bluuebunny/crossref_metadata_2025 huggingface dataset:
Total Volume and Component Flow Measurement in Industrial Slurries and Suspensions Using Correlation Techniques
Authors: Beck M. S. , Calvert G. , Hobson J. H. , Lee K. T. , Mendies P. J.
Published: November 2015

Flow velocity can be derived directly from the transit time of natural turbulence signals between two transducers spaced along the direction of flow. The transit time is determined by cross-correlating the transducer outputs with either a special purpose correlator or an on-line computer. Advantages are that the time delay can be measured absolutely by the correlator, the flowmeters are relatively insensitive to the effects of up-stream disturbances, the transducers do not obstruct the flow, and suspensions and slurries can be metered. Results are presented for flow measurement of sand/water slurries using electrical conductivity and ultrasonic transducers, and for heavily loaded gaseous suspensions using capacitance transducers.

A low cost mass flowmeter has been devised in which the mass flow of solids in a pneumatic conveyor is derived from measurement of variations in concentration intensity due to turbulence. Results are given for mass flow measurement of foodstuffs (flour, wheat and beans), pulverised fuel, cement and chemicals.
A Survey of Measurement and Control of Pollutants
Authors: Garrod D. J.
Published: November 2015

When the title of the symposium was first decided, the organising committee considered that a general survey of the subject was required so that (a) they would be in a position to judge whether or not the papers received were a reasonable cross section of the subject, and (b) it could be used to indicate to the delegates where the subject of the individual speakers comes within the general picture. Unfortunately, there was none readily available, and therefore the author as a member of the organising committee, decided to formulate such a survey. Some parts of the survey are not as detailed or informative as intended, and the author would be grateful for advice on any errors or omissions which are noticed.
Instrumentation Applied to Cryogenics Plants
Authors: Townsley H
Published: November 2015

The term “Cryogenic plant” refers to any plant or process designed to operate at very low temperatures, around 150 K and below. This paper deals generally with industrial air separation plants in which the separation of the main components is effected at about 70 to 90 K (−203 to −183° C).
Stability Determination for Linear Control Systems with Distributed Lags
Authors: N-Nagy F L , Al-Tikriti M N
Published: November 2015

The paper outlines a specially adapted stability criterion for linear control systems with distributed lags. The stability is studied with respect to two variable parameters, ie the loop-gain and the distributed lag. The criterion employs an easily constructed chart prepared beforehand and only requires the plotting of two curves derived from the open-loop transfer function. The stability of a simple control system is investigated to illustrate the scheme.
An Improved Method for the Design of Electronic Function Generation Networks
Authors: Aird R J , Court J T
Published: November 2015

A method is described to overcome the errors in diode function generators when operating at voltages considerably lower than the maximum, without a significant increase in the number of sections required. The technique, based on varying section length, produces a maximum error in each section which is nearly a constant percentage of the local value. An application of this to the production of a square root network is analysed in detail and the results are presented in graphical form to allow the designer to select a combination of accuracy and the number of sections for any particular problem. Several units have now been constructed using commercial components and the experimental results are in excellent agreement with the predicted values of error. The method has been found to be a simple and inexpensive way of producing fixed function generation with a considerable improvement in accuracy.
Fluidic Flow Measurement and Control Devices
Authors: Boucher R. F. , Royle J. K.
Published: November 2015

Some pure fluid digital flowmeters are described and factors determining their accuracy are discussed. One meter under development is described in detail and performance characteristics are given.

A new type of vortex flow controller is also described and shown to have advantages in performance and geometry over existing devices. Further improvements in performance and new devices which ease the control and interface problem are discussed. Flow diverters are also described and some characteristics are presented.
Design Requirements of Analogue Transmitters for Use in Hazardous Atmospheres
Authors: Towle L. C.
Published: November 2015

This paper considers some of the major design parameters of transmitters with direct current analogue output which are normally associated with measurement in the petrochemical industries. Specific recommendations are made for signal current, the number of wires to be used, techniques for achieving explosion protection, temperature classification, operating voltages and output impedance. Mechanical construction, termination requirements and interference rejection are discussed. The paper concludes with a reference to some practical examples of recently designed transmitters.
Instrumentation in the Post-Apollo Programme
Authors: Daniels S. A.
Published: November 2015

The paper discusses the programme of space exploration to be undertaken by the Space Shuttle Transportation System which is currently being developed by NASA. The basic parameters of Space Shuttle are identified and the major subsystems contributing to the shuttle are reviewed. The instrumentation-needs, and the constraints applying to it, are addressed; the paper concluding with a brief reference to the potentials of technical spin-off from this momentous programme.
Improved Temperature Measurement in Batch Reactors
Authors: Wansborough M. , Maarleveld A.
Published: November 2015

Good process control can be hindered by the build-up of fouling on temperature measuring elements. The problem can be particularly acute for batch processes, where deposits on the temperature bulbs may lead to dangerous reaction conditions during the start-up, prolongation of the batch cycle time, or off-specification product.

