In our business, we use the word “sieve” to describe a piece of equipment that separates desired elements from unwanted material using a woven wire screen or mesh net. To others, “sieve” can mean something very different.
Particle Size Sieves
Sieves – the screen or mesh kind – work by separating some particles from the others in their sample based on their size. Particles smaller than the holes in the mesh will be allowed through, while bigger particles will be caught in the net.
Sieves in the Computer World
In the computer programming world, “sieve” is a programming language used to create email filters. You could say its operation is based on the same concept as our sieves, separating certain emails from the entire batch, though not necessarily by the size of the email.
There are Even Sieves in Sports
The sports arena uses “sieve” to describe a goalie that causes his team to lose the game by allowing many goals to be scored by an opposing team. Here, the goalie is like the wire mesh in a sieve. He should be keeping some particles – or balls – in this case, from getting through, but in reality, the balls are slipping through the holes.
Mathematicians Have Their Own Kinds of Sieves
Mathematicians use sieves for a rather different purpose than the one we’re used to. To them, a “sieve” can be used to find prime numbers. Take the Sieve of Eratosthenes, which has to be the coolest name for a sieve I think I’ve ever heard. This sieve was named after Eratosthenes of Cyrene, a Greek mathematician in ancient times, and is known as one of the most efficient ways to find small primes (any prime number less than 1000). Like the mesh sieves that we use, this type of sieve is used to separate some numbers (in this case, small primes) from others based on certain criteria.
Dreams of a New Particle Size Sieve
We think it would be special if our particle sizing sieves acted more like the computer programming or mathematic version of the word – not the sports definition. That’s why we offer sieves that are manufactured to ASTM standards, and calibration beads to test their accuracy.
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What do an Irish music technology developer, a British manufacturer of arcade and retro-style furniture, and a dance bar in San Francisco have in common? Given a million guesses, I’d never have thought of this:
Of course, when I say “surface tension”, I don’t mean the phenomenon caused by cohesive forces on the molecules at the surface of a liquid that allow the surface to resist external force. It’s strange enough that all of those business owners thought that “Surface Tension” sounded like a compelling and relevant name for their companies. (Maybe they’re all science geeks at heart?)
I think it’s safe to say that most people don’t think of dance bars or arcade-style furniture when they think of the term “surface tension."
Much more likely, they’re thinking of the grade school science experiment they or their kids did involving a bowl of water, pepper flakes, and some soap. In this experiment, if you shake some black pepper onto a bowl of water and stick your finger into the water, the pepper will contract toward your finger and you’ll get it covered in little black flakes.
But, rub your finger with a bar of soap (after you’ve cleaned the pepper flakes off, of course) and stick it back in the water, and you’ll find that the pepper now moves away from your finger.
Why does this happen? Well, soap is a surfactant – a compound that lowers the surface tension of a liquid. When your soap-free finger entered the water, the pepper gravitated toward it because the molecules at the water’s surface were contracting to resist the external force your finger was making on the water. Adding soap to the mix lowered the surface tension of the water, so that the force of your finger displaced the water molecules outward.
That’s why we use soap to help us get things clean – if we didn’t, it would be harder to get the water molecules to spread out and into other things. The force on the surface of the water would keep it more contained and make it harder to be absorbed into another product.
I must admit that when I tried this experiment myself at my desk, I couldn't get it to work by using my finger. Apparently, I've got too much residual soap on my hands (that's a worry for another day). However, when I used a clean plastic knife instead, it worked like a charm.
I can't say the pepper flakes were really drawn in towards the clean knife in the first part of the experiment - they mostly stayed put, with a few kernals moving toward the knife - but when I coated the knife tip in Tide-to-Go (the only soapy thing I had on hand) and dipped it into the water, the pepper flakes shot back away from the knife like they'd seen a ghost. It was actually pretty fun.
Surface Tension may be a cool name for a company, but the scientific phenomenon is even more interesting. The next time you feel like reliving your childhood, instead of heading for a dance bar or buying some retro furniture, try out this experiment. If you want to learn more about surface tension, read our other posts on the topic here.
Till next time,
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When our customers tell me about the different places where CENCO and CSC Digital Moisture balances are used it always interests me.
