it.information theory – How does the choice of basis of parity check matrix affect the tanner graph

Given a binary linear block code defined by its parity check matrix $H$, many important characteristics of this code are determined by graph theoretic properties of the Tanner graph $Gamma$ derived from $H$. The girth of $Gamma$ and the distribution of low length cycles greatly affect the BER (bit error rate) performance when the commonly used iterative decoding algorithms are used (belief-propagation,…). We’re free to choose linear combinations of the rows of $H$ as another basis; this doesn’t affect the code (same codewords,…), but how does that affect the Tanner graph and its properties? What (if anything) is invariant under a change of basis?

computer architecture – How does virtual and physical memory affect cache structure?

Working with a question that states:

Consider a hypothetical machine in which physical address space is
of 512 words and virtual address space is of 2048 words. The page 
size is 8 words. What is number of bits used for: Page offset,
Physical Page Number, Virtual Page Number

Since my course uses MIPS, I’m assuming the word size is 4 bytes, so to determine the byte size of each I multiply them by 4 and get: 32, 2048, 8192 respectively.

The total amount of bits used to represent page offset is just those numbers log base 2 so I get 32 bytes which is 5 bits.

I used those 5 bits to determine the page number for physical and virtual memory

physical memory = 2048 = 11 bits - 5 bits = 6 bits
virtual memory = 8192 = 13 bits - 5 bits = 8 bits

I double-checked those by dividing the words in each space by the words in page size and then logging b2 that number as well and it checked out. Does my logic make sense, does this actually double check my work? Is page offset simply the bits needed to represent page size?

Now, let’s assume the cache size is 128 words in total. Directly
mapped with block size of 2 words(8) each. What is the number of
blocks, sets, and ways for the cache?

I immediately knew it was only 1 way because it was a direct mapped cache.
I determined that there were 64 blocks because there were two words per block and 128 words total so simply 128 / 2.
Since it’s directly mapped, I assumed there were 64 sets, one to go with each block.

If cache access and translation need to be done in parallel
How many bits of virtual address are used for byte offset? Which bits?

How many bits of virtual address are used for block offset? Which bits?

How many bits of virtual address are used for index? Which bits?

I assumed 2 byte offsets(at least) for the virtual address because I know that’s a given. Why is that a given?

For block offset I said 1 bit because there are two words per block and the offset is needed to represent them both in the same space.

For index I took my number of sets and found the bits needed to represent it (log base 2 64) and found 6.

Are there any flaws in my logic? Could anyone explain where I went wrong?

I’m confused about what I should be taking into consideration from the first half of the problem for the latter half. How are pages with the physical 6 bits stored when the index is larger than the entire address? How do the two problems relate to each other at all?

Will being blacklisted in the Philippines for overstay affect chances of US F1/F2 Visas, or my future medical career in the US?

I am a foreign medical graduate, who studied Doctor of Medicine in the Philippines with my wife. Upon our graduation, we secured a hospital in the country for our postgraduate internship. However, the immigration liaison officer at the hospital that supposed to extend my visa traveled out of the country. Eventually, my visa had already expired by the time she filed it for extension.

As a result, the immigration fined me huge amount of money for overstaying. However, the hospital refused to take responsibility for my expired visa. Instead, they laid me off in order to secure their operational license. The whole thing lingered until the pandemic started. My wife’s visa also expired during the pandemic.

Now, we want to exit the country on our own, to return to our home country. In processing for our exit from the Philippines, the immigration is charging both of us around  $2,500 as penalties for overstay. We appealed to them that we had no such money. Instead, they advised us to secure CERTIFICATE OF INDIGENCY from Nigerian embassy in the Philippines, stating that we are unable to pay the penalties. Having secured the CERTIFICATE OF INDIGENCY from our embassy, the immigration said that our names will be blacklisted for 10years for overstay, or we pay the penalties.

But my major concern now is that I just secured admission for masters in a US university for Fall 2021. With this, I will be applying for F1 visa and F2 for my wife next month. We plan to take USMLE while in the US, and match into the US medical residency program. But with our names being blacklisted in the Philippines, will it affect our chances of getting student visas at the US embassy? Will it also affect our future plans to practice medicine in the US as medical doctors?

In filling out the online DS-160 forms, what do we answer to the question that says, “Have you ever been removed or deported from any country?” Is blacklisting a form removal or deportation?

One of my friends in the UK advised me to answer NO to the DS-160 question of “Have you ever been removed or deported from any country?” He gave the reason that since I was the person  who opted to exit the country that I should answer NO to the question. But because my friend is not a lawyer, I decided to seek your professional advice.

My concern is: if I answer YES to the DS-160 question with the explanation as INDIGENCY, won’t the consular at the US embassy deny me visa and also doubt my financial capacity for my master’s program in the US, even though I have two sponsors for my US study. Again, if I answer NO to the DS-160 question, will it backfire against my US visa and my future medical career in the US? I am just confused.

Please, kindly use your professional experience to advise us on what to do.

Thank you

WILL BEING BLACKLISTED IN THE PHILIPPINES FOR OVERSTAY AFFECT MY CHANCES OF US F1 & F2 VISAS, OR AFFECT MY FUTURE MEDICAL CAREER IN THE US?

I am a foreign medical graduate, who studied Doctor of Medicine in the Philippines with my wife. Upon our graduation, we secured a hospital in the country for our postgraduate internship. However, the immigration liason officer at the hospital that supposed to extend my visa traveled out of the country. Eventually, my visa had already expired by the time she filed it for extension.

