Mechanical Processes - Science topic

Thankyou Heinrich Gruenwald

How did you solve the problem?

Hi Anthony, I have the same problem, I can't save the image with measurements. How did you do?

Thanks

But till now we believe that the operation of non conductive materials is difficult and gives inaccurate result for dimensions.

Dear Bruno,

Electrolyte imbalance also called water-electrolyte imbalance is an abnormality in the concentration of electrolytes in the body. Electrolytes play a vital role in maintaining homeostasis in the body. They help to regulate heart and neurological function, fluid balance, oxygen delivery, acid–base balance and much more. The major electrolytes: sodium, potassium, and chloride. t. These substances are located in the extracellular and intracellular fluid.

Principal symptoms of electrolyte imbalance are namely irregular heartbeat, weakness, bone disorders, twitching, changes in blood pressure, confusion, seizures and numbness.

An electrolyte imbalance treatment is possible by fixing fluid and electrolyte imbalance such as intravenous fluids and electrolyte replacement. A Minor electrolyte imbalance may be corrected by diet changes. For example; eating a diet rich in potassium if you have low potassium levels, or restricting your water intake if you have a low blood sodium level.

Most common form of electrolyte imbalance/ electrolyte disorder is Hyponatremia. Hyponatremia is a condition in which sodium (salt) levels become dangerously low. If your electrolytes drop toolow too quickly, it can be fatal.The symptoms are unspecific and include nausea, dizziness and often falls. Typical symptoms of severe hypernatremia are vomiting, cerebral seizures, somnolence and even coma.

Electrolytes provide a charge that is essential for life and human survival, and have to be maintained in proper concentrations in the body. But just like anything, too manyelectrolytes can be unhealthy: Too much sodium, formally referred to as hypernatremia, can cause dizziness, vomiting, and diarrhea.

Electrolytes imbalance can be rebalanced as normal as eat electrolytes regularly, make these electrolyte-rich foods part of your daily diet, go easy on the salt. Electrolyte can be replaced by best drink such as healthy drinks rich in electrolytes, coconut water (coconut water, or coconut juice, is the clear liquid found inside of a coconut), milk, watermelon water (and other fruit juices), electrolyte-infused waters, electrolyte tablets. Normally, replenish electrolytes after exercise every day is advisable. Push the electrolytes when you're sick. Just 1 teaspoon sodium salt daily need you body every day. Sodium is a vital electrolyte; your body doesn't need a lot.

Ashish

You can use ICP analysis

If you know your species, then Biocyc would be my suggestion. You can select your species and strain, and then do a search for compounds in your pathway, followed by looking at what process it is involved in. If do not know you're organism, you can use Metacyc. Some other databases are KEGG, EAWAG, Uniprot.

Here you can see the production steps: https://www.saar-hartmetall.de/english/produkte/rohteile.html

Dear Shabir Ahmed,

I have prepared for you a summary about the EFFECT OF REDOX POTENTIAL ON MICROBIAL GROWTH.

Redox or oxidoreduction potential is defined as the sum of all the oxidizing (dissolved oxygen, free radicals, hydrogen peroxide, some oxidized metal ions…) and reducing (some vitamins, some reduced metal ions, thiol-containing molecules, hydrogen…) couples found in the medium. This means when the concentration of oxidizing molecules increases the redox potential value of the medium increases (determined in millivolts or volts) but when the concentration of the reducing molecule increases the redox value of the medium decreases. For simplifying the term of redox, we can say that it expresses the concentration of mobile electrons (that can move from molecule to another) in the medium, whereas the pH value expresses the concentration of protons (H+) in the medium.

Now how can the redox potential affect the growth of microorganisms?

To respond to this question we must keep in the head the relationship between the oxygen as oxidant found in the atmosphere and the redox potential. When a microorganism is found in aerobic medium (containing dissolved oxygen) it means this medium is favorable for the growth of aerobic microorganisms which can use the oxygen as a final acceptor of electrons produced from the substrate via the metabolism.