A few weeks ago, I was asked if I understood the Black Liquor application for moisture testing. As far as I knew, it was something about maybe Extra Dark Bacardi Rum or Moonshine in a Black Bottle.
When I responded with that they replied:
“No Art, it’s about a major process in pulping for paper making”.
As those of you in the paper industry know, Black Liquor is the lignin and hemicelluloses taken out of the wood chips, the spent chemicals that were used to separate them from the wood and a lot of water.
The lignin and hemicelluloses are removed from the wood chips to release the cellulose fiber needed for papermaking.
That’s very interesting, but So what? Who cares? It turns out that this residue is very important – you get several side products that have significant economic value.
Tall Oil is the first. It is skimmed off the Black Liquor before you start getting rid of the water. This by-product is used in adhesives, rubber, drilling fluids and inks. It’s also an ingredient in some cements, soaps and lubricants.
And I used to think that this Black Liquor was just dark rum
When you get most of the water out, a black, gooey mess of lignin and hemicelluloses results (it’s still called Black Liquor). This will burn. It is lit-off to produce steam for the generation of electric power for the plant.
The Black Liquor burn is accomplished in a recovery boiler. It’s called “recovery” because they recover the residual material that is left after the fire. This material consists of inorganic chemicals that are known as smelt (not to be confused with the type fish of the same name).
When mixed with water, this smelt, the recovered inorganic chemicals left after burning the Black Liquor, is known as Green Liquor.
It seems that booze is a common denominator in this Kraft process. The chemical mix that is the principal ingredient that causes the separation of the lignin, hemicelluloses and other components from wood chips is called White Liquor.
White Liquor to Black Liquor to Green Liquor. Now what?
Maybe you already knew this, but I was surprised – the Green Liquor that was produced in the recovery process is reconstituted as White Liquor to be used to start the pulping process all over again.
This is a case of use, recovery, power generation and material reuse. Recycling on a grand scale – Tall Oil, electric power and reused process chemicals.
I don’t know about you, but I found this small glimpse into the paper making process to be an intriguing story.
The whole thing started from a simple question about where our moisture balances are used. Maybe you can now see why I am continually mesmerized by the test equipment world.
I hope you found this little trip around the edges of papermaking interesting. If you did, feel free to share it with your friends and associates.
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By Art Gatenby
At one end of the spectrum is the classic Speedy Moisture Tester where you use the reaction of water with calcium carbide to cause a mini explosion resulting in a moisture measurement reading. This method is used frequently for soils, concrete, and other like materials.
Then there are instruments that use absorption of electromagnetic frequencies to detect and quantify moisture. These work using frequencies in the near infrared microwave and radio spectra. Pretty sophisticated algorithms are needed to get the moisture measurement job done with some of these. The instruments that do this are above the $12,000 price range.
There is what I consider the "other side of the moisture measurement world". Here we measure how moisture travels between the environment and a material and how it travels between the material and the environment. I call this the "World of Sorption". In fact, there is a water sorption group on LinkedIn devoted to this type of moisture measurement.
The "sorption universe" is involved in measuring how much moisture is yielded into a controlled environment (sometimes referred to as water activity) and how much water is adsorbed from an environment of controlled humidity.
Devices called water activity meters are used to determine this moisture yield characteristic. This is done by putting a sample in a closed chamber and measuring the level of relative humidity created by the moisture leaving the material.
When water activity is generated for varying environmental conditions and at different water content levels, the relationship of moisture content and water activity can be developed and presented as Sorption Isotherms.
To measure the other direction (adsorption of water instead of shedding water), a technique known as Dynamic Vapor Sorption can be used. To give a simplified picture of this technique, imagine that you pass a gas with known moisture content over a sample in a closed environment. The amount of moisture adsorbed by the sample can be determined by weighing the sample at the start and then again when it has become saturated. The difference of before and after gives a measure of the absorbed moisture. This is kind of the opposite of loss on drying (LOD). I've named it Gain on Wetting or (GOW).
Hope this little ramble contained some useful insight. Please share it with associates who you think might enjoy it.