A special temperature measuring device has been developed to overcome this variable fouling lag. It has been tested experimentally and found to give a stable, more accurate temperature signal over a wide range of fouling.
A Coercive Force Grading Instrument for Relay Iron
Authors: Beckley P. , Mildoon J.
Published: November 2015

Low carbon soft iron is used in the manufacture of relays. An instrument is described which can grade the coercive force of such steel with a minimum of sample preparation.

Satisfactory correlation is found between results obtained from the grader described and classical testing methods.
Measuring Spool Displacement in a Totally-Enclosed Pressure Actuated Hydraulic Valve
Authors: Rose E.
Published: November 2015

This article discusses a straight forward method of measuring spool displacement in a totally-enclosed pressure actuated hydraulic valve. The method involves the total immersion of a rectilinear potentiometer in oil at a pressure of 140 bars.
An On-Line Instrument for Measuring Small Quantities of Dispersed Non-Conducting Liquid in a Conducting Liquid
Authors: Lee K. T. , Beck M. S. , McKeown K. J.
Published: November 2015

A method for continuously measuring the quantity of non-conducting immiscible liquid dispersed in a detergent slurry is developed. The instrument relies on measuring the rms value of fluctuations in the instantaneous resistance across electrodes in the flowing fluid. Fundamental concepts underlying this technique are discussed, together with the details of the measuring system and the construction of the electrodes. Some experimental results are presented which show that the output of the instrument is proportional to the quantity of the dispersed phase. This technique is generally applicable to any two-phase fluid system where the carrier is conducting and the minor discontinuous component has a different value of conductivity.
Relationships between Recent Developments in Linear Control Theory and Classical Design Techniques (Part 1)
Authors: MacFarlane A. G. J.
Published: November 2015

A comprehensive survey is given of recent work on the use of matrix-valued functions of a complex variable for the analysis and design of linear multivariable feedback systems. Several emerging design techniques are outlined and a simple illustrative design example given showing how such methods may be used in practice.
Environmental Influences on Pressure Transducer Performance
Authors: Davidson D. P.
Published: November 2015

The ideal pressure transducer responds to an input of pressure and pressure alone and has a unique, and preferably simple transfer function. The real transducer of course does not achieve this and its accuracy is characterised by the amount by which it deviates from ideal under the effect of pressure, the primary influence, or secondary influences such as temperature.

Hysteresis and creep are two of the most serious errors, which occur even under constant environmental conditions, but usually as a result of changing pressure. Non-linearity is not necessarily to be regarded as an error.

The errors that occur when the transducer is subjected to changes in a secondary influence such as acceleration, humidity and temperature are generally more severe. It is the purpose of this paper to demonstrate these effects, which fall into three categories: quasi-static changes, transient reversible and irreversible, in descending order of tolerability.

As an example, the effect of acceleration may fall into any one of these categories. An inversion of a transducer may cause a steady and entirely reversible change in the output; shaking the device may give rise to a transient output which disappears when the excitation is removed, whereas a sudden and severe shock may irreversibly derange the transducer.

In practice, the most important environmental influence is temperature, and the effects are examined in some detail.

Thermal errors in the first and last category are well understood and are usually fully covered in manufacturers' specifications, but the most serious errors, and those for which it is most difficult to allow, occur in the second category under conditions of changing temperature. A good understanding of these effects is essential for the design of transducers and their installations.
Measurement of the Angular Displacement of a Platform Mounted on a Flexible Column
Authors: Adams T. P. , Burrows C. R.
Published: November 2015

The work described in this paper arose from the need to control the orientation of a flexibly mounted platform. In the particular application described here it was not acceptable to use a gyroscope to measure the angular displacement of the platform and an alternative technique was required. The method which was developed is based upon a novel application of strain gauges.

The method is described and some experimental results are presented and evaluated.
Instrumentation and Control of Distillation Columns with Sharp Temperature Profiles
Authors: Bentley J. P.
Published: November 2015

Distillation columns separating components of high relative volatility are characterised by sharp temperature profiles and a highly non-linear relationship between temperature and reboil rate. This paper presents a stability analysis of the problem in a typical case which shows that both linearisation and dynamic compensation techniques are necessary to prevent limit cycling. Linearisation using an optimal linear combination of temperatures on different trays is compared with that of a diode function generator. The dynamic compensation of a band notch filter is compared with that of a standard three-term controller. The paper concludes that a diode function generator should be tried first and if limit cycling still persists, then a band notch filter should also be introduced into the control loop.
Human Operators and Simulation within a Chemical Industry
Authors: Doig R. M. M.
Published: November 2015

