1,078 research outputs found
Nanomechanics of confined polymer systems
Get PDFPolymers anchored to surfaces play an important role in nature and technology, and regulate diverse interfacial phenomena in areas such as tribology and colloidal stability. Polymers grafted to surfaces at high density form elongated “brushes” with characteristic lengths much larger than free coils in solution. These brushes can reduce interfacial friction and wear as well as impart fouling resistance to surfaces. In light of these functionalities it is important to understand the behaviour of surface-grafted polymers at the molecular and nanoscopic level. An emerging area of interest are polymers attached to nanopores. Theoretical studies predict interesting morphologies and dynamics of such confined brushes in and around nanopores, but nanopore environments have been difficult to study experimentally. In this thesis a unique polymer-functionalized nanopore-like experimental system is presented, functionalized with poly(ethylene glycol) (PEG). Atomic force microscopy (AFM) is employed to probe the PEG brushes with nanometre spatial precision and sub-nanonewton force sensitivity, revealing novel dynamics depending on the local grafting position of PEG with respect to the nanopore geometry. Further, AFM is used together with fluorescence microscopy to show how polymer–protein interactions can be used together with the anti-fouling property of PEG to sort specific biomolecules from complex biological fluids to nanoscale targets. This shows a way how to confer biological recognition and specificity to synthetic nanoscale systems which is important for biosensing and bioseparation applications
Reduction of dimensionality in Karyopherinβ1 mediated transport on FG domains
Get PDFMany molecular transport processes in living cells proceed by facilitated diffusion in two dimensions instead of three, but how this process works remains poorly understood. Known as “reduction of dimensionality” (ROD), this phenomenon has been implicated to underlie the transport of proteins through nuclear pore complexes (NPCs).
NPCs are biological nanomachines that regulate the selective exchange of macromolecular cargoes between the cytoplasm and nucleus in living cells. Small molecules diffuse freely through the NPC, whereas macromolecules >~5 nm in size are withheld. Access is limited to cargo-carrying transport receptors (karyopherins or Kaps, e.g. Kapß1), which interact with several intrinsically disordered Phe-Gly (FG)-repeat rich domains (i.e. FG domains) that pave the central pore. As each Kapß1 molecule contains ~10 hydrophobic pockets that bind FG repeats, Kap-FG domain binding involves highly multivalent interactions, which are generally known to impart a strong avidity that enhances stability and specificity. Consequently, in vitro studies have revealed very stable Kap-FG domain complexes. However, this is paradoxical in the context of the NPC, because the high Kapß1-FG domain binding affinities in the submicromolar range predict slow dissociation rates that contradict the short Kap-NPC dwell times measured in vivo (~5 ms). As this implies, Kap-FG domain binding ought to be sufficiently strong to ensure selectivity, but also weak enough to promote fast translocation through the NPC. However, an explanation as to how Kap-FG domain interaction balances the tradeoff between mobility and specificity during nucleocytoplasmic transport (NCT) is still lacking.
In the work presented here, this discrepancy is addressed in vitro using optical trapping-based photonic force microscopy (PFM). By measuring the thermal fluctuations of Kap-functionalized colloidal probes in contact with a surface grafted FG domain layer, it was found that Kap-FG interactions per se attenuate diffusive motion due to strong specific binding. This can be controlled by varying the amount of free Kaps in solution, which leads to differential behavior ranging from highly constrained to near-passive diffusion that is attributed to diminishing multivalent interactions between the Kap-probe and the FG domain layer. Measurements using surface plasmon resonance are consistent with this interpretation and show that a reduction of free FG-binding sites follows from a concentration-dependent increase in the occupancy of soluble Kapß1 molecules within the FG domain layer.
With the optical trap switched off, the probes exhibited two-dimensional diffusion at physiological Kap concentrations. The dissertation explains how multivalent interactions balance binding affinity and Kap-facilitated mobility on FG domains, leading to “reduction of dimensionality” in selective transport processes. This has implications for NCT, where a ROD-based scenario was proposed in which Kaps can diffuse in two dimensions along a layer of FG domains lining the central pore. Although this has not been validated in vivo, the physical display of Kap-facilitated two-dimensional diffusion on FG domains indicates that ROD can play a functional role in expediting selective transport through biological NPCs.
