Since Buffers represent raw C memory allocation, they are more appropriate for dealing with binary data than strings. There are two reasons why buffers are useful:. They are allocated outside of V8, meaning that they are not managed by V8. While V8 is generally high performance, sometimes it will move data unnecessarily.
Using a Buffer allows you to work around this and work with the memory more directly for higher performance.
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They do not have an encoding, meaning that their length is fixed and accurate. Strings support encodings such as UTF-8, which internally stores many foreign characters as a sequence of bytes. Manipulating strings will always take into account the encoding, and will transparently treat sequences of bytes as single characters.
This causes problems for binary data, since binary data like image files are not encoded as characters but rather as bytes - but may coincidentally contain byte sequences which would be interpreted as single UTF-8 characters. Working with buffers is a bit more complicated than working with strings, since they do not support many of the functions that strings do e. Instead, buffers act like fixed-size arrays of integers. You can create a new Buffer and work with it like an array of integers:. For example, ff in hex equals , the value we just wrote in index 0.
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Since Buffers are raw allocations of memory, their content is whatever happened to be in memory; this is why there are a number of different values in the newly created buffer in the example. Buffers do not have many predefined functions and certainly lack many of the features of strings. For example, strings are not fixed size, and have convenient functions such as String. Buffers are fixed size, and only offer the very basics:. However, if you need to use the string functions on buffers, you can convert them to strings using buffer. Note that Buffers offer access to the raw bytes in a string, while Strings allow you to operate on charaters which may consist of one or more bytes.
For example:. Note how buffer.
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When working with binary data, we frequently need to access data that has no encoding - and using Strings we could not get the correct length in bytes. More realistic examples could be, for example, reading an image file from a TCP stream, or reading a compressed file, or some other case where binary data will be accessed. Mixu's Node book A book about using Node. Node fundamentals: Timers, EventEmitters, Streams and Buffers In this chapter, I cover the fundamentals - the essential building blocks of Node applications and core modules.
Schedule the execution of the given callback after delay milliseconds. Returns a timeoutId for possible use with clearTimeout.
Optionally, you can also pass arguments to the callback. Schedule the repeated execution of callback every delay milliseconds. Returns a intervalId for possible use with clearInterval. Similar processes and techniques of that of Roman cementation were applied and diffused in Middle East 5 , India 15 , China 16 , 17 , Northern Europe 12 , 13 , A very limited number of studies about orichalcum coins 6 , 19 , 21 , 23 and their corrosion are reported and, above all, these contributions are based on the use of qualitative data or semi-quantitative data on dezincification process.
Nowadays, the most common techniques applied to investigate ancient alloys are Scanning Electron Microscope 6 , 26 , 27 and X-Ray Fluorescence 22 , Electrochemical analysis as Voltammetry of Immobilized Micro Particle and Electrochemical Impedance Spectroscopy 34 , 35 , 36 , 37 , 38 , 39 are also used to explore the state of conservation of the patina and to identify the corrosion products.
Some authors applied superficial techniques to investigate both corroded and uncorroded alloy composing samples However, the error related to major and minor elements is too high to help answer to archaeological issues. Nowadays, the most suitable way to investigate the depth of the dezincification process is to analyse cross sections obtained from samples in study with the authorisation of the owners of the coins.
Cross-section analysis allows comparing the real quantity of major elements, which composes orichalcum produced in different age and, thus giving information about the development of the cementation process during the Roman Era. Recently, EMPA technique was used obtaining quantitative chemical analysis of Roman alloys used for coinage We use SEM and EMP analyses to reconstruct the nature of the original alloy and to explore the mechanisms which induced corrosion 6.
In addition, a deep investigation of the microstructure is made. A set of 13 Roman orichalcum coins Fig. Numismatic examination, considering the weight, the size, the legend and the engraved type of each coin 41 , 42 , revealed that they are asses , sestertii , dupondii and semisses minted from Julius Caesar to Domitianus.
The majority of coins were minted after the two important monetary reform of Augustus 23 B. The orichalcum coins studied in this work. Indeed, one of the false certainties of the numismatists is the belief that orichalcum was used by Mithridates VI B.click here
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Finally, under the Julio-Claudian dynasty from Augustus to Nero , a limited number of denominations sestertii , dupondii and under Nero also semisses and quadrantes 43 were emitted in orichalcum. This research attempts to fill the scientific gap existing in the Roman orichalcum coinage, contributing to characterize this ancient alloy, to better understand the dezincification process and to highlight possible differences among samples minted in different years. This investigation is useful to test the presence of Zn in the surfaces even at low percentage, avoiding unnecessary cutting of the samples that are not in orichalcum.
Indeed, deep corroded orichalcum coins are similar in appearance to that in bronze alloy. Tin is present in all samples, with higher peaks particularly in A2, A and B14 samples than others. Chlorine occurs in all samples Fig. Exogenous elements, such as Ca, S, Si, Al, P and Mn are also present 19 and represent contaminants from soils through porosity of the external layer. This is the result of an efficient casting-cooling practice, suggesting a well-controlled cementation process Moreover, some grains present deformed borders with thin strain lines inside Fig. In addition, the twin lines do not present further deformation, suggesting that coins were struck only once.
The dendritic structures are not observed. The process of dezincification is showed in c and d , reaching 1. The red arrows in b indicate the trans-granular stress corrosion. We present and discuss here the results of samples 5 and B14 Fig. In addition, the chemical composition of the unaltered area gives information about the ratio of the two main metals in the alloy. The corroded patina has an irregular thickness with different degree of dezincification, followed by high porosity in the external areas.
Sample B14 Fig. On the contrary, the patina of the sample 5 Fig.
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In this sample an important dezincification process occurs, extending up to 1. The corrosion proceeds from the rim to the inner core with micro-areas of selective corrosion Fig. This selective corrosion is evident in sample 5 Fig. With the evolution of the dezincification process in the external layer is formed a sponge-type structure, typical of brass with low content of Sn, as observed by Constantinides et al. Moreover, in the most corroded areas of this layer porous microstructure was found as reported also in previous studies 21 , 48 mainly made by copper oxides.
BSE image of the external patina of sample 5 in cross section. ESD spectrum acquired on the lighter area shows a Cu-Zn alloy and that of the darker areas shows only Cu, due to the loss of Zn. In addition, qualitative EDS analysis Fig. Iron occurs in A1, A2, A, B4, 5 , X-ray maps of the elements composing the alloy provide information about their distribution along rim-core-rim cross-sections.
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The core of almost all the samples, as shown in the X-ray maps Fig. These patterns indicate an expertise in cementation process by Romans and a well-controlled procedure during the melting-cooling phase of the alloys in the Roman mint, with a diffusion of Zn at nanoscale level along with the absence of micro-domains of Cu and Zn. Lead, when present in the alloy, forms droplets of different size throughout the coin, due to the low solubility of these two metallic elements, which at low temperature do not give solid solution The homogeneous presence of Fe Fig.
However, the superficial Fe-enrichment can be explained with the contribution of exogenous Fe from the soils.