A review is made of the practical application of simulation techniques in a chemical industry. The techniques include mass balance steady state models, sequential plant start-up and shut-down models and simple plant simulators. A brief description of three applications is given.
Closed Loop Transient Response from the Open Loop Frequency Response
Authors: Hind E.C.
Published: November 2015

A method is shown for relating the closed loop transient response to the open loop frequency response, which is based on the use of the contour of constant closed loop phase angle, α = −90°. The method primarily yields a second order model of the closed loop system which covers the full range of relative damping (0 < ζ < +∞). A first order model is recommended when prescribed conditions apply. The method is simpler and yields better results than currently used methods. In all cases it is assumed that the negative feedback loop has a transfer function of unity and that the closed loop system is stable.
A Queuing Model for the Utilisation of Machines under Random Parallel Loading
Authors: Ream N.
Published: November 2015

In a system consisting of many identical machines, any set of machines may be reserved from any other machine in order that the set may carry out a production job simultaneously. A simple queuing model, entailing various approximations, is used to give formulae for utilisation, holding time and other parameters of the system. The model suggests that a practical system designed on these lines would become congested at between one-tenth and one-fifth of full loading.
Height Triangulation with Modern Engineering Theodolites
Authors: Stepec W. A.
Published: November 2015

Results from tests for the accuracy of the self positioning of the automatic vertical index built into the Kern DKM 2A theodolite are quoted. The advantage to be derived from theodolites with automatic vertical index are discussed. Height control established with reciprocal rays, auxiliary point and by traversing is analysed. Trigonometric levelling and spirit levelling are compared.
A Survey of Digital Transducer Instruments Used in the Weighing Industry - Part 2
Authors: Brendel Al
Published: November 2015

It should be remembered that the information in these two articles surveying digital transducer instruments was written for the American market, but has been included in Measurement and Control to show what is available outside the UK. In fact some are also available here.

The number of active digits is not necessarily an indication of the accuracy but of overall sensitivity of the instruments. If one is trying to compare these with European instruments, particularly to those approved to OIML or the BOT standards, the number of digits in these cases is restricted by the maximum error of the instrument. That is to say that if the instrument is being approved for 1 part in 3000 the error should not exceed 1 scale division.

This can hardly apply to some of the instruments that are listed in Al Brendel's chart which show performances of 1 part in 40 000.

The UK authorities would not normally expect to approve equipment better than 1 part in 5000, the norm being more like 1 part in 3500.
The Effect of Noise When Deriving Signals from Accelerometers
Authors: Ball R. , Lewis C. P.
Published: November 2015

The effect of noise is often ignored when accelerometer signals are integrated to give velocity and displacement. The main forms of noise to be found in a system which operates in this way are identified, and analysis shows the interdependence of the magnitude of the noise, the system bandwidth and the signal-to-noise ratio of the final displacement output. It is shown that the signal-to-noise ratio is degraded significantly by the integration process; thus noise introduced before integration, by signal amplification, recording, or other conditioning is critical.
Principles of Optical Fibre Sensors and Instrumentation
Authors: Harmer A. L.
Published: November 2015

An overview of optical fibre sensors and instrumentation is presented. Sensors can be divided into two types: continuous transducers in which light is modulated along the whole length of the fibre, and point transducers which are sensitive to an external variable at a single point. Optical effects in fibres are considered for the six types of physical perturbations: mechanical, electrical, magnetic, thermal, radiation and chemical perturbations. Instrumentation systems for fibre sensors may be categorised according to the way in which the light is modulated: Phase, amplitude, wavelength, polarisation, time-resolved or time varying modulation. These instrumentation schemes are compared for sensitivity and performance and numerous examples of practical sensors are cited for each category.
Instrument Science and Technology: A Systemised Discipline
Authors: Jones B. E.
Published: November 2015

Modern industry and commerce are dependent on accurate measurement, and there is a need throughout all industry for improvement in measurement skills. The science and technology of measurement is a multi-disciplinary subject, while measurement and control are interdependent. Sufficient and proper teaching and training in the subject, particularly in further and higher education, is unlikely to occur unless the subject becomes established as a systemised discipline in its own right. A set of unifying, underlying, general principles and concepts organised in a logical framework is required, although it is desirable to avoid both the temptation to overtheorise and to produce mere catalogues of devices. Of considerable importance is a suitable means of presenting theoretical and practical knowledge about primary sensing elements and measuring transducers. The paper will consider recent developments that are helping to establish the discipline of measurements.
AVTOPS — An Automatic Vehicle Tank Overfill Prevention System
Authors: Baker J N
Published: November 2015

The increased use of LPG as an automotive fuel coupled with the growth in self-service retailing has refocussed attention on the safety of refuelling operations on the forecourt.

