bluuebunny/crossref_metadata_2025 huggingface dataset:
Fractured Reservoir Characterisation: A Fully Integrated Study, from Borehole Imagery, Cores and Seismic Data to Production Logs - Example of an Algerian Gas Field (Sbaa Basin, SW Algeria)
Authors: Panien M.. , Portier E.. , Marcy F.. , Ghilardini L.. , Le Maux T.. , Dehaeck T..
Published: February 2010

GDF-SUEZ and Sonatrach will develop in partnership the main fields of the prolific Sbaa basin, SW Algeria. In this basin, the main gas levels comprise the Cambrian and Upper-Ordovician reservoirs, sealed and sourced by the Silurian "Hot Shales" Formation. During the exploration and appraisal phases of the project, an intensive drilling program, including coring, standard logging and imaging (FMI), following a 3D seismic campaign was performed.

Integrated study was done to investigate the suspected impact of natural fractures on the reservoir performances, to suggest potential geological drivers on fracture type (such as diffuse fractures and fracture swarms, if any) and on fracture distribution. The hydraulic properties of the fractures, based on available dynamic data were also evaluated. Indeed, accurate information on fault network and on fracture properties is essential to improve strategies for maximising hydrocarbon recovery, by optimising well location or directional drilling.

Various seismic anisotropy "fracture relevant" attributes (RMS, Coherence and Dip) were selected and jointly used in a multi-variable statistical process called Seismic Facies Analysis (SFA). This gave a preliminary interpretation of the seismic facies in terms of fracture density that was completed and validated with well data and curvature analysis. The curvature pointed out various scale lineaments fully consistent with previous work. It concludes on predominance of fault-related fractures. According to dynamic data, well productivity may be enhanced by fracturation by a factor up to 12.

The resulting fracture probability map was used to build a 3D fracture model with IFP and FracaFlow® software dedicated for fracture analysis and fracture modelling. For each well, a local discrete fracturation model was built. The length and intrinsic permeability of fractures were then calibrated using KH determined by well test interpretation and production log analysis. The final result consisted in computing the equivalent properties of the fracture network in each cell of the reservoir grid in order to perform the reservoir simulation. In this study, we present the results of production log (PLT) matched with success. The same fracture parameters were also used to match consistently the production log of the other wells.

The integration of a wide type of data to analyse the natural fractures of this Algerian gas field leads to a fully consistent and well-constrained fracture model.
SMART™ Technology Application, Preparation and Implementation Case History
Authors: Abd El Raheem Taher Ali , Hassaballa Sherif Aly , Pyott Gary
Published: February 2010

Maximizing the recoverable hydrocarbon reserve and reducing both the capital & operating cost are always challenges. One of the tools to achieve the above targets is to apply the smart completion technology. Application of a SMART™ completion represents a significant challenge, especially if it is combined with gravel packing in high rate producing wells. The equivalent production area between the SMART™ well completion component and the inner diameter of the screens represent a challenge to ensure that contributions from all the zones are possible without scarifying production. In addition, the affect of possible sand production and the affect on the overall system needed to be addressed.

Rashpetco have decided to apply this SMART™ technology as base case for the development of two offshore fields in the Mediterranean. One of the developments is from a remotely operated platform and the other is from a subsea field. Both of the developments will produce from two different horizons. The development selection was based on a comparison with other completion alternatives, the evaluation of the risk associated with using this relative new technology and the cost impact versus change in ultimate recovery.

Using SMART™ completion will minimize the number of wells to be drilled to obtain the same recovery factor and will minimize any intervention to open the conventional sliding sleeve. It will also help minimize water production at sand face, which will reduce the cost of expanding water separation facilities and will have a positive impact on the vertical flow performance. It should be noted that the SMART™ completion could be either on/off or chocking type. The selection will be based on the driving mechanism and the reservoir performance

This paper describes the process of preparation and implement of the SMART™ system for both platform and subsea developments. It will also show the results and benefits
Borehole Strengthening and Injector Plugging – The Common Geomechanics Thread
Authors: Loloi Mehdi , Zaki Karim S. , Zhai Zongyu , Abou-Sayed Ahmed
Published: February 2010

The high cost of offshore drilling and the safety aspects of penetrating depleted reservoirs bring borehole stability issues to the forefront of resource development. Drilling in deepwater fields, depleted reservoirs and/or low stress environments requires careful assessment of mud weights. Higher collapse pressures combined with lower fracture gradients limit or eliminate mud weight windows and lead to tight holes or lost circulation. Extended-reach wells require minimization of the number of casing shoes to reach the deeper targets. The need for long, open sections while drilling imposes restrictions on mud windows. Borehole strengthening has become the most effective method to address borehole stability in such circumstances.

