chongo@nsc.UUCP (Landon C. Noll) (08/27/84)
the other day while in a boat on Ceater Lake with some 1900 feet of water between me and the bottom, i began to wonder what the bottom looked like. so in my mind i constructed a probe with a camera on it to float down to the bottom and explore. but one problem got to me, how was i to pass control signals to the probe, and how was the probe to send pictures back? connecting a L O N G wires to the probe was not the answer i wanted. (i wanted to control the probe from the rim, so a 7 mile wire is the wrong choice) i have heard that radio waves have a hard time passing through large distances of water. is this true? what about other forms of electromagnetic rad? from what i can tell, visable light does not go more than 300 feet. what about micro-wave? etc? note that i am talking about high bandwidth transmission. sonor may not cut it. any ideas? any values on distances would be helpful. does salt water make it worse? chongo <> /\../\ -- 2 is the greatest odd prime because it is the least even prime. Dan Romulus Jurca Cal State Hayward
ron@brl-tgr.ARPA (Ron Natalie <ron>) (08/28/84)
I don't know, but if it floats, it seems like you are going to have a hard time getting it to the bottom. -Ron
dnc@dartvax.UUCP (David Crespo) (09/02/84)
2 is also the greatest even prime, (and the only one I know of). The only
thing it is not, is the greatest odd prime, and though I have that
somewhere in my notes, it would take too long to write it out.
(Fermat rules)
a question for the mathematical: in what manner is there no equivalent
for primeness in non-integral numbers (reals, transcendents, quaternions)?
i know the answer has to do with integral domains...how?
(if this question belongs alsewhere, guide!)
also: i am infinitely curious about : what is a lagrangian (related to
a hamiltonian, an operator for enegy in generalized coordinates, right?)
nd how does it relate to feynman diagrams, and then, sire, answer the
question about +-i at interaction. (see above)
as to passing info through water, it ain't gonna be easy. any form
of electromagnetic information will get dispersed (or is it attenuated,
i think it is attenuation...the signal will be absorbed, high frequency,
....energy will be lost, you'll never get a clear signal...but seven
mile long cables might not be that unusual in oil-digging application...
maybe if you convince someone there's oil on the floor...good luck.
damn near curious, i'll say
References: <1366@nsc.UUCP>Shinbrot.WBST@XEROX.ARPA (09/06/84)
Well, I'm no expert on transmission through water, but since nobody else has addressed the question, I'll have a go. Water severely attenuates all but extremely low frequencies (ELF). As a result, submarines have to surface to get information - a considerable hazard in military environs, obviously. The US Navy has attempted to resolve this issue by proposing an ELF transmitting station in the continental US. Almost by default, they decided upon Michigan as a likely broadcasting station. You may have heard in popular or scientific press the controversy surrounding ELF there, for ELF is reported to cause a variety of health problems. IN any case, the crux of the biscuit is that ELF can be transmitted through water where little else except neutrinos can pass. ELF obviously requires a correspondingly extremely large broadcasting antenna (c = f(lambda)). The curious thing to me in all of this is how the pentagon envisages receiving these waves. Perhaps making extremely long submarines??? - Troy
matt@UCLA-LOCUS.ARPA (09/07/84)
From: Matthew J Weinstein <matt@UCLA-LOCUS.ARPA>
A while back there was an article (in Aviation Leak?) that
mentioned development work on a sub-sub/ship-sub communication
system, which was to exploit a small range of (light) frequencies
in which seawater exhibits low attenuation.
Anyone have references?
- Matt
-------
UUCP: {ucbvax,ihnp4}!ucla-cs!locus.matt
ARPA: matt@ucla-locusjayl@athena.UUCP (Jay Lessert) (09/07/84)
> From: Shinbrot.WBST@XEROX.ARPA > IN any case, the crux of the biscuit is that ELF can be transmitted > through water where little else except neutrinos can pass. ELF > obviously requires a correspondingly extremely large broadcasting > antenna (c = f(lambda)). The curious thing to me in all of this is how > the pentagon envisages receiving these waves. Perhaps making extremely > long submarines??? > No problem. Try trailing a long wire. -- Jay Lessert - Tektronix Inc., Logic Design Systems Division uucp: {ucbvax,decvax,pur-ee,cbosg,ihnss}!tektronix!teklds!jayl CSnet: jayl@tek ARPAnet:jayl.tek@rand-relay
gwyn@Brl-Vld.ARPA (09/07/84)
From: Doug Gwyn (VLD/VMB) <gwyn@Brl-Vld.ARPA> The real problem with ELF is its extremely low information bandwidth. Receiving it is not a problem.
dnc%dartmouth.csnet@csnet-relay.arpa (09/09/84)
From: David Crespo <dnc%dartmouth.csnet@csnet-relay.arpa>
troy:
thank you for the transmission.
low freq -> high wavelength -> large receiver.
in space, the problem is not present, so they propose
using high freq (microwave) signals to send information.
those antennae are still big (100 ft diam???) and
i assume they would have to be even bigger to take into
account both the index of refraction of the medium
(elf i think would travel at c/n = f (lambda)) and
the attenuation (which i don't know how it works,
physically, though it has to do with energy lost, entropy,
diffraction around objects(?)(might be a small
significant problem since object smaller than
the wavelength. this, i assume, would call
for a quantum mechanical description),
and any other couplings applicable.
