Short Observation Research Articles

Severe tick-borne encephalitis in a patient recovered from COVID 19

North-eastern Poland is an endemic region for tick-borne encephalitis (TBE). The COVID-19 pandemic overlapped with the activity period of ticks that are the main vectors for TBE. As we know from short observation worldwide, SARS-CoV-2 virus affects significantly the immune system and can lead to serious complications of other infections even in previously healthy patients.A 24-year-old female patient, who lived close to the forest, was admitted to the Department of Neurology at Medical University of Bialystok with fever, dizziness, and progressive left-sided hemiparesis for three days. She had no medical history of chronic disease and was not vaccinated against TBE. The patient had SARS-CoV-2 infection three weeks prior to admission to the hospital (positive IgG against SARS-CoV-2). During COVID-19 infection she had fever, myalgia, a mild dyspnoea without indications for oxygen therapy and recovered after one week. During hospitalisation in the Department of Neurology the patient presented neck stiffness, progressing tetraparesis, dysarthria and weakness of the neck muscles. The magnetic resonance of the head revealed numerous lesions, mainly in both thalamus, longitudinal lesion was found in the cervical spinal cord. The cerebrospinal fluid analysis indicated lymphocytic inflammation. A high level of TBE antibodies in both serum and CSF was found. After immunoglobulin and symptomatic treatment her condition gradually improved. The recovery after SARS-CoV-2 infection overlapping with TBE might have influenced the course of tick-borne disease in a bad manner. The correct diagnosis can be a challenge as COVID-19 can lead to further complications, also neurological. The co-incidence we observed is very rare, however during the pandemic it is pivotal to remember about possible occurrence of other infections and their atypical course.

The comprehensive analysis of clinical trials registration for IgA nephropathy therapy on ClinicalTrials.gov

Objectives IgA Nephropathy (IgAN) is common chronic kidney disease with a high incidence. This study aims to analyze comprehensively therapeutic clinical trials for IgAN registered on ClinicalTrials.gov. Methods Therapeutic trials for IgAN registered on ClinicalTrials.gov. up to 15 August 2021 were obtained. The general characteristics, features of experimental design, treatment strategies, and some main inclusion criteria and outcome measures were accessed. Results A total of 104 therapeutic clinical trials for IgAN were extracted on ClinicalTrials.gov up to 15 August 2021. Most of these trials explored the treatment for primary IgAN confirmed by renal biopsy in adults. Only 9% of all selected trials had results. Forty-five percent of trials recruited 50 or fewer participants, and 73% were adults or older adults. 99% of trials were interventional studies, and of all the interventional trials, 70% of trials were randomized, and 68% exercised a parallel assignment of intervention model. Immunosuppression was the most studied for the treatment of IgAN. Moreover, many novel agents had been increasingly studied in recent years. Furthermore, the inclusion criteria and primary outcome measures in these trials were diverse, and the level of proteinuria and change of proteinuria levels were the most used as inclusion criteria and primary outcome, respectively. Conclusions The majority of therapeutic trials for IgAN were randomized, none masking and parallel-assignment interventional studies, primarily recruiting adult patients as research subjects. These trials had relatively small sample sizes and short observation. Thus, more large-scale, multicenter, and randomized controlled trials are still needed to improve the management for IgAN.

Screening of cytokines in blood serum and lacrimal liquid in wet and atrophic forms of age-related macular degeneration

