What is Focus: Definition and 201 Discussions

FOCUS is a fourth-generation programming language (4GL) computer programming language and development environment that is used to build database queries. Produced by Information Builders Inc., it was originally developed for data handling and analysis on the IBM mainframe. Subsequently versions for minicomputers and such as the VAX and other platforms were implemented. FOCUS was later extended to personal computers and (in 1997) to the World Wide Web: the WebFOCUS product.

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  1. G

    Ptolemy's Theory of the Empty Focus of an Elliptical Orbit

    An ellipse has two foci. For a planet in such an orbit, the star is at one of the foci. The other is empty. According to Ptolemy, if we draw a line connecting the planet and the empty focus, we will find that the line moves at a constant angular velocity. Is this true, or is it a crude...
  2. A

    Just how broad is a focus in signal processing?

    I see a lot of electrical engineering graduate programs that offer concentrations in signal processing (analog or digital or both). I understand signal processing is used virtually everywhere, but how does one break into a particular industry with a concentration in signal processing? Can you...
  3. astrololo

    Finding the focus points of a hyperbola

    Homework Statement So I have the following hyperbola x^2/4 - y^2/4 = -1 I need to find the focus points of this hyperbola. What is some analytical way to do this ? Thank yoU! Homework Equations I don't know... The Attempt at a Solution I need some analytical way to be able to do this. Can...
  4. Earnest Guest

    A Why should the Bullet Cluster focus light?

    In the Bullet Cluster, we have two well defined galaxy clusters that exhibit gravity lensing. Between them is a mass of gas (mostly hydrogen and helium) that is roughly eight to nine times the stellar (observable) mass of the two galaxies. The mass of gas doesn't exhibit any lensing. My question...
  5. H

    Which [Aerospace] subject should I focus on to study for the future?

    Hello everybody, I've registered to the forum to ask for some guidence and this is my first message in the forum so, yeah! Recently, I've earned a government scholarship to study Aerospace and Aircraft Engineering at M.Sc. and Ph.D. level abroad (preferably UK, decided by the Ministry). I have...
  6. R

    Physics Shall I just focus on getting a good job?

    I often wonder people's life in developed countries, not for the recreational activities or big houses, but that the people there are encouraged to pursue what they want and to turn their individual dreams into reality. I have long been fascinated by physics, and maths, and have been dreaming...
  7. G

    Optics - focused vs. defocused image

    Hello, (I am new here, so hopefully this is the right location to ask my question. please let me know if there is more relevant forum) I am trying to understand 2 situations: A) I have an object, lens and a detector. The detector is at the focal plane of the lens. I am reducing the aperture...
  8. R

    Harness Sea Wave Energy: Focus Waves w/ Diffraction & Floating Breakwaters

    Would it be possible to use diffraction to focus the enrgy of sea waves, on the principle of the zone plate (https://en.wikipedia.org/wiki/Zone_plate) but reduced to 2 dimensions? This could be done by an array of wave-opaque objects such as floating breakwaters, particularly along coasts...
  9. 2

    What subjects to focus on as an EE interested in Aerospace?

    Hello, I am currently pursuing my BS in EE. I am interested in avionics and would like to eventually work in the aerospace industry. What sort of topics should I focus on? I did an initial search on the forums and people have noted that these subjects are relevant: - Control Systems -...
  10. Shinwasha

    Find distance of focus point (conceptual)

    Homework Statement A lens has a radius of curvature of magnitude R on its left surface and a radius of curvature of magnitude 2R on its right surface. Parallel rays entering the lens from the left are focused to a point 135mm to the right of the right surface. At what distance from the lens is...
  11. T

    What focal length is needed for a 0.60x magnification with a diverging lens?

    Homework Statement What focus is needed for in order for a diverging lens to produce a magnification of 0.60x on an object located 1.40 meters away? Homework Equations M=hi/ho 1/do + 1/di = 1/f M= -di/do The Attempt at a Solution -di / 1.4 = 0.6 1/1.4 + 1/.84 =1/f -di=0.84 1.42
  12. Loop

    What Are Some Tips for Choosing a Focus in Physics Research?