In this paper, we provide geomechanics insights from the large knowledge base on waterflooding and injector performance to improve the practice of wellbore strengthening. The petroleum industry has morphed over its long history through fewer inventions but a long list of innovations derived from lessons learned from one sector to benefit another. Injector plugging, a nuisance to production/operation engineers, illustrates such an example. The vast amount of knowledge provides the fundamental reasoning and rationale for optimizing wellbore strengthening. Fractured injector geomechanics are extended to improve wellbore strengthening procedures. Strengthening is implemented through creation of plugged minifractures to raise loss circulation pressures. The mud contains particles to mitigate unstable fracture extension created by using higher mud weights. The particles deposit and plug initiated fractures and prevent further propagation. The propagation pressure is raised significantly and lost circulation stops. In the presented model, the stable fracture length and width are related to a given mud weight and rock characteristics. Accordingly, the plugging media (particle) size is optimized based on the fracture geometry and leakage scenarios. The model results are field-verified and demonstrate how the borehole stability problem could be optimized with proper design.
Merging 3D Seismic Data for IR Field Development
Authors: Widjiastono Agus , Aljilani Almhedwi , Hamrbtan Nasser
Published: February 2010

The development plan of IR field, located in Murzuk basin, SW Libya was approved in August 2007. The discovery well was drilled on NC186 block in 2005. Then, it was followed by appraisal wells on both NC186 and NC115 blocks in 2006. IR field straddles blocks NC115 and NC186 that have different partners and petroleum contracts, although the same development and production operating company. The field is relatively complex due to the reservoir heterogeneity of Ordovician sandstone Mamuniyat in the area of interest. 3D seismic is one of the important datasets for selecting producer and injector locations, developing the field effectively and reducing the risk associated to drilling those development wells. No specific development 3D seismic was acquired for IR field yet. The current available 3D cube is the result of merging two exploration 3D seismic datasets: NC186-2003 and NC115-2006. This cube has been used as the basis for the interpretation during the Phase 1 of IR development plan. Up to now, several well results deviated from the prognosis in terms of reservoir top depth, thickness and quality. Those deviations are indicative of a seismic dataset not robust enough for detailed reservoir interpretation. A further investigation identified different kinds of hiccups on transit time, amplitude and phase mismatch with borehole seismic data, and the footprint of the merge boundary of 2003 and 2006 exploration 3D seismic cubes. Those identified flaws have to be addressed prior to further use of the merged 3D cube as a predictive tool for main reservoir depth, presence, lateral extension and properties. This paper will present the efforts and strategies adopted to resolve the encountered inconsistencies and artifacts, and improve the quality and reliability of the merged 3D cube. Therefore, the enhanced quality 3D cube can be used for reliable and consistent reservoir characterization to support the Phase 2 of IR development plan in year 2010.
Structural Characterization, Development Optimization and Increase of OOIP in a North African Oil Field (SW Libya) Through Enhanced Seismic Methodology
Authors: Gómez Nacarino Cándido , Abusaq Walid , Ranero Alvaro , del Rio Carlos
Published: February 2010

B-NC186 field is located in the Murzuq Basin, SW Libya. Fifteen wells have been drilled up to July 2009; seven of them consisting of a pilot hole prior to the drilling of the horizontal main hole.

The producing reservoir is the Upper Ordovician Mamuniyat Formation. The field is conformed by the oil accumulation in one of the glacial palaeovalleys filled by the Mamuniyat Formation which was eroded and capped by the major Silurian marine transgression and gently deformed during later orogenic phases. Main regional seal is Silurian age Tanezzuf shale. Tanezzuft basal Hot Shale member acts as the main source rock in the Murzuq Basin.

150km2 of 3D reprocessed seismic data were reinterpreted in 2008 in preparation of an aggressive drilling campaign. The main objectives of that reinterpretation were: Exhaustive QC of the existing data: seismic versions, well coordinates, KB elevations, markers, deviation surveys and VSP surveysMap in detail the fault network affecting our reservoirEnhance the position of the boundaries of Hawaz palaeohighsPerform a reliable depth conversion with the objective of identifying untapped upside potential

A detailed analysis of seismic attributes: Grid based, Variance Cube and Volume attributes (Dip, Azimuth and DipAzi combined), made possible the definition of the fault network affecting Mamuniyat reservoir.

Some interpretation principles were established in order to accurately define the limits of the Hawaz palaeohighs optimizing the location of producers nearby B-4 Hawaz palaeohigh.

A new NW-SE oil-bearing structural trend was discovered between B-4 and J Field palaeohighs. Sedimentologically this structural high constitutes a deep palaeovalley containing more than 1,000ft of clean Mamuniyat sandstone (well B-14H pilot hole). The OOIP of this southwest extension amounts to more than 100mmbo.

An unexpected low velocity anomaly was encountered after B-13H pilot hole well results. The VSPs acquired on the pilot holes of wells B-13H and B-14H revealed that wrong dynamic corrections were applied for Top Mamuniyat due to the thickness reduction of Tanezzuft shale along this trend. Consequently, the seismic velocity was overestimated and Top Mamuniyat seismic reflector was interpreted deeper than found by the VSP.
Rock Typing approach for Reservoir Characterization of Ordovician Sandstones, Fields Case Study, Concessions NC115/NC186, Murzuq Basin, Libya
Authors: Salaheddin K.. , Laksana S.. , Schöbel M..
Published: February 2010

In order to quantify the high vertical and lateral petrophysical variability of the Late Ordovician sandstones of the Mamuniyat Formation, the GHE methodology (Corbett et al. 2004) has been applied to several fields of the Murzuq Basin in Libya. These reservoirs are characterized by various facies associations and depositional environments as locally interpreted from core.

