Low-frequency Events Research Articles

Ambidexterity: a possible balance to manage complexity

The present article originates from the effort to answer the following question: is it possible for an organizational structure to steer between organizational routines and Black Swans? (Taleb, 2007). Unexpected, unique and low-frequency events are “unknown variable” that, despite the planning and precautions deployed, catch an organization off-guard, and might have catastrophic consequences. Unexpected events impact organizations, undermining the knowledge and redefining the list of competences that an organization needs in order to be competitive. The main goal of the present article is to shed light on the role and the challenges that firms undertake in their defining moments of adaptation of their organizational assets – the structure –. The rational pattern of adaptation is exemplified by the use of ambidextrous organizational structures, which focus on activities that can be defined as exploration and exploitation. Within the analysis of “the science of complexity”, parallels, paradoxes and metaphors representing a synthesis of a largely shared doctrine will be investigated: firms need to utilize known variables, or sometimes unknown ones, that are inevitably complex, in order to find the right fit, react swiftly to change, successfully compete, and obtain results.

Unique, dual-indexed sequencing adapters with UMIs effectively eliminate index cross-talk and significantly improve sensitivity of massively parallel sequencing

BackgroundSample index cross-talk can result in false positive calls when massively parallel sequencing (MPS) is used for sensitive applications such as low-frequency somatic variant discovery, ancient DNA investigations, microbial detection in human samples, or circulating cell-free tumor DNA (ctDNA) variant detection. Therefore, the limit-of-detection of an MPS assay is directly related to the degree of index cross-talk.ResultsCross-talk rates up to 0.29% were observed when using standard, combinatorial adapters, resulting in 110,180 (0.1% cross-talk rate) or 1,121,074 (0.29% cross-talk rate) misassigned reads per lane in non-patterned and patterned Illumina flow cells, respectively. Here, we demonstrate that using unique, dual-matched indexed adapters dramatically reduces index cross-talk to ≤1 misassigned reads per flow cell lane. While the current study was performed using dual-matched indices, using unique, dual-unrelated indices would also be an effective alternative.ConclusionsFor sensitive downstream analyses, the use of combinatorial indices for multiplexed hybrid capture and sequencing is inappropriate, as it results in an unacceptable number of misassigned reads. Cross-talk can be virtually eliminated using dual-matched indexed adapters. These results suggest that use of such adapters is critical to reduce false positive rates in assays that aim to identify low allele frequency events, and strongly indicate that dual-matched adapters be implemented for all sensitive MPS applications.

Using high-resolution bedload transport tracer measurements to investigate the characteristics of bedload transport over a large urban flood event

Channel morphological change is often evaluated by employing sediment transport models since field data during high magnitude low frequency events is rarely available. However, sediment transport rate estimates are heuristic at best to within 1 - 3 orders of magnitude. Mimico Creek is an urban gravel-bed channel in Southern Ontario, Canada that has undergone intensive event-based sediment transport sampling and inter-event bed material particle tracking over a three-year period. A HEC-RAS model was developed of the study reach and calibrated to a series of discharge events where in-situ bedload sampling occurred. Both step-wise discharge and unsteady flow simulations were evaluated to compare sediment transport rates for a range of transport models which included the Meyer-Peter Müller and the Wilcock-Crowe. Calibration curves were developed to estimate sediment discharge in Mimico Creek. The results of the calibrated model were used to calculate the mean travel distance of bed material using the expression for the volumetric rate of bed material transport. Results from the modelling exercise found mean travel distances were similar and in some cases larger than those observed from field measurements, considering both mobile and immobile particles.

On the Predominant Nonlinear Response of the Extratropical Atmosphere to Meridional Shifts of the Gulf Stream

The North Atlantic atmospheric circulation response to the meridional shifts of the Gulf Stream (GS) path is examined using a large ensemble of high-resolution hemispheric-scale Weather Research and Forecasting Model simulations. The model is forced with a broad range of wintertime sea surface temperature (SST) anomalies derived from a lag regression on a GS index. The primary result of the model experiments, supported in part by an independent analysis of a reanalysis dataset, is that the large-scale quasi-steady North Atlantic circulation response is remarkably nonlinear about the sign and amplitude of the SST anomaly chosen over a wide range of GS shift scenarios. The nonlinear response prevails over the weak linear response and resembles the negative North Atlantic Oscillation (NAO), the leading intrinsic mode of variability in the model and the observations. Further analysis of the associated dynamics reveals that the nonlinear responses are accompanied by the shift of the North Atlantic eddy-driven jet, which is reinforced, with nearly equal importance, by the high-frequency transient eddy feedback and the low-frequency wave-breaking events. Additional sensitivity simulations confirm that the nonlinearity of the circulation response is a robust feature found over the broad parameter space encompassing not only the varied SST but also the absence/presence of tropical influence, the varying lateral boundary conditions, and the initialization scheme. The result highlights the fundamental importance of the intrinsically nonlinear transient eddy dynamics and the eddy–mean flow interactions in generating the nonlinear downstream response to the meridional shifts in the Gulf Stream.

