Low Beta Research Articles

Characteristics of Suprathermal Electrons in Small-Scale Magnetic Flux Ropes and Their Implications on the Magnetic Connection to the Sun

Small-scale magnetic flux ropes (SMFRs) are observed more frequently than larger-scale magnetic flux ropes (e.g., magnetic clouds) in interplanetary space. We selected 235 SMFRs by applying cylindrical linear force-free fitting to 20-year observations of the Wind satellite, which meets the criteria of low beta, low temperature, an enhanced magnetic field, and a rotation feature. By examining the pitch angle distribution of suprathermal electrons for these events, we found that approximately 45.1% of the SMFRs were accompanied by unidirectional beams (strahl). A much smaller percentage of SMFRs (∼10.7%) were associated with bidirectional beams. We also found a small percentage (∼7.2%) of (sunward) conic distributions during SMFR events. Last, the remaining ∼37.0% of SMFRs were associated with complex electron distributions. The unidirectional beams and most of the conics (together corresponding to ∼50% of the total 235 SMFRs) imply open-field SMFRs with only one end connected to the Sun. For ∼37.7% of the unidirectional beam SMFRs, the local IMF field polarity was orthogonal or inverted (possibly due to interchange reconnection). Based on the solar wind conditions around the bidirectional beams, we suggest that more than half of the bidirectional beams were not necessarily closed-field-line SMFRs.

Alpha activity neuromodulation induced by individual alpha-based neurofeedback learning in ecological context: a double-blind randomized study

The neuromodulation induced by neurofeedback training (NFT) remains a matter of debate. Investigating the modulation of brain activity specifically associated with NF requires controlling for multiple factors, such as reward, performance, congruency between task and targeted brain activity. This can be achieved using sham feedback (FB) control condition, equating all aspects of the experiment but the link between brain activity and FB. We aimed at investigating the modulation of individual alpha EEG activity induced by NFT in a double-blind, randomized, sham-controlled study. Forty-eight healthy participants were assigned to either NF (n = 25) or control (n = 23) group and performed alpha upregulation training (over 12 weeks) with a wearable EEG device. Participants of the NF group received FB based on their individual alpha activity. The control group received the auditory FB of participants of the NF group. An increase of alpha activity across training sessions was observed in the NF group only (p < 0.001). This neuromodulation was selective in that there was no evidence for similar effects in the theta (4–8 Hz) and low beta (13–18 Hz) bands. While alpha upregulation was found in the NF group only, psychological outcome variables showed overall increased feeling of control, decreased anxiety level and increased relaxation feeling, without any significant difference between the NF and the control groups. This is interpreted in terms of learning context and placebo effects. Our results pave the way to self-learnt, NF-based neuromodulation with light-weighted, wearable EEG systems.

Exploring the low tan beta region of two Higgs doublet models at the LHC

Current interpretations of the LHC results on two Higgs doublet models (2HDM) underestimate the sensitivity due to neglecting higher order effects. In this work, we revisit the impact of these effects using the current cross-section times branching ratio limits of the Arightarrow hZ, H rightarrow VV and Hrightarrow hh channels. With a degenerate heavy Higgs mass m_varPhi , we find that the LHC searches gain sensitivity to the small tan beta region after including loop corrections, even close to cos (beta -alpha )=0 which is not reachable at tree level for all types of 2HDM. For a benchmark point with m_varPhi =300 GeV, tan beta <1.8(1.2) can be probed for the Type-I(II) 2HDM model for cos (beta -alpha )=0. When the deviation from cos (beta -alpha )=0 is larger, the region for which current searches have exclusion potential becomes larger.