The Mamuniyat Formation is a major oil reservoir in the Murzuq Basin of Libya, made up of massive sandstones, representing a low-stand system track. The formation can be subdivided into Lower (LM), Middle (MM) and Upper Mamuniyat (UM) as recognized in outcrops and correlated to the sub-surface. LM commonly consists of fine- to medium-grained sands, deposited in a shelf-shoreface to tidally influenced estuarine setting, whereas heterolithic ripple laminated, dewatered, and slumped sediments typify the MM. Deposition occurred in a rapidly prograding, unstable braid-delta front system fed by melting ice sheets. UM represents the most prolific reservoir section with typically (very) coarse-grained to pebbly sands of a braided system in an active glacial outwash plain.

The complex facies associations entail large internal reservoir variability as reflected by routine core analysis data (poro-perm), log data and the petrophysical interpretation. The Global Hydraulic Element (GHE) approach is tested as a rock typing tool for response and synthesis of all parameters and critical path in the reservoir modeling work flow.

In this study ten (10) GHE have been identified for the Mamuniyat Fm. Detailed quality control of the log and core data available have been conducted. The methodology involves the analysis of the routine core porosity and permeability and calculation of the Normalized Porosity (ϕz), Reservoir Quality Index (RQI) and Flow Zone Indicator (FZI). Statistical analysis on GHE and Facies Associations has been performed to better define their relationship.
Temsah Field PLEMS Replacement - Challenges & Technology
Authors: Pomar Alina , Al Sayed Ahmed , D'addario Nico
Published: February 2010

The technology innovation applied and lessons learned acquired in the Temsah field PLEMs change over project further TNW blow out emergency, occurred in August 2004, bring to analyze a real case study for production optimization while operating on in service facilities subsea.

Following the Temsah NW accident, it was of paramount importance to recover the Temsah and Akhen fields' production with a fast track redevelopment project. To match a challenging production restart up (6 months for Akhen) temporary gas and condensate PLEMs were installed in the field. Such PLEMs, procured in 2 months and made of materials (piping and valves) not suitable for subsea applications, allowed operability initially up to one year and extended up to four.

The final Plan of re-Development, as conceived by Petrobel, allowed both PLEMs change over with limited impact on production compared with the original plan.

Smart plugs solutions have been applied in the condensate PLEM replacement while subsea hot tapping and stoppling have been implemented all at once in the gas PLEM replacement.

Due to the water depth of 85 m the offshore activities, in both cases, have been executed in saturation diving mode, operating on different sealines size, from 6″ up to 32″, with the aim to avoid the sealine flooding minimizing the impact in the production facilities.

The reconsideration of the overall Temsah field development with improvements in the subsea facilities allowed not only to recovery the production lost due to the accident but to increase the field production profile which remained almost constant while replacing the PLEM despite sealine were going to be disconnected. Moreover the field operability has been improved thanks to replacement methodology adopted.
The Cabao Fm.: A Transgressive Cretaceous Tidal Dunes Complex Along Djebel Nafusah, North-Eastern Libya
Authors: Rubino Jean-Loup , Lafont Francois , Metais Eddy , Blanpied Christian , Sbeta Ali
Published: February 2010

The Djebel Nafusah Cliff forms very continuous outcrop (300km Long) and can be traced from Libyan Mediterranean coast to southern Tunisia. The cliff is armed by Mid Cretaceous limestone's which prevent underlying Mesozoic series from erosion.

The Mesozoic series starts with Triassic deposits and ends in Maaestrichtian. In the central part of the djebel, a homogeneous sandy series unconformably rests over the pre-existing Mesozoic series and corresponds to the so called Cabao Formation. It is exposed in numerous quarries as well as in natural outcrops. It unconformably overlies the Shekshuk Fm. most likely of Oxfordian age.

In Tunisia, additional stratigraphic units onlap the Austrian unconformity such as the Bouloula and Douiret Formations, Ouaja et al (2002); laterally equivalent units also occurs in western Libya near Wazin.

The Cabao sandstones seems to grade into Chenini sandstones in southern Tunisia, however the relationship is not well constrains and ancient data tends to suggest a north westward pinchout of the lower part of this formation, Bouaziz et al. (1989).
Messinian Salinity Crisis Expression Along North African Margin
Authors: Rubino Jean-Loup , Haddadi Nourredine , Camy-Peyret Jacqueline , Clauzon George , Suc Jean-Pierre , Ferry Serge , Gorini Christian
Published: February 2010

The Mediterranean Messinian Salinity Crisis, Hsu et al. (1973) has two main expressions, 1/ very deep subaerial canyons incision on the the hinterland and along basin margins, 2/ deposition of marginal and abyssal evaporites in the basins. Boths are well known everywhere around Mediterranean Sea, but surprisingly the occurence of canyons is poorly documented along North African margin except in Egypt where the Nile canyon is well known from onshore, to offshore, since a long time, Chumakov (1973), Barber (1981), Dalla et al. (1997). More recently messinian canyons have been reported: –In Algeria with the Algiers complex, Rubino et al. (2005),–Offshore and onshore Tunisia, El Euch-El Koundi et al. (2008)–In offshore Libya, Barr et Walker (1978), Ryan & Cita (1978), or onshore in Sirte and Kufrah basins, Grifin (2002), Rubino et al. (2005), Nicolai (2008), Drake et al. (2008), Paillou et al. (2008).–Evidences have been also reported from Morroco, Loget. (2002).
Application of the Time Series Analysis to the Latest Cenomanian – Early Turonian Sequence Using Foraminifera in the Southern Tethyan Margin
Authors: Soua Mohamed , Smaoui Jalel , Zaghbib-Turki Dalila
Published: February 2010