49 Paediatric traumatic cardiac arrest – the development of a treatment algorithm

IntroductionPaediatric Traumatic Cardiac Arrest (TCA) is a high acuity, low frequency event with fewer than 15 cases reported per year to the Trauma Audit Research Network (TARN). Traditionally survival from...

Frequency-dependent velocity analysis and offset-dependent low-frequency amplitude anomalies from hydrocarbon-bearing reservoirs in the southern North Sea, Norwegian sector

Our aim was to identify some of the characteristics of low-frequency anomalies. Specifically, we have looked, in 3D broadband data from the North Sea, for any offset dependence in these anomalies and any frequency-related change in normal moveout (NMO) velocity that could influence stacking power over different frequencies. After high-resolution spectral decomposition, two types of low-frequency anomaly have been identified associated with hydrocarbon-bearing reservoirs: (1) at the reservoir top and (2) below the reservoir, with a time delay of approximately 100–200 ms. Both types of anomalies indicate offset dependence. On the near-offset stacks, they are relatively strong, but they tend to be absent on the far-offset stacks. In addition, horizon velocity analysis, which was performed along the horizons picked at the tops of reservoir and nonreservoir intervals, has revealed frequency-dependent NMO velocity. For nonreservoir events, we found no significant difference between the NMO velocities for the low-frequency and high-frequency filtered common-midpoint gathers. However, along the anomalously low-frequency events observed at the tops of, and below, oil-bearing reservoirs, lower velocity is observed for low-frequency and higher velocity for high-frequency filtered gathers. If these properties turn out to be universally typical, increased understanding and inclusion of them could lead to improved workflows and help increase the reliability of low-frequency analysis as a hydrocarbon indicator.

Retention of Vaginal Breech Delivery Skills Taught in Simulation.

The optimal frequency of conducting simulation training for high-acuity, low-frequency events in obstetrics and gynaecology residency programs is unknown. This study evaluated retention over time of vaginal breech delivery skills taught in simulation, by comparing junior and senior residents. In addition, the residents' subjective comfort level to perform this skill clinically was assessed. This prospective cohort study included 22 obstetrics and gynaecology residents in a Canadian residency training program. Digital recordings were completed for pre-training, immediate post-training, and delayed (10-26 weeks later) post-training intervals of a vaginal breech delivery simulation, with skill assessment by a blinded observer using a binary checklist. Residents also completed questionnaires to assess their subjective comfort level at each interval. Junior and senior residents had significant improvements in vaginal breech delivery skills from the pre-training assessment to both the immediate post-training assessment (junior, P <0.001; senior, P <0.001) and the delayed post-training assessment (P <0.001 and P = 0.001, respectively). There was a significant decline in skills between the immediate and delayed post-training sessions for junior and senior residents (P = 0.003 and P <0.001, respectively). Both junior and senior residents gained more comfort immediately after the training (P <0.001 and P <0.001, respectively), without a significant change between immediate post-training and delayed post-training comfort levels (P = 0.19 and P = 0.11, respectively). Residents retained vaginal breech delivery skills taught in simulation 10-26 weeks later, although a decline in skills occurred over this time period. Comfort level was positively affected and retained. These results will aid in determining the frequency of simulation teaching for high-acuity, low-frequency events in a residency simulation curriculum.

Developing a Canadian Curriculum for Simulation-Based Education in Obstetrics and Gynaecology: A Delphi Study.