    So, I am an undergraduate physics student and I need a little help/advice on deciding a focus to move forward into and eventually do research in. The reason that I have a difficult time deciding is that I am fascinated with nearly every aspect of physics from quantum mechanics to astrophysics. I...
  13. Prashasti

    Finding Focus Length in Broken Double Convex Lens

    Homework Statement A thin double convex lens of focal length f is broken down into two halves at the axis. The two haves are then combined, as shown in the figure. What will be the focal length for the arrangements...
  14. Salah_Abdulla

    What to do to focus on design field of refrigeration?

    I'm graduated in mechanical engineering. I would like to do MS on Refrigeration from USA. Then I would like to focus on design fields. But currently I'm working in the field of steel structure erection. Hope your suggestions and advices to change career.
  15. S

    The ratio of the distance of the focus and the point

    1. The problem statement: A ray of light is incident on a concave mirror. It is parallel to the principle axis and its height from principle axis is equal to the focal length of the mirror. the ratio of the distance of point B to the distance of the focus from the center of curvature is( AB is...
  16. R

    Exploring Focus Point in Optics

    What happens if we keep the object at focus point of any lens system( like convex lens ,Plano convex lens etc) ? Does image forms at infinity? What is exact definition of focus point in optics?
  17. M

    What kinds of nuclear physics should I focus?

    Hey everyone. I'm looking to study nuclear physics and want to look into new forms of every. So fusion would be cool but probibly new forms of fission or even using waste to make energy. But I don't know what I want to get into. Any dirrational help would be cool. Thanks!
  18. M

    Advice for an Undergraduate Physics major looking for focus

    I am a sophmore physics major, and I'm trying to decide on a concentration. I'm very interested in psychology, and am trying to find a way to combine the two, but I doubt that with the time remaining that I could even minor in bio or psychology in the time remaining to me. If I wish to pursue...
  19. G

    How do cameras focus on reflected images?

    I can remember from my distant school physics days that the image in a mirror lies beyond the mirror. But how does a modern camera sensor "know" this. If I face a mirror with my canon camera which has a cmos sensor and usm lens, it autofocuses correctly on the part of the reflection I select...
  20. X

    Math REU with focus on topology/analysis

    I have been looking through the AMS and NSF websites for REUs. And I have found some in particular that I am interested in(UChicago, Cornell, SMALL, MAPS-REU), but it seems these are the only ones that have projects that deal with topology/analysis. Do any of you have any suggestions for REUs...
  21. S

    MHB Find the equation of parabola with vertex (2, 1) and focus (1, -1)

    Hello friends. This is my first post. I am given the following problem: Find the equation of parabola with vertex (2, 1) and focus (1, -1) I have tried to solve this question in this way: Since vertex is mid point of Focus and the point which touches the Directrix. From this, I calculate that...
  22. AdityaDev

    Can a Convex Lens Converge a Tilted Wavefront?

    If I have a parallel beam of light parallel to x-axis, with the speed of light varying from bottom to top. Let it decrease from bottom to top. (To get such a beam one can pass the beam through a glass slab normal to its surface, whose refractive index increases linearly from bottom to top). Now...
  23. K

    Textbooks with a focus on how things were discovered?

    maybe I'm looking in all the wrong places or its too much detail for one text. all the books i find just give an overview of this without going into detail. I'm teaching myself maths, physics, chemistry and molecular biology, and I'm trying to understand the fundamental concepts (ive learned...
  24. M

    How does the power of a lens affect its ability to focus light?