The importance and relevance of the work lie both in the understanding of multivalent interactions and multivalency-regulated transport processes in biological systems, as well as in breaking ground for the development of controlled reduced dimensional diffusion and controlled motion in artificial systems. On a more technical note, this work demonstrates the use of PFM in accessing particle diffusivity in the presence of biochemical interactions at biointerfaces
Kap-Centric control of nuclear pores based on promiscuous binding to FG nucleoporins
Get PDFNuclear pore complexes (NPCs) are remarkable molecular machines that perforate the nuclear envelope (NE) in eukaryotic cells and mediate the rapid bidirectional traffic of hundreds of proteins, ribonucleoproteins, and metabolites across the nuclear envelope. Their enormous structure is composed of multiple copies of 30 different proteins (Nups) that add up to 60 – 120 MDa of mass depending on the organism. Each NPC contains a 50 nm-diameter central channel through which only molecules smaller than ~40 kDa or ~5 nm in size can diffuse passively. The movement of larger molecules is impaired by a permeability barrier generated by ~200 partly intrinsically disordered phenylalanine-glycine (FG)-rich nucleoporins (FG Nups) that are tethered to the NPC transport channel surface. These FG Nups interact promiscuously with nuclear transport receptors (NTRs), such as karyopherins (Kaps; e.g. Kap-beta1) or NTF2, that mediate rapid trafficking of cargoes.
Given that the number of FG repeats per FG Nup also varies from 5 to ~50, NTR-FG Nup binding involves highly multivalent interactions, which are generally known to impart a strong avidity that enhances stability and specificity. However, this is paradoxical in the context of the NPC, because the high submicromolar Kap-beta1-FG domain binding affinities predict slow off rates (given a diffusion-limited on rate) that contradict the rapid (~5 ms) in vivo dwell time. As this implies, Kap-FG binding ought to be sufficiently strong to ensure selectivity but also weak enough to promote fast translocation through the NPC. Nonetheless, an explanation as to how promiscuous binding of FG Nups to NTRs is balanced against the mechanistic control of the FG domain barrier is still lacking.
The purpose of my work was to investigate FG Nup-NTR binding promiscuity and multivalency by measuring the interaction kinetics, binding affinity and in situ associated conformational changes in Nsp1p FG domains when binding NTF2 and Kap-beta1, both separately and together. Experimentally, this was achieved by using a novel surface plasmon resonance technique to correlate in situ mechanistic changes (molecular occupancy and conformational changes) with FG Nup-NTR binding.
The obtained results show that surface-tethered Nsp1p FG domains form molecular brushes at physiological conditions. Kap-beta1 binding provokes brush extension while partitioning into a fast and slow kinetic phase, where the latter may form an integral part of the FG domain barrier. In contrast, NTF2 binding to pristine Nsp1p layers induced collapse, but not under competing interactions from Kap-beta1. Therefore, promiscuous binding of NTF2 to Kap-beta1-preloaded Nsp1p attenuates NTF2 towards higher off rates and more transient interactions.
My work demonstrates that promiscuous binding of NTRs to FG Nups ought to influence nucleocytoplasmic transport. This depends on the concentration, size and binding strength of each NTR. Indeed, some form of hierarchy may exist between different NTRs such that their relative concentrations may impact NPC barrier function. This interpretation departs from the conventional view that the FG Nups alone form the NPC permeability barrier. Rather I conclude that concentrating NTRs in the NPC transport channel also contributes to generating crowding-based selective barrier function of the pore
Dynamic response of an Offshore wind turbine using linear (LIM) and non-linear (NLIM) environmental interaction models: A Parametric study