Cytokines play an integral role in pathogenesis of age-related macular degeneration (AMD). Of particular interest are the late stages of this disease, which causes progressive visual impairment. Therapy-induced effects of post-treatment cytokine concentrations also need to be studied, both at long and short observation terms. These studies are of vital importance if the atrophy occurs during antiangiogenic therapy. Our purpose was to study an array of 45 cytokines, in blood serum (BS) and lacrimal liquid (LL) of the patients with wet and atrophic AMD.The study included 70 people (85 eyes) with stage 3-4 AMD according to AREDS. Depending on the form of AMD, 3 groups were discerned: I group (n = 24) included the patients with “geographic atrophy”; II group (n = 22), consisted of the patients with macular atrophy treated with antiangiogenic therapy of wet AMD; III group (n = 24), comprised the patients with a wet AMD who did not previously receive the treatment. Control group consisted of healthy volunteers (n = 25). All the groups were comparable for age and gender. The patients underwent a comprehensive ophthalmological examination to make a diagnosis. A multiplex study of the local (in the BS) and systemic (in the LL) cytokine status was carried out on a MAGPIX device (platform хMAP, Luminex Corporation, USA) in the Luminexx PONENT 3.1 software, using Procarta Plex kits (eBioscience, Austria). We determined 45 cytokines causing various biological effects, i.e., IL-1á, IL-1â, IL-1ra, IL-2, IL-4, IL-5, IL-6, IL-7, IL-9, IL-10, IL-12p70, IL-13, IL-15, IL-17A, IL-18, IL-21, IL-22, IL-23, IL-27, IL-31, IFNá, IFNã, IL-8/CXCL8, IP-10/CXCL10, SDF-1á/CXCL12, MCP-1/CCL2, MIP-1á/CCL3, MIP-1â/ CCL4, RANTES/CCL5, Eotaxin/CCL11, TNFá, TNFâ, GM-CSF, VEGF-A, VEGF-D, FGF-2, EGF, PDGF-BB, HGF, SCF, GRO-á, NGF-â, BDNF, LIF, PIGF-1.Screening of a wide range of cytokines showing various biological effects was carried out in BS and LL of patients with atrophic and wet forms of AMD. It has been shown that the late stages of the disease are associated with local and systemic changes of pro / anti-inflammatory mediators (IL-1â, IL-1ra, IL-18, LIF), chemoattractant cytokines (IL-8/CXCL8, IP-10/CXCL10, MCP-1/CCL2, MIP-1á/CCL3, MIP-1â/ CCL4, RANTES/CCL5, Eotaxin/CCL11), hematopoietic regulators (IL-7), and growth factors with known angiogenic activity (EGF, HGF, PDGF-BB, VEGF-A). Altered concentrations of numerous chemokines, e.g., IP-10/CXCL10, SDF-1á/CXCL12, MIP-1á/CCL3, MIP-1â/CCL4, RANTES/CCL5 and Eotaxin/CCL11 (p < 0.05) in BS of the patients with atrophic and wet AMD may be of interest for the search of biomarkers associated with various clinical phenotypes of the disease and may be also helpful for development of new therapeutic strategies.

Distribution and identification of the species in the genus Helicops Wagler, 1830 (Serpentes, Colubridae, Xenodontinae)

BackgroundThe aquatic snakes of the genus Helicops are widely distributed throughout northern South America, but understudied concerning some aspects, including morphological traits and distribution. The most recent publication that provided an identification key to all species of Helicops is over 50 years old. This key is of limited value today since it includes taxa no longer recognised and lacks 8 of the 19 species currently recognised. There never was a publication trying to summarise distributional and morphological information of all species of Helicops. Most knowledge of these species is distributed throughout many small publications, such as short observation notes.New informationHere, we present distribution maps (point records), an identification key and comments on identification for all species in this genus. We base our results on a comprehensive literature review of over 300 scientific publications and own examinations. Our examinations comprise 190 specimens of 10 of the 19 currently recognised species and one Helicops sp. We report range extensions for the species H.danieli, H.infrataeniatus, H.leopardinus, H.pastazae and H.polylepis.

