51 research outputs found
Spectral quantification of nonlinear behaviour of the nearshore seabed and correlations with potential forcings at Duck, N.C., U.S.A
Local bathymetric quasi-periodic patterns of oscillation are identified from
monthly profile surveys taken at two shore-perpendicular transects at the USACE
field research facility in Duck, North Carolina, USA, spanning 24.5 years and
covering the swash and surf zones. The chosen transects are the two furthest
(north and south) from the pier located at the study site. Research at Duck has
traditionally focused on one or more of these transects as the effects of the
pier are least at these locations. The patterns are identified using singular
spectrum analysis (SSA). Possible correlations with potential forcing
mechanisms are discussed by 1) doing an SSA with same parameter settings to
independently identify the quasi-periodic cycles embedded within three
potentially linked sequences: monthly wave heights (MWH), monthly mean water
levels (MWL) and the large scale atmospheric index known as the North Atlantic
Oscillation (NAO) and 2) comparing the patterns within MWH, MWL and NAO to the
local bathymetric patterns. The results agree well with previous patterns
identified using wavelets and confirm the highly nonstationary behaviour of
beach levels at Duck; the discussion of potential correlations with
hydrodynamic and atmospheric phenomena is a new contribution. The study is then
extended to all measured bathymetric profiles, covering an area of 1100m
(alongshore) by 440m (cross-shore), to 1) analyse linear correlations between
the bathymetry and the potential forcings using multivariate empirical
orthogonal functions (MEOF) and linear correlation analysis and 2) identify
which collective quasi-periodic bathymetric patterns are correlated with those
within MWH, MWL or NAO, based on a (nonlinear) multichannel singular spectrum
analysis (MSSA). (...continued in submitted paper)Comment: 50 pages, 3 tables, 8 figure
Neurotrophic requirements of human motor neurons defined using amplified and purified stem-cell derived cultures
Neurotrophic requirements of human motor neurons defined using amplified and purified stem-cell derived culturesHuman motor neurons derived from embryonic and induced pluripotent stem cells (hESCs and hiPSCs) are a potentially important tool for studying motor neuron survival and pathological cell death. However, their basic survival requirements remain poorly characterized. Here, we sought to optimize a robust survival assay and characterize their response to different neurotrophic factors. First, to increase motor neuron yield, we screened a small-molecule collection and found that the Rho-associated kinase (ROCK) inhibitor Y-27632 enhances motor neuron progenitor proliferation up to 4-fold in hESC and hiPSC cultures. Next, we FACS-purified motor neurons expressing the Hb9::GFP reporter from Y-27632-amplified embryoid bodies and cultured them in the presence of mitotic inhibitors to eliminate dividing progenitors. Survival of these purified motor neurons in the absence of any other cell type was strongly dependent on neurotrophic support. GDNF, BDNF and CNTF all showed potent survival effects (EC(50) 1-2 pM). The number of surviving motor neurons was further enhanced in the presence of forskolin and IBMX, agents that increase endogenous cAMP levels. As a demonstration of the ability of the assay to detect novel neurotrophic agents, Y-27632 itself was found to support human motor neuron survival. Thus, purified human stem cell-derived motor neurons show survival requirements similar to those of primary rodent motor neurons and can be used for rigorous cell-based screening.This work was funded by Project A.L.S., P2ALS and NYSTEM grant number CO24415. The work of N.J.L. was supported by the Portuguese Foundation for Science and Technology SFRH/BD/33421/2008 and the Luso-American Development Foundation. B.J.-K. was supported by the National Institute of Neurological Disorders and Stroke (NINDS). L.R. was supported by the Swedish Brain Foundation/Hjarnfonden. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Estimation of dimensions and orientation of multiple riverine dune generations using spectral moments
Metabolic rates of the antarctic amphipod Gondogeneia antarctica at different temperatures and salinities
Vulnerability and adaptation of Polish coast to impact of sea-level rise (SLR)
The paper presented contains results of the latest studies on assessment of the vulner-ability of the Polish coast to sea-level rise, thus providing the synthesis, development and update of all current works in this field. Apart from a general description of the basic physical and socio-economic coastal characteristics, boundary conditions were defined for further studies on Poland's vulnerability to ASLR. For each of the four areas, into which the Polish coastal zone was divided, a synthesis of threats and vul-nerability to the expected SLR was carried out, taking into account characteristic elements and features of the regions. Basing upon two extreme scenarios of sea-level rise, i.e. ASLR1 with 30 cm/100 yrs (optimistic variant) and ASLR2 with 100 cm/100 yrs (pessimistic variant), the assessment and cost calculation of total protection measures of the endangered areas in the coastal zone related to their capital value to be lost was executed. Finally, it was found that the protective investments should mainly be undertaken on the west and east coasts, where economically justified. Because of limited funds, it is necessary to concentrate on particularly important and simultaneously strongly threatened regions. The detailed analysis of costs implies that the activities should be undertaken first on the coastal segments adjacent to Gdańsk and Szczecin, where vast agglomerations are located, with concentrated industry and related infrastructure, as well as centres of science and culture