Time series analysis has been performed for the first time on the Cenomanian-Turonian sequence in Central Tunisia in order to shed light on its Milankovitch-like cyclicity. This analysis was tested and applied on two foraminiferal species: the biserial Heterohelix, an oxygen minimum zone (OMZ) dweller, and the triserial Guembelitria, a eutrophic surface dweller. Average sedimentary rates and the duration of the second Oceanic Anoxic Event OAE-2 in each studied section were estimated. Alternatively, the fluctuations of these two opportunistic species can be related mainly to both precessional (23–19 ka) and eccentricity (414–106 ka) cyclicity suggesting that changes in surface water fertility were linked to the Milankovitch parameters.
North Bardawil Development Project
Authors: Picciani F.. , El Din Ismail N.. , Luce R.. , Guarino M..
Published: February 2010

The energy demand in Egypt has enjoyed a sustained period of growth over the past decade and this is set to continue in the next years. In order to sustain the demand trend, a remarkable number of subsea gas projects were put on stream during the last years and some more are already under development.

Through its affiliate in Egypt Ieoc, Eni has planned to maintain the role of top foreign hydrocarbon producer in the Country. To achieve this target Eni made investments in cutting edge technology, in particular in the sub-sea production system and for the first time in Egypt, it applied an innovative smart completion system.

On August 2009 Eni begun producing natural gas from the subsea North Bardawil Field. The production rate is 3.0 million standard cubic meters per day, approximately 19,000 boepd, of which about 6,700 boepd is Eni's equity share.

The project consists of two sub-sea wells, Assad and Zaraf, drilled by the semi-submersible Rig Scarabeo-4, the installation of 24 km of sea line, umbilical and subsea equipments in a water depth ranging between 110 and 340 meters, and the tie-back to the existing production platform Barboni.

Assad was developed with well re-entry and intelligent completion in two gas levels in the Pleistocene sequence zones with ICGP sand control, in order to produce through two independent gas flowing intervals. Zaraf re-entry with side-track and completion was executed with single conventional completion and ICGP sand control.

The tie-back to Barboni Platform was performed through simultaneous operations, upgrading the top side facilities on a gas producing platform and minimizing the number of the platform production shutdowns.

Partners on the project include Eni's affiliate in Egypt IEOC with 60% and Kufpec Ltd with 40%. Petrobel is the JV operator. These results were made possible through IEOC and Kufpec with the cooperation of the Ministry of Petroleum and EGPC.

The paper presents the analysis of the challenges, the opportunities, the development strategy and the execution of North Bardawil project in the strategic context of Egypt.
Diversities in the Interpretation of the p-n Junction Under All Injection Conditions
Authors: Haque Mohammad Asadul , Rahman Jalalur
Published: February 2010

A comprehensive theory of the physical picture of a p-n junction under all injection conditions has been presented in this paper. The pn product in a junction must always be ≤ n1²eqVkT. By incorporating all suitable modification of the boundary conditions, the inconsistencies concerning the relation of the applied potential difference to the difference across the space charge region of a p-n junction were observed. Attempt were made to remove those inconsistencies. The transition region for abrupt p-n junction is analyzed in terms of carrier densities at the neutral bulk-space charge region boundaries and location of these boundaries with respect to the metallurgical junction and also analyzed by using quasi-equilibrium assumptions. The p-n junction is solved by using three-region approach and analytical solutions are derived for low, medium and high injections. Key words: Depletion region, Injection conditions, Quasi-Fermi-level Inconsistencies. DOI: 10.3329/bjsir.v44i3.4398 Bangladesh J. Sci. Ind. Res. 44(3), 265-270, 2009
The Effect of Stage of Harvest and Storage on the Seed Quality of Chickpea (Cicer arietinum L.)
Authors: Khatun A , Bhuiyan MAH , Ud-deen MM
Published: February 2010

Laboratory experiments were carried out to determine the effects of harvesting stages on the seed quality of chickpea. Chickpea seed of three varieties (BARI Chola-5, BARI Chola-6 and BARI Chola-8) were collected at three harvestings times i.e. from three different times at 7 days interval prior to harvesting, viz. i) when the pods were yellowish with a few yellow greens (H1 stage), ii) when most of the pods were light brown with a few yellow (H2 stage), and iii) when all the pods were completely brown and dry (H3 stage). Significant variation was observed in three varieties of chickpea for all the parameters studied except vigour-I. The highest germination percentage, root length, shoot length, root plus shoot length and vigour-II was observed in BARI Chola-5 which was significantly higher over BARI Chola-8. Dry weight was found to be significantly higher in BARI Chola-8 which was identical to BARI Chola-6. Moisture content was significantly higher in BARI Chola-8. Seed collected at the stage when most of the pods were light brown with a few yellow (H2 stage) recorded the highest germination percentage, dry weight, vigour-I and root length. Pods (H1 stage) gave the highest moisture content in seeds. BARI Chola-5 seeds recorded the highest germination at H2 stage. Interaction effects of varieties and harvesting stage had non-significant effect on germination percentage, vigour-I, shoot length and vigour-II in both the years. Keywords: Chickpea, Harvesting stage, Storage, Vigour, Moisture, Germination DOI: 10.3329/bjsir.v44i3.4403 Bangladesh J. Sci. Ind. Res. 44(3),303-310, 2009
Synthetic Applications of Chiral Unsaturated Epoxy Alcohols Prepared by Sharpless Asymmetric Epoxidation
Authors: Riera Antoni , Moreno María
Published: February 2010