Efficacy and safety of Abelmoschus manihot in treating chronic kidney diseases: A multicentre, open-label and single-arm clinical trial

Rationale and objectiveThe efficacy of Abelmoschus manihot (AM) in treating of chronic kidney disease (CKD) has been confirmed by prior trials. AM is also commonly combined to other medicines among CKD patients in clinic. This trial aimed at evaluating the safety of AM combination application, and further verifying the efficacy of AM in treating various types of CKD. Study designA multicentre, prospective, open-label, single-arm trial Setting and participantsApproximately 2000 CKD patients with proteinuria (≥ 150 mg/d), from 105 centres across China InterventionsAM was administered to patients three times per day for 24 weeks: the daily dose was based on age (> 12 years old: 2.5 g tid; 6∼12 years old: 1.5 g tid; 2∼6 years old: 1 g tid) OutcomesThe efficacy outcomes were the change in 24-hour proteinuria and estimated glomerular filtration rate (eGFR) from baseline to week 24. Safety outcomes included adverse events and laboratory tests. Results2054 CKD patients from 105 centres were enrolled in this trial, with 1843 (89.7%) completing the 24-week follow-up. The participants’ median age was 44 years old and 44.6% were female. Compared to baseline, 24-hour proteinuria decreased 471 mg (95% confident interval, 367 to 575, p < 0.001) at week 24. eGFR did not change significantly relative to baseline with the mean increase as 1.7 ml/min/1.73 m2 (95% confident interval, -0.3 to 3.7, p = 0.09). 902 (43.9%) participants combined medication to AM during follow-up. The total incidence of adverse events was 12.9%; and the most common adverse events were hyperlipidaemia (4.1%), abnormal liver function (2.3%), upper respiratory infection (1.8%), and hyperglycaemia (1.1%). Combined medications did not change the risk for hyperlipidaemia and upper respiratory infection. The combination application with antiplatelet reagents increased the risk of abnormal liver function, and with calcium channel blockers increased the risk of hyperglycaemia. LimitationsSingle-arm clinical trial and short observation time ConclusionWe have provided safety information of AM on various types of CKD in a large trial, especially when combination to medications most commonly prescribed to CKD patients. AM also showed to decrease proteinuria with stable kidney function during follow up. AM is a promising treatment for CKD patients.

The risk-benefit ratio of Covid-19 vaccines: Publication policy by retraction does nothing to improve it.

On June 24, 2021 we published a risk-benefit analysis of COVID-19 vaccines, admittedly based on a shaky database. This analysis resulted in the insight, that very likely for three deaths prevented by vaccination we will have to accept that about two people die as a consequence of these vaccinations.1 This analysis led to editors’ threatening to withdraw, and the journal indeed retracted the publication. After a thorough re-review, it was republished.2, 3 The database we based our analysis on was a large naturalistic study of the BioNTech vaccine in Israel.4 This was the only study at the time that allowed for a direct estimation of an absolute risk reduction (ARR) in mortality. Admittedly, the ARR estimate was only available for a short observation period of 4 weeks after the first vaccine dose, a point raised by critics. One might have wanted a longer observation period to bring out the benefit of vaccinations more clearly, and our estimate of a number needed to vaccinate (NNV) of 16 000 to prevent one death might have been overly conservative. The recently published 6-month interim report of the BioNTech-regulatory clinical trial now covers a period long enough to let us look at this risk benefit ratio once again.5 In Table S4 of this publication,5 14 deaths are reported in the placebo group (n = 21 921) and 15 in the vaccination group (n = 21 926). Among them, two deaths in the placebo-group were attributed to COVID-19, and one in the vaccination group was attributed to COVID-19 pneumonia. This leads to an ARR = 4.56 × 10–5, and conversely to an NNV = 1/ARR = 21 916 to prevent one death by COVID-19. This shows that our original estimate was not so far off the mark. These passive pharmacovigilance data, different from the active reporting system of trials and observations, are notorious for underestimating casualties and side effects.6 Other severe side effects occur, such as myocarditis in young males who according to a recent study suffer a 13.6 fold risk of myocarditis.7 Thus, we have novel and worrying data that confirm the analysis we published in summer 2021, urging us to repeat our call for an installment of a European-wide active monitoring system that documents the safety and efficacy of COVID-19 vaccines long-term and for a rational public debate about the risk-benefit ratio of these novel vaccines. The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

