children showed increased ReHo in the right anterior cingulate gyrus, and several prefrontal regions, while decreased ReHo in the left middle occipital gyrus, and right fusiform gyrus and anterior cingulate gyrus. Our findings demonstrate that regional brain activity in GHD children exhibits extensive abnormalities, and these abnormalities are related to specific frequency bands, which may provide bases for understanding its pathophysiology significance.

Synthesis, Structural, Spectroscopic, Fluorescence, and Dielectric Studies of Bis-(4-Aminopyridine)-Zinc(II) Acetate: A Metal-Organic Crystal.

The advancement of crystalline growth and characterization tools allows us to investigate novel nonlinear optical substances suitable for photonic applications. Bis-(4-aminopyridine)-zinc(II) acetate (B4AZA), a metal-organic crystal was produced in this study using the slow evaporation procedure at room temperature. Analytical studies such as X-ray crystallography, Fourier transform infrared (FT-IR), UV-visible (UV-Vis), fluorescence, second harmonic generation (SHG), and dielectric tests were used to characterize the as-grown B4AZA crystals. According to the solubility data, the sample has a positive temperature coefficient of solubility. The crystallographic findings show that the B4AZA crystallized in a monoclinic structure with the P21/n space group. Molecular vibrations and functional groups in the substance were determined using the FT-IR technique. The UV-Vis absorbance and transmittance spectra have shown the wide transparency and minimum absorbance of the B4AZA in the near UV and entire visible regions of the electromagnetic spectrum. The bandgap of the B4AZA has been calculated using the Tauc relation and found to be 4.32eV. The fluorescence spectra have shown a prominent emission peak at 584nm with an excitation wavelength of 280nm. The larger Stokes shift found in the fluorescence spectra is advantageous for practical applications. The SHG study revealed that the powdered B4AZA samples generated a second harmonic output. The dielectric test revealed frequency-dependent changes in the dielectric constant and loss factor. Both the dielectric constant and the loss factor decrease exponentially as frequency increases, reaching low values at higher frequencies. The experimental results illustrate the suitability of the B4AZA crystals for photonic applications.

Regulation of vagally-evoked respiratory responses by the lateral parabrachial nucleus in the mouse

Vagal sensory inputs to the brainstem can alter breathing through the modulation of pontomedullary respiratory circuits. In this study, we set out to investigate the localised effects of modulating lateral parabrachial nucleus (LPB) activity on vagally-evoked changes in breathing pattern. In isoflurane-anaesthetised and instrumented mice, electrical stimulation of the vagus nerve (eVNS) produced stimulation frequency-dependent changes in diaphragm electromyograph (dEMG) activity with an evoked tachypnoea and apnoea at low and high stimulation frequencies, respectively. Muscimol microinjections into the LPB significantly attenuated eVNS-evoked respiratory rate responses. Notably, muscimol injections reaching the caudal LPB, previously unrecognised for respiratory modulation, potently modulated eVNS-evoked apnoea, whilst muscimol injections reaching the intermediate LPB selectively modulated the eVNS-evoked tachypnoea. The effects of muscimol on eVNS-evoked breathing rate changes occurred without altering basal eupneic breathing. These results highlight novel roles for the LPB in regulating vagally-evoked respiratory reflexes.

Local Control Model of a Human Ventricular Myocyte: An Exploration of Frequency-Dependent Changes and Calcium Sparks.

Calcium (Ca2+) sparks are the elementary events of excitation-contraction coupling, yet they are not explicitly represented in human ventricular myocyte models. A stochastic ventricular cardiomyocyte human model that adapts to intracellular Ca2+ ([Ca2+]i) dynamics, spark regulation, and frequency-dependent changes in the form of locally controlled Ca2+ release was developed. The 20,000 CRUs in this model are composed of 9 individual LCCs and 49 RyRs that function as couplons. The simulated action potential duration at 1 Hz steady-state pacing is ~0.280 s similar to human ventricular cell recordings. Rate-dependence experiments reveal that APD shortening mechanisms are largely contributed by the L-type calcium channel inactivation, RyR open fraction, and [Ca2+]myo concentrations. The dynamic slow-rapid-slow pacing protocol shows that RyR open probability during high pacing frequency (2.5 Hz) switches to an adapted "nonconducting" form of Ca2+-dependent transition state. The predicted force was also observed to be increased in high pacing, but the SR Ca2+ fractional release was lower due to the smaller difference between diastolic and systolic [Ca2+]SR. Restitution analysis through the S1S2 protocol and increased LCC Ca2+-dependent activation rate show that the duration of LCC opening helps modulate its effects on the APD restitution at different diastolic intervals. Ultimately, a longer duration of calcium sparks was observed in relation to the SR Ca2+ loading at high pacing rates. Overall, this study demonstrates the spontaneous Ca2+ release events and ion channel responses throughout various stimuli.