An overview of the synthesis and applications of chiral 2,3-epoxy alcohols containing unsaturated chains is presented. One of the fundamental synthetic routes to these compounds is Sharpless asymmetric epoxidation, which is reliable, highly chemoselective and enables easy prediction of the product enantioselectivity. Thus, unsaturated epoxy alcohols are readily obtained by selective oxidation of the allylic double bond in the presence of other carbon-carbon double or triple bonds. The wide availability of epoxy alcohols with unsaturated chains, the versatility of the epoxy alcohol functionality (e.g. regio- and stereo-selective ring opening; oxidation; and reduction), and the arsenal of established alkene chemistries, make unsaturated epoxy alcohols powerful starting materials for the synthesis of complex targets such as biologically active molecules. The popularization of ring-closing metathesis has further increased their value, making them excellent precursors to cyclic compounds.
Therapeutic Effects of a New “Indigenous Vaccine” Developed Using Novel Native “Indian Bison Type” Genotype ofMycobacterium aviumSubspeciesparatuberculosisfor the Control of Clinical Johne's Disease in Naturally Infected Goatherds in India
Authors: Singh S. V. , Singh P. K. , Singh A. V. , Sohal J. S. , Sharma M. C.
Published: February 2010

Therapeutic efficacy of an “Indigenous vaccine” has been evaluated with respect to a commercial vaccine (Gudair, Spain), for the control of clinical Johne's disease (JD) in naturally infected goatherds. Seventy-one goats (JD positive) were randomly divided into 3 groups (“Bison”, “Gudair” and “Sham-immunized”). After vaccination, goats were monitored for physical condition, morbidity, mortality, body weights, shedding ofM. paratuberculosis(MAP) in feces, internal condition and lesions, as well as humoral and cell-mediated immune responses for 210 days. Study showed marked overall improvement in physical condition of vaccinated goats and average body weight gain was significantly higher (P<.05) in “Bison” group as compared to “Sham-immunized” goats. Mortality due to JD was significantly (P<.05) lower in vaccinated groups than in “sham-immunized”. Morbidity rates (due to diarrhea and weakness) were lower in “Bison” group as compared to other groups. Died goats from vaccinated groups showed regression of gross JD lesions and regeneration of fat layer around visceral organs while “Sham-immunized” goats exhibited frank lesions. Vaccinated goats had higher protective CMI response and also higher antibody titer for the trial period as compared to “Sham immunized”. Both vaccines also reduced shedding of MAP in feces significantly (P<.05). Though the two vaccines effectively restricted the severity of clinical symptoms of JD, however “Indigenous vaccine” was superior in many respects.
Dual-Task Interference: The Effects of Verbal Cognitive Tasks on Upright Postural Stability in Parkinson's Disease
Authors: Holmes J. D. , Jenkins M. E. , Johnson A. M. , Adams S. G. , Spaulding S. J.
Published: February 2010

Although dual-task interference has previously been demonstrated to have a significant effect on postural control among individuals with Parkinson's disease, the impact of speech complexity on postural control has not been demonstrated using quantitative biomechanical measures. The postural stability of twelve participants with idiopathic Parkinson's disease and twelve healthy age-matched controls was evaluated under three conditions: (1) without a secondary task, (2) performing a rote repetition task and (3) generating a monologue. Results suggested a significant effect of cognitive load on biomechanical parameters of postural stability. Although both groups increased their postural excursion, individuals with Parkinson's disease demonstrated significantly reduced excursion as compared with that of healthy age-matched controls. This suggests that participants with Parkinson's disease may be overconstraining their postural adjustments in order to focus attention on the cognitive tasks without losing their balance. Ironically, this overconstraint may place the participant at greater risk for a fall.
Action Potential: Ionic Mechanisms
Authors: Elmslie Keith S
Published: February 2010

The generation and propagation of the action potential requires sodium influx via voltage‐dependent sodium channels that drives the upstroke of the action potential. This positive feedback cycle is terminated by sodium channel inactivation that shuts down the channel at depolarized membrane potentials. The reduced sodium influx along with increased potassium efflux permits rapid action potential repolarization. The enhanced potassium efflux is mediated by the activity of both voltage‐dependent and voltage‐independent potassium channels. The recovery of sodium channels from inactivation and the slow closing of potassium channels following the action potential determine the refractory period, which is a period of increased action potential threshold. Thus, the kinetics of sodium and potassium channel gating determine not only the action potential shape and duration, but also the threshold for action potential generation.

Key concepts:

Sodium influx via voltage‐dependent sodium channels depolarizes the membrane to activate more sodium channels in a positive feedback mechanism that generates the ballistic rising phase of the action potential.