Small Spacecraft Payload Study for X-ray Astrophysics including GRB Science

This paper presents microsatellite spacecraft payload study for prompt observation of transient astrophysical objects in X-ray energy range. By combining telescope concepts and miniaturized detectors, the small spacecraft will be able to probe the X-ray temporal emissions of bright events such as Gamma-Ray Bursts (GRBs), X-ray transients or the electromagnetic counterparts of Gravitational Wave Events (GWEs), but also short and long term observations of other types of variable X-ray sources. The spacecraft is based on the CubeSat nanosatellite platform with a volume of 16U. The spacecraft carries two types of X-ray telescopes onboard. The first is intended for X-ray transient monitoring and localization, and the second for detailed spectroscopic observation. The X-ray monitor/localization telescope with wide field of view of several arc degrees is used for localization and flux measurement of X-ray transients, as well as for permanent monitoring of Galactic center area. This telescope is based on Lobster Eye X-ray optics together with pixel detector based on the Timepix3 Quad detector. Rapid follow-up observation by soft X-ray spectroscopy is enabled by a second X-ray spectroscopic telescope with limited FOV (Field of View) of several arcmins with no spatial and/or angular resolution. The spectroscopic telescope uses condenser optics based on replicated parabolic total reflection system (or, alternatively, Wolter system) and a Ketek X-ray SDD detector with energy resolution of about 130 eV as a detector. In addition to technical and instrumental aspects, observational strategy and astrophysical issues and justifications are also addressed in the paper.

Long-Term Effects of Human Papillomavirus Vaccination in Clinical Trials and Real-World Data: A Systematic Review.

The preventive effect of HPV vaccines against anogenital and oropharyngeal cancers has been proven in both clinical trials and real-world data. We reviewed the published evidence about the long-term efficacy and effectiveness of the HPV vaccine in available papers of clinical trials and real-world data. As far as we searched, the longest period of preventive effect for the bivalent, 4-valent, and 9-valent vaccine were 11 years in the Costa Rica trial, 14 years in the FUTURE II, and 8 years in the LTFU extension study of V503-002 and the Scandinavian study, respectively. The sustained clinical effect during the observation period was longest for the 4-valent vaccine. In real-world data, the longest observation period of the vaccine effectiveness was 12 years in an Australian study for the 4-valent vaccine. On the other hand, the longest period of long-term persistence of HPV vaccine-induced seropositivity was 14 years in FUTURE II for the 4-valent vaccine. For the bivalent vaccine, additional long-term follow-up studies may not have been planned due to the launch of the 4-valent and 9-valent vaccines. In some studies of the 9-valent vaccine, the results have not yet been published because of the short observation period. The additional results are expected in the future. In a national immunization program, most girls and boys are inoculated with HPV vaccine by the time puberty begins; thus, it is important to monitor the vaccine effect at least until the sexually active period in their 20s and 30s.

Usefulness of rapid molecular tests in pediatric respiratory tract infections

ObjectiveTo evaluate the role and the advantages of nasopharyngeal swabs in the detection of Influenza A and B viruses and Respiratory syncytial virus through a rapid test based upon a nucleic acid amplification reaction in order to avoid improper antibiotics use.DesignCase-control retrospective study.SettingEmergency Room of “Sandro Pertini” General Hospital, Rome, Italy.ParticipantsChildren (< 14 years old) who consecutively arrived in the Emergency Department (ED) for respiratory tract infections, without obvious signs of bacterial respiratory tract infections and other comorbidities, in the maximal seasonal incidence period of November-to-March of every year between 2016 and 2020.MethodsMedical records of children included in the study were retrospectively examined. Children were subdivided according to the following intervals: 2016–2017 and 2017–2018 (Group 1), 2018–2019 and 2019–2020 (Group 2). Children in Group 2 undertook a nasopharyngeal swab, while those in Group 1 did not undergo any specific diagnostic test.Primary outcomeAvoidance of improper antibiotics administration.ResultsA total of 386 children were included in the study: 174 in Group 1, 212 in Group 2. The Odd Ratio (OR) of prescribing an antibiotic in the groups of children not being swabbed compared to those of children undertaking a swab was 9.21 (CI95% 5.6–15.2, p < 0.001). The overall percentage of hospitalizations, both in the short observation unit or in the pediatric unit, did not differ between the two groups.ConclusionsNasopharyngeal swabs for the detection of Influenza A and B viruses and Respiratory syncytial virus proved to be a useful means to a correct and timely diagnosis and allowed for a significant reduction in the prescription of antibiotic therapy.Trial registrationRetrospectively registered.