Sediment grain size features versus shoreline changes in view of field investigations
The paper presents the results of analyses of relationships between variability of shoreline position, grain size distributions of sediments and the wave climate at the IBW PAN Coastal Research Station in Lubiatowo. The study reports the 2 year long field investigations, which have comprised registrations of shoreline evolution, grain size parameters of nearshore sea bed and wave motion in the nearshore zone. The analysis of the experimental data provides a realistic assessment of morphodynamic processes occurring and interacting in the investigated coastal region. In the study, the following sand characteristic parameters have been considered: the median diameter d50, the representative diameters d25 and d75, the sorting parameter S0 and the skewness parameter Sk. The values of these parameters are found to correlate with the features of the coastal forms, mainly the shoreline migration
Relationships between coastal processes and properties of the nearshore sea bed dynamic layer
The paper discusses the notion of a layer of sandy sediments overlying a substratum
of cohesive deposits in the coastal zone. This layer of sand is generally more mobile
and is therefore conventionally referred to as the dynamic layer. Its parameters
are important to coastal lithodynamic and morphodynamic processes caused by
waves and currents. On the other hand, the dynamic layer is formed by nearshore
hydrodynamic impact. The variability of the features of the dynamic layer on the
southern Baltic dune and cliff shores in Poland is analysed on the basis of selected
geological data supported by local seismo-acoustic field investigations. It appears
that the conventional notion of the dynamic layer makes sense only in specific
geomorphologic conditions. In such cases, mostly related to cliff shores, theoretical
modelling of sediment transport should take the properties of the dynamic layer
into account
Condition of South-Eastern Baltic Sea Shores and Methods of Protecting Them
The paper describes lithodynamic and morphodynamic processes occurring in the main part of the south-eastern Baltic coastal area, namely on the sea shores from the Vistula mouth in the Gulf of Gdansk to the Lithuanian-Latvian border. The study area is subject to intensive natural coastal changes, as well as shore evolution caused by anthropogenic impacts at several locations. Methods of coastal protection against erosion and shore stabilization systems applied in the past and currently are described. The paper deals with the causes of the dynamics of beach/dune shores and cliffs. It presents the authors’ field observations of 2010-2013, as well as previously gained knowledge and the results of Polish, Russian and joint Polish-Russian field surveys
Application of Dean's curve to investigation of a long-term evolution of the Southern Baltic multi-bar shore profile
The paper presents the results of studies on the long-term evolution of the multi-bar
cross-shore profiles. The analysis is focused on time-dependent variability of shoreline position, a
modified parameter A of the conventional Dean's equation and a parameter F describing the
amount of nearshore sediment resources in the multi-bar cross-shore profile. The study also deals
with interrelationships between these quantities. The analysis is carried out using
field data
collected at Lubiatowo, Poland, on the dissipative shore, representative for the south Baltic. The
considered coastal segment is found to be stable in the long-term scale. The results of analysis
show that the parameter A can either increase or decrease together with the shoreline advance.
It is concluded that the shoreline position change is a parameter unsatisfactorily representative
for behaviour of the seashore. The use of the Dean's approximation for estimation of the sediment
resources F on the multi-bar seashore profiles is found reasonable to eliminate the effects of
peculiarities of such shores
Long period oscillations in the longshore current on a sandy, barred coast investigated with singular spectrum analysis
The presence of infragravity waves in nearshore regions can be sought in the records
of both water levels and wave-driven longshore currents. For this reason, time series
of such currents in close proximity to the shoreline were analysed using Singular
Spectrum Analysis (SSA). Simultaneously, the results obtained with this method
were confronted with the output of Discrete Wavelet Transform (DWT), which
had previously been applied to this data. The records of longshore currents were
collected on a daily basis during field experiments in the autumns of 2002 and
2003 with sampling rates of 3 Hz and 0.5 Hz. This produced a large data set
that allowed for the use of an advanced signal processing technique, capable of
extracting patterns characteristic of low-, medium- and high-frequency bands. It provided similar evidence to that produced by DWT for the existence of infragravity
waves along a dissipative coast with multiple bars. The study also demonstrated
the utility of SSA for studies on coastal hydrodynamics. It also showed up the
better user-friendliness of DWT in terms of pattern extraction and interpretation.
On the other hand, SSA demonstrated a higher precision of pattern extraction once
the DWT output was known, which is a manifestation of the synergy of the two
methods when applied jointly
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