Neural signatures of hyperdirect pathway activity in Parkinson\u2019s disease

Parkinson’s disease (PD) is characterised by the emergence of beta frequency oscillatory synchronisation across the cortico-basal-ganglia circuit. The relationship between the anatomy of this circuit and oscillatory synchronisation within it remains unclear. We address this by combining recordings from human subthalamic nucleus (STN) and internal globus pallidus (GPi) with magnetoencephalography, tractography and computational modelling. Coherence between supplementary motor area and STN within the high (21–30 Hz) but not low (13-21 Hz) beta frequency range correlated with ‘hyperdirect pathway’ fibre densities between these structures. Furthermore, supplementary motor area activity drove STN activity selectively at high beta frequencies suggesting that high beta frequencies propagate from the cortex to the basal ganglia via the hyperdirect pathway. Computational modelling revealed that exaggerated high beta hyperdirect pathway activity can provoke the generation of widespread pathological synchrony at lower beta frequencies. These findings suggest a spectral signature and a pathophysiological role for the hyperdirect pathway in PD.

Uncertainty and detection limits of 241Pu determination by liquid scintillation counting (LSC)

Determination of 241Pu is an essential issue for radiation protection, as it is the precursor of some nuclides with high radiotoxicity. 241Pu is a low energy beta emitter, which makes its measurement more challenging than that of Pu alpha emitters. The most widely used method for the measurement of 241Pu is liquid scintillation counting (LSC). In this method, the assessment of Pu radiochemical yield is done by measuring the sample by alpha spectrometry before being lixiviated and measured by LSC. This double measurement affects uncertainty analysis, as well as decision threshold and detection limit, considering that both components of the total yield (radiochemical and lixiviation) should be contemplated.In this paper, and for quality assurance (QA) purposes, in-depth uncertainty and detection limit formulae for the proposed method, controlling correlations and considering all the parameters involved including chemical and lixiviation yields, have been developed. A sensitivity analysis of the uncertainty budget together with an assessment of 242Pu tracer quantity to be used, ensuring a total yield of at least 50% and a relative uncertainty of the leaching yield of at most 5%, have been carried out. In addition, an analysis of the impact of the real lixiviation yield value and its uncertainty on the results has been done.As a general conclusion, and considering the values of the parameters chosen for this work (samples of 1 g measured for 24 h by LSC), the 241Pu uncertainties range from 5% to 30% depending on the activity concentration values and the detection limits range from 14 to 30 Bq kg-1, depending on yield values. The main components of the uncertainty budget are the net 241Pu and background counts obtained in the LSC measurement for low contaminated samples while this is the case for the alpha gross count rate in LSC measurement of the alpha calibration source for highly contaminated samples.In addition, an analysis of possible interference by Pu alpha emitters in the 241Pu signal and a comparison of quench standard curves of 3H and 241Pu are also performed.

Preliminary BCP Flow Field Investigation by CFD Simulations and PIV in a Transparent Model of a SRF Elliptical Low Beta Cavity

Preliminary BCP Flow Field Investigation by CFD Simulations and PIV in a Transparent Model of a SRF Elliptical Low Beta Cavity

On the design of early-phase Alzheimer's disease clinical trials with cerebrospinal fluid tau outcomes.

The focus of Alzheimer's disease studies has shifted to earlier disease stages, including mild cognitive impairment. Biomarker inclusion criteria are often incorporated into mild cognitive impairment clinical trials to identify individuals with "prodromal Alzheimer's disease" to ensure appropriate drug targets and enrich for participants likely to develop Alzheimer's disease dementia. The use of these eligibility criteria may affect study power. We investigated outcome variability and study power in the setting of proof-of-concept prodromal Alzheimer's disease trials that incorporate cerebrospinal fluid levels of total tau (t-tau) and phosphorylated (p-tau) as primary outcomes and how differing biomarker inclusion criteria affect power. We used data from the Alzheimer's Disease Neuroimaging Initiative to model trial scenarios and to estimate the variance and within-subject correlation of total and phosphorylated tau. These estimates were then used to investigate the differences in study power for trials considering these two surrogate outcomes. Patient characteristics were similar for all eligibility criteria. The lowest outcome variance and highest within-subject correlation were obtained when phosphorylated tau was used as an eligibility criterion, compared to amyloid beta or total tau, regardless of whether total tau or phosphorylated tau were used as primary outcomes. Power increased when eligibility criteria were broadened to allow for enrollment of subjects with either low amyloid beta or high phosphorylated tau. Specific biomarker inclusion criteria may impact statistical power in trials using total tau or phosphorylated tau as the primary outcome. In concert with other important considerations such as treatment target and population of clinical interest, these results may have implications to the integrity and efficiency of prodromal Alzheimer's disease trial designs.