It is important to indicate here also that every microorganism possesses a favorable value of redox for growth (this behavior likes that found for pH, water activity and temperature; and a microorganism found in a medium “swims” to a location with a favorable redox value. Furthermore, it was reported that the redox potential value affects the pH intracellular of a microorganism, which forms a component of the proton-motive force. This effect of the redox on the pH intracellular was attributed to the change of the permeability of the cellular membrane, which increased by the decrease of the redox value of the medium. Other studies reported the effect of redox potential on the surface properties of the cellular membrane such as the hydrophobicity and the character of donor/acceptor of electrons. The ability of redox potential of the medium on the toxin production capacity and spore germination in some microbial strains was also reported. It is important here to remind that the bacterial membranes have an essential function in energy conservation as the location about which a proton motive force is generated. This proton motive force (also called electrochemical gradient) forms a source of energy for bacteria.

We can summarize the mechanism of the effect of redox potential on the growth of microorganisms as follows:

1) Its effect on the structural composition of some sensitive-components/molecules found on the surface of the cell. These redox-sensitive components/molecules could be enzymes located in the surface of the cell, which its protein part (Apoenzyme) could be composed of sulfur-containing amino acids making it sensitive to the redox potential of the medium. Furthermore, the cofactors of these enzymes such as Fe, Zn, Mg and Cu could be found in oxidized or reduced form, which means the susceptibility of these metal ions to the redox potential of the substrate or/and the medium.

By the same manner, we can discuss the effect of redox potential on several redox-sensitive molecules located in the surface of the cell such as proteins, phospholipids, saturated and unsaturated fatty acids, which could be affected directly by the redox potential of the medium. The modification in the structural or the composition of these molecules affects different cellular systems such as the transport and energetic ones.

2) If the energetic system of the cell (proton motive force) changes the ATP content of the cell will change which can affect many essential functions of the cell.

Best Reading

Duried Alwazeer

Iron is a very common impurity in aluminum alloys, which can come from the melting and casting process. So in Al–Si–Fe system there are Fe-rich precipitates that you can found: Al3Fe, Al13Fe4, Al8Fe2Si, Al12Fe3Si2, Al5FeSi, Al4FeSi2 and Al3FeSi.

I recommend you read the literature bellow:

P. Skjerpe, Metall. Mater. Trans. A, 18A (1987), pp. 189-200

M.V. Kral, H.R. McIntyre, M.J. Smillie, Scr. Mater., 51 (2004), pp. 215-219

Please tale a look at this paper:

Especially point 2. There are a few references avaliable mentioned in this paper.

Hi friends. Here is the paper. If you want, we need your specialized comments!!!.

There are two types of dielectrics, polar and non-polar. Non-polar dielectrics do not have a permanent electric dipole moment, when you apply a field, you generate dipolar moments in the direction of the applied field. You can see the microscopic polarization (the response to the field), as the sum of all the dipolar moments induced. For polar dielectrics, when you applied a field, the pre-existent dipolar moments suffer a torque and tend to align with the applied field, in this case the polarization can now be seen as an average of all the dipoles orientations.

Copy the principles of a car chassis to suit your needs.

Try to have a low centre of mass and a wide wheel track to help stability.

Use strategic, short struts to add torsional stiffness instead of using much larger sizes of wood.

Using some type of suspension component will allow much lower stresses on the frame but may be practically impossible.

Dear Pretom

As far as I know, the chemical reaction depends on the acid and the method of treatment. acid treatment may introduce functional groups and structural defects over the carbon material surface.  If you apply Sulfuric acid, both carboxylation and sulfonation takes place.  The product depends on the type of acid used, the oxidation of C-C-bonds leads to the formation of CO2 or -COOH group, or some other functionional groups derived from the acids (e.g. sulphate group, etc).

Thanks for sharing the question. I couldn't agree more with Dear Demetris. I feel we are not ready to proceed further with an effective next step yet. Time will show if and how our boundaries are extended.

Regards

refer the following article

If you want to enhance tribological properties of any surface using composite/ single layer coatings, you should use PVD/HiPIMS for super hard/protective coating.

Dear Pavel, I have been to China for International Wood Machining Seminar, and people from the Nanjing University colaborated with Leitz very closely. You could write to the Leitz branch in China (http://www.leitz.com.cn/en/ArticleRead.asp?ArticleId=5) and I hope they suggest you the proper person. Regads

No your image is correct.

If your error is not zero you will get a ‘Epsilone’ since you have the difference between a positive setpoint and a negative output.