As a result, the immigration fined me huge amount of money for overstaying. However, the hospital refused to take responsibility for my expired visa. Instead, they laid me off in order to secure their operational license. The whole thing lingered until the pandemic started. My wife’s visa also expired during the pandemic.

Now, we want to exit the country on our own, to return to our home country. In processing for our exit from the Philippines, the immigration is charging both of us around  $2,500 as penalties for overstay. We appealed to them that we had no such money. Instead, they advised us to secure CERTIFICATE OF INDIGENCY from Nigerian embassy in the Philippines, stating that we are unable to pay the penalties. Having secured the CERTIFICATE OF INDIGENCY from our embassy, the immigration said that our names will be blacklisted for 10years for overstay, or we pay the penalties.

But my major concern now is that I just secured admission for masters in a US university for Fall 2021. With this, I will be applying for F1 visa and F2 for my wife next month. We plan to take USMLE while in the US, and match into the US medical residency program. But with our names being blacklisted in the Philippines, will it affect our chances of getting student visas at the US embassy? Will it also affect our future plans to practice medicine in the US as medical doctors?

In filling out the online DS-160 forms, what do we answer to the question that says, “Have you ever been removed or deported from any country?” Is blacklisting a form removal or deportation?

One of my friends in the UK advised me to answer NO to the DS-160 question of “Have you ever been removed or deported from any country?” He gave the reason that since I was the person  who opted to exit the country that I should answer NO to the question. But because my friend is not a lawyer, I decided to seek your professional advice.

My concern is: if I answer YES to the DS-160 question with the explanation as INDIGENCY, won’t the consular at the US embassy deny me visa and also doubt my financial capacity for my master’s program in the US, even though I have two sponsors for my US study. Again, if I answer NO to the DS-160 question, will it backfire against my US visa and my future medical career in the US? I am just confused.

Please, kindly use your professional experience to advise us on what to do.

Thank you

Will a refused UK Visa based on false documents affect my Canada application?

The UK and Canada are both part of the “Five Eyes” group and exchange immigration data with each other. That means (as you seem to know already) that you should assume Canada will be aware of your previous UK visa refusal. This information will certainly be taken into account when deciding on any future visa application.

I once applied to UK in the year 2017, the Visa was refused based on false business documents presented. I never new my business documents was fake. The agent in africa who did the business documents did a fake one for me in which the embassy confirmed from the source.

It sounds like you’re saying the false documents were provided by some agent you hired to apply for the UK visa, and you believed they were genuine documents. You don’t say where you are more specifically than Africa, but I’ve certainly heard stories of such dishonest agents before, including from people in various African countries. Explaining about the dishonest agent is unlikely to help your case. Somebody else, who had a refusal after knowingly submitting false documents, could also claim the agent included them without their knowledge. The agents assessing your application (both the UK agents who rejected the past application, and Canadian agents assessing a future application) will assume that you are responsible for all contents of your application.

Nobody here can tell you for certain whether an application will be approved. That decision can only be made by the appropriate authorities on the basis of far more information than would be appropriate to post here. But visa refusals for submitting false documents are taken very seriously. Having such a refusal on your record will severely reduce your chances of being granted a visa. That doesn’t mean it’s completely impossible, but you should consider it very unlikely unless there are very compelling reasons to make an exception in your case. Based on what you’ve told us, it seems unlikely that such reasons exist.

dnd 5e – Does darkvision granted by a magic item affect what a caster can see in a dark location using the Clairvoyance spell?

The description of clairvoyance states:

When you cast the spell, you choose seeing or hearing. You can use the chosen sense through the sensor as if you were in its space.

The wording “as if you were in its space” arguably leaves room for ambiguity.

If a creature with innate darkvision — e.g., an elf — uses the spell to see into a dark location, there is no question that the caster would benefit from that darkvision. If “you,” the elf casting the spell, were physically present in the dark location, you undeniably would have the benefit of your darkvision.

The same logic might not apply, however, to a creature who has darkvision solely by dint of a magic item. If “you,” a human caster wearing goggles of night, were physically present in the dark location, whether you would benefit from darkvision would depend on whether “you” means just you or you and your equipment.

The by-now-familiar wisdom that spells do only what they say they do (and anything more is left up to the DM) seems not to resolve this issue, because it is not clear what the spell is saying it does.

How does darkvision granted by a magic item interact with clairvoyance?

image quality – Lens with small scratches on the front element – how do they affect IQ?

Here are two lenses I got off Ebay – they look pretty nice on images. The Canon 85mm 1.8 does have marks visible to the naked eye on the front element but they are very small. The Helios looked perfect on front and back but on an internal glass there is some dust particles.

Canon 85mm 1.8:

Canon85mm

Helios 44-2 58mm F2:

Helios

[image examples from two lenses I got from ebay]

Here are two shots with them, with wide apertures:

Canon85mm

Canon85mm

Helios

Helios

Confirms that “dust inside” or “scratches in front” doesn’t affect IQ.

But then I noticed spots when stopped down:

I used Helios when taking a macro of a brie and I needed to stop with to F16 to get just a little bit DOF – the black speckles are dust particles:

Dust shows up

But this turned out to be on the sensor, because the spots were the exact some place as the 85mm stopped down. I cleaned the sensor and it is fine now! Yeah :]