Neural correlates of speech and limb motor timing deficits revealed by aberrant beta band desynchronization in Parkinson’s disease

ObjectiveWe used a classical motor reaction time paradigm to examine the effects of Parkinson’s disease (PD) on the mechanisms of speech production and upper limb movement. MethodsElectro-encephalography (EEG) signals were recorded in PD and control groups during speech vowel production and button press tasks in response to temporally predictable and unpredictable visual stimuli. ResultsMotor reaction times were slower in PD vs. control group independent of stimulus timing and movement modality. This effect was accompanied by stronger desynchronizations of low beta (13–18 Hz) and high beta (18–25 Hz) band neural oscillations in PD vs. control prior to the onset of speech and hand movement. In addition, pre-movement desynchronization of beta band oscillations were correlated with motor reaction time in control subjects with faster responses associated with weaker beta band desynchronizations during the planning phase of movement. However, no such effect was found in the PD group. ConclusionsWe suggest that the aberrant pattern of beta band desynchronization is a neural correlate of speech and upper limb motor timing deficits as a result of cortico-striatal pathology in PD. SignificanceThese findings motivate interventions targeted toward normalizing beta band activities for improving speech and upper limb movement timing in PD.

Balance between competing spectral states in subthalamic nucleus is linked to motor impairment in Parkinson's disease.

Exaggerated local field potential bursts of activity at frequencies in the low beta band are a well-established phenomenon in the subthalamic nucleus of patients with Parkinson’s disease. However, such activity is only moderately correlated with motor impairment. Here we test the hypothesis that beta bursts are just one of several dynamic states in the subthalamic nucleus local field potential in Parkinson’s disease, and that together these different states predict motor impairment with high fidelity.Local field potentials were recorded in 32 patients (64 hemispheres) undergoing deep brain stimulation surgery targeting the subthalamic nucleus. Recordings were performed following overnight withdrawal of anti-parkinsonian medication, and after administration of levodopa. Local field potentials were analysed using hidden Markov modelling to identify transient spectral states with frequencies under 40 Hz.Findings in the low beta frequency band were similar to those previously reported; levodopa reduced occurrence rate and duration of low beta states, and the greater the reductions, the greater the improvement in motor impairment. However, additional local field potential states were distinguished in the theta, alpha and high beta bands, and these behaved in an opposite manner. They were increased in occurrence rate and duration by levodopa, and the greater the increases, the greater the improvement in motor impairment. In addition, levodopa favoured the transition of low beta states to other spectral states. When all local field potential states and corresponding features were considered in a multivariate model it was possible to predict 50% of the variance in patients’ hemibody impairment OFF medication, and in the change in hemibody impairment following levodopa. This only improved slightly if signal amplitude or gamma band features were also included in the multivariate model. In addition, it compares with a prediction of only 16% of the variance when using beta bursts alone.We conclude that multiple spectral states in the subthalamic nucleus local field potential have a bearing on motor impairment, and that levodopa-induced shifts in the balance between these states can predict clinical change with high fidelity. This is important in suggesting that some states might be upregulated to improve parkinsonism and in suggesting how local field potential feedback can be made more informative in closed-loop deep brain stimulation systems.

Neurophysiological biomarkers to optimize deep brain stimulation in movement disorders.