A block-movement-based analysis for cohesive powders in a rotating drum experiment

The precise characterization of the flow behavior of cohesive powders can be challenging. With the block-movement-based analysis, we introduce a more immediate characterization technique that even works for highly cohesive powders. Based on the strongly discontinuous dynamics in rotating drums dominated by the formation of large blocks and their subsequent breakage in abrupt avalanche events, it describes the flow behavior with geometrical properties of the falling down structures like block height or speed. Its advantages are the higher information content and the short observation time to get stable results. These properties make it a promising candidate for calibrating parameters for computer simulations. In addition, its high sensitivity allows to detect even small changes in the flow behavior. We demonstrate the method with three metal powders and identify the differences in their flowability. Furthermore, we investigate the influence of preconditioning at different humidity to underline the sensitivity of our approach.

Sleep disturbances predict active suicidal ideation the next day: an ecological momentary assessment study

BackgroundSleep disturbances are an underestimated risk factor for suicidal ideation and behavior. Previous research provided preliminary support of a temporal relationship between sleep disturbances and suicidal ideation. The present study therefore sought to investigate the prospective association between sleep disturbances, passive and active suicidal ideation, and further psychological risk factors, such as state impulsivity and depression.MethodsSeventy-three psychiatric inpatients (71% female) with unipolar depressive disorder and current or lifetime suicidal ideation took part in an ecological momentary assessment (EMA). Participants filled out a baseline assessment and data were collected via smartphones over a 6-days period. Multilevel analyses with sleep disturbance as predictor for active and passive suicidal ideation, state impulsivity, and depression were carried out.ResultsPatients with sleep disturbance experienced more active suicidal ideation, but no passive suicidal ideation, the following day. Of the four state impulsivity items, one item was significantly associated with sleep disturbance. Sleep disturbance had no effect on next-day depression. Limiting factors are the small and homogeneous sample along with the rather short observation period in an inpatient setting.ConclusionsThe micro-longitudinal study provides preliminary support for sleep disturbance as a proximal risk factor for next-day active suicidal ideation. Clinically, results indicate to consider the evaluation and treatment of sleep disturbances for an improved risk assessment and prevention of suicide.

Epithelial-Cell-Derived Cytokines in Patients with Obesity before and after Bariatric Surgery

/Purpose: Epithelial signals such as interleukin (IL)-25, IL-33, and thymic stromal lymphopoietin (TSLP) are stimulators of group 2 innate lymphoid cells (ILCs2) that are integral regulators of adipose tissue type 2 immunity. The purpose of this study was to assess cytokines activating ILCs2 in the serum of patients with obesity and the effect of bariatric surgery on these parameters. Material and Methods: In a single-center prospective study, serum IL-25, IL-33, TSLP, and ST2L levels were assayed at the baseline and at 6 months after bariatric surgery and correlated with anthropometric changes and metabolism parameters. Results: Mean age and median of body mass index (BMI) of study participants were 41.9 years ± 11 and 45.6 kg/m2 (range 36.3–56.3), respectively. Six months after surgery, excess weight loss percentage was 43.1 ± 10.2%. Serum TSLP was significantly lower in patients with obesity both before and after surgery than in healthy controls. TSLP values before operation were significantly correlated to glycated hemoglobin percentage and BMI. Serum IL-25, IL-33, and ST2L levels were comparable to controls both before and after operation. Conclusions: Decreased serum levels of TSLP may be a characteristic trait for obesity however nonmodifiable by body mass surgical reduction in short time observation. Low serum levels of TSLP are related to disturbances in glucose metabolism and BMI.

