Deprecated function: Return type of DatabaseStatementBase::execute($args = [], $options = []) should either be compatible with PDOStatement::execute(?array $params = null): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in require_once() (line 2244 of /home/eduvai/public_html/includes/database/database.inc).
Deprecated function: Return type of DatabaseStatementEmpty::current() should either be compatible with Iterator::current(): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in require_once() (line 2346 of /home/eduvai/public_html/includes/database/database.inc).
Deprecated function: Return type of DatabaseStatementEmpty::next() should either be compatible with Iterator::next(): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in require_once() (line 2346 of /home/eduvai/public_html/includes/database/database.inc).
Deprecated function: Return type of DatabaseStatementEmpty::key() should either be compatible with Iterator::key(): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in require_once() (line 2346 of /home/eduvai/public_html/includes/database/database.inc).
Deprecated function: Return type of DatabaseStatementEmpty::valid() should either be compatible with Iterator::valid(): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in require_once() (line 2346 of /home/eduvai/public_html/includes/database/database.inc).
Deprecated function: Return type of DatabaseStatementEmpty::rewind() should either be compatible with Iterator::rewind(): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in require_once() (line 2346 of /home/eduvai/public_html/includes/database/database.inc).
ক্রমবর্ধমান ফিশনের হারকে নিয়ন্ত্রণের জন্য যে গ্রাফাইট খন্ড দিয়ে পারমাণবিক চুল্লির মজ্জা তৈরি হয় তাকে মন্থরক বলে। মন্থরক নিউট্রনকে ধীরগতি করে। ভারী পানি, গ্রাফাইট প্রভৃতি মন্থরক হিসেবে ব্যবহার করা হয়।
