1,555 research outputs found

    Inlet stability and case histories, Part II

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    Inlets which require frequent channel dredging due to gradual shoaling, exhibit migration, or shoal up during storms, are in general unstable and pose a problem to the engineer. This problem of inlet stability is a complex one, because of the rather large number of variables that go into defining stability. The reference here is to inlets on sandy coasts only, because the absence of sand or similar sedimentary material the problem does not arise. Shell is also found in varying proportions with sand. Some of this is. new, whereas in some areas it is ancient reworked material whose size distribution is close to that of the sand with which it is associated. (PDF has 24 pages.

    Part I. Hydraulics of tidal inlets: simple analytic models for the engineer

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    Inlets are common coastal features around the world. Essentially an inlet connects a lagoon, a bay or an estuary to the ocean (or sea), and the flow through the inlet channel is primarily induced by the tidal rise and fall of water level in the ocean. When speaking of the hydraulics of an inlet, one is interested mainly in determining the flow through the inlet and the tidal variation in the bay, given the following: (1) Inlet geometry (2) Bay geometry (3) Bottom sediment characteristics in the inlet (4) Fresh water inflow into the bay (and out through the inlet) (5) Ocean tide characteristics A combination of all these factors can produce a rather complex situation. (PDF contains 34 pages.

    Sediment storage at tidal inlets

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    Accumulation of sediment around tidal inlets has become a matter of renewed interest mainly for three reasons. The first of these is the need to estimate the shoal volumes, particularly in the ebb shoal, as a potential source of sediment for beach nourishment. The second reason is the need to assess the role of the inlet in influencing the rate of erosion of downdrift shoreline, as a result of interruption or deflection of the littoral drift. Finally, an evaluation of inlet sediment accumulation is essential to account for the long term sedimentary budget of shorelines interrupted by inlets

    Laboratory experiments on cohesive soil bed fluidization by water waves

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    Part I. Relationships between the rate of bed fluidization and the rate of wave energy dissipation, by Jingzhi Feng and Ashish J. Mehta and Part II. In-situ rheometry for determining the dynamic response of bed, by David J.A. Williams and P. Rhodri Williams. A series of preliminary laboratory flume experiments were carried out to examine the time-dependent behavior of a cohesive soil bed subjected to progressive, monochromatic waves. The bed was an aqueous, 50/50 (by weight) mixture of a kaolinite and an attapulgite placed in a plexiglass trench. The nominal bed thickness was 16 cm with density ranging from 1170 to 1380 kg/m 3, and water above was 16 to 20 cm deep. Waves of design height ranging from 2 to 8 cm and a nominal frequency of 1 Hz were run for durations up to 2970 min. Part I of this report describes experiments meant to examine the rate at which the bed became fluidized, and its relation to the rate of wave energy dissipation. Part II gives results on in-situ rheometry used to track the associated changes in bed rigidity. Temporal and spatial changes of the effective stress were measured during the course of wave action, and from these changes the bed fluidization rate was calculated. A wave-mud interaction model developed in a companion study was employed to calculate the rate of wave energy dissipation. The dependence of the rate of fluidization on the rate of energy dissipation was then explored. Fluidization, which seemingly proceeded down from the bed surface, occurred as a result of the loss of structural integrity of the soil matrix through a buildup of the excess pore pressure and the associated loss of effective stress. The rate of fluidization was typically greater at the beginning of wave action and apparently approached zero with time. This trend coincided with the approach of the rate of energy dissipation to a constant value. In general it was also observed that, for a given wave frequency, the larger the wave height the faster the rate of fluidization and thicker the fluid mud layer formed. On the other hand, increasing the time of bed consolidation prior to wave action decreased the fluidization rate due to greater bed rigidity. Upon cessation of wave action structural recovery followed. Dynamic rigidity was measured by specially designed, in situ shearometers placed in the bed at appropriate elevations to determine the time-dependence of the storage and loss moduli, G' and G", of the viscoelastic clay mixture under 1 Hz waves. As the inter-particle bonds of the space-filling, bed material matrix weakened, the shear propagation velocity decreased measurably. Consequently, G' decreased and G" increased as a transition from dynamically more elastic to more viscous response occurred. These preliminary experiments have demonstrated the validity of the particular rheometric technique used, and the critical need for synchronous, in-situ measurements of pore pressures and moduli characterizing bed rheology in studies on mud fluidization. This study was supported by WES contract DACW39-90-K-0010. (This document contains 151 pages.