One potentially unsafe operation is that of overfilling the vehicle tank. In the liquid phase LPG has a particularly high coefficient of thermal expansion and an overfilled tank, if subjected to a sufficiently large temperature rise, could discharge flammable LPG through its pressure relief valve.

The present paper reports the development of an Automatic Vehicle Tank Overfill Prevention System, AVTOPS, designed to prevent this occurrence. The system is entirely self-contained within the forecourt installation and requires no additions or modifications to the customers vehicles, nor any additional action on the part of the customer.
Review of Modulating Techniques for Fibre Optic Sensors
Authors: Medlock R S
Published: November 2015

For instrumentation purposes there are six main types of signal which can be used to modulate sensors. These are mechanical, thermal, electrical, magnetic, chemical and radiant. Fibre optic sensors depend mainly for their operation on the modulating effect of the first five on visible or infrared radiation carried by optical fibres and components. Many modulating techniques have been described in the literature over the past five years and an attempt is made to review the breadth rather than the depth of this new and interesting branch of sensor development
The Historical Development of Flow Metering
Authors: Medlock R S
Published: November 2015

Historical interest in flow measurement can be traced back for more than a thousand years but it was less than four hundred years ago that the first principles began to be understood. The initial incentive to measure flow was the need to charge consumers and this led to the early development of positive/semipositive and inferential type integrating meters. Later, towards the end of the 19th century, measurement of flowrate became important for industrial and utility purposes. Pressure differential techniques held sway to satisfy this demand until about 1950 when alternative methods started to become available. Currently there are about sixty different flow measuring techniques in use to meet the ever-increasing requirements for domestic, custom transfer and industrial flow measurement of liquids, gases, vapours and solids in single or polyphase form.
Economic Consequences of Measurement Errors
Authors: Napper John
Published: November 2015

In this article John Napper highlights the monetary effect of measurement errors for the loading of road tankers. His example of a terminal with 40 million litres per month where 0.1% error is equivalent to £200,000 per annum highlights the problem. He indicates sources of error and the way that microprocessors can control errors and thereby avoid the large financial consequences.
Economics of Gas Flow Measurement
Authors: Peignelin G , Marque D , Smid J , Brandt O , Ballez G , Rombouts P , Musilek O
Published: November 2015

It seemed very important to have a section on gas flow measurement. The UK's production of natural gas in 1984 was about 35×109 m3 and its consumption about 50×109 m3 with a reserve of about 0.7×1012 m3.* The value of this gas is 0.43 DM/m3† or about £0.12/m3 or about $0.18/m3. Unfortunately we were unable to find anyone able to write a section for this issue in the time available. However, I am grateful to Mr R J Simpson for drawing my attention to a report by Peignelin et al. † The authors have kindly agreed to an edited version of this paper.

This paper considers two sizes of metering stations and considers the use of orifice or turbine meters. For these stations it considers investment costs and maintenance costs. It then examines the uncertainty in the energy content determination. The paper concludes that the major uncertainty lies in the flowmeter; that while turbine meter installations seem to be lower in cost than orifice meter installations, reliability must also be taken into account; and the cost of the instrumentation is a small proportion (15–20%) of the total cost of the station — R Baker.
Developments in Flammable Gas Monitoring
Authors: Simons W R
Published: November 2015

The increasing use of flammable gas monitoring in industry over the past couple of decades has focused attention on the need of higher integrity monitoring equipment, especially sensors, and its more effective utilisation in an increasingly wide range of applications and environments. This paper reviews some related developments in flammable gas monitoring, including the emergence of national standards and codes of practice.
Pipeline Integrity Conference Covers a Wide Field
Authors: Tiratsoo John
Published: November 2015

The recent conference entitled ‘Pipeline Integrity Monitoring’ and organised by Pipes and Pipelines International, was held in Aberdeen in October 1986. It created a useful opportunity for delegates from the pipeline industry in seven countries to discuss the technology associated with on-line pipeline monitoring. The paper presents a review of the conference and discusses the highlights of a very successful event.
The Engineering of On-Line Process Analysers
Authors: Meredith W D
Published: November 2015

The design of process analysers involves multi-disciplinary overall involvement, therefore this paper can only highlight the difficulties associated with this work and relate these to the engineering tasks. The requirements, problem areas and user specifications are discussed, and also other areas are considered where design can play a vital role in reducing costs and improving the acceptability of the analyser in the market place.
The Use of Fibre Optic Techniques for Temperature Measurement
Authors: Grattan K T V
Published: November 2015