This positive feedback cycle is terminated by a separate gating process called inactivation, which shuts down sodium flux even though the membrane is still depolarized.

The reduction of sodium influx resulting from inactivation combined with potassium efflux from the cell via both voltage‐dependent and voltage‐independent potassium channels drive the repolarization phase of the action potential.

The voltage‐dependent potassium channels often remain active following the action potential (slow to close) to generate an after‐hyperpolarizing potential (AHP).

The AHP can speed sodium channel recovery from inactivation, which is faster at more hyperpolarized voltages, so that the channels are more rapidly reset to participate in generating the next action potential.

Action potential threshold is determined by the relative activity of sodium versus potassium channels with an action potential being generated if the sodium influx is larger than the potassium efflux.

Insulating the axon with myelin increases the speed of action potential propagation by limiting action potential generation to small unmyelinated gaps called nodes of Ranvier.

High‐density clustering of sodium channels at the nodes of Ranvier ensures sufficient current is generated to exceed threshold at the next node so that the action potential is faithfully propagated along the axon.
Immunology of Fish
Authors: Fletcher Thelma C , Secombes Christopher J
Published: February 2010

Innate immunity provides some form of defence against pathogens in all multicellular organisms but with cartilaginous and bony fish, although the lowest group of jawed vertebrates, the addition of a classic adaptive immune response becomes apparent. This provides the refinements of specificity for antigen recognition and memory. The T‐ and B lymphocytes are the effector leucocytes, acquiring their antigen‐specific receptors (immunoglobulin for B cells and T‐cell receptor for T cells) in the anterior kidney (bone marrow being absent) and thymus. The B cells are responsible for the production of antibodies that function as different immunoglobulin classes, whereas subsets of T lymphocytes are capable of killing target cells or helping with B‐ and other T‐cell functions. Knowledge of these mechanisms is important for the use and design of vaccines, now so essential for the aquaculture industry, whereas studies of fish immunology contribute to the understanding of the evolution of adaptive immunity.

Key concepts:

Fish possess innate and adaptive immune responses, with classical adaptive immunity present only in jawed vertebrates.

Adaptive immunity allows memory of prior exposure to foreign molecules (antigens), so that on subsequent contact protective mechanisms are more rapidly mobilized: the basis of vaccination.

Lymphocytes mediate adaptive immunity and have surface receptors that recognize antigens, initiating the production of circulating antibodies and the activation of cell‐mediated responses.

The functions of the immune system are similar in fish and mammals although there are differences due to the aquatic physiology and ectothermic nature of fish that provide evolutionary interest.

Leucocyte–antigen interactions take place in immune sites, such as the kidneys, spleen, gills and intestine. Bone marrow and lymph nodes are lacking.

Knowledge of fish immunology is proving essential for the development of vaccines for the expanding aquaculture industry.
Vertebrate Central Nervous System: Pattern Formation
Authors: Vermeren Matthieu , Keynes Roger
Published: February 2010

Deciphering the genetic instructions used by the embryo to establish the spatial order of its neuronal populations and their interconnections is the key to understand the wonderfully complex structure of the adult brain and spinal cord. The vertebrate central nervous system develops from a single ‘plate’ of ectoderm cells that fold into the neural tube. Localized signalling centres are placed at defined positions both outside and within the neural plate and tube, and trigger the differentiation of nerve cells. The centres secrete and combine a variety of morphogens that determine, in time and space, the repertoire of genes expressed by neurons in different regions of the nervous system. Gradients and countergradients of morphogens act along the three principal axes – antero‐posterior, dorso‐ventral and left–right – to regulate and coordinate the appearance of diverse neuronal subtypes in their correct anatomical locations.

Key Concepts:

The central nervous system develops from an epithelial ‘plate’ of ectoderm cells, triggered by molecular signals from the early midline mesoderm (‘neural induction’).

Several localized signalling centres, placed both outside and within the neural tube, coordinate patterning and regional differentiation of the nervous system.

The centres establish gradients and countergradients of a variety of morphogens that generate a patterned array of different nerve cell types.

Morphogen gradients generate discrete changes in the populations of transcription factors expressed by individual cells.

Morphogens have different effects according to the differentiation state of the cells they influence.

Diversity in the nervous system arises from the action of a small set of morphogen families expressed in the right place at the right time, such as: SHH, retinoic acid, Wnts, BMPs/TGFβs and FGFs.
Sjögren's Syndrome
Authors: Jonsson Roland , Brun Johan G
Published: February 2010

Sjögren's syndrome is a lymphoproliferative disease with autoimmune features characterized by mononuclear cell infiltration of exocrine glands, notably the lacrimal and salivary glands (autoimmune exocrinopathy). These lymphoid infiltrations lead to dryness of the eyes (keratoconjunctivitis sicca), dryness of the mouth (xerostomia) and frequently, dryness of the nose, throat, vagina and skin. Sjögren's syndrome is associated with the production of autoantibodies because B‐cell activation is a consistent immunoregulatory abnormality. The spectrum of the disease extends from an organ‐specific autoimmune disorder to a systemic process (musculoskeletal, pulmonary, gastric, haematologic, dermatologic, renal and nervous system involvement). Sjögren's syndrome may occur alone (primary) or in association with almost any of the autoimmune rheumatic diseases (secondary), the most frequent being rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Sjögren's syndrome also is associated with an increased risk of B‐cell lymphoma development. Current treatments are mainly symptomatic.
Vitamin B12: Disorders of Absorption and Metabolism
Authors: Watkins David , Rosenblatt David S
Published: February 2010