Good understanding 

Dear Annu, thank you for your answer, you can think in that manner there is no wrong with your assumptions, but more correct is condensing nature of moisture that create vacuum due to more volume of moisture becomes/occupies less volume on condensing with decrease in partial pressure of moisture portion in the atmospheric air is responsible for low atmospheric pressure.

Sorry, because I could not apprecciate the deffect in your image. In the attach file is very clear. You can measure with an optical instrument the heigth between the edge of piece and the dross heigth. Another methodology, because the pieces are like a sheet, is to use an comparador (Excuse me because I dont know the name in english). With this you can obtain always the maximun value.

Dross and burrs are material that can be eliminated from final part. This work is and additional work than influence over the cost. If you find parameters than minimize the dross, you can make a good work!!!!!

Yes, colleague is right, FEM software ABAQUS  may be implemented succesfully for your goal.

But contact problems are better solved by Boundary Element Method (BEM). For example, BEASY software is recommended (UK, Wessex Institute of Technology). Good luck! 

Gas compression is an exothermic process, and exothermic processes involve a negative enthalpy change. So your example with the 100 gram charge provides the expected result. But a positive enthalpy change is associated with an endothermic process, and an endothermic effect would be expected with gas expansion, rather than compression. If your measurements and calculations are correct, this appears to be what happened with the 80 gram charge.

I can only guess why that might have happened.  If 80 grams happens to be a significant undercharge for the system, then evaporator pressures would be low, leading to higher compression ratios, causing a higher than normal amount of heat to be generated during compression. Volumetric efficiencies would go down and the sum of the associated inefficiencies might possibly be the cause of the unexpected results.

Dear Alex

It is experiments, not a model.

Hello, Kapil! The topic you're interested in is described in Chapter 2 of the attachment. This stuff is feasible for any type of an electric motor. Regards.

Thank you for your help. Your answers is about advanced materials directly. I want to apply that process/cycle on steel (max 800C). 

Dear Ms Othman,

I regret to say, your question is questionable for me. I believe there is no one who could provide a defendable answer. The reasons are multifold: (i) design of a mechanical system is a complex process, including many different phases, (ii) different phases of design (e.g. conceptualization, architectural design, embodiment, etc. need dedicated methodologies, (iii) every methodology include multiple alternative methods (as well as procedures, instruments, criteria), (iv) design methods should be selected considering design contexts (product, requirements, objectives, etc.), (v) there are large number of contexts to be investigated, (vi) ..... What kind of mechanical system are you designing? Is it a gearbox, a manipulator arm, a clutch, or what? If you look for methods, first of all study the related textbooks and literature. Design is much more than stress or deformation calculation ... Kind regards, I.H.

Schmidt-Nielsen points out that the oxygen consumption must  be taken into account, since the more oxygen required for a specific 'fuel', the more water is lost

from the lungs. He calculates that, for a gain of 10,000 kcal,

oxidation water for fat is 1.13 kg, whereas water lost in

respiration is 1.8 kg (a net loss of 0.67 kg).

This mean that  fat oxidation in the hump as a source of metabolic water may rather leads to water loss and deficit. 

Hello,

If you have a machine from Stratasys Dimension Elite also FDM system then the problem with the temperature does not exist.

Almost all home FDM systems have this problem, depending on who is producer of.

So it must be that explores that temperatures are optimal.

Best regards,

Dear sir,

You can prefer cryogenic cooling. though some of the main issues such as initial investment and safety are concerned with Cryogenics, it gives better results with the materials in this category.

Depends how accurately you need to measure transient response and what your machining conditions are, i.e., dry or lubricant use. Lubricant will interfere with pyrometer readings. Quick response thermocouples do quite well at measuring transients. These are available in wire sizes down to 0.076 mm.

Though I have no practical backing for my answer, but seems the middle nugget should form first, as this is the region offering maximum electrical resistance and minimum cooling rate (assuming of course, sufficient pitch among the spots) since this region is farthest from the cooled and high thermal conductivity electrodes. The nugget diameters should depend on electrode diameter and sheet thickness. Assuming all parameters to be same and symmetrical, the nugget diameter for the middle one should be maximum. Destructive sectioning on a couple of jobs should provide the required insight and I too would like to see the results in this respect.

Please find the attached file here. Hope it may help you.

Regard

Sandeep Kumar

The use of palladium is to avoid the intergranular penetration of Cu into SS. As you want to avoid penetration of Fe into brazement, you may have to optimize the time for brazing (use lesser time). Even the thickness of palladium, braze gap and temperature will matter. 