The subject area of fibre optic sensing is one in which there has been shown a very rapid expansion of interest over the last few years. Many novel techniques are appearing in the literature and some products are available to the industrial user. The background to fibre optic means of temperature sensing and some recent developments will be reviewed in this paper.
An Expert System for Monitoring Helicopter Airworthiness
Authors: Karwatzki J M
Published: November 2015

Recent disasters caused by mechanical failures in helicopter drive systems have highlighted the need for much more stringent monitoring of aircraft condition. This article describes how an Expert System has been developed to provide early warning of possible failure in helicopter rotor blades and could be expanded to provide monitoring of total helicopter airworthiness. The article identifies some of the features required of Expert Systems in the engineering environment.
‘Do-it-Yourself’ Measurement and Control CAE Package
Authors: Sydenham P H , Skinner A , Beijer R W
Published: November 2015

A knowledge-based, Computer Aided Engineering project, denoted DIYM&C, has begun that allows casual users, untrained in measurement, to develop and apply measurement and control in such areas as materials handling, process control, machine tool automation, scientific research and testing.

Essential information helps the user, who needs no prior training, to select a system of sensors and actuators. It provides documents for purchasing or self manufacture. It will eventually give guidance for installation, commissioning and for operation of the system with automatic diagnostics and self-calibration.

Its current extent covers setting up the system requirement, printing specifications and provision of selection and manufacturing information for pressure, length and temperature sensors.

Experience has proven that an effective, generally applicable, designer/users aid can be constructed with reasonable resources. A framework is now ready on which can be developed a more complete support service.
Intelligent Condition Monitoring of Gas Compressor Engines
Authors: Smallman Clive
Published: November 2015

The intelligent condition monitoring of industrial plant is a rapidly expanding area of research. It combines two radically different disciplines: classical condition monitoring and intelligent knowledge-based systems.

The paper presents an overview of the areas of orthodox condition monitoring systems, intelligent knowledge-based systems and intelligent condition monitoring. The paper also includes two examples of the diverse work underway in this area.

Finally, there is a discussion of a current British Gas intelligent condition monitoring project, which is investigating the application of intelligent systems techniques to condition monitoring of gas compressor engines. This features a detailed summary of a particular element of the problem area. In addition the nature of the future development of this system is also discussed.
Effect of Assumed Tow Architecture on Predicted Moduli and Stresses in Plain Weave Composites
Authors: Chapman Clinton , Whitcomb John
Published: November 2015

This paper examines the effect of assumed tow architecture on the predicted moduli and stresses in plain weave textile composites. In particular, the effect of how a constant cross-section is assumed to sweep-out the volume of a tow is explored. Two architectures are examined which have a sinusoidal tow path and a lenticular cross-section. Three-dimensional finite elements are employed to model a T300/Epoxy plain weave composite with symmetrically stacked mats. Macroscopically homogeneous in-plane extension and shear and transverse shear loadings were considered. Symmetries are exploited which permitted modeling of only 1/32nd of the unit cell. Accounting for the variation of material properties throughout each element is determined to be necessary for accurate prediction of stresses in the composite. For low waviness, the two tow architectures examined are very similar. At high waviness, the stress predictions are much more sensitive to the assumed tow geometry.
Protein Production and Secretion in Exocrine Cells
Authors: Castle J. D. , Arvan P. , Cameron R.
Published: November 2015

Acinar cells of exocrine glands are highly specialized for producing, storing, and discharging secretory proteins for use on surfaces that represent interfaces between the organism and the surrounding environment. These functions are achieved through the secretory pathway that includes a series of functionally distinct intracellular compartments — the endoplasmic reticulum, subcompartments of the Golgi complex, and the secretion granule in which exportable macromolecules are stored at high concentrations. Most secretion occurs by granule exocytosis in response to external hormonal or neural stimuli. Although these processes have been traced in a variety of morphological and biochemical studies, very Utile is known about the mechanisms involved in facilitating and maintaining secretory storage, orchestrating discharge at the apical cell surface, and in ensuring conservation and re-internalization of the granule membrane. Recent studies initiated on cell fractions obtained from the rat parotid gland have provided significant insight into the protein storage conditions that prevail in the granule interior and the components of the granule membrane that are likely to be involved in general secretory function such as exocytosis.
Ion Transport and Water Movement
Authors: Martinez J. R.
Published: November 2015