Anisotropic diffusion of ellipsoidal tracers in microswimmer suspensions

Tracer particles immersed in suspensions of biological microswimmers such as E. coli or C. reinhardtii display phenomena unseen in conventional equilibrium systems, including strongly enhanced diffusivity relative to the Brownian value and non-Gaussian displacement statistics. In dilute, 3-dimensional suspensions, these phenomena have typically been explained by the hydrodynamic advection of point tracers by isolated microswimmers, while, at higher concentrations, correlations between pusher microswimmers such as E. coli can increase the effective diffusivity even further. Anisotropic tracers in active suspensions can be expected to exhibit even more complex behaviour than spherical ones, due to the presence of a nontrivial translation-rotation coupling. Using large-scale lattice Boltzmann simulations of model microswimmers described by extended force dipoles, we study the motion of ellipsoidal point tracers immersed in 3-dimensional microswimmer suspensions. We find that the rotational diffusivity of tracers is much less affected by swimmer-swimmer correlations than the translational diffusivity. We furthermore study the anisotropic translational diffusion in the particle frame and find that, in pusher suspensions, the diffusivity along the ellipsoid major axis is higher than in the direction perpendicular to it, albeit with a smaller ratio than for Brownian diffusion. Thus, we find that far field hydrodynamics cannot account for the anomalous coupling between translation and rotation observed in experiments, as was recently proposed. Finally, we study the probability distributions (PDFs) of translational and rotational displacements. In accordance with experimental observations, for short observation times we observe strongly non-Gaussian PDFs that collapse when rescaled with their variance, which we attribute to the ballistic nature of tracer motion at short times.

ABANDONED SITES: BOON OR BANE FOR URBAN BIRD NESTINGA CASE STUDY FROM TIRUNELVELI, TAMIL NADU (INDIA)

A short duration observation on birds' nesting in an abandoned bungalow premise in the heart of Palayamkottai, Tirunelveli district in Southern Tamil Nadu is reported as a case study. Three species of water birds namely Black-crowned Night Heron (Nycticorax nycticorax), Intermediate Egret (Mesophoyxin termedia), and Little Cormorant (Phalacrocorax niger) were found to show mixed roosting. Recently infrastructural modification of the premise was undertaken, which influenced the nesting site of these colonial birds, considering their high sensitivity to disturbance.

Total mesometrial resection (TMMR) for cervical cancer FIGO IB-IIA: first results from the multicentric TMMR register study.

SynopsisAvailable data on total mesometrial resection and therapeutic lymphadenectomy (TMMR+tLNE) for the treatment of cervical cancer show excellent locoregional control rates without adjuvant chemoradiation. In 116 patients with cervical cancer stages IB–IIA the overall recurrence rate was 7.8% in a median follow-up time of 24 months. Locoregional recurrences occurred in 6.0% of patients.

An increase in early cancer detection rates at a single cancer center: Experiences from Sun Yat-sen University Cancer Center

Cancer has become a major fatal disease in China. The relatively lower early detection rates for multiple cancer types have been one of the main reasons for a relatively lower cancer curative rate in China compared with the developed countries. To investigate trends in the early cancer detection rate over the past 5 years in a major city of China, 45,260 patients with newly diagnosed cancers of the nasopharynx, lung, thyroid, colorectum, liver, breast, uteral cervix, stomach, esophagus, blood, and kidney from 2016 to 2020 at Sun Yat-sen University Cancer Center were evaluated. The early detection rate (stage I disease) for all cancer types in combination significantly increased from 14.4 to 23.07%. Among the studied cancer types, a significant increase in stage I cancers was proportionally seen in cancers of the lung, thyroid, colorectum, and uterine cervix. While for cancers of the liver and stomach, a significant proportional increment was only observed when combining stage I and stage II diseases. No significant alteration in early cancer detection of the nasopharynx, breast, esophagus, blood, or kidney was observed. Three limitations of this present study include relatively small cohorts of cancer patients, relatively short observation periods, and limited sample representativeness. Further efforts are anticipated to validate our findings with larger patient cohorts from different parts of China and enhance early cancer detection rates by promoting public awareness, applying better health care policies, and improving insurance coverage and medical resources.