    Fine sediment erodibility in Lake Okeechobee, Florida

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    The critical need to predict the turbidity in water due to fine-grained sediment suspension under wave action over mud deposits for sedimentation and erosion studies, as well as sorbed contaminant transport, is well known. Since fall velocities of fine sediment particles are very small, they can be easily transported by hydrodynamic flows such as waves and currents. The presence of these particles in the water column affects accoustic transmission, heat absorption and depth of the eutrophic zone (Luettich et al., 1989). Because these sediments also have a strong affinity for sorbing nutrients and toxic chemicals, sediments which have been deposited on the bottom may function as a source of contaminants to the water column if they are disturbed by eroding forces resulting, for instance, from wave action. An outstanding example of a water body for these problems is Lake Okeechobee, the largest shallow lake in Florida. This lake shows typical signs of artificial eutrophication mainly due to increased phosphorus loading associated with the surrounding region. Resuspension of sediment at the bottom of Lake Okeechobee composed of fine-grained material has been examined. A sediment transport model was used to simulate likely trends in the evolution of the vertical suspended sediment concentration profile resulting from wave action, and the corresponding eroded bed depth was calculated through mass balance. Requisite information on characteristic parameters and relationships related to fine sediment erodibility were derived from field sampling of bottom sediment in the lake, and through laboratory experiments using this sediment and lake water. (161pp.

    Some considerations on coastal processes relevant to sea level rise

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    The effects of potential sea level rise on the shoreline and shore environment have been briefly examined by considering the interactions between sea level rise and relevant coastal processes. These interactions have been reviewed beginning with a discussion of the need to reanalyze previous estimates of eustatic sea level rise and compaction effects in water level measurement. This is followed by considerations on sea level effects on coastal and estuarine tidal ranges, storm surge and water level response, and interaction with natural and constructed shoreline features. The desirability to reevaluate the well known Bruun Rule for estimating shoreline recession has been noted. The mechanics of ground and surface water intrusion with reference to sea level rise are then reviewed. This is followed by sedimentary processes in the estuaries including wetland response. Finally comments are included on some probable effects of sea level rise on coastal ecosystems. These interactions are complex and lead to shoreline evolution (under a sea level rise) which is highly site-specific. Models which determine shoreline change on the basis of inundation of terrestrial topography without considering relevant coastal processes are likely to lead to erroneous shoreline scenarios, particularly where the shoreline is composed of erodible sedimentary material. With some exceptions, present day knowledge of shoreline response to hydrodynamic forcing is inadequate for long-term quantitative predictions. A series of interrelated basic and applied research issues must be addressed in the coming decades to determine shoreline response to sea level change with an acceptable degree of confidence. (PDF contains 189 pages.

    Effect of eclampsia on pregnancy outcome at the tertiary care center

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    Background: Eclampsia is a common medical and life-threatening emergency condition mainly seen in 5-10% of all pregnancies and that is a major cause of maternal and perinatal morbidity and mortality The aim of the study to find out the fetomaternal outcomes of eclampsia in tertiary care hospital and to analyse the trend of eclampsia and associated epidemiological variables.Methods: This retrospective analytical study was undertaken with 40 clinically diagnosed women with eclampsia in their third trimester of pregnancy in the Department of Obstetrics and Gynaecology, at tertiary care hospital from July 2020 to December 2021. Women who came to the hospital with eclampsia or developed eclampsia during hospital stay were included in our study.Results: In our study, the antepartum eclampsia was in 32 cases (80%), primigravida 27 cases (67.5%), maternal age (21-30 years) 26 cases (65%). Cesarean section was the mode of delivery in 26 cases (65%). NICU admission is required by 20 neonates (50%).Conclusions: Eclampsia is an important cause of maternal and perinatal morbidity and mortality. Providing quality antenatal health care services, increasing awareness of patients about warning symptoms, proper investigations, timely delivery, and proper monitoring in the intrapartum and postpartum period have the potential to improve maternal and perinatal outcomes.