Altered Thalamocortical Signaling in a Mouse Model of Parkinson's Disease.

Activation of the primary motor cortex (M1) is important for the execution of skilled movements and motor learning, and its dysfunction contributes to the pathophysiology of Parkinson's disease (PD). A well-accepted idea in PD research, albeit not tested experimentally, is that the loss of midbrain dopamine leads to decreased activation of M1 by the motor thalamus. Here, we report that midbrain dopamine loss altered motor thalamus input in a laminar- and cell type-specific fashion and induced laminar-specific changes in intracortical synaptic transmission. Frequency-dependent changes in synaptic dynamics were also observed. Our results demonstrate that loss of midbrain dopaminergic neurons alters thalamocortical activation of M1 in both male and female mice, and provide novel insights into circuit mechanisms for motor cortex dysfunction in a mouse model of PD.SIGNIFICANCE STATEMENT Loss of midbrain dopamine neurons increases inhibition from the basal ganglia to the motor thalamus, suggesting that it may ultimately lead to reduced activation of primary motor cortex (M1). In contrast with this line of thinking, analysis of M1 activity in patients and animal models of Parkinson's disease report hyperactivation of this region. Our results are the first report that midbrain dopamine loss alters the input-output function of M1 through laminar and cell type specific effects. These findings support and expand on the idea that loss of midbrain dopamine reduces motor cortex activation and provide experimental evidence that reconciles reduced thalamocortical input with reports of altered activation of motor cortex in patients with Parkinson's disease.

Rotational and radio emission properties of PSR J0738−4042 over half a century

ABSTRACT We present a comprehensive study of the rotational and emission properties of PSR J0738−4042 using a combination of observations taken by the Deep Space Network, Hartebeesthoek, Parkes (Murriyang) and Molonglo observatories between 1972 and 2023. Our timing of the pulsar is motivated by previously reported profile/spin-down events that occurred in 2005 September and 2015 December, which result in an anomalously large braking index of n = 23 300 ± 1800. Using a Gaussian process regression framework, we develop continuous models for the evolution of the pulsar spin-down rate ($\dot{\nu }$) and profile shape. We find that the pulse profile variations are similar regardless of radio observing frequency and polarization. Small-scale differences can be ascribed to changes in the interstellar medium along the line of sight and frequency-dependent changes in magnetospheric radio emission height. No new correlated spin-down or profile events were identified in our extended data set. However, we found that the disappearance of a bright emission component in the leading edge of archival profiles between 1981 and 1988 was not associated with a substantial change in $\dot{\nu }$. This marks a notable departure from the previous profile/spin-down events in this pulsar. We discuss the challenges these observations pose for physical models and conclude that interactions between the pulsar and in-falling asteroids or a form of magnetospheric state-switching with a long periodicity are plausible explanations.

Effect of bronchial thermoplasty on static and dynamic lung compliance and resistance in patients with severe persistent asthma

RationaleBronchial thermoplasty (BT) reduces severity and frequency of bronchoconstriction and symptoms in severe, persistent asthmatics although it is usually not associated with change in spirometric variables. Other than spirometry. there are almost no data on changes in lung mechanics following BT. ObjectiveTo assess lung static and dynamic lung compliance (Cst,L and Cdyn,L, respectively) and static and dynamic lung resistance (Rst,L and Rdyn,L, respectively) before and after BT in severe asthmatics using the esophageal balloon technique. MethodsRdyn,L and Cdyn,L were measured at respiratory frequencies up to 145 breaths/min, using the esophageal balloon technique in 7 patients immediately before and 12–50 weeks after completing a series of 3 BT sessions. ResultsAll patients experienced improved symptoms within a few weeks following completion of BT. Pre-BT, all patients exhibited frequency dependency of lung compliance, with mean Cdyn,L decreasing to 63% of Cst,L at maximum respiratory rates. Post-BT, Cst,L did not change significantly from pre-thermoplasty values, while Cdyn,L diminished to 62%% of Cst,L. In 4 of 7 patients, post-BT values of Cdyn,L were consistently higher than pre-BT over the range of respiratory rates. RL in 4 of 7 patients during quiet breathing and at higher respiratory frequencies decreased following BT. ConclusionsPatients with severe persistent asthma exhibit increased resting lung resistance and frequency dependence of compliance, the magnitudes of which are ameliorated in some patients following bronchial thermoplasty and associated with variable change in frequency dependence of lung resistance. These findings are related to asthma severity and may be related to the heterogeneous and variable nature of airway smooth muscle modeling and its response to BT.