Intraoperative neurophysiological information could increase accuracy of surgical deep brain stimulation (DBS) lead placement. Subsequently, DBS therapy could be optimized by specifically targeting pathological activity. In Parkinson’s disease, local field potentials (LFPs) excessively synchronized in the beta band (13–35 Hz) correlate with akinetic-rigid symptoms and their response to DBS therapy, particularly low beta band suppression (13–20 Hz) and high frequency gamma facilitation (35–250 Hz). In dystonia, LFPs abnormally synchronize in the theta/alpha (4–13 Hz), beta and gamma (60–90 Hz) bands. Phasic dystonic symptoms and their response to DBS correlate with changes in theta/alpha synchronization. In essential tremor, LFPs excessively synchronize in the theta/alpha and beta bands. Adaptive DBS systems will individualize pathological characteristics of neurophysiological signals to automatically deliver therapeutic DBS pulses of specific spatial and temporal parameters.

Predicting the success rate of healthy participants in beta neurofeedback: Determining the factors affecting the success rate of individuals

Despite the considerable success of neurofeedback techniques in the treatment of various neurological disorders and the improvement of cognitive performance of healthy individuals, some people fail to learn how to control their brain activities using neurofeedback. Given the time-consuming and costly nature of neurofeedback, the prediction of people’s success rate in training by neurofeedback is of paramount importance. Therefore, the present study aimed to determine the factors affecting the success rate of 7 healthy women over 10 sessions (30 trials) in terms of enhancement of low beta band activities (βL). The relative power of different frequency bands (delta, theta, alpha and beta) of EEG signals obtained in the first training session was considered as the predictor variable along with the participants’ IQ test score. Afterwards, we assessed the predictor variables’ impact on the mean low beta power (15–18 Hz) values of the participants’ EEG signals in the last session (βL(last sess)). According to the results, the mean low beta power in the first session (βL(sess1)) had the most effect on βL(last sess) (R2 = 73.9 %). In the next stage, we designed three systems using the RBF network, which predicted the βL(last sess), mean score of each participant in the last training session and the slope of βL changes of each subject during the training sessions using βL(sess1) (prediction error < 10−11). The designed prediction system may be able to increase training efficiency with neurofeedback and save time and financial resources.

Analysis of Default Mode Network in Social Anxiety Disorder: EEG Resting-State Effective Connectivity Study.

Recent brain imaging findings by using different methods (e.g., fMRI and PET) have suggested that social anxiety disorder (SAD) is correlated with alterations in regional or network-level brain function. However, due to many limitations associated with these methods, such as poor temporal resolution and limited number of samples per second, neuroscientists could not quantify the fast dynamic connectivity of causal information networks in SAD. In this study, SAD-related changes in brain connections within the default mode network (DMN) were investigated using eight electroencephalographic (EEG) regions of interest. Partial directed coherence (PDC) was used to assess the causal influences of DMN regions on each other and indicate the changes in the DMN effective network related to SAD severity. The DMN is a large-scale brain network basically composed of the mesial prefrontal cortex (mPFC), posterior cingulate cortex (PCC)/precuneus, and lateral parietal cortex (LPC). The EEG data were collected from 88 subjects (22 control, 22 mild, 22 moderate, 22 severe) and used to estimate the effective connectivity between DMN regions at different frequency bands: delta (1–3 Hz), theta (4–8 Hz), alpha (8–12 Hz), low beta (13–21 Hz), and high beta (22–30 Hz). Among the healthy control (HC) and the three considered levels of severity of SAD, the results indicated a higher level of causal interactions for the mild and moderate SAD groups than for the severe and HC groups. Between the control and the severe SAD groups, the results indicated a higher level of causal connections for the control throughout all the DMN regions. We found significant increases in the mean PDC in the delta (p = 0.009) and alpha (p = 0.001) bands between the SAD groups. Among the DMN regions, the precuneus exhibited a higher level of causal influence than other regions. Therefore, it was suggested to be a major source hub that contributes to the mental exploration and emotional content of SAD. In contrast to the severe group, HC exhibited higher resting-state connectivity at the mPFC, providing evidence for mPFC dysfunction in the severe SAD group. Furthermore, the total Social Interaction Anxiety Scale (SIAS) was positively correlated with the mean values of the PDC of the severe SAD group, r (22) = 0.576, p = 0.006 and negatively correlated with those of the HC group, r (22) = −0.689, p = 0.001. The reported results may facilitate greater comprehension of the underlying potential SAD neural biomarkers and can be used to characterize possible targets for further medication.