No full textThe present state-of-the-art modelling tools (such as FAST, BLADED) used for modelling an offshore wind turbine (OWT) are too detailed and computationally expensive. These tools are required only at detailed design stages of a project. For the preliminary phase, however, a much simpler (yet reliable) 3D model can improve and speedup the design process. Therefore, the aim of this thesis was to develop two different finite element models of an offshore wind turbine and compare their dynamic responses. In order to assess the extent of non-linearities in the environmental interactions arising due to structural motions, one model included the non-linear models of soil, hydrodynamic and aerodynamic loads (called NLIM henceforth) while the other used linearized expressions for modelling them (called LIM henceforth). The soil was modelled as a series of non-linear (and linear) elastic springs using p-y curves. The conventionally used Morison's equation was compared with MacCamy and Fuchs' equation for modelling the hydrodynamic loads on a large diameter pile. It was found that the MacCamy and Fuchs' equation is a better way of modelling the hydrodynamic loads on submerged cylinders than Morison's equation as it takes the wave diffraction effects into account. Several load cases were defined and the models were subjected to these load cases to check whether they are able to capture the physical behaviour of the OWT. The modal decomposition technique was used for reducing simulation time. It was found that the model(s) adequately captured the physical behaviour of the OWT till a wind speed of 20 m/s. Its side-side plane physical behaviour needs further investigation for a constant wind speed of 24 m/s. The LIM and the NLIM compared well for most load cases. For the side-side plane responses, however, the LIM developed a phase lag. A strong coupling was found between the motions (rotations) in fore-aft plane and the motions about the yaw axis. The structural velocities were found to be very small to influence hydrodynamic drag terms. Also, the defections of the pile in the soil were found to be too small suggesting that p-y curves do not capture the non-linear behaviour of soil accurately. Finally, a damping matrix resulting from the linearised aerodynamic forces was used for calculating the modal damping ratios related to different modes. The results were compared to the literature, with addition of side-side and yaw damping.Mechanical, Maritime and Materials EngineeringHydraulic EngineeringOffshore Engineerin
Nucleocytoplasmic Transport: A Paradigm for Molecular Logistics in Artificial Systems
Get PDFArtificial organelles, molecular factories and nanoreactors are membrane-bound systems envisaged to exhibit cell-like functionality. These constitute liposomes, polymersomes or hybrid lipo-polymersomes that display different membrane-spanning channels and/or enclose molecular modules. To achieve more complex functionality, an artificial organelle should ideally sustain a continuous influx of essential macromolecular modules (i.e. cargoes) and metabolites against an outflow of reaction products. This would benefit from the incorporation of selective nanopores as well as specific trafficking factors that facilitate cargo selectivity, translocation efficiency, and directionality. Towards this goal, we describe how proteinaceous cargoes are transported between the nucleus and cytoplasm by nuclear pore complexes and the biological trafficking machinery in living cells (i.e. nucleocytoplasmic transport). On this basis, we discuss how biomimetic control may be implemented to selectively import, compartmentalize and accumulate diverse macromolecular modules against concentration gradients in artificial organelles
Phosphorylation but Not Oligomerization Drives the Accumulation of Tau with Nucleoporin Nup98