Secretion of water and electrolytes in salivary glands occurs by a dual process involving the formation of a plasma-like, isotonic primary-secretion in salivary acini and its subsequent modification in salivary-ducts by the removal and addition of specific ions. The mechanisms underlying the formation of primary acinar secretion have been investigated with a number of experimental approaches such as electrophysiology, the measurement of ion transport in gland fragments and dispersed acinar cells, and the evaluation of the ionic requirements for secretion in isolated, perfused gland preparations. The ac-cumulated evidence suggests that salivary secretion is formed by a complex interaction between passive and active ion movements across acinar cell membranes, resulting in the trans-acinar movement of Cl and Na* and, by the osmotic gradient which develops, of water. A major consequence of stimulation is the release of K+ through Ca++ -and voltage-sensitive channels and its subsequent recycling back into the cells by ouabain- and furosemide-sensitive transport systems. This results in NaCl uptake across the basolateral cell membrane and the subsequent efflux of Cl through luminal membrane channels, which also appear to be sensitive to cellular Ca++. The rates of these various ion movements appear to be, therefore, closely linked and interdependent. Ductal modification of the primary secretion has been studied in microperfused duct preparations. The evidence likewise indicates that it involves interactions between complex conductance pathways in the luminal cell membrane and a Na, K pump present in the basolateral cell membrane and that it is under autonomic and hormonal control. Activation of ductal transport mechanisms results in NaCl reabsorption and KHCO3 secretion. Final saliva thus differs from primary secretion in electrolyte composition and, because water permeability is low in the duct epithelium, becomes hypotonic. Alterations in fluid and electrolyte secretion such as those observed in disease can result, therefore, from disturbances in one or more of these complex transport processes in acinar or duct cells.
Physiological Factors Affecting Salivary Flow Rate, Oral Sugar Clearance, and the Sensation of Dry Mouth in Man
Authors: Dawes C.
Published: November 2015

This paper discusses methods for collection of both whole saliva and individual gland secretions, the normal ranges of salivary flow rate, the effects of physiological variables which influence flow rate, and the role of saliva in oral sugar clearance. The physiological basis for the sensation of dry mouth is discussed, and a new concept is advanced which states that the sensation of dry mouth will occur when the salivary flow rate is less than the sum of the rates of water absorption and evaporation from the mouth. In a study of the effects of anticholinergic agents on salivary flow, the subjects experienced the sensation of dry mouth when the normal flow rate of unstimulated saliva was reduced by from 40 to 50%.
Chemical and Crystallographic Events in the Caries Process
Authors: Legeros R.Z.
Published: November 2015

The chemical and crystallographic events associated with the caries process can be described based on the results from the following studies: (a) effects of carbonate, magnesium, fluoride, and strontium on the physicochemical properties—lattice parameters, crystallinity (crystal size and strain); dissolution properties of synthetic apatites; (b) factors influencing the in vitro formation and transformation of DCPD, OCP, AP (Ca-deficient apatites), FAP, β-TCMP (Mg-substituted), and CaF2; and (c) studies on properties (crystallinity, composition, chemical, and thermal stabilities) of enamel, dentin, and bone.

The dissolution of CO3-rich/Mg-rich/F-poor dental apatite crystals and re-precipitation of CO3-poor/Mg-poor/F-rich apatite in the presence of F- ions in solution contribute to a more acid-resistant surface layer of the caries lesion. Fluoride promotes the formation of less Ca-deficient and more stable apatite crystals. The presence of Ca, P, and F in solution inhibits dissolution of apatite more than does the presence of F alone. Low levels of F in solution promote the formation of (F, OH)-apatite, even under very acid conditions; an increase in F levels causes the formation of CaF2 at the expense of DCPD or apatite, especially in acid conditions. F in apatite and/or in solution suppresses extensive dissolution of dental apatite and enhances the formation of (F, OH)-apatite crystals which are more resistant against acid-dissolution than are F-free apatite crystals.
Physical and Chemical Considerations of the Role of Firmly and Loosely Bound Fluoride in Caries Prevention
Authors: White D.J. , Nancollas G.H.
Published: November 2015

Historically, there has been considerable debate concerning the roles of loosely bound (calcium fluoride) and firmly bound (fluorapatite) fluoride for caries prevention. Research now shows that fluorapatite (FAP) is a finite reaction product of enamel/apatite fluoridation with or without CaF2 formation, suggesting that CaF2 always be considered as a supplement to, rather than a substitute for, FAP formation. In the presence of low levels of fluoride in the solution phase, the crystallization of hydroxyapatite is enhanced, while the corresponding dissolution is retarded. Fluoride in the bulk FAP or CaF2 solid phase, in contrast, has limited impact on crystal growth or dissolution kinetics. Both FAP and CaF2 can provide F to the solution phase to enhance remineralization and retard demineralization of enamel HAP crystallites. The FAP provides most of this F under low pH conditions, while CaF2 provides F at neutral or lower pH. The reactivity of fluoride on sound and carious enamel differs significantly. Carious enamel acquires more fluoride, acquires it more quickly, and itself acts as a source of retained fluoride in comparison with the more limited reactivity of sound enamel. Overall, the most important question concerning fluoride reactivity relates to its efficiency in enhancing remineralization or retarding demineralization processes. This is influenced not only by the reaction products, e.g., loosely or firmly bound fluoride, but also by the nature of the enamel substrate and frequency of application of the topical fluoridating agent. Inasmuch as the reactivity of bulk HAP is dominated by surface layers of FAP material, the debate over usefulness of various fluoride reaction products solely on a chemical level is no longer critical. Instead, all factors influencing the efficiency of a fluoridating regimen must be considered in the development of improved systems for caries prevention.
Physicochemical Perspectives on the Cariostatic Mechanisms of Systemic and Topical Fluorides
Authors: Margolis H.C. , Moreno E.C.
Published: November 2015