Modal sensitivity analysis of acoustic metamaterials for structural damage detection

Metamaterials have garnered significant research interest over the past few decades, primarily due to their unique properties not found in naturally occurring materials. However, when integrated into operational engineering structures, metamaterials can sustain damage, compromising their extraordinary attributes and potentially leading to structural failure. This work marks a novel advancement in the field of metamaterials research, providing an in-depth analysis into the impact of damage on the structural dynamic properties of finite acoustic metamaterials (AMMs) consisting of periodic locally resonant mass-in-mass units. A modal sensitivity analysis is formulated based on equations of motion of a damaged AMM, along side with associated eigenvalue problem and frequency response functions. The critical role of the internal spring is analytically revealed in determining the effective mass of a damaged unit. To evaluate the effects of damage on AMMs, an extensive numerical investigation is conducted on a finite AMM; an damage index is proposed for measuring the modal deformation of each spring. It is unequivocally demonstrated that frequency response functions, eigenvalues, and mode shapes of damaged AMMs undergo substantial changes at frequencies near bandgaps and these changes diminish as frequencies move away from the bandgaps. This behavior directly corresponds to the frequency-dependent changes in the effective mass of a mass-in-mass unit due to damage. Hence, this work constitutes a leap forward in our understanding of the structural dynamics of damaged metamaterials and offers valuable insights that could facilitate the development of more effective damage identification techniques and the realization of resilient metamaterial-based structures.

Nicotine Dependence and Perceived Stress during the Pandemic

Background The development of COVID-19, which continues to increase in Indonesia, impacts the Indonesian people and causes stress due to the impact of the COVID-19 pandemic. Prior studies in several countries have shown that stress affects smokers during the COVID-19 pandemic. It affects smokers in two different ways, either they increase smoking or decrease smoking. This study aimed to determine the effect of Nicotine, smoking history, and changes in smoking habits during the COVID-19 pandemic on stress in smokers. Methods We conducted an online survey among active smokers in one of the villages in the South Lampung district, Indonesia November 2020 (n = 150). The survey includes sex, marital status, age of smoking initiation, duration as a smoker, changes in smoking frequency, questionnaire for nicotine dependence (the Fagerstrom Test for Nicotine Dependence questionnaire) and The Perceived Stress Scale (PSS). Data were analyzed with Chi-square<0.05). Results The results showed that the PSS score had a significant association with changes in smoking frequency (p=0.004) and nicotine dependence (p=0.001). Conclusions The study concluded that variations in nicotine dependence and changing smoking habits impacted perceived stress in smokers during the pandemic. There is a significant relationship between age at starting to smoke, number of cigarettes per day, duration of smoking habits, degree of smoking habits, and changes in smoking habits with stress levels in smokers in the COVID-19 pandemic era, and there is no relationship between types of cigarettes consumed, and stress levels in smokers in COVID-19 pandemic era.

Determining electron column density fluctuations in a dominant scattering region using pulsar scintillation

ABSTRACT Density fluctuations in the ionized interstellar medium have a profound effect on radio pulsar observations, through angular scattering, intensity scintillations, and small changes in time delays from dispersion. Here we show that it is possible to recover the variations in dispersive delays that originate from a dominant scattering region using measurements of the dynamic spectrum of intensity scintillations, provided that the pulsar velocity and scattering region location are known. We provide a theoretical framework for the technique, which involves estimating the phase gradient from the dynamic spectra and integrating that gradient to obtain phase variations. It can be used to search for “extreme scattering events” (ESEs) in pulsars for which precision dispersion delay measurements are not otherwise possible, or to separate true dispersion variations from apparent variability caused by frequency-dependent pulse shape changes. We demonstrate that it works in practice by recovering an ESE in PSR J1603−7202, which is known from precision dispersion delay measurements from pulsar timing. For this pulsar, we find that the phase gradients also track the long-term variations in electron column density observed by pulsar timing, indicating that the column density variations and the scattering are dominated by the same thin scattering screen. We identify a sudden increase in the scintillation strength and magnitude of phase gradients over ∼days in 2010, indicating a compact structure. A decrease in the electron density in 2012 was associated with persistent phase gradients and preceded a period of decreased scintillation strength and an absence of scintillation arcs.