I remain mystified, as usual, by the consequences of looking into what seems like a simple question.
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By Art Gatenby
Which looks more durable to you?
The value of a Bostwick Consistometer is that it’s easy to use, which makes it simple to do repeatable testing. The Consistometer is made of stainless steel. One would think that this means a long and useful life. However, as I regularly discover, the real world often defies theory.
A Consistometer’s value is diminished if its leveling plate and screws get bent out of alignment. The story that follows tells how people in the real world handle, or mishandle, this instrument, and what can be done to save it.
A Bostwick’s Life
It’s 11:30 in the morning, and my humans have just pulled me out of the package in which I was shipped to them. After taking a moment to admire me, a brand-new Bostwick Consistometer, they put me to use. The screws at one end of me are adjusted to make me level on the table, and the door to my sample section is lowered and held in place with a spring-operated trigger.
My humans fill the sample trough, ready a timer, and release the trigger, opening the gate. They note how long it takes for the sample they’ve loaded to spread to a certain notch on my trough.
Their test complete, they walk me over to a sink and gently wash and dry me. We’re ready for the next test!
Two weeks later…
My humans sure have put me to work! I think we’ve both gotten used to the drill now, because it’s not taking quite as long to run each test. I love our efficiency, but I wonder if my humans haven’t taken it a step too far. They’ve started tossing me into the sink after we’ve finished a test, rather than taking the time to walk me over to it, and the wear is starting to show.
Some time later…
I think my humans are starting to get frustrated with me. It’s taking them longer to adjust my leveling screws because a particularly large dent on the plate that holds the screws has made it difficult to keep me level. I know they’re wondering if the results they’re getting are correct. What are we going to do?
Some time after that…
I’ve been relegated to the work closet – right in the back behind an old pail and some out-of-date cleaning supplies. It’s pretty dark back here. And quiet. Too quiet.
I miss getting tossed around.
Blinding light…and then…
I find myself in a different warehouse. A mechanic starts to remove the metal piece holding my leveling screws. Oh no! He’s going to take me apart!
Wait a minute…he’s not taking me apart. He’s putting a new piece on – a much thicker piece of metal that has its own, sturdier-looking screws. He makes some final adjustments and sets me down.
I’m back in the old warehouse – not in the dingy closet, but back out in full view. My humans see me and walk over, curious. They pick me up and inspect the alterations. I wait in a state of nervous tension as they set me down and walk away…
But they come back! With a load of sample! In no time, we’re running tests again. This time, when they toss me to the sink, the metal around my leveling screws doesn’t dent. We can run test after test, and I’ll still be going strong.
It’s a good life.
We developed what we call an Abuse Protection Option (APO) that extends the testing life of Bostwick Consistometers in the face of very rough treatment. Click on the image below to discover more details and to find out how to get APOs for your Bostwicks.
Click this image to learn more about the Abuse Protection Option
I hope that this short saga of a Bostwick Consistometer’s Life was useful and entertaining.
I remain a bewildered citizen of the Test Equipment World.
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By Art Gatenby
I used to think that liquids were pretty simple things. Is that what you think too?
Not so fast. Let’s take a look at three properties of liquids and see if we change our view.
Here at CSC, we work with Consistency, Surface Tension and Viscosity of liquids.
As an indicator of Consistency, sometimes defined as thickness or runniness, we use a Bostwick Consistometer. Producers of ketchup, soups, sauces, paints, liquid mixes and the like use the property of Consistency as a check of quality on their incoming and finished product.
Surface Tension, the property that resists external forces at the surface, is a characteristic we measure with duNouy Ring Tensiometers. Research and Development projects for coatings, adhesives and surfactants use these measurements. Surface tension changes are a basic in monitoring processes such as parts cleaning and electroplating.
Viscosity, the measurement of the resistance of a liquid to flowing, is the third quality of liquids that we work with. This characteristic is important in many food products, particularly where flow is important. For example, with pancake syrup, the effectiveness of petroleum compounds are dependent on Viscosity as well as the design characteristics of liquid handling systems.