The cariostatic mechanisms of systemic and topical fluoride agents are considered in light of a previously proposed model for the caries process. It is noted that fluoride, in principle, can induce a cariostatic effect: by (1) reducing enamel solubility when incorporated into the mineral structure; (2) by fostering the remineralization of incipient enamel lesions and the deposition of fluoridated phases (within dental plaque) which provide a source of mineral ions (Ca, P, F) under acidic conditions; and (3) by reducing the net rate of transport of matter out of the enamel surface, under acidic conditions, by inducing the reprecipitaion of fluoridated hydroxyapatite phases within enamel. It is also noted that relatively high (~ 12,000 ppm) concentrations of professionally applied topical fluorides significantly reduce the rate of acid production of cariogenic organisms (e.g., S. mutans). Based on an analysis of available clinical and laboratory data, it is concluded that the benefits provided by water fluoridation result, to a large degree, from a topical effect. It is suggested that clinical procedures be developed to establish and maintain low levels of free fluoride in plaque fluid. It appears that this will require frequent exposure to topical fluorides.
Biochemical Effects of Fluoride on Oral Bacteria
Authors: Hamilton I.R.
Published: November 2015

Fluoride inhibition of carbohydrate metabolism by the acidogenic plaque microflora is well-established, although it has not always been appreciated that oral bacteria vary considerably in their susceptibility to fluoride. Early studies demonstrated that the F-induced reduction in acid production was due, in part, to the inhibition of the glycolytic enzyme, enolase, which converts 2–P-gfycerate to P-enolpyruvate. The decreased output of PEP in the presence of F, in turn, results in the inhibition of sugar transport via the PEP phosphotransferase system (PTS). Bacterial accumulation of fluoride involves the transport of HF, a process requiring a transmembrane pH difference or pH gradient, which is generated only by metabolically active cells. The uptake of HF into the more alkaline cytoplasm results in the dissociation of HF to H+ and F- and, if allowed to continue, the accumulation of protons acidifies the cytoplasm, causing a reduction in both the proton gradient and enzyme activity. Current information indicates that in addition to enolase, F- also inhibits the membrane-bound, proton-pumping H+/ATPase, which is involved in the generation of proton gradients through the efflux of protons from the cell at the expense of ATP. Thus, fluoride has the dual action of dissipating proton gradients and preventing their generation through its action on H*/ATPase. The collapse of transmembrane proton gradient, in turn, reduces the ability of cells to transport solutes via mechanisms involving proton motive force. In spite of these known effects on the bacterial cell, there is no general agreement that the anti-microbial effects of F contribute to the Anticaries effect of fluoride. The resolution of this question will require new information on the nature and concentration of F in plaque, the minimal level of F required to provide an Anticaries effect, and the influence of cellular integrity and activity on F uptake and accumulation by plaque bacteria.
Environmental and Physiological Factors Affecting Dental Fluorosis
Authors: Angmar-Månsson B. , Whitford G.M.
Published: November 2015

In addition to differences in fluoride intake and possibly to calcium deficiency or malnutrition, there are several factors which may account for individual differences in the occurrence of dental fluorosis. Disorders in acid-base balance affect the renal handling of fluoride such that, in acidosis, the excretion rate is diminished and, in alkalosis, the excretion rate is enhanced. Thus, any factor that can decrease urinary pH would be expected to increase the likelihood of dental fluorosis and vice versa. Results from studies with both rats and dogs have shown that acid-base disturbances per se, especially acidosis, adversely affect the mineralization of enamel in a manner that resembles fluorosis. It has been found that the retention and tissue levels of fluoride are increased by residence at high altitude. It has also been found that, in the absence of fluoride exposure, residence at high altitude per se can have a profound disruptive effect on ame-logenesis which could be confused with fluorosis. The effects of diseases which lead to increases in urinary flow rate and water intake on the likelihood of the occurrence of dental fluorosis are also discussed.
Differential Diagnosis of Dental Fluorosis
Authors: Cutress T.W. , Suckling G.W.
Published: November 2015