Eigenvalues-Based Detector Design for Radar Small Floating Target Detection in Sea Clutter

In this letter, the correlation structure inherent in the received data is exploited to improve detection performance for sea-surface small floating targets in short observation time. Three detectors are devised resorting to the eigenvalues of covariance matrix that are versatile statistics reflecting the signal correlation. Specifically, the proposed detectors respectively exploit the maximum eigenvalue to arithmetic mean (MAM) of all eigenvalues, the maximum eigenvalue to geometric mean (MGM) of all eigenvalues, and the maximum eigenvalue to minimum eigenvalue (MME) to form test statistics. At the analysis stage, the three-parameter Burr function is exploited to approximate the statistical distributions of the test statistics under null hypothesis and alternative hypothesis. Besides, the analytic expressions of false alarm probability, detection probability, and thresholds of the proposed detectors are derived. Finally, simulation results on real sea clutter show that the proposed detectors provide effective solutions to the problem of target detection in sea clutter.

Phase Estimation of Single Tones Next to Modulated Signals in the Medium Frequency R-Mode System

Position, navigation, and timing information are critical to today&#x2019;s infrastructures; as a result, the possibility of estimating ranges is being explored in more and more radio systems. One way to achieve this is to extend the modulation with time-synchronised aiding carriers and to estimate their phase at the receiver side. In this paper, we present two ways to minimise the negative influence of the modulation on the phase estimation.We show that the classical maximum likelihood estimator is still an efficient estimator for our problem, using a medium-frequency R-Mode signal as an example, and is therefore used in receiver designs. We then describe two possible ways to precondition the signal to increase the accuracy for short observations. As a first approach, we describe how window functions can positively change the signal-to-noise ratio for our estimation. As a second approach, we show the use of a narrowband bandpass filter. Finally, we show that these approaches, applied to real measurements, improve the variance of the estimate by up to two orders of magnitude.

Small Target Detection in X-Band Sea Clutter Using the Visibility Graph

Small target detection in high-resolution sea clutter is one of the important problems in radar target detection. We propose a new detector that adopts the visibility graph (VG) algorithm and the graph convolution neural network (GCN). This detector extracts the graph feature of radar echo networks for target detection after converting the phase information of radar echo into complex networks. Different from the existing detector based on graph connectivity, the VG algorithm does not need radar data preprocessing and it can directly convert the radar data into complex networks by judging whether the series data are visible mutually. We extracted the graph feature that can effectively distinguish the background clutter and target echo by GCN instead of calculating the statistic of graphs manually. Experiments on the IPIX radar datasets show that the proposed method achieves superior performance than the existing detector based on graph connectivity, especially in a short observation time. When the observation time is 0.256 s, the average accuracy of &#x0023;17, &#x0023;54, and &#x0023;320 datasets can reach 84.82&#x0025;, 94.84&#x0025;, and 90.59&#x0025;, respectively.

Accurate Damping Factor and Frequency Estimation for Damped Real-Valued Sinusoidal Signals

The interpolated discrete Fourier transform (IpDFT) is one of the most popular techniques to estimate the parameters of a damped real-valued sinusoidal signal (DRSS). However, its accuracy is affected by strong noise presence and short observation windows. To this end, this letter proposes a novel two-point IpDFT method, called I2pZDFT, for the parameter estimation of a DRSS. The proposed I2pZDFT uses the zero-padding technique to increase the sampling rate in the frequency domain. The conjugate symmetry and the parity of the zero-padded signal are utilized to eliminate the influence of the spectral leakage. Simulation results highlight that the proposed I2pZDFT outperforms the existing IpDFT-based methods in terms of noise immunity, especially in the case of observation windows as short as 0.5 ~ 1 cycles.