We are constantly asked how these properties relate to one another. There are very few factors that are associated between these properties. First, there is the general impression of thickness – a liquid with higher viscosity usually means a comparatively higher consistency, but not necessarily a higher surface tension. As temperature increases all three properties become lower in an inverse relationship to temperature.
Other than these associations, across the board correlations do not exist.
This is due to what is behind each of the properties. Consistency is a measure of how a liquid material reacts to gravity. Surface Tension, the resistance of the surface to external forces is a result of the attraction of the molecules and the level of hydrogen bonding. Viscosity’s resistance to flow is a combination of the size of the molecules and the shape of the molecules.
Because of these differences, correlation or conversion of readings between the properties of Consistency, Surface Tension and Viscosity is not possible except between liquids of very similar molecular structure, shape and attraction. Some studies of selected alkanes have shown linear relationship between the log of Surface Tension and the reciprocal of Viscosity, but for a narrow range of molecular structure.
As a result we must give the answer – there is no general correlation of Viscosity to Consistency, or Viscosity to Surface Tension, or Surface Tension to Consistency.
The measurements of Consistency and Surface Tension are straightforward and only need a fixed temperature to assure consistent readings from test to test. Check out the videos.
Surface Tension Test
Measuring Viscosity adds several complications. First, there are several types reactions to the movement of liquids. Then there is the relationship of the force used to the speed of movement.
Viscosity, as the resistance to flow has two critical aspects. The first is a measurement of the force needed to move the layers of a liquid against each other. The second complication arises from the speed at which you move the layers.
Two new terms come into play when dealing with Viscosity. The force needed to move a liquid is known as shear stress and the speed of movement is known as shear rate. The ratio of shear stress to shear rate (shear stress/ shear rate) is the basis of the term viscosity.
Adding these two factors (force and speed) begins to complicate the development of Viscosity measurement. In addition, There are different kinds of liquids. There are fluids in which the viscosity stays constant at any velocity or shear rate, fluids in which viscosity declines with velocity, yet another ( you may have guessed) where viscosity increases with shear rate, others include liquids which show a change in viscosity over time at a given rate and fluids in which viscosity changes with speed but does not even start to move until a specific levelof force is applied.
The first type is known as a Newtonian fluid: water, hydrocarbons, mineral oils, syrup and resins are examples. The Viscosity of Newtonian fluids does not change with changes in speed/velocity.
The second type belongs to a category known as Non-Newtonian, and there are several types of Non-Newtonian fluids in this category some examples include.
The group of fluids for which an increase in speed lowers Viscosity is known as Shear Thinning or Pseudoplastic; ketchup, paint, nail polish, and polymer solutions are examples.
Next are liquids that increase in Viscosity as the speed increases, called Dilatant (almost like a playboy - Dilettante) or Shear Thickening; silica, glycol,cornstarch solutions and some slurries are included here.
Liquids that experience a changes in viscosity as a constant stress is applied to them over time are known as Thixotropic, if the viscosity decrease or Rheopectic if viscosity increases. Examples are inks, Clays and drilling muds.
Finally, there are fluids that require a certain stress is needed before they flow, called Plastic. This type includes gels, latex paints, lotions, and toothpaste. (Just to further complicate matters, a fluid can be both plastic and another type of non-Newtonian fluid, often pseudoplastic or thixotropic.)
Viscosity measurement = simplicity personified, right?
These details of the basic two-phase measurement requirement (stress and velocity) for Viscosity and the complex actions of the different fluid categories hopefully illustrate that the lack of direct correlations of Viscosity to Surface Tension and Consistency is based on the fundamental differences of the these three properties of a liquid.
I hope this helped shine light on the reasons that there are no general correlations among these three properties, and that the requirements for instruments to measure them are significantly different.
Now you may understand why I am continuously baffled by this test equipment undertaking.
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By Art Gatenby
Since I joined CSC Scientific in July 2013, I’ve been on a steep learning curve. You see, I’ve never been much of a science person. There was even one particular chemistry class in high school used to give me migraine headaches - routinely.
Having no real background in the sciences means that I’ve had a lot to learn since I joined a company that sells scientific testing equipment. Maybe you’re nodding in sympathy with me right now. Many of our clients – that is, the people doing the purchasing on behalf of their company – are not scientists and don’t have a thorough knowledge of the scientific principles behind the products they’re told to buy.