Differentiating between fluorotic and non-fluorotic defects of dental enamel is an important diagnostic decision in epidemiology and public health dentistry. The commonly accepted diagnostic criteria for fluorosis discriminate between non-discrete symmetrical and asymmetrical distributions of opacities of dental enamel. These criteria appear to identify most cases of dental fluorosis. However, it is not yet confirmed that the pattern and distribution of dental fluorosis are a unique phenomenon. Metabolic, physiological, other trace elements, and malnutrition have been reported to induce bilateral symmetrical developmental enamel opacities. Misdiagnosis of non-fluoride-induced opacities remains a possibility. Reports of unexpectedly high population prevalence and individual cases of fluorosis, where such diagnoses are incompatible with the known fluoride history, indicate the need for a more precise definition and diagnosis of dental fluorosis. A more discriminating diagnostic procedure is recommended. This calls for a positive identification of the levels of fluoride available to communities and individuals before a diagnosis of fluorosis is confirmed. We believe a more critical approach to the diagnosis of fluorosis will be helpful in the rational use and control of fluorides for dental health, and in the identification of factors associated with inducing developmental defects of enamel.
Dental Caries Prevalence and the Use of Fluorides in Different European Countries
Authors: Kalsbeek H. , Verrips G.H.W.
Published: November 2015

Data in a WHO report relating caries prevalence and the use of fluorides in different European countries were compared with data obtained directly from investigators in the field of oral epidemiology. The reliability of DMFT indices of 12–year-old children, mentioned in the WHO report, appeared sufficient to make comparisons between countries on the basis of these data. The WHO data files on the different applications of fluoride were incomplete. When figures were present, they were not always in agreement with those from the investigators. A decrease of the DMFT indices could be shown in a large number of countries. In further comparative studies between European countries, cultural differences (in dietary habits, for instance) should be taken into account.
The Future of Water Fluoridation
Authors: O'mullane D.M.
Published: November 2015

Recently, questions have been raised about the possible reduced effectiveness and cost-effectiveness of water fluoridation in the prevention of dental caries in developed countries. The increase in environmental fluorides since water fluoridation was first introduced in 1945 (particularly from fluoride toothpastes, mouthrinses, and from foods and drinks) generally provided the basis for these questions. A related phenomenon which might decrease the efficiency of water fluoridation is the reduced caries levels in many developed countries. It has also been suggested that excessive fluoride intake, especially in fluoridated communities where there is widespread use of fluoride toothpastes, is likely to manifest itself in an increased dental fluorosis prevalence. In this paper, recent data from Ireland which are similar to those recorded in many developed countries are used to answer these questions in part. It is concluded that water fluoridation continues to be an effective and cost-effective strategy for caries prevention in areas where the overall caries level has declined and where the cost of water fluoridation implementation has increased. Also, there is no evidence of excessive fluoride intake in fluoridated communities where fluoride toothpastes are widely used.
Reefer Madness Caribbean Style
Authors: Rubenstein Hymie
Published: November 2015

“Reefer madness,” a spurious psychiatric affliction that was widely promulgated in the United States during the 1930s, is rarely mentioned today as a possible sequela of acute cannabis consumption. Because reefer madness (RM) was questioned and generally dismissed in the West by the 1940s, I was surprised to find that it was still widely accepted as a genuine psycho-pharmacological affliction in the Eastern Caribbean country of St. Vincent and the Grenadines in the 1990s. This paper describes and analyzes the reasons for this discontinuity between the West and the Rest by referring to the multiplicity of factors supporting the Vincentian RM syndrome: a generalized tropical “intellectual backwardness” and associated moral apathy; the real and alleged behavioral-psychological effects of acute cannabis ingestion; the peculiarly Caribbean character of Vincentian RM and the way it differs from its American counterpart; the types of people promoting the affliction; the larger anti-marijuana context that Includes opposition to any involvement with the substance; and, most importantly, the national system of racial and class stratification.
Resistance to Drug Abuse Treatment: A Comparison of Drug Users Who Accept or Decline Treatment Referral Assessment
Authors: Boyle Kathleen , Polinsky Margaret L. , Hser Yih-Ing
Published: November 2015

Many drug abusers do not seek help in formal treatment settings, and little is known about their resistance to treatment. In this study, we offered a treatment referral assessment to a sample of 283 drug users. Only 58 subjects (or 20.5% of the sample) accepted this offer. We explored differences between those who accepted the treatment referral assessment and those who declined the opportunity. Logistic regression identified predictors of acceptance related to higher levels of severity in drug use and higher scores on a motivation and readiness scale. Among those who declined the assessment, 43.1 % denied drug use, 37.3% thought their drug use was not a problem, and 16.4% expressed no interest in treatment. Further analysis showed that scores on motivation and readiness were positively related to a higher level of severity In employment problems, family problems, and drug use, and to having a history of prior treatment.