Price Informativeness with Equity Market Factors

Price informativeness measures how and when information is aggregated into asset prices. We study the price informativeness of realized earnings growth for U.S. stocks with a focus on exposures to factors that have historically outperformed the market index. Our study includes the largest one thousand stocks from 1975 to 2019 and approximately 180 thousand individual corporate net income observations aligned by report date. Stock returns are sensitive to concurrent and realized earnings growth reports up to 15 months into the future, but not to old earnings reports. The decomposition of Value, Momentum, Small Size, Low Beta, and Profitability factor active returns into components that are explained and unexplained by earnings aids in understanding the anomalous nature of their positive market-relative performance. The active returns to Momentum stocks are largely attributable to the growth of realized earnings during the next several quarters. Low Beta, Small Size, and Profitability stocks have little of their active returns explained by realized earnings, suggesting the anomalies are associated with other drivers such as changes in expected long-term earnings growth and discount rates. In contrast, the active returns to Value stocks explained by concurrent and future realized earnings are negative.

Low liquidity beta anomaly in China

The conventional risk-based theory does not reconcile with the liquidity-beta anomaly in China: Low liquidity-beta stocks outperform high liquidity-beta stocks on a risk-adjusted basis. This striking pattern is robust to different weighting schemes, competing factor models, and other well-known return determinants in the cross section. We propose a competing behavioral-based explanation on the low liquidity beta anomaly in China. Consistent with our new perspective, liquidity beta is a negative return predictor in the cross section. Moreover, the time variation of the return differential between low and high liquidity beta stocks is led by investor sentiment after accounting for other possible economic mechanism.

Supraspinal Effects of Dorsal Root Ganglion Stimulation in Chronic Pain Patients

Dorsal root ganglion stimulation (DRGS) has become a popular neuromodulatory treatment for neuropathic pain. We used magnetoencephalography (MEG) to investigate potential biomarkers of pain and pain relief, based on the differences in power spectral density (PSD) during varying degrees of pain and how these oscillations change during DRGS-mediated pain relief. Thirteen chronic pain patients with implanted dorsal root ganglion stimulators were included in the MEG analysis. MEG Recordings were performed at rest while the stimulator was turned ON or OFF. Numerical rating scale (NRS) scores were also recorded before and after DRGS was turned OFF and ON. Power spectral and source localization analyses were then performed on preprocessed MEG recordings. With DRGS-OFF, patients in severe pain had significantly increased cortical theta (4-7 Hz) power and decreased cortical alpha (7-13Hz) power compared to patients reporting less pain. This shift in power toward lower frequencies was contrasted by a shift toward the higher frequency power spectrum (low beta 13-20Hz activity) during DRGS-mediated pain relief. A significant correlation was found between the increase in low beta activity and the degree of reported pain relief. Our results demonstrate increased low-frequency power spectral activity in chronic pain patients in the absence of stimulation which shifts toward higher frequency power spectrum activity in response to therapeutic DRGS. These cortical changes in response to DRGS provide support for the use of neuroimaging in the search for potential biomarkers of pain.

135-OR: Impaired Awareness of Hypoglycemia Is Associated with Residual Beta-Cell Function and Glucose Variability Parameters in Patients with Type 1 Diabetes

