For which complex numbers bj , we have b0= \sum_{j=1}^3 bj exp(i vj) for some real vj?

05 June 2015 8,415 0 View

If sin(a sk)/a= sin(b sk)/b for the sequence sk\to infty as k \to infty for some a not equal to b, then a/b is rational and sk=2k pi/b? Is it true?

For particular case b=2a we have sin(2b sk)/(2b)= sin(b sk)/b which yields cos(b sk)=1 or sk=2k pi/b. It is true also if the sequence sk that approaches infinity as k approaches infinity is...

31 December 2013 1,229 4 View

Are there unbounded solutions of (1-cos(x pi))/x-(1-cos(y pi))/y+(1-cos((x-y)pi))/(x-y)=0 but with even integers?

The sequence x=2k y=2n where k and n are natural numbers solves this equation. Is there any other unbounded sequence of solutions?

11 December 2013 3,637 7 View

Quadratic equation (complex coefficients) have roots with equal real parts if and only if discriminant is real, non-positive. What about quartic?

z^2-(2+3i)z+3i-1=0 has discriminant=-1, roots (1+i) and (1+2i) have equal real parts. Find a similar statement for the quartic equation: z^4+az^2+bz+c=0.

10 November 2013 2,425 8 View

2 roots of x^3+6a x+2b=0 where a, b are complex have the equal real parts if a, b are real and discriminant is non-positive. Is it true?

For the quadratic equations with complex coefficients 2 roots have the equal real parts if and only if the discriminant is nonpositive.

07 August 2013 2,957 4 View

e^(z_1)+e^(z_2)=0 if and only if Re(z_1)=Re(z_2) and Im(z_2-z_1)=pi(2n+1), where z_1, z_2 are complex numbers. Is there a similar statement for the sum of 4 exponents e^(z_1)+e^(z_2)+e^(z_3)+e^(z_4)=0 ?

This question is connected with the oscillations of differential equations. Since every solution of the linear equation with constant coefficients is the linear combination of exponents this...

04 May 2013 2,279 51 View

Mobius transformation maps arcs of circles to arcs of circles. Is there similar geometric property for the quotient of quadratic functions?

The quotient of linear functions with complex variable z (Mobius transformation) maps arcs of circles to arcs of circles. Is there similar geometric meaning for the quotient of quadratic functions...

01 January 1970 4,132 3 View

Physics: Why do we describe light by referring to its wavelength, but microwaves and radar pulses by referring to their frequency?

In physics, the description of the properties of light generally refers to its wavelength (nm), while in the range of microwaves and radio waves we refer to the frequency of a signal (e.g. kHz or...

03 March 2021 1,682 3 View

Why are the velocities so high in my Boussinesq approximation Fluent simulation?

Hello, I have a mechanism where air rises due to convective flows. In this simulation, nothing is driving the air except this. I understand that the Boussinesq approximation only works for small...

02 March 2021 4,910 3 View

Why almost every element would be metallized in sufficiently high pressure and low temperature?

(This statement is from wikipedia, BTW). What is so special about metallic bond that is limiting high-P low-T state of a matter (as long as individual atoms exist, not white dwarf of neutron star...

02 March 2021 3,309 2 View

New Journal, "Integrative Psychological and Behavioral Science" -- do you not know, and have you not seen, this done before?

Question to you and THEM, the New Journal, "Integrative Psychological and Behavioral Science" -- do you not know, and have you not seen, this done before? There appears to be a core problem for...

02 March 2021 3,024 2 View

How to add a journal?

I would like to know how to register the journal Flora Montiberica (ISSN 1138-5952 - eISSN 1988-799X) in Research Gate.

02 March 2021 8,156 2 View

Is it possible to remove a preprint posted by a journal which is already rejected?

As we know many journals are posting preprints (DOI) in advance before the peer-review process. However, there is no guarantee that the preprints get published. The journal's reviewers undergo the...

01 March 2021 5,778 2 View

No title

Hi, I have several doubts about one paper (Systematic Literature Review) that was rejected. The main topic is Single-Board Computers in engineering education during the period 2010-2020. The...

01 March 2021 9,015 3 View

How to figure out easily the right journal with the right scope for your paper?

According to my experience most of the selected journals during paper submission are based on journal text matching suggested results from Springer, Elsevier,,,Etc. then the manuscript happened to...

01 March 2021 1,786 3 View

Any research paper call for publication related to management or finance or economics?

It should be standard journal (Indexed)

01 March 2021 8,379 1 View

What is the most reliable source to get Impact factor of journals?

Source to get Impact factor of journals

01 March 2021 6,654 2 View