Get PDFTau is a neuronal protein that stabilizes axonal microtubules (MTs) in the central nervous system. In Alzheimer’s disease (AD) and other tauopathies, phosphorylated Tau accumulates in intracellular aggregates, a pathological hallmark of these diseases. However, the chronological order of pathological changes in Tau prior to its cytosolic aggregation remains unresolved. These include its phosphorylation and detachment from MTs, mislocalization into the somatodendritic compartment, and oligomerization in the cytosol. Recently, we showed that Tau can interact with phenylalanine-glycine (FG)-rich nucleoporins (Nups), including Nup98, that form a diffusion barrier inside nuclear pore complexes (NPCs), leading to defects in nucleocytoplasmic transport. Here, we used surface plasmon resonance (SPR) and bio-layer interferometry (BLI) to investigate the molecular details of Tau:Nup98 interactions and determined how Tau phosphorylation and oligomerization impact the interactions. Importantly, phosphorylation, but not acetylation, strongly facilitates the accumulation of Tau with Nup98. Oligomerization, however, seems to inhibit Tau:Nup98 interactions, suggesting that Tau-FG Nup interactions occur prior to oligomerization. Overall, these results provide fundamental insights into the molecular mechanisms of Tau-FG Nup interactions within NPCs, which might explain how stress-and disease-associated posttranslational modifications (PTMs) may lead to Tau-induced nucleocytoplasmic transport (NCT) failure. Intervention strategies that could rescue Tau-induced NCT failure in AD and tauopathies will be further discussed
Crocodylus porosus Schneider 1801
No full textCrocodylus porosus Schneider, 1801 — Native. Crocodilus porosus Schneider, 1801: 159–160. Lectotype: ZMB 278, designated by Wermuth (1954: 485); paralectotypes (2): ZFMK 40955–56, according to B̂hme (2010: 107); type material as “cited by Schneider (1801) included this specimen [lectotype] from the Bloch collection, three specimens from the Ĝttingen Museum [the two paralectotypes], and specimens figured by Seba (1734: pl. 104, fig. 12) and Knorr (1766: vol. 2: pl. 5, fig. 4)” according to Bauer & Ģnther (2006: 245). Type locality: None stated/traced; later designated as “the East Indies” by Deraniyagala (1939: 278); later restricted to “ India ” via lectotype designation; later restricted to “Mainland of Hither India ” by Wermuth (1960: 26); later restricted to “ Ceylon ” (= Sri Lanka) by Mertens (1960: 271). Estuarine Crocodile (Figure 7G) Singapore records. Crocodilus porosus — Cantor, 1847a: 622.— Cantor, 1847c: 1067.— Boulenger, 1889a: 285.— Flower, 1896: 862 (Pandan River; Serangoon).— Hanitsch, 1898: 9.— Flower, 1899: 623, 625 (Tanjong Pagar Wharf [= Tanjong Pagar Terminal]).—Ridley, 1899: 189.—Hanitsch, 1908: 40.— Hanitsch, 1912b: 14.— de Rooij, 1915: 337–338.—D.S. Johnson, 1964: 25 (Jurong-Pandan Area).— Chuang, 1973: 3.— Harrison & Tham, 1973: 253.—L.M. Chou et al., 1980: 71.—L.M. Chou & T.J. Lam, 1989: 92.—D.S. Johnson, 1992: 34. “Alligators”—Oxley, 1849: 596. “[A]lligators”— Crawfurd, 1856: 398. Crocodilus biporcatus —M̧ller, 1878: 749. “Crocodile”— Knight, 1887: 99 (“Ponggol-river” [= Sungei Punggol]).— Moulton, 1922: 567 (Pandan River).—K. Lim, 1989h: 40.—M.E.Y. Low & Pocklington, 2019: 20. Crocodylus porosus —Sharma, 1973: 233.—F.L.K. Lim, 1984: 18.— Gremli, 1988: 62.—K. Lim & F. Lim, 1988c: 75 (Woodlands).—K. Lim, 1989e: 39 (Sungei Seletar Reservoir).—K. Lim, 1990a: 11 (Sungei Buloh Bird Sanctuary [= SBWR]).—K.K.P. Lim & L.M. Chou, 1990: 56.—K.K.P. Lim, 1991a: 4 (Sungei Seminei [Pulau Tekong]).—K.K.P. Lim & F.L.K. Lim, 1992: 123–124, 151.— K.K.P. Lim & Subharaj, 1992: 9 (Kranji Reservoir; Marina East).—P.K.L. Ng, 1992a: 143.—P.K.L. Ng, 1992b: 143.—L.M. Chou et al., 1994: 105.—K.K.P. Lim, 1994b: 224, 331.—J.K.Y. Low et al., 1994: 158.—K. Lim, 1995: 19 (Johor Straits [Woodlands]; Pulau Seletar; Punggol Estuary).— P.K.L. Ng et al., 1995: 124.—R. Subaraj, 1995: 33, 36 (Pulau Ubin).—R.C.H. Teo & Rajathurai, 1997: 392 (MacRitchie Reservoir; Upper Seletar Reservoir).—Sharma, 1998: 149.—Chan-ard et al., 1999: 41.—P.K.L. Ng & Sivasothi, 1999: 147.—K.P. Lim & F.L.K. Lim, 2002: 151.— Anonymous, 2003: 32, 93 (Sungei Buloh Wetland Reserve).—E.K. Chua, 2007b: 165.