    Utility of first trimester ultrasound before 12 weeks of gestation at tertiary care centre in western India

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    Background: The first trimester begins on the first day of the last menstrual period (LMP) and lasts until the end of 12 weeks of gestation. Transvaginal ultrasound is modality of choice for establishing the presence of an intrauterine pregnancy in the first trimester. The focus of our study is routine early pregnancy ultrasound. The purpose of this study was to diagnose various conditions of pregnancy at an early stage by using ultrasound.Methods: We conducted retrospective data analysis of random 250 pregnant patients who had undergone first-trimester ultrasonography USG) (transvaginal/abdominal) in their first antenatal visit at S.V.P. Hospital, Ahmedabad, Gujarat, India from March 2021 to February 2022. The patient was selected by a simple randomized method. Maternal age, parity, gestational age, and special features regarding maternal gestational history were compared with USG findings. Patients were divided into 13 groups on the basis of ultrasonographic diagnosis.Results: We noted 76.8% of patients had single, viable, intrauterine pregnancies, while 23.2% had complicated pregnancies with uterine anomalies, ovarian cysts, leiomyoma, caesarean scar pregnancy or subchorionic hematomas.Conclusions: Ultrasound measurement of fetus in first trimester is most accurate method to confirm gestational age. It is less expensive and easily available modality. First-trimester ultrasound is useful to define embryonic landmarks in developmental stages with reference to gestational age, early diagnosis of miscarriage, ectopic pregnancy, molar pregnancy, multifetal pregnancy, major fetal malformation. And also, to diagnose pregnancy with leiomyoma, caesarean scar pregnancy, uterine anomaly and pre-eclampsia with the help of uterine artery PI

    The Perth Alexithymia Questionnaire-Short Form (PAQ-S): A 6-item measure of alexithymia

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    Background: Alexithymia is a trait characterized by difficulties identifying feelings, difficulties describing feelings, and externally orientated thinking. It is widely regarded as an important transdiagnostic risk factor for a range of psychopathologies, including depressive and anxiety disorders. Whilst several well-validated psychometric measures of alexithymia exist, these are relatively lengthy, thus limiting their utility in time-pressured settings. In this paper, we address this gap by introducing and validating a brief 6-item version of the Perth Alexithymia Questionnaire, called the Perth Alexithymia Questionnaire-Short Form (PAQ-S). Method: Across two studies with adult samples (Study 1 N = 508 United States community; Study 2 = 378 Australian college students), we examined the psychometric properties of the PAQ-S in terms of its factor structure, reliability, and concurrent/criterion validity. Results: In exploratory and confirmatory factor analyses, all PAQ-S items loaded well on a single general alexithymia factor. The PAQ-S total score had high reliability, and correlated as expected with the long-form of the PAQ, as well as other established markers of alexithymia, emotion regulation, and affective disorder symptoms. Limitations: Our samples were general community or college student samples from two Western countries; future validation work in clinical samples and more diverse cultural groups is thus needed. Conclusions: The PAQ-S retains the psychometric strengths of the PAQ. As such, the PAQ-S can be used as a quick, robust measure of overall alexithymia levels. The introduction of the PAQ-S hence enables valid assessments of alexithymia in a more diverse range of settings and research designs

    Alexithymia and emotion regulation

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    BackgroundAlexithymia is a key transdiagnostic risk factor for emotion-based psychopathologies. Conceptual models specify that this is because alexithymia impairs emotion regulation. However, the extent of these putative emotion regulation impairments remains underexplored. Our aim in this study was to begin to address this gap by examining whether people with high, average, or low levels of alexithymia differ in the types of emotion regulation strategies they typically use.MethodGeneral community adults from the United States (N = 501) completed a battery of alexithymia and emotion regulation measures. Participants were grouped into high, average, and low alexithymia quantiles.ResultsAfter controlling for demographics and current levels of distress, the high, average, and low alexithymia groups differed in their use of cognitive and behavioral emotion regulation strategies. Compared to the other groups, the high alexithymia group reported lesser use of generally adaptive regulation strategies (cognitive reappraisal, approaching problems, and seeking social support) and greater use of generally maladaptive regulation strategies (expressive suppression, behavioral withdrawal, ignoring).LimitationsOur data were cross-sectional and from self-report questionnaires. Future work in other cultural groups would be beneficial.ConclusionsOur results support the view that alexithymia is associated with impaired emotion regulation. In particular, people with high alexithymia seem to exhibit a less adaptive profile of emotion regulation strategies. Direct targeting of these emotion regulation patterns in psychotherapy may therefore be a useful pathway for the treatment of emotional disorder symptoms in people with high alexithymia.</p
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