The Aim: to evaluate the relationships between impaired awareness of hypoglycemia (IAH), residual beta cell function and short-term glucose variability (GV) in patients with type 1 diabetes (T1D). Materials and Methods: We observed 400 patients, 145 M/255 F, age 18-85 years (median - 36 years), diabetes duration 0.5-52 years (median - 16 years), HbA1c 4.7-15.1% (median - 8%). The Clarke's questionnaire was used for IAH recognition. Beta cell function was estimated by fasting and 2-h postprandial C-peptide levels. Day-time (6.00-23.59), nocturnal (0.00-5.59) and 24-h Time In target Range (TIR), Time Above target Range (TAR), Time Below target Range (TBR), and GV parameters, including Standard Deviation (SD), Coefficient of Variation (CV), Mean Amplitude of Glucose Excursions (MAGE), 2-h Continuous Overlapping Net Glycemic Action (CONGA), Lability Index (LI), J-index, Low Blood Glucose Index (LBGI), High Blood Glucose Index (HBGI), M-value and Mean Absolute Glucose (MAG), were calculated from short-term (3-7 days) continuous glucose monitoring (CGM). Results: In our cohort, IAH was recognized in 163 (40.8%) individuals. Patients with IAH, as compared to those without, demonstrated longer diabetes duration (P&amp;lt;0.0001), lower C-peptide postprandial level and increment (p=0.02 and p=0.0003 respectively) and increased day-time and nocturnal mean glucose, SD, CONGA, J-index, HBGI and M-value (all P≤0.02). Nocturnal MAGE, LI and LBGI, as well as 24-h mean glucose, SD, CV, MAGE, CONGA, J-index, HBGI, and M-value were also higher in patients with IAH (all P≤0.01). No differences in HbA1c, TIR, TAR and TBR were found between the groups. Day-time, nocturnal and 24-h SD, CV, LI, J-index, and HBGI, as well as day-time and 24-h MAGE, correlated negatively with postprandial C-peptide. Conclusion: In patients with T1D, IAH is associated with low (or zero) residual beta cell function. This relationship could be mediated via enhanced GV. Disclosure V. Klimontov: Advisory Panel; Self; Boehringer Ingelheim International GmbH, Sanofi, Research Support; Self; Boehringer Ingelheim International GmbH, Speaker’s Bureau; Self; AstraZeneca, Medtronic. J. F. Semenova: None. A. I. Korbut: None. Funding Russian Science Foundation (20-15-00057)

Event-Related Desynchronization During Mirror Visual Feedback: A Comparison of Older Adults and People After Stroke.

Event-related desynchronization (ERD), as a proxy for mirror neuron activity, has been used as a neurophysiological marker for motor execution after mirror visual feedback (MVF). Using EEG, this study investigated ERD upon the immediate effects of single-session MVF in unimanual arm movements compared with the ERD effects occurring without a mirror, in two groups: stroke patients with left hemiplegia and their healthy counterparts. During EEG recordings, each group performed one session of mirror therapy training in three task conditions: with a mirror, with no mirror, and with a covered mirror. An asymmetry index was calculated from the subtraction of the event-related spectrum perturbations between the C3 and C4 electrodes located over the sensorimotor cortices contralateral and ipsilateral to the moved arm. Results of the effect of task versus group in contralateral and ipsilateral motor areas showed that there was a significant effect of task condition at the contralateral motor area in the high beta band (17–35 Hz) at C3. High beta ERD showed that the suppression was greater over the contralateral hemisphere than it was over the ipsilateral hemisphere in both study groups. The magnitude of low beta (12–16 Hz) ERD in patients with stroke was more suppressed in contralesional C3 under the no mirror compared to that of the covered mirror and similarly more suppressed in ipsilesional C4 ERD under the no mirror compared to that of the mirror condition. The correlation analysis revealed that the magnitude of ERSP power correlated significantly with arm severity in the low and high beta bands in patients with stroke, and a higher asymmetry index in the low beta band was associated with higher arm functioning under the no-mirror condition. There was a shift in sensorimotor ERD toward the contralateral hemisphere as induced by MVF accompanying unimanual movement in both stroke patients and healthy controls. The use of ERD in the low beta band as a neurophysiological marker to indicate the relationships between the amount of MVF-induced ERD attenuation and motor severity, and the outcome indicator for improving stroke patients’ neuroplasticity in clinical trials using MVF are warranted to be explored in the future.