—K.K.P. Lim et al., 2008: 173, 266 (Kallang River Estuary; Kranji Reservoir; Pulau Tekong; Singapore River Estuary; Seletar Reservoir; Sungei Buloh Wetland Reserve).—N. Baker & K.P. Lim, 2008: 121, 159.— Das, 2010: 166.—P.K.L. Ng et al., 2008: 170.—T.H. Ng & K.K.P. Lim, 2010: 119 (Lower Seletar Reservoir; Sarimbun Reservoir).—H.T.W. Tan et al., 2010: 1117.—Webb et al., 2010: 99.—L.M. Chou, 2011: 75.—M.A.H. Chua, 2011: 278 (Semakau Landfill [PS]).—P.K.L. Ng et al., 2011: 281.—N. Baker & K.P. Lim, 2012: 121, 159.— Davison et al., 2012: 88.— Jaafar et al., 2012: 82.—M.F.C. Ng, 2012: 146.—M. Ng & Mendyk, 2012: 34–37 (Sungei Buloh Wetland Reserve).—The Straits Times, 2014 (East Coast Park; “Strait of Johor off Admiralty Road”; Sungei Buloh [= SBWR]; Sungei Seletar Reservoir [= LS]; Tampines River canal [= Sungei Tampines]).— Chan-ard et al., 2015: 296.—T. Lim, 2015: 36 (Sungei Buloh Wetland Reserve).—K.K.P. Lim, 2016: 176 (Pulau Tekong).—L. Lam, 2017 (National Sailing Centre [= ECP]).—A. Tan, 2017 (Sungei Tampines).—W. Wong, 2017: 81.— Fukuda et al., 2018: 812.—M.L. Kwak et al., 2019a: 128 (Sungei Buloh Wetland Reserve).—M.E.Y. Low & Pocklington, 2019: 192.—Mumpuni et al., 2019: 85.—Pocklington, 2019: 5–24 (Kallang River; Lim Chu Kang; Potong Pasir; Punggol; “Rochore” River; Sungei Kadut; Whampoa River).— Begum, 2019 (Sungei Kadut).—Z. Tee, 2019b (Lower Seletar Reservoir).—J. Aw & M.E.Y. Low, 2020: 26.—Pocklington, 2021: 46–70 (“14th mile, East Coast” [= Changi]; Anson Road; Arthur Road; Balai Quarry, Pulau Ubin; Berlayer Hill [= LNR]; “Between Fairy Point and Pulo Obin” [= SJ]; Boon Lay Road [= Jalan Boon Lay]; Botanic Gardens Lake [= Swan Lake, SBG]; Bukit Chermin; Bukit Sembawang; “Canal alongside Campong Java Road” [= Sungei Rochor]; Causeway, Johore Straits [= SJ]; Central Beach, Sentosa [= Pulau Blakang Mati]; “Chan Chu-Kang, Selitar” [= Sungei Seletar]; “Changhie” [= Changi]; Changi Beach Park; Changi Ferry [= Changi Point Ferry Terminal]; Changi Road; Chinese Garden Lake [= Jurong Lake]; Chinese Swimming Club [= Tanjong Katong]; Chua Chu Kang; Crescent Road; Dalhousie Pier [= Asian Civilisations Museum Green]; “Diving stage, Swimming Club” [= Tanjong Rhu]; East Coast beach [= ECP]; Esplanade; Fort Road; Garden Club, Katong [= Tanjong Katong]; Gaylang [= Geylang]; Gaylang River [= Sungei Geylang]; Geylang Swamp, Grove Estate [= Chung Cheng Lake]; Harbour [= Keppel Harbour]; “Harbour, Master Attendant’s pier” [= Collyer Quay]; Impounding Reservoir [= MacRitchie Reservoir]; “In river close to Adamson, Gilfilan and Co’s godown” [= Collyer Quay]; “In sea off the Causeway” [= SJ]; Jalan Teck Whye; Johor Strait [= SJ]; “Johore Straits near Kranji” [= SJ]; “Johore Straits near Senoko Way” [= SJ]; Jurong; Jurong Lake; Jurong Prawn Ponds [= Sungei Jurong]; Jurong River [= Sungei Jurong]; Jurong Road; Kallang Basin [= Mountbatten Road]; Kallang District [= Kallang]; Kallang River [= Sungei Kallang]; Kampong Java Road; Kampong Pond, Kankar Fishing Village [= Sungei Serangoon]; Katong [= Tanjong Katong]; Katong Lake [= Chung Cheng Lake]; “Katong, near the Swimming Club” [= Tanjong Katong]; Katong Park; Keppel Harbour; Khatib Bongsu [= KBNP]; Kranji; Kranji Dam; “Kranji extension” (Sungei Buloh WR) [= KCNP]; Kranji Nature Trail [= KCNP]; Kranji Reservoir; Kranji River [= Sungei Kranji]; “Kranji River to Bukit Timah” [= Sungei Pang Sua]; Kranji Sports Fishing Ground [= KR]; Kranji Way; Kuala Johore [= SJ]; Lim Chu Kang; Lim Chu Kang Fish Farm; Lim Chu Kang Jetty; Lorong Chuntum [= Lor Lada Hitam]; Lorong Gambas; Lorong Halus; MacRitchie Reservoir; Marina East; Marina Reservoir; McPherson Road; “Mouth of small river between Changie and Pasir Ris” [= Sungei Selarang]; “Mr Lim Koh Eng’s bungalow, 6¾ mile, Pasir Panjang” [= WCP]; “Muddy creek running past Ice Works at Sirangoon, 3rd milestone” [= Sungei Rochor]; “Nearby river of Jalan Gemala off Lim Chu Kang” [= Sungei Simpang Mak Wai]; Pandan River [= Sungei Pandan]; Park Road; “Pasa Labar” [= Pasir Laba]; Pasir Panjang; Pasir Panjang Beach; Pasir Panjang Road; Pasir Ris Beach; Pasir Ris Park; Ponggol [= Punggol]; Pongol [= Punggol]; Pongol Beach [= Punggol Beach]; Pongol River [= Sungei Ponggol]; Pongol Road [= Punggol Road]; Powder Magazine [= Alkaff Quay]; Pulau Buloh; Pulau Retan Laut [= Pasir Panjang Terminal]; Pulau Saigon [= Sungei Singapore]; Pulau Seletar; Pulau Tekong, Sungei Seminei [= PT]; Pulau Tekong Besar; Pulo Obin quarry [= Pekan Quarry]; Pulau Ubin Jetty; Pulo Sirimbun [= Pulau Sarimbun]; Pulo Tekong [= PT]; Punggol Estuary; Raffles Country Club; “River off Lim Chu Kang” [= Sungei Kangkar]; River Valley Road; Robertson Quay; Robinson Road; Rochore Canal [= Sungei Rochor]; Rochore River [= Sungei Rochor]; Sarimbun Reservoir; “Seabeach opposite old Fort near Swimming Club, Katong” [= Tanjong Katong]; Sea View Hotel [= Tanjong Katong]; Seletar; Seletar Reservoir; Semakau Landfill [= PS]; “Sembawang waters” [= Sembawang Park Fishing Pier]; Serangong [= Serangoon]; Serangoon River [= Sungei Serangoon]; Serangoon Swamp (near Lavender Street) [= Bendemeer]; “Side of Grove Road” [= Tanjong Rhu]; “Side of the river in Pongol” [= Sungei Serangoon]; Siglap; Singapore River [= Sungei Singapore]; Sirangoon [= Serangoon]; Sirangoon River [= Sungei Serangoon]; “Small lake in the plantation at McPherson Road” [= Potong Pasir]; “Southeastern coast line” [= Singapore Strait]; St John’s Island [= Pulau Sekijang Bendera]; Straits of Johore [= SJ]; Straits of Singapura [= SJ]; Sungei Battu Belyhar [= Berlayer Creek]; Sungei Buloh [= SBWR]; Sungei Buloh Besar; Sungei Buloh Bird’s Sanctuary [= SBWR]; Sungei Buloh Wetland Reserve; Sungei Jurong; Sungei Jurong Road [= Jurong Canal Drive]; Sungei Kadut; Sungei Kechil, Serangoon Road [= Sungei Whampoa]; Sungei Kranji; Sungei Pandan; Sungei Seletar Reservoir [= Lower Seletar Reservoir]; Sungei Sembawang; Sungei Tampines; “Swamp near 6th milestone, Swimming Club” [= Tanjong Katong]; Tampines; Tampines farm; Tampines River Canal [= Sungei Tampines]; Tanglin Barracks; Thompson Road [= WNP]; Tanjong Balai [= Pulau Ubin]; Tanjong Katong; Tanjong Kling; Tanjong Pagar; Tanjong Pagar Wharf [= Tanjong Pagar Terminal]; Tanjong Rhoo [= Tanjong Rhu]; Tanjong Rhu; Telok Mata Ikan [= Changi South Ave 3]; Tengah Reservoir; Tengah Reservoir Golf Course [= Raffles Country Club]; “Thompson Road Stream” [= TRF]; Thomson Road; “Trafalgar Estate, cocoa-nut plantation” [= Buangkok]; Tuas; Tuas River [= Tengah Reservoir]; Tuas Shipyard; Ulu Pandan River [= Sungei Pandan]; Ulu Sungei Pongol [= Sungei Punggol]; Upper Seletar Reservoir; Vaughan Road; Victoria Dry Dock [= Tanjong Pagar Terminal]; West Coast Rise; West Coast Road; Whampoa River [= Sungei Whampoa]; Wilkinson Road; Woodlands Causeway; Woodlands Town Garden [= Marsiling Park]; Woodlands Town Park [= Woodlands Town Park East]; Woodlands Waterfront Park).—E.K. Chua, 2022: 57 (Sungei Buloh Wetland Reserve).— Kurniawan et al., 2022: 108.—M.L. Kwak & A. Ng, 2022: 929. “Estuarine crocodile”—Qing, 2021 (East Coast Park).— Lean, 2022a (“Lim Chu Kang waters between S’pore & M’sia”).—Zheng, 2022a (“Choa Chu Kang canal”). Remarks. Recently, there were two books published on crocodiles in Singapore. The first is Buayapura (Pocklington 2019), a short historical and philosophical examination of C. porosus that imparts that the first mention of crocodiles from Singapore comes from the book, Hikayat Hang Tuah, which was written between 1641 and 1739. In there, the author declared that “…the Straits of Singapura was infested with man-eating crocodiles…” (Pocklington 2019). This represents the earliest reference of any herpetofauna from Singapore, and although no specimen was collected and no description was provided, we can be assured that the identity of the species was C. porosus since it is the only native crocodilian to Singapore. The second book, Beast, Guardian, Island: The Saltwater Crocodile ( Crocodylus porosus Schneider, 1801 ) in Singapore, 1819–2017, explored human interactions with crocodiles in Singapore, and collated newspaper records between 1819 and 2017 providing the most comprehensive historical distribution and analysis for any herpetofauna species in