    So I've been doing some experiments, using bottles filled with various liquids and timing how long they take to burn paper which is placed at the focal point (where the light was focused). I've noticed that using denser liquids with high refractive indexes lower the focal length, and thus...
  25. E

    Engineering Job Positions for US Engineering Job Market for VLSI Design Focus Grad

    I have no clue about the engineering job market as I'm in IT, he's looking for guidance. What kind of job positions would he be eligible for in US and which state(s) is the best for this field? I have attached the undergrad curriculum. He did his Masters with VLSI design focus. His Masters...
  26. A

    How do i calculate this -- Using numerous parabolic mirrors to focus light

    So for my semester project, I was given something that most scientists think is "impossible". Using numerous parabolic mirrors, i need to focus the reflected light onto a mutual point, and achieve a temperature of about 3000*C. Why 3000? That is when thermal decomposition of H2O occurs. What i...
  27. R

    (help) physician wants to focus on quantum biology

    Dear members of this forum. My name is Roberto, I am a medical doctor who wants to study and focus on quantum biology. I have this idea that the cure for a lot of diseases, specially cancer may be in the atomic level. I am very passionate about physicis and I would like to match the best...
  28. L

    Optics: how to make eye focus in distance?

    Hello! I have a theoretical & practical question. Theorecical: I noticed that when I turn on my smart phone camera application and look 'through it' on some distant object, holding smart phone 30 cm from my eyes, then my eyes are focused on 30 cm and not in distance. Is there a way...
  29. Warpspeed13

    Plasmoid Contamination in a Dense Plasma Focus

    Ok I'm posting this here as well since It falls under both engineering and high energy physics, since I haven't gotten an answer on the high energy physics thread. So I've been researching Dense Plasma Focus devices for a while now and a question just occurred to me. Since the fill gass such as...
  30. Warpspeed13

    Plasmoid contamination in a Dense Plasma Focus

    So I've been researching Dense Plasma Focus devices for a while now and a question just occurred to me. Since the fill gass such as deuterium is being ionized and then compressed and fused in the Plasmoid, wouldn't some of the cathode material also be ionized and the trapped in the Plasmoid...
  31. adjacent

    Proof: Parabola reflects light to the focus

    Homework Statement The title.Homework Equations ##y=mx+c## $$\frac{dy}{dx}(kx^2)=2kx$$ The Attempt at a Solution https://www.physicsforums.com/attachment.php?attachmentid=69745&stc=1&d=1399976415 I have proved that the angle of reflection will be a° since the angle of incidence=a° The picture...
  32. M

    Why does a positive lens focus two images at different lengths?

    Missed this part of the lab and I need to complete my lab write up. We have a light source at one end of a track, and at the other end a screen. there is a positive lens in between them. When we set the screen at a distance away from the light source, let's say one meter, and slide the lens...
  33. Saitama

    MHB Finding focus, given four tangents

    Problem: Find the coordinates of focus of a parabola which $x=0, y=0, x+y=1$ and $y=x-2$. Attempt: I noticed that the we are given two pairs of perpendicular tangents. Since perpendicular tangents intersect at directrix, the equation of directrix is $y=-x/3$. I am clueless about the next...
  34. Spinnor

    Approximate cost auto focus reading glasses?

    Take an 80 dollar pair of adjustable focus glasses, http://www.ebay.com/itm/ADLENS-HEMISPHERE-Adjustable-Reading-Glasses-Plastic-Round-Eyeglass-Frame-Gray-/310892439221?_trksid=p2054897.l4275 and use range finding hardware from a camera, add micro servos to control focus, add a computer to run...
  35. Spinnor

    Neutrino beam passes through optics lens, focus the neutrinos?

    If a neutrino beam passes through an optics lens in principle does the matter in the lens focus the neutrino beam granted it may be ridiculously small amount? If the lens were instead made of compressed matter of nuclear densities would the answer change much? Thanks for any help!
  36. MarkFL

    MHB Find Equation of Parabola Given Focus & Directrix - Jose's Q&A

    Here is the question: I have posted a link there to this thread so the OP can view my work.
  37. Saitama

    MHB Finding focus, given two tangents

    Problem: Let focus of parabola is $S(x,y)$ which touches the x-axis and $y=x$ at $(1,0)$ and $(1,1)$ respectively, then find the focus of parabola. Attempt: Honestly, I am lost on this. I don't know how to make use of the given information to find the focus. I need a few hints to start with...
  38. Ascendant78

    Programs What to focus on in calculus (as a physics major)?