I have found the answer

in http://iopscience.iop.org/0022-3727/37/16/001

InsyAllah I will explain in detail soon.

InsyAllah I will explain in detail soon.

First of all I seek a clarification. The approximate solution is said to become erroneous when the concentrated mass increases. In that case the condition should be M/m > 5 and not m/M >5.

According to Aleksandar his approximate dynamic analysis of an Euler-Bernoulli beam becomes erroneous when M/m > 5 (if my correction is accepted) where m = beam mass and M = tip mass. The exact solution to this problem is known and it is based on a linear elastic beam response. In that case the error in his approximate method is not due to violation of the linear elastic assumption when M/m > 5. All the same it will be interesting to answer Aleksandar's question on the limiting deflection of a cantilever beam beyond which the beam responds inelastically (violates small deflection assumption).

The tip deflection of a cantilever beam of self weight w loaded by a tip weight W is given by Δ = (W/3+w/8)*L^3/EI--- (1) The slope at the tip is given by . θ = (W/2+w/6)*L^2/EI ----- (2) The maximum bending moment occurs at the base of the cantilever and is given by M_B = L* (W+.5w) ----(3) It is at the base that a uniform beam will begin to behave inelastically and subsequently plastically. Let the limiting linear elastic stress that can be sustained by the beam be σ_y and the section modulus of the beam be Z, then at the limit of linear elasticity L* (W+.5w) = Z*σ_y ----(4) Then the ratio of the tip mass to beam mass at the limit of small deformation is given by M/m = W/w = Z*σ_y/(wL) - 0.5.                                               By substituting the expression for W into Eqs (1) and (2) the limiting deflection and slope can be computed. A hypothetical example shall now be considered. What is the M/m ratio for a 2 metre long 100 by 100 mm concrete beam to violate small deformation if σ_y = (2/3)*20 N/mm^2?. Solution: Assuming unit weight of concrete to be 24 KN/m^3 then w = 24*.1*.1*2 = 0.48KN, Z = bh^2/6 = 10^6/6 mm^3. Using consistent units M/m can be computed to be M/m = 1.81. As M/m increases beyond 1.81 the beam response deviates more and more from the linear elastic beam theory. The calculated limiting M/m ratio would have been much lower for a longer beam. However, I am suggesting that the discrepancy observed by Aleksandar is not due to nonlinear effects because the exact solution for the problem is based on linear elasticity. I do not know of an exact closed-form formula for beam vibration based on nonlinearity. In conclusion, the violation of small deformation restriction is not likely to be the problem. Aleksandar should please check carefully the theory behind his approximate method to discover some hidden errors. In addition, possible numerical instability in the solution scheme should be investigated.

I familiar with 0.8% C , 2% Cr  and 0.4% Mo steel and I have conducted a lot of research about it. If you think my information about this steel is useful, do not hesitate to inform me. 

I still have some confusions about the differences of characteristic defect frequencies (CDF) in a spherical roller bearing and a deep groove ball bearing. The enclosed word file is the way to calculate the CDFs of a deep groove ball bearing. However, how can we calculate the CDFs of a spherical roller bearing? Could you give some help or advice?

I'm assuming, since your application is deep drawing, that you are having difficulty measuring elongation in the weld due to strain localization and the narrow weld zone. There have been many articles on the use of photogrammetry techniques to measure strain in the various zones of a weld. I would suggest looking at this technique.

Mention the range of parameters in your machine and electrode material and cutting conditions(Flushing type) 

I hope that the following thesis/articles may help you:

Use an EDM wire to cut out a 300 micron groove to the central axis of a rod of suitable diameter. The better if you can get a 250 micron EDM wire! Now insert your 250 micron wire into the groove & solder at the exit end. Then mount the rod-wire assembly onto your chuck. The wire should now rotate without any fuss!

Apart from brazing, adhesives for bonding metals may also be an option ... (one of the advantages being that they do not cause distortion, discoloration, or weld worms that may require secondary operations such as grinding or painting). Fins and parental part should appropriately be configured for this.

Though the best PATENT awailable is :

Grade M-343,

Yet a methed to produce Antimony impregnated carbon graphite mechanical seals is outlined here. The word “ OUTLINED” is intentionally used because the exact conditions/ composition of the constituents is a trade secret.