The good news is that you don’t have to be a scientific expert to make an informed decision about our products. A basic understanding of the scientific principles behind an instrument can lead you to ask the right questions to help you choose the instrument that will fit your testing needs. To that end, I’ve started to create a video series called “The Basics”.
This series is comprised of short videos that explain the basic concepts around such subjects as viscosity, Karl Fischer titration, and surface tension. I hope they’ll be both fun and informative, and would love to hear your feedback and requests for future episodes.
I’m starting the series with the topic I’ve focused on most since my arrival at CSC Scientific: Viscosity.
Viscosity is a notoriously tricky subject, but one that I hope will be made a little clearer by this entertaining little video:
(I pop up into a bigger frame when you click on me.)
Hope you enjoyed the video! Leave a comment below and let me know what would make it better, or what topic you'd like me to address next.
Till next time,
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Sieve testing, as I have stated many times, is the Cinderella of particle size analysis because it delivers more value than expected from something that’s so easy to use and relatively inexpensive. However, the problem with standard sieving techniques using wire mesh sieves is that they begin to exhibit accuracy problems in the lower micron sizes.
Standard sieves are advertised with openings as low as 30m (microns). At these small sizes, tests usually end with poor and inconsistent results. Inherent variability in wire mesh causes wide relative difference in aperture sizes at these small sizes.
This is the area where alternate techniques such as laser diffraction become the accepted way to get accurate particle size analysis. These techniques, however, are significantly more costly and are technically more difficult to use.
There is another culprit contributing to the difficulty of getting good results for particle size analysis in the lower micron ranges.
However, Cinderella and Prince Charming have a couple of tricks up their sleeves.
The process of electroforming can produce sieves with apertures in the 2 to 3 micron range with acceptable variation between opening sizes – a far cry from woven wire mesh.
Their second trick is the development of the vacuum siever. This design places a rotating vacuum below a sieve that moves the sample over the sieve surface while pulling the particle through the openings. These vacuum sievers can be effective down to the 20m levels. One drawback of these vacuum-sieving instruments is that they will only process one sieve at a time.
Cinderella and the Prince have one more trick, which is the Sonic Sifter. This instrument can process 3 to 5 sieves at a time. The Sonic Sifter applies a vertical, oscillating column of air to the sieves; the air column oscillates 60 times per second to present the particles to the sieve openings. This, along with a mechanical pulse, shears agglomerates and reorients the particle in the air column. The Sonic Sifter is effective in the separation of 3m particles and can complete a test in as little as 10 seconds. Check it out.
Costs for the different techniques of particle size analysis begin at about $1,000 for a basic shaker and 5 non-certified sieves. The Sonic Sifter prices are at the level of $7,000 without sieves. Vacuum sievers cost approximately $9,000. Finally, the Laser Diffraction equipment begins in the $25,000 to $30,000 level and frequently costs in excess of $50,000.
If it seems that the design of reliable particle size analysis in the low micron range is esoteric you are thinking correctly. The determination of the best method is a combination of the nature of the material, the accuracy and repeatability of the results needed, the budget available, and the technical ability of the operators.
The range of equipment and techniques available should provide an alternative that will work in most situations.
As usual, even analyses that should be easy turn out to disconcert and perplex me.
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By Art Gatenby
Can you do a fast moisture test? The answer is, “maybe”.
The direct methods of Loss on Drying and Karl Fischer have the benefit that between them they can get a good moisture content result on almost any product or material.
But these tests usually take several minutes.
When you need the moisture content in a truck load of grain while the load is being dumped, or when you need to check several hundred bags of coffee at an auction, or when you need to get a moisture gradient in a pile of corn, a faster test is crucial.
Can you do it?
The short answer is, “yes”. There are, however certain caveats to this answer.
The techniques available for getting a faster moisture reading are based on the presence of an electrical/electronic signature of moisture in a material or substance. These techniques measure change in resistance, conductivity, capacitance or RF power absorption as an indication of change in moisture. In products where changes in any of these characteristics can be see with a change in moisture, the resulting levels will reflect a relative amount of moisture.