As obstetrics and gynaecology (Ob/Gyn) residency training programs move towards a competence-based approach to training and assessment, the development of a national standardized simulation curriculum is essential. The primary goal of this study was to define the fundamental content for the Canadian Obstetrics and Gynecology Simulation curriculum. A modified Delphi technique was used to achieve consensus in three rounds by surveying residency program directors or their local simulation educator delegates in 16 accredited Canadian Ob/Gyn residency programs. A consensus rate of 80% was agreed upon. Survey results were collected over 11 months in2016. Response rates for the Delphi were 50% for the first round, 81% for the second round, and 94% for the third round. The first survey resulted in 84 suggested topics. These were organized into four categories: obstetrics high acuity low frequency events, obstetrics common events, gynaecology high acuity low frequency events, and gynaecology common events. Using the modified Delphi method, consensus was reached on 6 scenarios. This study identified the content for a national simulation-based curriculum for Ob/Gyn residency training programs and is the first step in the development of this curriculum.

Over 5,000 Years of Ensemble Future Climate Simulations by 60-km Global and 20-km Regional Atmospheric Models

Abstract An unprecedentedly large ensemble of climate simulations with a 60-km atmospheric general circulation model and dynamical downscaling with a 20-km regional climate model has been performed to obtain probabilistic future projections of low-frequency local-scale events. The climate of the latter half of the twentieth century, the climate 4 K warmer than the preindustrial climate, and the climate of the latter half of the twentieth century without historical trends associated with the anthropogenic effect are each simulated for more than 5,000 years. From large ensemble simulations, probabilistic future changes in extreme events are available directly without using any statistical models. The atmospheric models are highly skillful in representing localized extreme events, such as heavy precipitation and tropical cyclones. Moreover, mean climate changes in the models are consistent with those in phase 5 of the Coupled Model Intercomparison Project (CMIP5) ensembles. Therefore, the results enable the assessment of probabilistic change in localized severe events that have large uncertainty from internal variability. The simulation outputs are open to the public as a database called “Database for Policy Decision Making for Future Climate Change” (d4PDF), which is intended to be utilized for impact assessment studies and adaptation planning for global warming.

Characterisation and functional mapping of surface potentials in the rat dorsal column nuclei.

The brainstem dorsal column nuclei (DCN) process sensory information arising from the body before it reaches the brain and becomes conscious. Despite significant investigations into sensory coding in peripheral nerves and the somatosensory cortex, little is known about how sensory information arising from the periphery is represented in the DCN. Following stimulation of hind-limb nerves, we mapped and characterised the evoked electrical signatures across the DCN surface. We show that evoked responses recorded from the DCN surface are highly reproducible and are unique to nerves carrying specific sensory information. The brainstem dorsal column nuclei (DCN) play a role in early processing of somatosensory information arising from a variety of functionally distinct peripheral structures, before being transmitted to the cortex via the thalamus. To improve our understanding of how sensory information is represented by the DCN, we characterised and mapped low- (<200Hz) and high-frequency (550-3300Hz) components of nerve-evoked DCN surface potentials. DCN surface potentials were evoked by electrical stimulation of the left and right nerves innervating cutaneous structures (sural nerve), or a mix of cutaneous and deep structures (peroneal nerve), in 8-week-old urethane-anaesthetised male Wistar rats. Peroneal nerve-evoked DCN responses demonstrated low-frequency events with significantly longer durations, more high-frequency events and larger magnitudes compared to responses evoked from sural nerve stimulation. Hotspots of low- and high-frequency DCN activity were found ipsilateral to stimulated nerves but were not symmetrically organised. In conclusion, we find that sensory inputs from peripheral nerves evoke unique and characteristic DCN activity patterns that are highly reproducible both within and across animals.

Evaluation of the Use of Remodelable Pericardial Bolsters during Cystectomy and Diversion to Prevent Enterocutaneous Fistulas

IntroductionEnterocutaneous fistula is one of the most serious and potentially devastating complications after radical cystectomy, a complex operation with a significant morbidity rate. In this analysis we examined the potential benefit of biomaterial buttressing of staple lines in reducing the incidence of enterocutaneous fistula in patients undergoing cystectomy. MethodsWe retrospectively reviewed 398 patients undergoing cystectomy for bladder cancer during an approximately 11-year period at the University of Colorado Hospital, and compared the frequency of enterocutaneous fistula before and after the implementation of biomaterial buttressing for bowel anastomosis. ResultsIn total, 301 surgical cases preceded biomaterial buttressing and 97 received buttressing with bovine pericardial strips. Seven cases (2.3%) of enterocutaneous fistula occurred without adjunctive reinforcement whereas zero cases were identified in the period using buttressing with bovine pericardial strips. Thus buttressing was associated with a nonsignificant reduction in the odds of enterocutaneous fistula (OR 0.20; 95% CI 0.01, 3.56; p=0.20). Although risk factor adjustment was prohibited by the low frequency of events, none of the cases of enterocutaneous fistula had received prior radiation therapy. Incidentally, the odds of postoperative functional bowel obstruction were significantly decreased after the implementation of buttressing (OR 0.28; 95% CI 0.08, 0.93; p=0.03). ConclusionsThe absolute reduction in the incidence of enterocutaneous fistula and significantly decreased odds of functional bowel obstruction in this cohort warrant future investigation to confirm the benefit of bovine pericardial strip buttresses for bowel anastomoses in cystectomy.