Derivatives of vitamin B12(cobalamin) are required for activity of two enzymes:methylmalonylCoA mutase, which catalyses conversion ofmethylmalonylCoAtosuccinylCoAandmethionine synthase, which converts homocysteine to methionine. Cobalamin deficiency results in accumulation of methylmalonic acid and homocysteine in blood and urine. Clinically, deficiency results in megaloblastic anaemia, subacute combined degeneration of the spinal cord, loss of sensation, ataxia, dementia and psychosis. Dietary cobalamin deficiency is rare in developed countries, except for individuals consuming a vegan diet. A more common cause of cobalamin deficiency is pernicious anaemia, an autoimmune disease that results in inability to absorb dietary cobalamin from the intestine. A number of rare genetic disorders have been identified that result in inability to absorb dietary cobalamin, inability to transport cobalamin from the intestine to cells that require it for metabolism, or inability to convert intracellular cobalamin to one or both of its coenzyme derivatives, adenosylcobalamin and methylcobalamin.

Key Concepts:

Cobalamin (vitamin B12) is required for activity of two enzymes, methylmalonylCoA mutase and methionine synthase, in mammalian cells.

Cobalamin deficiency results in accumulation of methylmalonic acid and homocysteine in blood and urine.

Clinically, deficiency is characterized by megaloblastic anaemia and neurological problems.

Uptake of dietary cobalamin requires the binding protein intrinsic factor, secreted by parietal cells of the stomach, and the intestinal receptor cubam.

Autoimmune destruction of gastric parietal cells results in pernicious anaemia.

Mutations in the genes encoding intrinsic factor or components of cubam result in heritable cobalamin malabsorption.

Peripheral cells take up cobalamin bound to the transport protein transcobalamin by carrier‐mediated endocytosis.

Cells convert cobalamin to adenosylcobalamin, required by methylmalonylCoA mutase, and methylcobalamin, required by methionine synthase.

Rare mutations affecting genes involved in cobalamin metabolism, result in decreased synthesis of either or both cobalamin derivatives.
Infectious Mononucleosis
Authors: Epstein MA , Rickinson AB
Published: February 2010

Infectious mononucleosis is an acute self‐limiting disease caused by an orally transmitted herpesvirus,

Epstein–Barr virus

. The disease typically involves fever, enlarged lymph glands and malaise, with elevated blood lymphocyte counts that reflect an exaggerated cellular immune response to the infection.

Epstein–Barr virus

is widespread in all human populations and is most often acquired asymptomatically in infancy. However, in affluent societies, primary infection can be delayed until the second or third decade, when 25–50% of those involved may develop symptoms. Hence infectious mononucleosis is typically a disease affecting adolescents or young adults in the Western world. Almost all patients recover completely within a few weeks but rare cases with persistent, even fatal, symptoms do occur and involve those with a pre‐existing immune defect or rare individuals where the virus infection spreads into atypical cell types. There is no obvious association between this virus and so‐called chronic fatigue syndrome.

Key concepts:

Infectious mononucleosis is caused by
Epstein–Barr virus
, an orally transmitted human herpesvirus that is common in all human populations.

Most individuals acquire
Epstein–Barr virus
asymptomatically early in life, then carry the virus for life without undue effect.

Only when primary infection has been delayed until adolescence or young adulthood is there a substantial risk of mononucleosis developing; hence, the disease is largely confined to affluent societies where delayed infection is more common.

Infectious mononucleosis is self‐limiting and ‘immunopathological’ in nature: that is, the symptoms (fever and malaise) are caused not by the virus infection per se, but by the patient mounting an exaggerated cellular immune response to that infection.

Most (but not all) cases with the relevant clinical symptoms and large numbers of atypical mononuclear cells in the blood will be
Epstein–Barr virus
‐related; however, definite diagnosis requires serological testing for IgM antibodies to
Epstein–Barr virus
.

Cases where severe disease symptoms persist are extremely rare and involve either patients with a pre‐existing immune defect or individuals where the virus infection has spread into atypical cell types.

A history of proven infectious mononucleosis brings with it an increased risk of subsequently developing another
Epstein–Barr virus
‐associated disease, Hodgkin lymphoma.
RNA
Structure: Tetraloops
Authors: Cheong Chaejoon , Cheong Hae‐Kap
Published: February 2010

Ribonucleic acid
(RNA) hairpins are among the most common RNA secondary structural elements that are frequently capped by tetraloops. An RNA tetraloop structure is composed of a Watson–Crick base‐paired stem and four loop nucleotides. The structure is compact and stable. The first and the fourth nucleotides form a base pair in most of the tetraloops, leaving two unpaired nucleotides in the loop. A sharp turn in the backbone is stabilized by ribose–base, base–phosphate hydrogen bonds and base stacking interactions. Tetraloops help in the folding of RNA by initiating the process. Additionally, they provide sites for RNA tertiary contacts and for protein binding, facilitating the assembly of
ribonucleoprotein
particles. Certain interactions, some of which are sequence‐specific and others structure‐specific, can be involved in the recognition of tetraloops by proteins and RNAs.