To get actual moisture from a range of these electrical readings, a comparison has to be made to results from a direct method of moisture determination (such as Loss on Drying). These comparisons result in what is called a calibration curve, which is a plot of direct method vs. electrical readings.
For any of these indirect techniques used to get a fast moisture reading, the calibrations represent a curse.
This curse is manifest first in that different substances have different relationships between moisture and electrical signal. For example, a calibration curve for corn is different than a calibration curve for soya. Each provides accurate measurements. However if you mix soya and corn, let’s say 40% corn and 60% soya, a new calibration will have to be done for this mix. Furthermore, if the mix proportions change, the calibration curve will be different.
The second part of the curse is that as moisture levels increase a state of relative saturation occurs. At this point, the change in electrical signal becomes small in relation to the change in moisture and an accurate, repeatable reading cannot be made.
Finally there are some materials that do not have an inherent relationship between electrical characteristic and moisture change, and these techniques cannot be used.
In conclusion, the answer is “yes” to getting a fast moisture measurement if your product exhibits changes in electrical/electronic characteristics with a change in moisture and it is lower than the cut of relative moisture saturation.
Check out our range of indirect moisture measurement products to see what might be available as a fast test for your material.
Everywhere I turn, what seems simple (fast moisture test) becomes indecipherable.
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by Art Gatenby
Automatic digital tensiometers are expensive - three to four times more so than a high-precision manual tensiometer. We hope to clearly depict when an automatic digital tensiometer is not merely nice to have, but essential.
duNouy Ring and Wilhelmy Plate Techniques.
The duNouy Ring method is based on a technique developed by P. Lecomite duNouy and popularized in a paper published in 1925. In this technique a platinum ring is first submerged below the surface of a liquid. The ring is then brought up through the surface. The force necessary to do this and break the meniscus formed at the surface of the fluid is measured. This force is transformed into surface tension terms, usually dynes per cm.
The duNouy method has been used for measuring a wide range of products. It can be used for very low surface tensions, and any surface tension up to a high of 90 dynes/cm. Traditional torsion balance tensiometers are still in wide use because of their inherent precision and stability.
The Wilhelmy plate method is based on the force applied by a liquid to pull on a material immersed in that liquid. The higher the surface tension the greater the force. Wilhelmy plates are well suited for high surface tension liquids and can be used to measure changes in surface tension over time. Tensiometers based upon electronic balances are often used for Wilhelmy Plates applications. These usually provide a digital readout but have limited capability for time-based surface tension analysis.
If your requirements call for measuring only surface tension, the more basic duNouy ring tensiometer is probably the best choice. When you have very thick, high viscosity requirements, a Wilhelm Plate instrument will work.
When conducting basic surface tension tests, in normal ranges, we recommend the duNouy Ring Tensiometer.
Requirements that Point to the Need for an Automatic Tensiometer
If you have requirements for measuring surface tension which change over time, such as measuring the reaction times of surfactant, the Automatic Tensiometer is a good solution.
An automatic tensiometer has unique capabilities for determining Lamella Length, which is the amount of stretch in a liquid between the development of maximum force and the total release of a duNouy ring.
Measurements of changes in apparent surface tension or wettability of different substrates are enhanced with automated techniques.
Most automatic tensiometers have attachments that will control the temperature of the sample.
Most automatic tensiometers also perform routine duNouy Ring and Wilhelmy plate tests. These instruments also record historical results, perform statistical analyses of multiple tests, and plot test readings.
When Do You Need An Automated Solution?
A number of testing requirements clearly point to the need for an automatic tensiometer.
- Time based surface tension tests
- Measurement of Lamella Length
- Wettability analysis
- Temperature controlled samples and/or
- Continuous recording, plotting and retention of all test results
If these are part of your analysis requirements, an automatic Tensiometer is the only practical answer. The ability to conduct your routine duNouy and Wilhelmy Method tests comes as a free added benefit.
We hope this has provided some guidance for the answer to When Do I Need An Automatic Tensiometer?
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The wide range of issues involved with selection and use of laboratory test equipment frequently baffle but always interest me.
Hope we help.
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