Source mechanism of low-frequency seismic events at Unzen volcano, Kyushu, Japan : volcanic tremor on May 10 and explosion earthquake on June 11, 1991

Source mechanism of low-frequency seismic events at Unzen volcano, Kyushu, Japan : volcanic tremor on May 10 and explosion earthquake on June 11, 1991

Use of Simulation to Improve Cardiopulmonary Resuscitation Performance and Code Team Communication for Pediatric Residents

Cardiorespiratory events are infrequent in pediatric teaching hospitals but can lead to significant morbidity and mortality. Clear communication within the response team prevents delays in action and allows all team members to contribute to providing optimum management. This resource was developed to simulate high-acuity and low-frequency events for pediatric residents. The scenario options are recurrent supraventricular tachycardia, prolonged QT syndrome, myocarditis, and respiratory syncytial virus bronchiolitis. The simulation is best performed in a simulation center with audio- and video-recording capabilities but could also be performed in situ in the pediatric intensive care unit or emergency room. Necessary personnel include a simulation technician and two instructors. A code cart, mock medications, and defibrillator with hands-free pads appropriate for the mannequin are necessary supplies. Critical actions include initial survey and intervention, rhythm recognition, cardiopulmonary resuscitation (CPR), use of defibrillator, and administration of anti-arrhythmic medications when needed. At the conclusion of the scenario, a formal debriefing with learners using structured feedback is performed. These cases have been used with groups of pediatric or emergency medicine residents approximately 16 times over the past 3 years. Learners have reported that participation increased their confidence and comfort with management of cardiorespiratory events and that communication technique practice improved their teamwork and sign-out skills. Rhythm recognition and CPR performance scores during the simulation scenarios improved, with subjective improvement during actual cardiorespiratory events. This resource advances learner knowledge of Pediatric Advanced Life Support algorithms and teamwork communication and identifies learner knowledge and management deficits.

Risk of Extreme Precipitation under Nonstationarity Conditions during the Second Flood Season in the Southeastern Coastal Region of China

Abstract This study analyzes the variation and risk changes of extreme precipitation under nonstationarity conditions using the Generalized Additive Models for Location, Scale, and Shape (GAMLSS) and the Mann–Kendall (MK) test. The extreme precipitation series is extracted from the observations during the second flood season (July–September) from 1960 to 2012 derived from 86 meteorological stations in the southeastern coastal region of China. The trend of mean (Mn) and variance (Var) of extreme precipitation is detected by MK. Ten large-scale circulation variables and four greenhouse gases are selected to construct a climate change index and a human activity index, which are based on principal component analysis. The recurrence risk of extreme precipitation is calculated by GAMLSS while considering climate changes and human activities. The results demonstrate that the nonstationarity characteristic of extreme precipitation is widespread in this region. A significant increasing trend of Mn is found in Shanghai, eastern Zhejiang, and northern and southern Fujian. An enhanced Var is found in eastern Guangdong. A significant positive correlation exists between climate changes/human activities and Mn/Var, especially in Zhejiang and Fujian. Generally, the contribution of climate changes and human activities to Mn is greater than it is to Var. In this region, the precipitation amount of high-frequency (2-yr return period) and low-frequency (100-yr return period) events increases from inland to coastal and from north to south. The government should pay careful attention to these trends because the intensity of extreme precipitation events and their secondary disasters could result in serious losses.