(is hte above correct?)
(no, ...)
but, i assume they are not trying to transmit
sound, but e-m. yes. they must. i thought of
wondering if they could proceed by analogy to
sea animals, if any of them communicate over
such long distances?
what about telescoping antennae on a sub? dnc%dartmouth.csnet@csnet-relay.arpa (09/09/84)
From: David Crespo <dnc%dartmouth.csnet@csnet-relay.arpa>
john:
thank you for the reply.
the original question, if i am not mistaken, was about
a propagator term in a lagrangian and why it had to be
sqr(-1)(=i), or have i as a factor. After looking at
Lurie Particles and Fields (i.e. by Lurie) which has
an advanced formulation of Hamiltonians, Lagrangians,
and Noether's Thm., as well of Feynman Diagrams and
propogators, and a large number of pages in between,
i am grateful for your lucid and brief answer.
if there were a last prime, it would be less than
the product of "all" the primes + 1, which must be a
prime.
you answer raises a question about whether there are
any of these more complex rings with finite/infinite
number of primes. must they all be well ordered (have
>,<,= defined (is this a part of being a ring?) )
(a friend of mine told me that in z[sqr(5)] the number
nine has two prime factorizations (!!!) but i got a
little lost when he tried to explain z[sqr(5)]...
or maybe it was 8? now, THAT's weird! no, i think it was 14
into ...9 into 14+sqr(5) x 14-sqr(5), where each of htese is
prime in z[r5].
of course i don't expect you to have the answer to these
questions, but i am going to
get an algebra book (MacLaine and Birkhoff?) and find out.
(if it's been found out) Also the mechanics book.
again, gracias for the clues, onward ho.
dnc @ dartmouth
gino@voder.UUCP (Gino Bloch) (09/11/84)
<l_o_n_g w_a_v_e_l_e_n_g_t_h s_n_a_c_k> re-Re: wavelength vs size of antenna My AM radio is about 1/3000 the size of the wavelengths that it receives. -- Gene E. Bloch (...!nsc!voder!gino)
scw@cepu.UUCP (Stephen C. Woods) (09/12/84)
*<- kills bugs dead
I recall reading an autobiography of a WWII submariner that discribed
what happened when they took their boat into the Great Lakes for some training.
In addition to having to remove a great wopping chunk of iron ballast from the
boat, they discovered that they were able to communicate by radio just as well
submerged as they could on the surface. Now the I'm not sure just what
frequency band was used for W/T communications durring WWII but at least it
shows that some communication is possiable via radio from under fresh water.
--
Stephen C. Woods (VA Wadsworth Med Ctr./UCLA Dept. of Neurology)
uucp: { {ihnp4, uiucdcs}!bradley, hao, trwrb, sdcrdcf}!cepu!scw
ARPA: cepu!scw@ucla-cs location: N 34 3' 9.1" W 118 27' 4.3"jerry@oliveb.UUCP (Jerry Aguirre) (09/15/84)
I don't remember all the details but I did one read an article about a way of transmitting signals thru water. The diagram was something like this: ------ | | | XMTR | ----------------------| |-------------------------- | ------ | | | ////////|////////////////////////////////////////////////////////|//// | | ------- ------- | | | | | Metal | Water | Metal | | Plate | | Plate | | | | | ------- ------- ---- ---- | | ---- | | | |-|RCVR|-| | | | ---- | | ---- ---- Transmission range is restricted to the general area between the two plates. Go to deep or to far off to the side and you lose the signal. Still, plates on either end of a lake or section of river would give you total coverage of the area. The transmission should be low frequency, probably in the 1 to 500 Khz. range. I don't think the effect can properly be considered radio. I think that it depends on the conductivity of the water to transmit the signal. The receiver just intercepts the current flowing thru the water. This results in the signal only being available between the tranmission plates. For your application this would still require long wires to reach both ends of the lake but does result in a "free" probe. It does not address the problem of how to get pictures back from the probe. I think that if it was possible to have a wireless underwater probe then someone would have done it. As other netr's have pointed out there is a lot of effort going into communicating with underwater subs and drone probes of the type you suggest. Every one I have heard of either used a tether (fiber optic is the latest) or took photographs for later recovery. It is probably possible to sent pictures via sonar but not very quickly. Ham radio operators send slow-scan pictures but at 14 seconds a frame you might have trouble dodging the cliffs. Ah, if someone would only invent a nutrino transmitter and receiver. Jerry Aguirre {hplabs|fortune|idi|ihnp4|ios|tolerant|allegra|tymix}!oliveb!jerry