Key concepts:

RNA hairpins play important structural and functional roles in RNA.

Tetraloops help the folding of RNA and provide sites for RNA–RNA and RNA–protein interactions.

U turn motif, a sharp backbone turn in tetraloops, is stabilized by ribose–base, base–phosphate hydrogen bonds and base stacking interactions.
Parental Care and Investment
Authors: Gonzalez‐Voyer Alejandro , Kolm Niclas
Published: February 2010

Parental care is common throughout the animal kingdom and among caring species there is a bewildering variation in how parents care for offspring, as well as in the amount of resources parents invest in care. For instance, there is considerable variation in the relative parental investment by the sexes – in some species females invest more, in others males invest more, and in some investment is more or less equally shared. Different hypotheses have been proposed to explain patterns of parental investment between the sexes, as well as among species, and work is still ongoing to develop an overarching hypothesis that can explain the various patterns observed.

Key concepts:

Among species there is ample variation in how parents care for their offspring, if at all, as well as in how much they invest in offspring.

Differences between the sexes in relative parental investment have been recently proposed to depend on sexual selection and the operational sex ratio, rather than sexual selection patterns resulting from relative parental investment by the sexes, as previously suggested.

Individual decisions on the optimal parental investment can lead to conflict between parents as well as between parents and the offspring.

In some species, care of the offspring is not the exclusive responsibility of the parents but is shared among members of a group, termed cooperative breeding. In other species, adults sometimes take care of unrelated offspring, either willingly (as in adoptions) or unwillingly (as in brood parasitism).

Within species, parents may adjust the amount of investment in offspring based on signals from their partner or from the offspring themselves.
Meiotic Sex Chromosome Inactivation
Authors: Daish Tasman J , Grützner Frank
Published: February 2010

The differentiation of sex chromosomes through evolution has resulted in significant loss of homology and gene content which has profound consequences on gene dosage between the sexes and impacts on their behaviour through meiosis. During spermatogenesis the unpaired DNA, of heteromorphic sex chromosomes becomes transcriptionally silenced and sequestered into a ‘sex body’, a process termed ‘meiotic sex chromosome inactivation’. This essential meiotic event involves an ordered hierarchy of epigenetic changes to the sex chromosome DNA initiated by conserved DNA damage, repair and checkpoint machinery. Although the reason for this repression remains unclear, it is thought to prevent recombination between nonhomologous sex chromosome DNA and to avoid stringent meiotic checkpoints. Recent work has extended our understanding of the evolutionary conservation of meiotic silencing to include the avian ZW sex chromosome system providing new insights into the evolutionary dynamics of meiotic sex chromosome organization in diverse species.

Key concepts:

The accumulation of mutation and rearrangements on sex chromosomes lead to blocks in recombination, accumulation of sexually antagonistic genes and the differential degradation of sex chromosomes.

Heteromorphic sex chromosomes result in gene dosage imbalance between the sexes and unsynapsed DNA in meiosis I.

Meiotic sex chromosome inactivation protects unpaired sex chromosome DNA from aberrant recombination and checkpoint surveillance machinery.

Sex chromosomes undergo transcriptional silencing during late prophase due to the accumulation of conserved epigenetic changes.

Therian mammals have active X‐borne retrogenes on autosomes to compensate for the loss of transcription of sex chromosome genes important for spermatogenesis.
Ehrenberg, Christian Gottfried
Authors: Oren Aharon
Published: February 2010

Christian Ehrenberg (1795–1876), a German naturalist, palaeontologist and microbiologist who was the first to systematically study the microscopic world of protozoa, microalgae and bacteria, and who founded the science of micropaleontology.
Adhesion and Percolation Parameters in Two Dimensional Pd–LSCM Composites for SOFC Anode Current Collection
Authors: Boulfrad Samir , Cassidy Mark , Irvine John T. S.
Published: February 2010

This paper is concerned with palladium–(La0.75Sr0.25)0.97Cr0.5Mn0.5O3 (LSCM) composite current collectors for solid oxide fuel cells (SOFCs); the composites, which are in a 2D configuration (thickness of about 8–10 µm), are deposited upon an LSCM electrode layer on top of an yttria zirconia electrolyte substrate. The influence of the LSCM particle size on the adhesion between palladium and LSCM are reported and discussed. Compositions using four different LSCM particle sizes (0.21, 0.49, 0.64, and 0.81 µm) with sintered Pd particle sizes approaching 10 µm are investigated. The best bonding is obtained when smaller particles are used. The electrical dc conductivity of the composite is reported as a function of the palladium volume fraction for all used LSCM particle sizes. The measured experimental values present typical insulating–conductive percolation. However, the transition occurs at ∼33% of the conductive phase, that is, a lower percentage than for 2D ideal systems and a higher percentage than for 3D ideal systems. This is consistent with lower‐dimension percolation for a system of large‐grained conductors and small‐grained insulators. The general effective media (GEM) equation is used to fit the experimental data, and the two main parameters (the threshold point ϕc and the exponent t) are defined.