Singapore (Pocklington 2021). Prior to the first report of C. porosus from Singapore in the scientific literature (Cantor 1847a), Pocklington (2021) listed two additional earlier records. The first is from sometime between 1819 and 1823 and involves a crocodile Farquhar hung from a fig tree along the Rochor River that ate his dog. The second was of a crocodile that ate someone along the Rochor Canal in March 1842. Early in history, C. porosus was considered quite abundant (Flower 1899), but due to coastal development and a government initiative to rid Singapore of crocodiles (Sharma 1973; Pocklington 2021), this species became quite rare and was even considered extinct (Chuang 1964; Lim 1984; Webb et al. 2010). Correspondingly, the IUCN-SSC Crocodile Specialist Group assigned C. porosus as regionally extinct in Singapore in 1996 (Pocklington 2021). In the scientific literature, after Moulton (1921) reported an “ 11 ft. ” specimen that was killed in the Pandan River and donated by Choo Seng Yen, C. porosus was not reported from Singapore until 43 years later (Table 2) by Johnson (1964) who described it as rare, but noted that some individuals were occasionally seen in the Jurong-Pandan area. Shortly thereafter is when Chuang (1973) classified C. porosus as extinct. Thereupon, wild individuals from the early 1990s were believed to be a mixture of escaped individuals from breeding farms and abandoned pets (Teo & Rajathurai 1997; Ng & Lim 2010). Sharma (1973) remarks that the Singapore population may have been sustained by individuals swimming over from Johor Bahru, Malaysia. However, Pocklington (2021) discloses a conflicting reality, one where C. porosus was still frequently encountered. Thus, there appears to be no credible evidence that C. porosus was ever truly extinct in Singapore (Pocklington 2021). Although, C. porosus once occupied much of Singapore (Pocklington 2021), today the only resident population persists in SBWR. Yet, the first record from SBWR is only from November 1990 (Lim 1990a; Pocklington 2021). On occasion, some individuals will stray away from SBWR to explore new areas such as one sighted at LS in July 1989, one seen at ECP in December 1992, one seen swimming in the Straits of Johor off Admiralty Road in June 1995, one seen at Sungei Tampines in August 2008 (The Straits Times 2014), one photographed basking along Sungei Tampines on 1 August 2017 (Tan 2017), likely the same individual seen in a drain adjacent to the National Sailing Centre at ECP on 8 November 2017, one seen at LSR on 23 February 2019 (Tee 2019b), one found in Sungei Kadut drain on 21 June 2019 (Begum 2019), one filmed at ECP near Fort Road on 5 October 2021 (Qing 2021), and one floating in Choa Chu Kang canal on 16 May 2022 (Zheng 2022a). Given the extent of reclamation, urban development, and barriers such as dams, sluice gates, litter traps, and float booms restricting access inland along waterways, it seems unlikely that C. porosus will establish populations elsewhere in Singapore. Occurrence. Restricted to a few confined locations. Uncommon. SBWR represents the stronghold. Singapore conservation status. Critically Endangered. Conservation priority. Highest. IUCN conservation status. Least Concern [2021]. LKCNHM & NHMUK Museum specimens. Singapore (no locality): BMNH 1883.11.28.3–12 (no date), ZRC.2.304– ZRC. 2.306 (8-22-1897); Sungei Seletar Reservoir [USR] : ZRC.2.2556 (1988); Sungei Buloh Wetland Reserve : ZRC.2.6841– ZRC.2.6843, ZRC.2.6848 (8-Apr-2009). Additional Singapore museum specimens. Singapore (no locality): NMW, RBINS, ROM, SAMA, ZMB. Singapore localities. Alkaff Quay*—Anson Road*—Arthur Road*—Asian Civilisations Museum Green*— Berlayer Creek*—Bendemeer*—Buangkok*—Bukit Chermin*—Bukit Sembawang*—Changi*— Changi Beach Park*—Changi Point Ferry Terminal*—Changi Road*—Changi South Ave 3*—Choa Chu Kang*—Chung Cheng Lake*—Collyer Quay*—Crescent Road*—East Coast Park*—Esplanade*—Fort Road*—Geylang*—Jalan Boon Lay*—Jalan Teck Whye*—Jurong*—Jurong Canal Drive*—Jurong Lake*—Jurong-Pandan Area*—Jurong Road*—Kallang*—Kampong