5-Year Safety and Efficacy of Resolute Zotarolimus-Eluting Stent: The RESOLUTE Global Clinical Trial Program

ObjectivesThe authors evaluated the 5-year cumulative incidence of cardiovascular events following Resolute zotarolimus-eluting stent (R-ZES) implantation. BackgroundIndividual trials are often underpowered to show differences for low-frequency adverse events. The R-ZES was studied in 10 prospective clinical trials, designed with identical adverse event definitions, ascertainment, and adjudication. MethodsThe RESOLUTE Global Clinical Trial Program includes 7,618 patients treated with R-ZES: RESOLUTE first-in-human study (N = 139), RESOLUTE All Comers (N = 1,140), RESOLUTE International (N = 2,349), RESOLUTE US (N = 1,402), RESOLUTE US 38 mm (N = 114), RESOLUTE Japan (N = 100), RESOLUTE Japan Small Vessel Study (N = 65), RESOLUTE Asia (N = 311), RESOLUTE China Randomized Controlled Trial (N = 198), and RESOLUTE China Registry (N = 1,800). The 5-year cumulative incidence of events was calculated. ResultsThe 5-year cumulative incidence of cardiac events was 13.4% for target lesion failure and included 5.0% cardiac death, 4.4% target vessel myocardial infarction, and 6.3% clinically driven target lesion revascularization. Dual-antiplatelet therapy at 1, 3, and 5 years was 91%, 37%, and 32%, respectively. The 5-year cumulative incidence of definite or probable stent thrombosis was 1.2%, which comprised 0.7% at 1 year and an annualized rate of 0.1% thereafter. Five-year use of dual-antiplatelet therapy varied geographically from 63% in Japan to 11% in Europe. ConclusionsIn the largest group of R-ZES patients examined to date, the majority of stent-related events, including target vessel myocardial infarction and stent thrombosis, occurred within the first year of implantation with much lower risks of these events out to 5 years.

Microscopic Evolution of Laboratory Volcanic Hybrid Earthquakes

Characterizing the interaction between fluids and microscopic defects is one of the long-standing challenges in understanding a broad range of cracking processes, in part because they are so difficult to study experimentally. We address this issue by reexamining records of emitted acoustic phonon events during rock mechanics experiments under wet and dry conditions. The frequency spectrum of these events provides direct information regarding the state of the system. Such events are typically subdivided into high frequency (HF) and low frequency (LF) events, whereas intermediate “Hybrid” events, have HF onsets followed by LF ringing. At a larger scale in volcanic terranes, hybrid events are used empirically to predict eruptions, but their ambiguous physical origin limits their diagnostic use. By studying acoustic phonon emissions from individual microcracking events we show that the onset of a secondary instability–related to the transition from HF to LF–occurs during the fast equilibration phase of the system, leading to sudden increase of fluid pressure in the process zone. As a result of this squeezing process, a secondary instability akin to the LF event occurs. This mechanism is consistent with observations of hybrid earthquakes.

Characterization and Decoding the Spatial Patterns of Hand Extension/Flexion using High-Density ECoG.

During awake brain surgeries, electrocorticogram (ECoG) was recorded using a high density electrode grid from the motor cortex of two subjects while they were asked to execute spontaneous hand extension and flexion. Firstly, we characterized the spatio-spectral patterns of high-density ECoG during the hand movements. In both subjects, we observed event related desynchronization (ERD) in low frequency band (LFB: 8-32 Hz) and event related synchronization (ERS) in high frequency band (HFB: 60-200 Hz) where HFB-ERS was more spatially localized and movement specific compared to LFB-ERD. In particular, improved spatial resolution of high density ECoG revealed HFB-ERS patterns with distinct timing in different anatomical regions. A few channels located anterior to the central sulcus were associated with HFB-ERS which started several hundred milliseconds prior to the movement onset. Several channels were associated with HFB-ERS which started close to the movement onset. Most importantly, only a small number of channels in the motor cortex regions exhibited long duration ERS which lasted while the subjects maintained their hand posture. A common spatial pattern (CSP) algorithm fused with linear discriminant analysis (LDA) was used to distinguish between hand extension and flexion at different time points based on subband features. ECoG data recorded from the channels located either anterior or posterior to the central sulcus were tested separately in classification. For both subjects, using channels located in motor area, HFB yielded almost 100% classification accuracy within 150-250 ms after the movement onset. The classification accuracies obtained from sensory areas were poor compared to motor areas and lagged the movement onset. These results suggest that spatial patterns of motor cortex captured with high-density ECoG in HFB can effectively drive a neural prosthetic to perform hand flexion and extension.