    I just finished up calc II this semester. So far, seems fairly easy and I got an A no problem. However, there was a lot of material in each of the chapters that we didn't cover as well as more difficult problems in the sections that we didn't work on. Our professor told us it really isn't...
  39. MarkFL

    MHB Find Parabola Given Focus & Directrix - Help Needed

    Here is the question: I have posted a link there to this topic so the OP can see my work.
  40. S

    Diverging lens problem -image should be between focus & optical centre

    Homework Statement Problem: An object 2.0 cm high is placed in front of a diverging lens of focal length 1.8 cm. The object is 2.7 cm from the optical centre of the lens. Questions: 1) Where is the image located with respect to the focus and the optical centre of the lens, qualitatively? 2)...
  41. S

    Cno cycle dense plasma focus fusion

    hello, new to site. This is my first post. I just was wondering what any ones thoughts were on using the carbon, nitrogen, oxygen cycle in a dense plasma focus device to produce aneutronic fusion power.
  42. Spinnor

    Can matter focus neutrinos in a supernova event?

    The initial flux of neutrinos from a supernova is mostly radial (say we are far from where they are produced but also far below the top of the dying star)? As the neutrinos help blow the top off the star do the density variations of the outer portions of the star act like a variable index of...
  43. S

    Problems with dense plasma focus

    Is here some people who knows something about dense plasma focus fusion technology? I`m interested to know how main problems of the technology are supposed to be solved. For example: 1) if it is assumed that pinching device supposed to be surrounded with ambient deuterium gas,then how heating...
  44. S

    Why can't the focus of a plane mirror be virtual like in a concave mirror?

    I read somewhere that the focus of a plane mirror is at infinity because rays after reflection from a plane mirror don't intersect anywhere. But why can't the focus be virtual as in case of concave mirror ?
  45. T

    Considering a PhD in EE: Mechanical or Electrical Engineering Focus?

    Just finished with my B.S.M.E. and now my M.S.M.E. and have been considering a Ph.D. in Electrical Engineering. I've been offered research opportunities in both the mechanical and electrical engineering departments, so really it's up to me to decide. Can anyone put an industry spin on what I...
  46. S

    MHB Reflecting Ray from Concave Mirror: Parabola Focus

    A ray of light is coming along the line $y=b$,($b>0$), from the positive direction of the x-axis and strikes a concave mirror whose intersection with the $x-y$ plane is the parabola $y^2 = 4ax$,($a>0$). Find the equation of the reflected ray and show that it passes through the focus of the parabola.
  47. W

    Focus of studies for spacecraft

    So, being intensely interested in space in general and more specifically in the possibilities of travel through it, I would like to ask about possible locations and courses of study to get into the engineering and design aspects of space travel. I'm especially interested in the propulsion and...
  48. T

    What should I focus on to get admitted to a good masters program?

    Hi, I'm fresh out of high school, studying physics on Charles University in Prague. It's not a bad school, but my ambitions are bigger. I'd like to continue with my master's or phd degree somewhere like ETH Zurich (I've read about the excellence scholarship - covers tution and living costs) or...
  49. D

    What Masters Degree Should I Pursue to Achieve My Career Goals?

    Hello all! Not new to the forums but new to post. I recently received my B.S. in Applied Physics with a minor in Math and Comp Sci and have entered the work force with a great company, but I don't want to stop there. I want to further my education and lucky for me my company pays for roughly...
  50. H

    MHB Equation of ellipse from directrix and focus

    I'm trying to find the polar equation first, and I learned this today but I forgot a lot of it and we're not allowed to take notes in class (professor says it helps to learn better) so I'm trying to look it up online but it's not much help because I can't find any elementary lessons on polar...
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