Motor network connectivity predicts neuroplastic response following theta burst stimulation in healthy adults.

A patterned repetitive transcranial magnetic stimulation protocol, known as continuous theta burst stimulation (cTBS), can suppress corticospinal excitability via mechanisms that appear similar to long-term depression synaptic plasticity. Despite much potential, this technique is currently limited by substantial response variability. The purpose of this study was to investigate whether baseline resting state functional connectivity is a determinant of response to cTBS. Eighteen healthy young adults participated in up to three experimental sessions. Single-pulse transcranial magnetic stimulation was used to quantify change in corticospinal excitability following cTBS. Three minutes of resting electroencephalographic activity was recorded, and functional connectivity was estimated using the debiased weighted phase lag index across different frequency bands. Partial least squares regression identified models of connectivity between a seed region (C3) and the whole scalp that maximally accounted for variance in cTBS responses. There was no group-level effect of a single cTBS train or spaced cTBS trains on corticospinal excitability (p = 0.092). A low beta frequency band model of connectivity accounted for the largest proportion of variance in spaced cTBS response (R2 = 0.50). Based on the low beta frequency model, a-priori regions of interest were identified and predicted 39% of variance in response to spaced cTBS at a subsequent session. Importantly, weaker connectivity between the seed electrode (C3) and a cluster approximating a frontocentral region was associated with greater spaced cTBS response (p = 0.02). It appears M1-frontocentral networks may have an important role in determining the effects of cTBS on corticospinal excitability.

Plant community response to thinning and repeated fire in Sierra Nevada mixed-conifer forest understories

Fire suppression in the western United States has significantly altered forest composition and structure, resulting in a higher risk of stand-replacing fire, large-scale drought mortality, and bark beetle outbreaks. Mechanical thinning and prescribed fire are common treatments designed to reduce high-severity fire risk, but few studies have tracked long-term understory plant community response to these treatments with repeated fire application that emulates historic fire regimes. We evaluate changes in understory plant diversity and composition, as well as light availability, soil moisture, and litter depth over two decades following a factorial field experiment crossing thinning and two applications of prescribed fire at the Teakettle Experimental Forest (TEF) in the southern Sierra Nevada. We compare responses in experimental fuels treatments against those in nearby old-growth, mixed-conifer forests with restored low-severity fire regimes in Yosemite and Kings Canyon National Parks. We hypothesized that 1) understory plant richness, evenness, and beta diversity would increase with each burn event; 2) repeated fire after initial thinning would produce the highest understory plant diversity; 3) the second burn would reduce shrub cover, especially in the initially thinned treatments that demonstrated vigorous Ceanothus cordulatus growth after initial treatments; 4) the second burn would increase light availability and bare ground while reducing litter depth; and 5) treatments with initial thinning followed by multiple prescribed burns would show the greatest similarities to reference forests in diversity metrics, shrub cover, and environmental conditions. Although initially local (10 m2-scale) understory plant richness and diversity increased most following thinning combined with prescribed fire, this treatment did not generate understory conditions similar to those in nearby reference forests over the long term. Vigorous shrub growth resulted in low understory evenness and beta diversity over time, which a secondary burn treatment did not alter. Burning without thinning retained a more heterogeneous understory following initial treatment. Two years after the second burn treatment, this burning without thinning resulted in high understory richness and evenness similar to reference forest understories. Our results suggest management treatments may need to focus on creating heterogeneity in burn effects to limit shrub cover and foster more diverse understory communities.

Equity tail risk and currency risk premiums

We find that an option-based equity tail risk factor is priced in the cross section of currency returns; more exposed currencies offer a low risk premium because they hedge against equity tail risk. A portfolio that buys currencies with high equity tail beta and shorts those with low beta extracts the global component in the tail factor. The estimated price of risk of this novel global factor is consistently negative in currency carry and momentum portfolios, and in portfolios of other asset classes, suggesting that excess returns of these strategies can be partially understood as compensations for global tail risk.