A Method of Estimating Operational Risk: Loss Distribution Approach with Piecewise-defined Frequency Dependence

In loss distribution approach (LDA), the most popular approach to operational risk aggregation, modeling the dependence across business lines has been recognized, however, the research of separately modeling dependence of high-frequency low-severity and low-frequency high-severity loss events is scarce so far. In this paper, we present an approach to estimate operational risk by modeling frequency dependence for high-frequency low-severity and low-frequency high-severity loss events separately across business lines in the framework of LDA, named LDA with piecewise-defined frequency dependence (LDA-PFD), and then apply this approach to calculate operational risk capital of the overall Chinese banking based on the largest bank, operational risk data set, the Chinese Operational Loss Database (COLD), which consists of 2132 operational risk records. The empirical results reveal that the operational risk capital calculated by LDA-PFD is significantly less than the loss distribution approach simply considering frequency dependence of the entire data (LDA-FD) and loss distribution approach based on piecewise-defined distribution but not considering dependence (LDA-PD).

The Pregnancy Vaccine Effectiveness Network (PREVENT): Establishing a Multi-Country Cohort to Estimate Vaccine Effectiveness (VE) against Hospitalized Influenza During Pregnancy

BackgroundPregnant women are at greater risk of complications from influenza (flu) infection than the general population. Although vaccination is an effective method to prevent influenza, the vaccine is underutilized during pregnancy. A challenge to maternal flu vaccination is the paucity of data about the effectiveness of inactivated influenza vaccines (IIV) in preventing severe outcomes in pregnant women. To inform policy and address this knowledge gap, CDC developed a multi-country collaboration to investigate the preventive value of IIV during pregnancy during multiple flu seasons. We present the progress to date of this Network.MethodsPREVENT was established in April 2016 to: i) estimate incidence of influenza and vaccination rates; ii) describe epidemiologic characteristics associated with illness; and iii) estimate IIV effectiveness in preventing hospitalizations during pregnancy associated with RT PCR -confirmed influenza. We selected sites that could identify the population of women known to be pregnant during flu seasons and integrate their hospitalization data, clinical laboratory testing, and vaccination records. We will assess VE using the case test-negative control design and use meta-analyses to pool VE estimates across sites and account for significant differences. Primary analyses will be completed by August 2017.ResultsSeven sites in Australia, Canada, Israel, and the US were selected; a protocol and data dictionary were finalized. We identified 1,024 pregnant women hospitalized with acute respiratory illness and RT-PCR tested, during six influenza seasons (2010–11 through 2015–16). Of the qualifying women, 550 (54%) tested positive for flu. Positivity varied by site (range 41% (US)–61.8% (Ontario, CAN)), and vaccination coverage varied across sites and seasons (range 7.3% (Ontario, CAN)–46% (US)). Analyses will examine flu season characteristics, vaccination patterns, and clinical and birth outcomes related to respiratory illness during pregnancy and flu incidence.ConclusionLaboratory-confirmed influenza hospitalization during pregnancy is a relatively low-frequency event. Pooling data across multiple sites offers a way to estimate VE against severe influenza outcomes in pregnant women that is informative to influenza vaccine policy.Disclosures A. Naleway, MedImmune: Investigator, Research grant; Pfizer: Investigator, Research grant; Merck: Investigator, Grant recipient; N. P. Klein, GSK: Investigator, Research grant; sanofi pasteur: Investigator, Grant recipient; Merck & Co: Investigator, Grant recipient; MedImmune: Investigator, Grant recipient; Protein Science: Investigator, Research grant; Pfizer: Investigator, Grant recipient; S. Irving, Medimmune/AstraZeneca: Investigator, Research support

TLEs and early VLF events: Simulating the important impact of transmitter‐disturbance‐receiver geometry

AbstractEarly very low frequency (VLF) events are perturbations to subionospherically propagating VLF radio transmitters which sometimes occur when lightning activity is near the transmitter‐receiver path. They are often correlated to Transient Luminous Events (TLEs). Recent analysis have focused on a new type of early events whose recovery time persists for many minutes, called LOng Recovery Events (LOREs). The underlying cause of these events is still unclear. Curiously, LOREs sometimes appear on only one path, while the same event observed on a different transmitter‐receiver path does not indicate a LORE. In this paper we observe and simulate two cases of early signal perturbations: The first is a typical early VLF event, and the second is a LORE. Both were recorded by two AWESOME VLF receivers in North Africa on 12 December 2009, during the EuroSprite campaign. We combine observations with theoretical modeling to infer the electron density change that most closely reproduces the observed perturbation. Our results explain the cases where LOREs are detected on only one path as resulting from transmitter‐receiver geometry significantly which impacts the modal content and therefore the observed VLF recovery time.