Java Road*—Katong Park*— Keppel Harbour*—Khatib Bongsu Nature Park—Kranji—Kranji Coastal Nature Park—Kranji Dam— Kranji Reservoir*—Kranji Way—Labrador Nature Reserve*—Lim Chu Kang—Lim Chu Kang Fish Farm*—Lim Chu Kang Jetty—Lor Lada Hitam*—Lorong Gambas*—Lorong Halus*—Lower Seletar Reservoir*—MacRitchie Reservoir*—Marina East*— Marina Reservoir *—Marsiling Park*—McPherson Road*—Mountbatten Road*—Park Road*—Pasir Laba*—Pasir Panjang*—Pasir Panjang Beach*— Pasir Panjang Road*—Pasir Panjang Terminal*—Pasir Ris Beach*—Pasir Ris Park*—Pekan Quarry*— Potong Pasir*—Pulau Blakang Mati*—Pulau Buloh—Pulau Sarimbun—Pulau Sekijang Bendera*— Pulau Seletar*—Pulau Semakau*—Pulau Tekong*—Pulau Tekong Besar*—Pulau Ubin*—Pulau Ubin Jetty*—Punggol*—Punggol Beach*—Punggol Estuary*—Punggol Road*—Raffles Country Club*— River Valley Road*—Robertson Quay*—Robinson Road*—Sarimbun Reservoir*—Seletar*—Seletar Reservoir*—Sembawang Park Fishing Pier—Serangoon*—Siglap*—Singapore Botanic Gardens*— Singapore Strait*—Sungei Buloh Besar—Sungei Buloh Wetland Reserve—Sungei Geylang*—Sungei Jurong*—Sungei Kadut*—Sungei Kallang*—Sungei Kangkar*—Sungei Kechil*—Sungei Kranji*— Sungei Pandan*—Sungei Pang Sua*—Sungei Punggol*—Sungei Rochor*—Sungei Selarang*—Sungei Seletar*—Sungei Sembawang*—Sungei Serangoon*—Sungei Simpang Mak Wai*—Sungei Singapore*— Sungei Singapore Estuary*—Sungei Tampines*—Sungei Whampoa*—Straits of Johor—Tampines*— Tanglin Barracks*—Tanjong Katong*—Tanjong Kling*—Tanjong Pagar Terminal*—Tanjong Rhu*— Tengah Reservoir*—Thomson Ridge Forest*—Thomson Road*—Tuas*—Tuas Shipyard*—Upper Seletar Reservoir*—Vaughan Road*—West Coast Park*—West Coast Rise*—West Coast Road*—Wilkinson Road*—Windsor Nature Park*—Woodlands—Woodlands Causeway—Woodlands Town Park East*— Woodlands Waterfront Park*. Order Testudinata Batsch, 1788 (17 species) Testudines Batsch, 1788: 437, footnote. Family Cheloniidae Oppel, 1811 (4 species) Chelonii Oppel 1811: 8 (type genus Chelonia Brongniart, 1800). Genus Caretta Rafinesque, 1814 (1 species)Published as part of Figueroa, Alex, Low, Martyn E. Y. & Lim, Kelvin K. P., 2023, Singapore's herpetofauna: updated and annotated checklist, history, conservation, and distribution, pp. 1-378 in Zootaxa 5287 (1) on pages 63-66, DOI: 10.11646/zootaxa.5287.1.1, http://zenodo.org/record/796031
A remark on approximation with polynomials and greedy bases
No full textWe investigate properties of the m-th error of approximation by polynomials with constant coefficients D(x) and with modulus-constant coefficients D (x) introduced by Berná and Blasco ([2]) to study greedy bases in Banach spaces. We characterize when lim infD(x) and lim infD (x) are equivalent to ‖x‖ in terms of the democracy and superdemocracy functions, and provide sufficient conditions ensuring that limD (x)=limD(x)=‖x‖, extending previous very particular results.The first author was supported by a PhD fellowship of the program “Ayudas para contratos predoctorales para la formación de doctores 2017” (MINECO, Spain) and the grants MTM-2016-76566-P (MINECO, Spain) and 20906/PI/18 (Fundación Séneca, Región de Murcia, Spain). Also, the first author would like to thank the Isaac Newton Institute for Mathematical Sciences, Cambridge, for hospitality during the program Approximation, Sampling and Compression in Data Science where some work on this paper was undertaken. This work was supported by EPSRC grant number EP/R014604/1. The second author acknowledges financial support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa Programme for Centres of Excellence in R&D” (SEV-2015-0554
Prescribing Practices of Australian Dispensing Doctors
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Gate-crashing the nuclear pore complex
No full textAs a third in a series of MD simulations investigating the binding dynamics between nuclear transport receptors and FG-repeats, Isgro and Schulten (2007b) unveil that close, physical intimacy between partners is likely to ensure a hassle-free passage through the nuclear pore complex
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