Compositions:

Mechanical carbons contain graphite with self-lubricating characteristics. To make mechanical carbons, fine graphite particles are bonded with a hard,strong, amorphous carbon binder to produce a mechanical carbon material that is called carbon~graphite.

Further, the heat treating causes the amorphous-carbon binder to become graphitized resulting in a material known as electrographite.The electrographite is generally softer and weaker than the carbon-graphite material but has superior chemical resistance, oxidation resistance and thermal conductivity compared to the carbon-graphite

Impregnation:

Both carbon-graphite and electrographite are normally produced so that they contain approximately 159 mess porosity by volume. To produce mechanical carbon grades with enhanced properties, the porosity in the carbon-graphite and electrographite materials can be impregnated — by vacuum or pressure processes,with thermal setting resins, metals or inorganic salts as explained below:

Resins:

The most common thermal setting resins used are phenolic poly-ester, epoxy and torso resins. Resin impregnation produces materials that are impermeable (to 100 psi air) and have improved lubricating characteristics.

Metals:

The most common metal impregnations are babbitt (an alloy of' tin,

antimony and copper ) ,copper, ANTIMONY ,bronze,nickel~chrome and silver. Metal impregnation produces materials that are harder stronger and impermeableI to 100 psi air with improved lubri cating qualities and better thermal and electrical conductivity.

Inorganic salts:

The inorganic salt impregnations are formulations that provide improved lubricating qualities. These salt impregnated materials also exhibit improved lubricating qualities

Ask directly support at www.dynamore.de/

they are providing very professional support

;) ;) ;)

Which kind of oxygen mask do you develop : for fighter aircrafts ? safety oxygen mask in commercial flights ?

The austenitic stainless steel grades (the 300 series) are more difficult to machine that the ferritic and martensitic stainless steel grade families. Austenitic stainless steels are more highly alloyed and more prone to higher work-hardening rates. This leads to the need for higher horsepower and more rigid setup. Milling of stainless steel involve generally high cutting forces and powerful machines are necessary. As for turning, it is recommended to use coated carbide tools or inserts. For carbide end milling tools, cutting speeds between 90 and 200 m/min are possible for free-machining grades (like X8CrNiS18-9/1.4305 – AISI 304 grade with high sulphur content) and between 50 and 150 m/min for regular materials (like 1.4301 – AISI 304). Feed rates vary between 0.012 and 0.125 mm/rev/tooth, depending on the cutter diameter. For face milling equipped with carbide inserts, cutting speeds range from 80 to 400 m/min for free-machining grades and from about 50 to 300 m/min for standard alloys. Feed rates are between 0.05 and 0.20 mm/rev/tooth.

Machining setup recommendation for turning austenitic stainless steel AISI 304, depth of cut, in: 0.3;

- High-speed steel tool: speed (fpm): 60, feed (irp): 0.020, tool material AISI M2 and M3

- Coated tool: speed (fpm): 325, feed (irp): 0.020, tool material CC-2

References:

1. Michael McGuire, Stainless Steels for Design Engineers, ASM International 2008

2. P.J. Cunat, Working with stainless steel, Euro-Inox, 1998

Which equation set?

A thesis (Masters or Ph.D) should be work of investigative nature involving analytical/ experimental tools. A very popular tool for the analysis of rolling (or metal forming in general) is FEA and Altan's work (referred above) could be a good starting point. There are a number of recent publications on the topic. Regarding experimental work, it should be controlled experiments on dedicated equipments (in industry or laboratory). One may not attempt both the approaches in single thesis. The starting point for obtaining the broad idea of the problems involved (so as to choose one for investigation) could be the books referred by Posinasetti.

Stresses have been measured in various amorphous materials using relaxation methods. See the attached Researchgate link for an example suing the slitting (crack compliance) method on bulk metallic glass. You could also do layer removal, see for example in silicate glass DOI: 10.1126/science.283.5406.1295, or other relaxation methods like hole drilling if you can drill a hole. You asked about amorphous materials in general, for actual glass, photoelasticity/birefringence is commonly used.

I did some measurement work with steel shots (round and sharp), brass chips and sand on wheel blasting machine. From my point of view the minimum diameter of steel particles is approx. 0.5 mm. The wheel blades are not very smooth and the acceleration of smaller spheres is poor. Sharp shots accelerate even worse. Glass particles are used in pneumatic driven devices for cleaning of hardly reachable spots. From my point of view glass particles might be used in wheel machines instead of sand, but their field of use is limited to soft material (aluminum) and mostly for making surface less light reflecting.

I am using Electrochemical discharge machining, as part of my research work for channels and holes with its characterization. So I cannot change the machining process.

What is the question here?

It is straightforward to show that the slip systems you mention exist, simply by considering the number of possible permutations of the indices. For the {110}<1-11> systems, for example:

(110)[1-10] (101)[10-1] (011)[01-1]

(110)[-110] (101)[-101] (011)[0-11]

(1-10)[110] (10-1)[101] (01-1)[011]

(1-10)[-1-10] (10-1)[-10-1] (01-1)[0-1-1]

Note that six of these are simply the other six running in the reverse direction. Whether you consider there to be twelve {110}<1-11> systems or six is a matter of convention.

(Note also that while these systems may be physically distinct, only five of them can be truly independent. For proof of this statement, see Kelly & Knowles, 'Crystallography and Crystal Defects'.)

If you are asking whether all 48 systems can be activated in any given bcc material, that is a very different question. It can only be answered by looking for papers on the material in question.

I agree with Amin Ezazi, Kevlar has good strength to weight ratio. It is good in low temperatures. Kevlar fabric has wide applications where strength to weight ratio plays major role. Example: Kevlar finds importance in aviation industries as it is good impact resistant and in tailored composites with directional properties.

Strain to failure gives the measure of how much the specimen is elongated to failure. By this it means that, it you have strain to failure of 3% measured in specimen of length 100 mm, the material will fail when it it elongated 3 mm, as experimented in tensile test. Therefore, for a material with higher strain to failure rate, the ductility is higher and tensile strength is lower.

here is an article about tool wear, I hope that it help you;

A-TIG stands for Activated Flux TIG welding. ATIG process can be used for titanium, steel and stainless steel. I have developed activated flux for TIG welding of titanium. Using this flux I am able to weld 6 mm thick Ti plate in a single pass using square-butt joint geometry. The weld joints passed in radiography and qualified as per ASME section IX requirement. you can see my publish paper in the following link: http://link.springer.com/article/10.1007/s40194-013-0084-9

(a) Cast products have greater flexibility in design of geometry so they can take up less volume, hence lighter. For example investment casting can create intricate internal features, weight-saving regions, and even interconnected internal macroscopic voids, that are simply not possible to create with machining processes that are driven from the outside.

(b) Cast products may be foamed, as part of the casting process. This is established technology for plastic injection molding, and involves a blowing agent. Cast metal foams also exist, some also using a blowing agent (there are other production methods too), though this is still an area under development.

(c) Some cast products suffer from porosity. For example cast aluminium can have a tendency to form internal hydrogen bubbles (which can be visible to the naked eye), and consequent hydrogen embrittlement. This is usually considered a quality defect, rather than a design feature. The location at which the porosity is most likely to appear can be predicted by casting simulation software, so I suppose someone will eventually use that in a deliberate way!

(d) Differences in density of crystalline microstructure between cast and wrought products are not usually significant at the macroscopic level. Having said that, different material grades (i.e. composition) are often used for cast vs. wrought materials, so you are not always comparing things that are exactly the same.

Short answer is yes. The best process would be to use Stereolithography with one of the optically clear resins. The Objet technology is also a possible but it may be that you will have more difficulty because of the post-processing required. However, the main issue would be to match the refraction index to the lens angle, which may take a little experimentation. have seen car light cluster covers, which use Fresnel lenses, made using these materials.

How to remove is difficult to answer: maybe freezing down or heating up the sample? But, all the effects of grit-blasting will disappear and it should be repeated. I would try to change the grit and take harder material having greater particles. Or consider other methods of surface preparation such as waterjet.

The track magnets used in maglev systems are electromagnetic coils, so no ferromagnetic material is needed.

Most train magnets are also electromagnets, often using liquid nitrogen-cooled superconductors to lower the energy required to create such large fields (and hence currents). Some newer trains do use permanent magnets, usually a neodymium-iron-boron alloy, but it is only recently that permanent magnets have been arranged into sufficiently powerful arrays, called Halbach arrays.